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Polímeros / Associação Brasileira de Polímeros. vol. 1, nº 1 (1991)
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Quarterly v. 32, nº 4 (October 2022)
ISSN 0104-1428
ISSN 1678-5169 (electronic version)
1. Polímeros. l. Associação Brasileira de Polímeros.
Website of the “Polímeros”: www.revistapolimeros.org.br
Potential antioxidant migration from polyethylene packaging to food: a systematic review
Mayara de Simas Mesquita and Shirley de Mello Pereira Abrantes .....................................................................................................e2022042
Obtaining and characterization of bioplastics based on potato starch, aloe, and graphene
Mercedes Puca Pacheco1, Oscar Rafael Tinoco Gómez, Gonzalo Canché Escamilla, Santiago Duarte Aranda and María Guadalupe Neira Velázquez ........................................................................................................................................................e2022037
Polymer composite produced with Brazil nut residues and high impact polystyrene
Jefferson Renan Santos da Silva, João Christian Paixão Fonseca, Thais da Silva Santos, Josiel Bruno de Oliveira, Thiago Monteiro Maquiné, Bruno Mello de Freitas, Raimundo Nonato Alves Silva, Nayra Reis do Nascimento, João Martins da Costa, Roger Hoel Bello and José Costa de Macedo Neto
Selection of materials with entropy-topsis by considering technological properties of impregnated wood
Nadir Ersen, Hüseyin Peker and İlker Akyüz
Surface and micromechanical analysis of polyurethane plates with hydroxyapatite for bone structure
Wenderson da Silva do Amaral, Milton Thélio de Albuquerque Mendes, João Victor Frazão Câmara, Josué Junior Araujo Pierote, Fernando da Silva Reis, José Milton Elias de Matos, Ana Cristina Vasconcelos Fialho and Walter Leal de Moura
Synthesis and characterization of native and modified bitter yam starch grafted with acrylonitrile
Funmilayo Deborah Adewumi, Labunmi Lajide, Ezekiel Adewole and Jonanthan Abidemi Johnson
e2022038
e2022039
e2022040
e2022041
O evento acontecerá este ano nos dias 29 de Outubro
O evento acontecerá este ano nos dias 29 de Outubro a 02 de Novembro de 2023 no Centro de Convenções a 02 de Novembro de 2023 no Centro de Convenções Expoville em Joinville - SC. Expoville em Joinville - SC.
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Scientists at Lawrence Berkeley National Laboratory have developed a conductive polymer coating – called HOS-PFM – that could prove significant for the future of lithium-ion battery use in EVs.
Gao Liu, a senior scientist in Berkeley Lab’s Energy Technologies Area explains: ‘The HOS-PFM coating conducts both electrons and ions at the same time. This ensures battery stability and high charge/discharge rates while enhancing battery life. The coating also shows promise as a battery adhesive that could extend the lifetime of a lithium-ion battery from an average of 10 years to about 15 years.’
Silicon and aluminium both have potentially high energy storage capacity and lightweight profiles which makes them of interest as electrode materials for lithiumion batteries but the downside is that they wear down quickly after multiple charging cycles. This is exactly why the research team used those materials, coated with HOS-PFM to showcase the polymer’s conductive and adhesive properties in a lithium-ion battery setup. Experiments demonstrated that the HOS-PFM coating significantly prevented the silicon and aluminiumbased electrodes from degrading during battery cycling, while delivering high battery capacity over 300 cycles – a performance rate on par with current state-of-the-art electrodes. And of course silicon and aluminium are both inexpensive and abundant.
Liu said: ‘The advance opens up a new approach to developing EV batteries that are more affordable and easy to manufacture. The HOS-PFM coating could allow the use of electrodes containing as much as 80% silicon. Such high silicon content could increase the energy density of lithium-ion batteries by at least 30%. And because silicon is cheaper than graphite, the standard material for electrodes today, cheaper batteries could significantly increase the availability of entry-level electric vehicles.’ The team next plans to work with companies to scale up HOS-PFM for mass manufacturing.
Lithium batteries are a hot topic at the moment with recent research into lithium-air batteries attracting attention. There is also a growing effort to curtail the not inconsiderable implications of throwing away 9m tonnes of lithium-ion batteries a year.
Source: Plastic Today – plasticstoday.com
WACKER offers improved solubility in new polymer resin for packaging coatings, printing inks, and more
WACKER will unveil its VINNOL L-6868 polymer resin binder – set to formulate wood, paper, film, and solvent-borne coatings, suitable for printing inks and high-solids and UV-curing systems, and compatible with food-grade packaging – at this year’s European Coatings Show.
As the newest product in WACKER’s VINNOL family of solid resins, the VINNOL L-6868 polymer resin has the lowest viscosity of the range and is apparently compatible with a range of UV monomers and reactive diluents. Its function as a binder involves enclosing the pigment particles to bond them to each other and to the substrate, yet its features have been further developed from the previous VINNOL H 40/43 polymer resin grade to meet the demands of WACKER’s customers.
VINNOL L-6868 contains a minimised 44% copolymerised vinyl chloride and maximised 56% vinyl acetate. These adjustments are said to provide hardness, durability, and chemical resistance in the coating, as well as improve the formulations’ processing properties and the product’s solubility in ketones, esters, acrylic monomers, UV monomers, and glycol esters.
Additionally, the polymer resin’s viscosity is attributed to a combination of the modified polymer composition and a low molecular weight. Its viscosity in a 20-% methyl ethyl ketone solution at 20°C is reported at 7 mPa*s –with the corresponding value for the VINNOL H 40/43 placed at 25 mPa*s – while the low molecular weight is also thought to equip formulators against challenges related to float, intercoat adhesion, and flexibility in UVcuring systems.
The binder is expected to formulate high-solid systems, or systems with high pigment and binder contents, for applications such as printing inks, plastic coatings, wood coatings, and paper and film coatings. It can be used to formulate coatings for food-contact packaging and is also suitable for reactive curing systems.
Source: Packaging Europe – packagingeurope.com
March
Plástico Brasil — International Plastic Exhibition
Date: March 27-31, 2023
Location: São Paulo, São Paulo, Brazil
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PETtalk — International Conference of the PET industry
Date: March 28, 2023
Location: São Paulo, São Paulo, Brazil
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European Coatings Show (ECS)
Date: March 28 – 30, 2023
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Website: www.european-coatings-show.com
April
24th International Conference on Wear of Materials
Date: April 16-20, 2023
Location: Banff, Alberta, Canada.
Website: www.wearofmaterialsconference.com
Polymers in Flooring Europe – 2023
Date: April 18-19, 2023
Location: Berlin, Germany
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4th World Expo on Biopolymers and Bioplastics
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Website: biopolymers.materialsconferences.com/
38th International Conference of the Polymer Processing Society
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Location: St. Gallen, Switzerland
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Polymer Sourcing & Distribution – 2023
Date: May 23-25, 2023
Location: Hamburg, Germany
Website: www.ami-events.com/event/7e7d5b18-b87b-4167bbbe-ed4142955f44/summary
Frontiers in Polymer Science 2023 — Seventh International Symposium Frontiers in Polymer Science
Date: May 30 – June 1, 2023
Location: Gothenburg, Sweden
Website: www.elsevier.com/events/conferences/frontiers-inpolymer-science
June
Gordon Research Seminar — Polymers
Date: June 3-4, 2023
Location: South Hadley, Massachusetts, United State of America
Website: www.grc.org/polymers-grs-conference/2023/
Gordon Research Conference — Polymers
Date: June 4-9, 2023
Location: South Hadley, Massachusetts, United State of America
Website: www.grc.org/polymers-conference/2023/
Polymer Testing World Expo Europe – 2023
Date: June 14-15, 2023
Location: Messe Essen, Germany
Website: eu.polymertestingexpo.com/
10th International Conference on Polymer Science and Polymer Chemistry
Date: June 19-20, 2023
Location: Rome, Italy
Website: polymer.conferenceseries.com/
Fluoropolymer 2023
Date: June 18-21, 2023
Location: Denver, Colorado, United State of America
Website: www.polyacs.net/23fluoropolymer
Chemical Recycling - 2023
Date: June 26-28, 2023
Location: Frankfurt, Germany
Website: www.ami-events.com/event/7aa8d789-efda-4178-bf363321aa5caca1/summary?RefId=AMI%20Website
MACRO2024 — 50th World Polymer Congress
Date: June 30 – July 4, 2023
Location: Coventry, United Kingdom
Website: iupac.org/event/50th-world-polymer-congressmacro2024/
August
9th Edition of International Conference on Polymer Science and Technology
Date: August 28-29, 2023
Location: London, United Kingdom
Website: polymerscience.annualcongress.com/
September
14th International Workshop on Polymer Reaction Engineering
Date: September 5-8, 2023
Location: Fraunhofer-IAP, Potsdam, Germany
Website: dechema.de/en/PRE2023.html
Performance Polyamides Europe - 2023
Date: September 12-13, 2023
Location: Cologne, Germany
Website: www.ami-events.com/event/30903ccf-d7f1-400e-add4332bba09af6a/summary
European Symposium on Biopolymer - ESBP
Date: September 13-15, 2023
Location: Brno, Czech Republic Website: esbp2023.com/
Polyolefin Additives - 2023
Date: October 3-4, 2023
Location: Barcelona, Spain
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Plastics Recycling Technology
Date: October 10-12, 2023
Location: Vienna, Austria
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Sustainable Polymers
Date: October 15-18, 2023
Location: Safety Harbor, Florida, United State of America
Website: www.polyacs.net/23sustainablepolymers
7th Global Summit on Polymer Chemistry
Date: October 18-19, 2023
Location: Paris, France
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17th Brazilian Polymer Congress
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Controlled Radical Polymerization
Date: November 12-15, 2023
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18th Pacific Polymer Conference
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Location: Puerto Vallarta, Mexico Website: www.ppc18.com.mx/index.html
Polymer Engineering for Energy
Date: December 5-6, 2023
Location: London, United Kingdom
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1Laboratório de Contaminantes, Departamento de Química, Instituto Nacional de Controle de Qualidade em Saúde, Fundação Oswaldo Cruz – FIOCRUZ, Rio de Janeiro, RJ, Brasil
*mayarasimas@yahoo.com.br
Abstract
This systematic review investigates evidence concerning antioxidant migration from polyethylene packaging to food. The review protocol was based on the Preferred Reporting Items for Systematic Reviews guidelines. Several electronic databases were consulted for relevant studies, as well as references in eligible studies. Of the 44 eligible studies, only two did not indicate antioxidant migration. The reported migrations were influenced by numerous factors, the most important comprising the fatty contents of food and/or fat simulants, with higher fat amounts resulting in higher migration rates. Migrated antioxidant values ranged from 3.42 mg kg-1 to 231.70 mg kg-1, far above the maximum permissible amounts established by the current legislation regarding foods in contact with plastic resins.
Keywords: antioxidants, health surveillance, migration, polyethylene.
How to cite: Mesquita, M. S., & Abrantes, S. M. P. (2022). Potential antioxidant migration from polyethylene packaging to food: a systematic review. Polímeros: Ciência e Tecnologia, 32(4), e2022042. https://doi.org/10.1590/0104-1428.20220081
Plastic packaging significantly contributes to human chemical exposure, as numerous chemicals are employed in the manufacturing of plastic food packagings[1]. In this regard, health surveillance plays a role in essential public health actions to ensure the necessary safety for human populations always seeking to control the health risks assigned in the manufacture and consumption of products and services[2]. Concerning health safety associated to plastic packagings, Brazilian legislation presents a list of permitted compounds, such as polymers, resins and additives, and certain restrictions concerning these compounds, such as specific migration limits (SML) for additives[3]
Plastics comprise the packaging class that most interacts with food, due to their permability, although barrier properties vary between different materials, potentially leading to the presence of harmful substances in food[4]. These may, in turn, damage organismal health, depending on the food concentration, ingestion frequency and absorbed dose, among others[5]
In this context, the aim of this study was to carry out a systematic literature review to address evidence on the migration of certain antioxidants established by Brazilian Resolution of the Collegiate Board of Directors (RDC) No. 326/2019[6] present in high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE) packagings. These antioxidants include butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), propyl gallate, octyl gallate (OR 3,4,5-trihydroxybenzoic acid octyl ester OR octyl gallate dihydrate), lauryl gallate (OR dodecyl gallate OR antioxidant
E-312), methyl 4-hydroxybenzoate, propyl 4-hydroxybenzoate; hydroquinone (OR 1,4-dihydroxybenzene), irganox 1076 (octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate) and 4-sec-butyl-2,6-di-tert-butyl-phenol. Several food simulants associated with these antioxidants, namely 8, 10, 50, 95 and 100% ethanol, olive oil, 3% acetic acid, distilled water, water; poly (2,6-diphenyl-p-phenylene oxide) (PPPO or TENAX); α-tocopherol; sunflower oil and iso-octane and HB 307 (mixture of synthetic triglycerides, primarily C10, C12 and C14 - Fatty food simulant) will also be discussed. Determining antioxidant levels in plastic furthers information on the migration potential of these compounds and on plastic quality. However, a need for a systematic analysis to assess the consequences of antioxidant migration in polyethylene packaging is noted. Therefore, the purpose of this review is to support an adequate and updated antioxidant migration potential analysis, providing data on the safety of antioxidant use in different polyethylene packagings to ensure human health safety and further Sanitary Surveillance and Public Health actions.
This study was guided by Center for Reviews and Dissemination recommendations[7], Cochrane Collaboration[8] and structured in five steps, as follows: (a) The elaboration of the study guiding question; (b) a search for primary studies on the migration potential of antioxidants present
E V I E W A R T I C L E
in polyethylene packaging for food/food simulant; (c) the identification and selection of studies associated to antioxidants according to established inclusion and exclusion criteria; (d) data extraction followed by the analysis, description and evaluation of the parameters and outcomes of each selected study; in addition, the bibliographic references of eligible studies were consulted (manual search), which could contain citations of articles that met the inclusion criteria proposed by this work and that eventually had not been located in the databases. Finally, an electronic search of the gray literature was performed using the Google Scholar database; (e) a critical opinion on the methodological quality of the selected studies.
The searches covered all studies on the subject up to September 4, 2020. All searches were carried out employing Medical Subject Headings Terms (MeSH), PUBMED and Health Sciences (DeCS) descriptors, from BIREME (Latin American and Caribbean Center on Health Sciences Information), as well as author-selected keywords, later adapted to the other searched databases, namely: # 1. Migration; # 2. Diffusion; # 3. Antioxidants; # 4. Polyethylene packaging; # 5. Low density polyethylene; # 6. High density polyethylene; # 7. Food; # 8. Food simulants.
To further detail the searches, the following antioxidants and other descriptors were also used: #9. Butylated hydroxytoluene (BHT); # 10. Butylated hydroxyanisole (BHA) # 11. Propyl gallate; # 12. Octyl gallate (OR 3,4,5-trihydroxybenzoic acid octyl ester OR octyl gallate dihydrate) # 13. Lauryl gallate (OR dodecyl gallate OR E-312 antioxidant); # 14. Methyl 4-hydroxybenzoate # 15. Propyl 4-hydroxybenzoate; # 16. Hydroquinone (OR 1,4-dihydroxybenzene); # 17. Irganox 1076 Octadecyl (3-(3,5-di-tert- butyl-4-hydroxiphenyl) propionate); # 18. 4-sec- butyl-2,6-di-tert- butyl- phenol; AND # 19. Food packaging (OR food containers OR foodcontact plastics OR food contact materials).
An alphanumeric coding was assigned to each article, with studies coded by the letter (E) followed by a sequential number (E1, for example). After extracting the relevant information, qualitative analyses were critically carried out for data synthesis and interpretation.
After including the eligible articles, a Methodological Quality Assessment was performed following the criteria described in Table 1, attributing one point for each obtained criterion. Total points ranks high from 10 to 14 points, average from 6 to 9 points, and low from 0 to 5 points.
The search process for primary studies carried out at the electronic databases retrieved a total of 491 references, with an extensive screening carried out in order to reach a significant number of studies. Of this total, eleven duplicates were discarded. Table 2 depicts the result of the search strategy and the total number of eligible studies.
Several studies are usually excluded from systematic reviews, especially those employing wide searches, whose
Table 1. Eligible study methodological quality assessment.
1. Is the research design well defined with a focus on antioxidant migration?
2. Is a description of the methodology used to evaluate the antioxidant migration test available?
3. Is the migration test based on any regulations?
4. Is a description of the employed reagents available?
5. Was antioxidant characterization carried out in the tested packaging?
6. Was antioxidant characterization performed employing at least three techniques?
7. Is a description of the type of evaluated packaging available?
8. Does the article report how the antioxidant was incorporated into the packaging?
9. Is antioxidant quantification described in the study?
10. Does the article determine which antioxidant is present in the tested packaging and in the food?
11. Does the article use an antioxidant reference standard?
12. Are the employed methods validated?
13. Does the study include a statistical analysis?
Score: High (10 to 14 points); Average (6 to 9 points); Low (0 to 5 points).
Table 2. Search strategy results from the selected databases after eliminating duplicate studies and total number of articles identified on antioxidant migration assays.
aim is to prevent any important and pertinent article from not being reached by this screening method[9]. After analyzing all studies, a manual search was performed on all eligible articles. A total of 468 studies were obtained, 17 of which were eligible and included in this review, as well as the 27 studies displayed in Table 3. Thus, a total of 44 studies were included herein to answer this review’s question.
The applied Methodological Quality Assessment indicated 42 of the 44 eligible studies as presenting high quality (10 to 14 points) and only two of medium quality (6 to 9 points). None were categorized as low quality (0 to 5 points).
Migration studies are carried out to identify the best simulants for food product evaluation assays and to define the test conditions (temperature/contact time) that best simulate real product packaging situations[10]
The mass transfer or migration phenomenon involves the diffusion of substances from materials in contact with food. Several parameters can influence this process, such
Table 3. Eligible studies employed in this systematic review and their alphanumeric coding.
Article/ Code
Author(s)
Article/ Code
Author(s)
E1 Figge et al.[10] E23 DopicoGarcía et al.[11]
E2 Till et al.[12] E24 Han et al.[13]
E3 Figge and Freytag[14] E25 Stoffers et al.[15]
E4 Bieber et al.[16] E26 Stoffers et al.[17]
E5 Bieber et al.[18] E27 Begley et al.[19]
E6 Schwope et al.[20] E28 DopicoGarcía et al.[21]
E7 Gandek et al.[22] E28 Torres-Arreola et al. [23]
E8 Goydan et al.[24] E30 Jeon et al.[25]
E9 Ho et al.[26] E31 Vitrac et al.[27]
E10 Limm and Hollifield[28] E32 Cruz et al.[29]
E11 Yam et al.[30] E33 Soto-Cantú et al.[31]
E12 O’Brien et al.[32] E34 Machado et al.[33]
E13 Wessling et al.[34] E35 MauricioIglesias et al.[35]
E14 Cooper et al.[36] E36 Coltro and Machado[37]
E15 Linssen et al.[38] E37 Beldí et al.[39]
E16 Bailey et al.[40] E38 Reinas et al.[41]
E17 O’Brien et al.[42] E39 Jakubowska et al.[43]
E18 Wessling et al.[44] E40 Haitao et al.[45]
E19 O’Brien and Cooper[46] E41 García-Ibarra et al.[47]
E20 Brandsch et al.[48] E42 Rubio et al.[49]
E21 Feigenbaum et al.[50] E43 Vera et al.[51]
E22 Helmroth et al.[52] E44 Liang et al.[53]
as type of food, fat content, temperature, contact duration, migrant packaging concentration, polymer morphology, migrant density and molecular size and physical state[47], as well as pH and alcohol content, among others[16]
In addition, Specific Migration Limits (SML) have been established, comprising the “maximum admissible amount of a specific component of the material in contact with food transferred to simulants under the rehearsal conditions”[54:28]
Of the 44 primary eligible articles, 20 reported no evidence of antioxidant migration above the LME, while the other 24 reported evidence of migration above the LME (Table 4).
Fat is a significant migration enhancer, and the higher the fat content of the food or simulant, the greater the antioxidant packaging migration. For example, one study reported migration values of various fatty foods (pork sausage, liver sausage, yogurt, fresh, hard and processed cheese, and margarine) above the LME in LDPE packaging, and antioxidant migration below the LME in all HDPE packaging[18], indicating that LDPE seems to be unsuitable for fatty food packaging.
Concerning food simulants, studies E41[47] and E13[34] reported that the antioxidant BHT migrated to a lesser extent in the food simulant in 50% ethanol when compared to 95% ethanol, especially as this compound displayed a lower
Table
Studies evidencing antioxidant migration and SML above permissible values
Studies evidencing antioxidant migration and SML below permissible values
E2, E3, E8, E13, E15, E17, E21, E23, E24, E25, E26, E28, E30, E31, E34, E36, E38, E40, E42, E44. Specific Migration Limits (SML).
E1, E4, E5, E6, E7, E9, E10, E11, E12, E14, E16, E18, E19, E20, E22, E27, E29, E32, E33, E35, E37, E39, E41, E43.
affinity for 50% ethanol at all test temperatures. However, migrations were of 90% even in 50% ethanol tested at 20 °C and 40 °C, with a migration value of 821.97 mg kg-1 reported from an initial antioxidant polymer concentration of 913.30 mg kg-1
Similarly to E40[45],E41 and E6[20] reported a fast BHT migration of 1 hour at similar temperatures (49 °C and 21 °C), also using 50% ethanol, exceeding the established LME of 3 mg kg-1. However, the same was not observed in 8% ethanol and water, and migration results were lower than in water when employing 3% acetic acid, increasing the migrated amount only with increasing exposure times.
In aqueous solutions, part of the BHT migrates and then decomposes into unknown substances. The accepted hypothesis is that BHT migrates by diffusion from the polymer to the surface of the food or simulant, and an equilibrium takes place after BHT increases, reducing migration rates, although migration continues, as BHT is simultaneously decomposed[20]. Furthermore, BHT decomposition rates seem to be much lower in acidic solutions than in aqueous ones.
The simulant favoring the highest rate of antioxidant migration is olive oil used in the primary studies is olive oil, due to its high fat content (100%), as reported by E1[10], E4[16], E12[42], E14[36], E19[46], E22[52], E27[19], E35[35] and E37[39]. This compound is considered the official simulant for fatty foods[50]. However, the migration test for olive oil is not only somewhat imprecise but also very time consuming and, therefore, expensive[15]
Most studies clearly identify lower antioxidant migration rates in acidic and non-acidic aqueous simulants, especially irganox 1076. For example, E37 and E60 reported no measurable migration of this compound when determining antioxidant migration in LDPE using 3% acetic acid, distilled water and 10% ethanol as simulants, due to hydrophobic antioxidant behavior.
Solubility, comprising the maximum amount that a substance can dissolve in a liquid, on the other hand, depends on antioxidant molecular dimensions[55]. Increasing molecular sizes result in increased solubility, leading to higher migration rate. In this regard, even BHT and irganox 1076, which display some insolubility in water, have been reported as exhibiting high migration levels, and some studies report that complete extraction may take place [20] . In addition, BHT solubility in water in LDPE packaging increases with temperature[12], in contrast with HDPE, where this does not occur.
Regarding fatty food simulants, ranging from 8% to 100% ethanol, the higher the ethanol concentration, the
greater the antioxidant migration rate[27]. This also applies to temperature, where higher temperatures lead to greater migration rates for greasy simulants.
Some contradictory data are noteworthy, such as, for example, no migration detected in fat and migration observed in water or aqueous simulants. Study E21[50], for example, analyzed BHT migration from LLDPE packaging (2 mm thickness) to 95% ethanol and olive oil, and detected this antioxidant at trace levels only. Polyethylene thickness could explain this fact, as thick samples are unlikely to present migration[32]. On the other hand, olive oil can lead to higher migration values than most fatty foods, so it is unusual not to detect at least residual migrated levels in this simulant. Furthermore, E9[26], E10[28], E11[30], E28[23], E30[25], E34[33] and E44[53] reported antioxidant migration in water or aqueous simulants, all above the LME for BHT and irganox 1076. E9[26], which evaluated BHT migration to LDPE water at 38 ºC, reported 6.26 mg kg-1 of migrated antioxidants more than double the LME for BHT, of 3 mg kg-1.
E6[20] presented evidence of migration in water when compared to acetic acid, with BHT migrating less to 3% acetic acid solutions than to water, probably due to the fact that BHT decomposition rates are much lower in acidic solutions. Studies E10[28], E28[23], E30[25] and E44[53] also evaluated antioxidant migration in water or aqueous simulants, all detecting antioxidant migration, albeit below the LMEs. However, determinations concerning overall migration to water may contain significant errors, as the applied method gravimetrically measures the migrated amounts as residue following complete water evaporation[56]
In addition, migration takes place even though in dry food (e.g., rice, milk powder, soup mixes). The results reported by E6[20] and E2[12], for example, indicate that BHT migrated at a considerable rate and that differences were particularly noticeable in the case of dry solid foods, with much lower differences for simulants. E39[43] tested BHT migration in a dry food simulant, poly (2,6-diphenyl-p-phenylene oxide) (PPPO or Tenax) (1 g), in LDPE containing 300 mg kg-1 of the antioxidant at 60ºC for 10 days. The obtained data indicated that BHT is very sensitive to the tested simulant, with a migrated value of 15.61 mg kg-1, comprising 5.20% of the BHT value added to the polymer and 5-fold higher than the LME.
Studies E38[41] and E42[49] also evaluated migration in PPPO, which has been used as a simulant for the specific migration concerning dry foods, according to Commission Regulation (EU) 10/2011[57]. Both studies reported migration values, although below the LME of the evaluated antioxidants. E42[49] detected BHT in all PPPO samples, averaging 4.7 x 10-5 mg kg1. The study, however, did not specify the type of evaluated polyethylene. E38[41] compared LDPE migration in rice and in PPPO, noting that migration to PPPO is faster and higher compared to rice. Furthermore, temperature effects are more significant concerning migration to PPPO compared to rice, regardless of the migrant. Therefore, this food simulant tends to overestimate migration values and can, therefore, be safely used to assess material conformity. In addition, the results indicate that PPPO is a more severe simulant for rice. This must be considered when assessing material compliance under EU Regulation 10/2011, which
mentions that the “results of specific migration tests obtained in food shall take precedence over results obtained in food simulants”[57:12]
Irganox 1076 equilibrium in PPPO at 70 °C was reached after 15 days and at 40 °C, after 10 days, in contrast to rice, where the antioxidant did not reach an equilibrium at any of the tested temperatures. These behavior differences can be explained mainly by PPPO’s high porosity and adsorption capacity[41]. It is important to note, as mentioned previously, that migration results obtained in the food prevail over results obtained with simulants.
E16[40] was the only study that did not mention the type of analyzed simulant, but demonstrated that over 95% of BHT was lost from the assessed film in 36 h at 40 °C, in 5 days at 30°C and in 16 days at 23°C. BHT can be depleted from films in short periods of time and may, therefore, not be effective as an antioxidant during packaged product shelf lives.
Food simulant standardization is required considering the importance of food simulants. Furthermore, it is essential that antioxidant packaging concentrations are determined experimentally prior to migration tests, in order to correlate measured values to real sample values, as in the case reported by E12, so results may truly express antioxidant behavior, and, therefore, accurately evaluate their safety as packaging additives[32]
Migration experiments endorse the importance of physicochemical food matrix properties, that is, combinations of high temperature and high fat content greatly aid antioxidant migration, increasing with increasing temperatures, while fat content alone has also been proven a determining migration parameter, as mentioned previously. Finally, antioxidant migration levels in simulants were reported by all studies as higher than in foods at all evaluated temperatures. Our assessment of all eligible studies confirms that the use of simulants in migration studies provides a good safety margin and that the transfer of low molecular weight hydrophobic components from plastic packaging material to food is governed by the fat releasing properties of the investigated food, i.e., the amount of fat available on the food surface.
Antioxidant migration was assessed by the studies included in this systematic review in three types of polyethylene, LDPE, HDPE and LLDPE. Of the 44 studies, only one (2%) did not specify the type of investigated polyethylene (E42)[49], while 39% evaluated LDPE, 30% analyzed LDPE and HDPE, 18% only HDPE, 9% LLDPE and 2% analyzed the three types.
LDPE is the most widely employed food packaging material, used as coating in food containers, especially in bakery products, milk, margarine, water and poultry[12,20,51]
A different scenario was reported by E33[31], which evaluated a solid and fatty food (cheese), indicating different losses from films, which contained 8 mg kg-1 and 14 mg kg-1 of BHT per kilogram of plastic. BHT losses from resins containing 8 and 14 mg kg-1 tested at 5 °C in 3 days corresponded to over 69 and 75%, respectively, while
Potential antioxidant migration from polyethylene packaging to food: a systematic review
losses were much higher in 20 days, corresponding to over 82 and 88%, respectively. Therefore, migration was higher during longer storage periods, and both migration results were above the BHT LME. It should be noted that most of the migrated BHT may have been deposited on the cheese surface, where antioxidants are more necessary, due to light exposure effects. E33, however, did not quantify BHT in the cheese samples as, once the antioxidant reaches the product, it can be consumed by reactions with free radicals. Most of the BHT was diffused from the LDPE layer to the cheese during the first 20 d of storage at 5°C. The release of BHT from the film added with 8 mg/g of the antioxidant in the LDPE layer complied with the legal limit in the cheese. However, the film added with 14 mg/g of the antioxidant in the LDPE layer could exceed that limit if all the BHT is released to the cheese. Thus, LDPE monolayer films are not suitable for cheese packaging, due to their high oxygen transmission rates, accelerating oxidation reactions.
LLDPE films are widely used in situations requiring flexibility and strength[25]. Studies investigating LLDPE only (E15[38], E21[50], E30[25] and E35[35]) reported no significant migration values above the LME. All studies employed mostly the same temperature (up to 40 °C) and fat simulants, although thickness differences were noted, with the thinnest package measuring 0.05 mm and the thickest, 2 mm, a 40fold increase. This high variation, however, does not seem to have contributed to greater or lesser migration.
E11[30] evaluated the effect of resin type on BHT migration, determining the extent of HDPE odor and offflavor release. A sensory study indicated that the BHT-free resin led to less off-flavor compared to the BHT-containing resin. In addition, resin containing a natural antioxidant (vitamin E) produced less off-flavor compared to the resin containing BHT. One study limitation, however, was that only one processing condition was applied to all evaluated resins, although each resin is likely to require a unique processing condition.
Among articles assessing antioxidant migration potential in more than one type of plastic packaging, E7[22] was the only one to evaluate the three main polyethylene types (LDPE, HDPE, LLDPE) in water, reporting that only 40% of BHT was extracted from the resins after three months, while 10% of BHT migrated in less than one day. Articles evaluating LDPE and HDPE, comprising E3[14], E8[24], E24[13], E25[15], E26[17], E28[21] E43[51], and E36[37] did not report migration values above the LME. However, E3, despite having detected a migration value below the irganox 1076 LME of 6 mg kg-1 reported a value very close to the limit, of 5.82 mg kg-1 in HDPE tested at 40 ºC in 10 days.
E3 also reported greater fatty food simulant migration in LDPE when compared to HDPE. However, the study did not determine irganox 1076 concentrations prior to the migration test and after the plastic formation process. The ideal scenario would be to test the amount of additive before and after processing.
Studies E1[10] and E27[19] evaluated HDPE (0.3 mm and 0.5 mm thick, respectively) and irganox 1076, with the former reporting no antioxidant migration and the latter, a migrated value exceeding the LME by 62.26%. Both studies evaluated migration in olive oil at the same temperatures
(40 ºC), with only film thickness as the differing variable. However, no migration was reported for the thinner HDPE.
Studies E12[42] and E14[36] also evaluated irganox 1076 HDPE olive oil migration at 40 ºC for 10 days, reporting the same migrated value of 6.2 mg kg-1. At 121º C for 2 hours, values were reported as 58 mg kg-1 and 55.9 mg kg-1 in E12 and E14, respectively.
A temperature of 121ºC was used to simulate HDPE autoclave for sterilization conditions, considered adequate for this polymer and covering the most rigorous use conditions. However, E14[36], which investigated a thicker film compared to E1[10] (2 mm), reported a migrated value above the LME. The packaging thickness used by E12[42] resembles the packaging thickness studied by E27[19], with antioxidant migrated values above the LME.
Comparing these studies with E25[15], which also employed HDPE, olive oil and a similar temperature (100 ºC for 2 h), no irganox 1076 migration above the LME was noted. Similarly to E12[42], E25[15] reported a significant amount of antioxidant present in the resin prior to the migration test (896 mg kg-1 or 0.09%) and the film thickness was significant (1.043 mm) which may explain the reason for the reported low antioxidant migration (0.437 mg kg-1).
For polyolefin samples (HDPE), specific migration values obtained with 95% ethanol under the same exposure conditions agreed with the values obtained with olive oil, in line with FDA recommendations[58].
Regarding antioxidants, the most studied was irganox 1076. According to Beldì et al.[39], this compound is commonly used as a migrant model as it is a typical antioxidant in food packaging polymers, as well as stable and available as a certified reference material. It protects plastic materials against thermo-oxidative degradation, presents low volatility and high extraction strength, and is not present naturally or as a food additive in foods.
BHT is one of the most commonly employed antioxidants used to protect plastics against oxidation due to heat and light exposure, also used in other applications as a food additive and in cosmetics, pharmaceuticals and petroleum products[47]. It is a fat-soluble and synthetic antioxidant, widely used in the food industry, with a legal limit for addition to most foods of 200 mg kg-1 of fat, increasing to 500 mg kg-1 in packaging. During film processing, part of the antioxidant is lost due to its ability to function as a free radical scavenger, also lost to the environment due to high volatility at processing temperatures[31]
Study E7[22] evaluated both BHT and irganox 1076 migration from LLDPE to water, reporting that irganox 1076 migration was slower than BHT under similar conditions, probably due to the fact that it is a much larger molecule than BHT, with a much lower diffusivity and slower oxidation compared to BHT. In addition, BHT solubility in the polymer and in water increased with temperature, all leading to faster and more significant BHT migration compared to irganox 1076 to water.
Study E23[11] demonstrated undetectable irganox 1076 migration to water in LDPE, similarly to results reported for butylated hydroxyanisole (BHA), considered one of the best antioxidants and preservatives employed by the industry, widely used in bulk oils and oil-in-water emulsions, as well as in packaging materials, aiming at food protection, as well as in many cosmetic products, alongside BHT[59]
Study E18[44] also compared BHT with vitamin E, as did E9[26], but with a dry food (oatmeal). The BHT content of the LDPE film became depleted much faster than vitamin E content, possibly due to diffusion to the surface of the film and evaporation, as BHT is a volatile molecule. After evaporation, it is likely that the BHT was either absorbed into the oatmeal or lost to the environment. Unfortunately the article does not mention the amount of BHT remaining in the oatmeal.
BHT is known to inhibit oxidation processes in food products and polymers. However, due to its migratory nature, a growing interest in the use of vitamin E as an alternative antioxidant for polymer stabilization has been noted. This vitamin has been reported as more effective at levels lower than those required for other antioxidants in reducing aftertaste, especially concerning resins used to store water, as noted by E18[44], E7[22], E9[26]. Directive 90/128/EC recommends a migration vitamin E limit of 60 mg kg-1[60]
In studies comparing natural and synthetic antioxidants, BHT is rapidly lost from resins, especially LDPE, within a few days of storage at all tested temperatures, due to its small size, volatile and migratory nature[22,26,44,45]. Both E32[29] and E33[31] emphasize that the highest migration rates occur in polyolefins, especially in LDPE films, and BHT, as it is one of the smallest phenolic antioxidants, passes more easily from the resin to the food or food simulant, especially those rich in fat. Both E13[34] and E41[47] evaluated migration to 95% ethanol and observed that the relative amount of BHT migrated from LDPE to the simulant food was almost total, migrating to a lesser extent to 50% ethanol, considering that BHT exhibits a lower affinity for this simulant.
An evaluation carried out in fatty food simulants demonstrated that a BHT-containing film exhibited rapid BHT decreases soon after contact with the two simulants. After one week of storage at 4 °C, BHT levels in the film dropped below the limit of detection, with an even faster decay observed at 20°C, with only one day of storage enough to reduce BHT levels to undetectable in films in contact with sunflower oil and ethanol, thus indicating rapid BHT polymer migration[34,45]
Regarding irganox 1076, most analyzed samples contained several antioxidants at the same time, especially high molecular weight compounds, with irganox 1076 detected in almost 50% of the samples. In addition, most studies mentioned the importance of plastic film thickness and antioxidant concentration concerning migration. Furthermore, irganox 1076 results are very similar to the BHT results reported by the eligible studies included in this systematic review. One of the most mentioned issues for both is associated to antioxidant fat exposure, in turn associated with most of the migration that occurs from the packaging to the material. irganox 1076 migration was also reported as much higher in
oil than in aqueous simulants, explained by its hydrophobic properties, i.e., insolubility in water, therefore dissolving in other organic compounds. Olive oil, isooctane and 95% ethanol are, thus, routinely used as simulants, as described by Directive 82/711/EEC (European Commission 1982) due to a higher affinity with irganox 107639
Study E8[24] demonstrated similar migrations for two aqueous simulants, water and 8% ethanol, at 135 ºC in HDPE and LDPE and, higher, albeit comparable, rates for two non-aqueous simulants for 95% ethanol and corn oil. For the non-aqueous simulants, migration was faster in LDPE and slower in HDPE. Study E43[51] also indicated higher migration values for the 95% ethanol simulant, as expected, as this antioxidant is more soluble in ethanol than in acidic or aqueous simulants.
Study E28[21] reported the marked presence of irganox 1076 in different commercial packages, and migration to permitted food simulants, such as distilled water, 3% acetic acid, 10% ethanol and olive oil, were observed in most samples (RDC No. 51, 2010)[61]
Study E25[15] reported migration values for sunflower oil, a very good choice for a certified reference material, relevant to compliance testing, where over 35% of the irganox 1076 was transferred to the simulant.
As foods are complex matrices, different protocols comprising different extraction times and modes, as well as temperature, must be adapted for each food matrix. Highfat matrices contained higher antioxidant concentrations, due to the difficulty of extracting irganox 1076 from fatty foods. High irganox 1076 migration rates have generally been detected in high-fat, low-water foods. The physical state of the food is also an important factor in the migration process. The results for 95% ethanol and olive oil indicated comparable migration levels at all temperatures Irganox 1076 migration in iso-octane was always the highest at all study temperatures and times. The maximum migration level achieved in food applying the same time and temperature conditions, was, in all cases, lower than that obtained with the corresponding simulants.
Fat food content seems to significantly influence additive migration. Study E5[18] also analyzed several food matrices, but compared low-calorie and low-fat foods under normal storage conditions and, in most cases, demonstrated equivalent migration to more caloric and higher fat content foods. Migration from polyolefins to the fat food simulant HB 307 is higher than for real foods, except for margarine and hard cheese under normal storage conditions.
Furthermore, temperature changes display a dramatic influence on antioxidant migration. At 100 ºC, irganox 1076 migration in 8% ethanol was higher in LDPE than HDPE, while migration in 95% ethanol at 100 ºC reached 100% of the irganox 1076 content in LDPE and around 70% in HDPE. At all temperatures, the highest migration for the aqueous simulant was from LDPE, followed by HDPE. For non-aqueous simulants such as olive oil, HDPE migration is minimal. In most cases, most antioxidant content was lost from LDPE packaging after a few hours.
This systematic review study assessed primary studies investigating the migration capacity of antioxidants from polyethylene packaging to food. Studies addressing the issue of antioxidant migration have been published since the 1970’s, increasing up to the 2010’s, when a slight drop from 2011 to the present date is noted. Of the 44 primary articles included in this systematic review, only two (E21 and E23) did not report antioxidant migration, with E21 detecting only traces of BHT and E23, no detection. This demonstrates that most studies report migration of the evaluated additives to foods and/or food simulants, and this exposure to synthetic substances, thus, takes place daily, via food, at minimum and sometimes maximum doses, with long still unknown-term health consequences.
Regarding migration assessments, one of the most important observations concerns BHT motility. BHT is considered an extremely mobile antioxidant in LDPE films, especially compared to natural antioxidants such as vitamin E, a harmless substance with a comparatively low food migration rate. Thus, vitamin E comprises a suitable BHT substitute as an antioxidant in plastic and more beneficial for use in food films, especially LDPE.
Concerning the different types of packaging evaluated in the eligible articles, LDPE promotes the highest antioxidant migration rate, followed by HDPE. Several packaging factors can influence migration, such as packaging density and thickness and contact time between the packaging and the food, among others.
With regard to type of simulant, antioxidant migration rates in simulants were higher than those in foods at all evaluated temperatures, indicating that the use of simulants in migration studies provides a good safety margin.
A higher trend for antioxidant migration in food/fatty simulants is noteworthy, as all the articles analyzing antioxidant migration in these cases reported higher migration rates in the presence of food or simulant containing higher fat content, with gradual migration increases with increasing contact time and temperature.
The eligible studies evaluated only the antioxidants BHT and irganox 1076, with no research on other antioxidants included in the search method applied to this review obtained, indicating that research on a wider range of antioxidants is paramount.
The growing application of antioxidants, especially in the food packaging industry, proves that human exposure to these substances is extremely relevant and the lack of further research on the subject represents a major challenge for the scientific community.
The findings reported here are conclusive regarding antioxidant migration, as the included studies evaluated wide time and temperature ranges, several simulants and food matrices, and employed several techniques to verify migrated amounts. In addition, values migrating above the LME ranged from 3.42 mg kg-1 to 231.7 mg kg-1, much higher than the maximum permissible amounts regarding foods in contact with plastic resins, potentially leading to harmful human health effects.
Part II of this article intends to present the toxicological results regarding the antioxidant migration research presented herein.
• Conceptualization – Mayara de Simas Mesquita.
• Data curation – Mayara de Simas Mesquita.
• Formal analysis – Mayara de Simas Mesquita.
• Funding acquisition – Shirley Pereira Abrantes.
• Investigation – Mayara de Simas Mesquita.
• Methodology – Mayara de Simas Mesquita.
• Project administration – Shirley Pereira Abrantes.
• Resources – Shirley Pereira Abrantes.
• Software – Mayara de Simas Mesquita.
• Supervision – Shirley Pereira Abrantes.
• Validation – Shirley Pereira Abrantes.
• Visualization – Shirley Pereira Abrantes.
• Writing – original draft – Mayara de Simas Mesquita
• Writing – review & editing – Shirley Pereira Abrantes.
This article is part of a doctoral thesis defended at the Instituto Nacional de Controle de Qualidade e Saúde (INCQS) and was financed in part by the Coordenação Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001. Funding acquisition by Shirley Pereira Abrantes.
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Potential antioxidant migration from polyethylene packaging to food: a systematic review
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37 Coltro, L., & Machado, M. P. (2011). Migração específica de antioxidante de embalagens plásticas para alimentos. Polímeros, 21(5), 390-397 http://dx.doi.org/10.1590/S010414282011005000064
38 Linssen, J. P. H., Reitsma, J. C. E., & Cozijnsen, J. L. (1998). Research note: migration of antioxidants from polyolefins into ethanolic simulants. Packaging Technology & Science, 11(5), 241-245.
39 Beldì, G., Pastorelli, S., Franchini, F., & Simoneau, C. (2012). Time‐ and temperature‐dependent migration studies of Irganox 1076 from plastics into foods and food simulants. Food Additives & Contaminants: Part A, 29(5), 836-845 http://dx.doi.org/10 .1080/19440049.2011.649304 PMid:22313384.
40 Bailey, L. A., Lin, J. F., & Giacin, J. R. (1999). The mass transfer of 3, 5-di-tertiary-butyl-4-hydroxy toluene and α-tocopherol from coextrusion film structures. Polymer-Plastics Technology and Engineering, 38(2), 201-219
41 Reinas, I., Oliveira, J., Pereira, J., Machado, F., & Poças, M. F. (2012). Migration of two antioxidants from packaging into a solid food and into Tenax. Food Control, 28(2), 333-337. http://dx.doi.org/10.1016/j.foodcont.2012.05.023.
42 O’Brien, A., Goodson, A., & Cooper, I. (1999). Polymer additive migration to foods - a direct comparison of experimental data and values calculated from migration models for high density polyethylene (HDPE). Food Additives and Contaminants, 16(9), 367-380 http://dx.doi.org/10.1080/026520399283858 PMid:10755128.
43 Jakubowska, N., Beldì, G., Bach, A. P., & Simoneau, C. (2014). Optimisation of an analytical method and results from the inter-laboratory comparison of the migration of regulated substances from food packaging into the new mandatory European Union simulant for dry foodstuffs. Food Additives & Contaminants: Part A, 31(3), 546-555 http://dx.doi.org/1 0.1080/19440049.2013.874046. PMid:24409838.
44 Wessling, C., Nielsen, T., & Giacin, J. R. (2001). Antioxidant ability of BHT- and α-tocopherol-impregnated LDPE film in packaging of oatmeal. Journal of the Science of Food and Agriculture, 81(2), 194-201 http://dx.doi.org/10.1002/10970010(20010115)81:2<194::AID-JSFA801>3.0.CO;2-R
45 Haitao, C., Ying, L., Xia, G., Weili, L., & Yunjun, L. (2015). Antioxidant BHT modelling migration from food packaging
of high density polyethylene plastics into the food simulant. Journal of Food Science and Technology, 9(7), 534-538
46 O’Brien, A., & Cooper, I. (2002). Practical experience in the use of mathematical models to predict migration of additives from food-contact polymers. Food Additives and Contaminants, 19(Suppl. 1), 63-72 http://dx.doi.org/10.1080/10196780110082295 PMid:11962716.
47 García-Ibarra, V., Sendón, R., García-Fonte, X.-X., Losada, P. P., & Quirós, A. R. B. (2018). Migration studies of butylated hydroxytoluene, tributyl acetylcitrate and dibutyl phthalate into food simulants. Journal of the Science of Food and Agriculture, 99(4), 1586-1595 http://dx.doi.org/10.1002/ jsfa.9337 PMid:30151848.
48 Brandsch, J., Mercea, P., Rüter, M., Tosa, V., & Piringer, O. (2002). Migration modelling as a tool for quality assurance of food packaging. Food Additives and Contaminants, 19(Suppl), 29 -41 . http://dx.doi.org/10.1080/02652030110058197. PMid:11962712.
49 Rubio, L., Valverde-Som, L., Sarabia, L. A., & Ortiz, M. C. (2019). The behaviour of Tenax as food simulant in the migration of polymer additives from food contact materials by means of gas chromatography/mass spectrometry and PARAFAC. Journal of Chromatography. A, 1589, 18-29. http://dx.doi. org/10.1016/j.chroma.2018.12.054 PMid:30598289.
50 Feigenbaum, A., Scholler, D., Bouquant, J., Brigot, G., Ferrier, D., Franz, R., Lillemark, L., Riquet, A. M., Petersen, J. H., Van Lierop, B., & Yagoubi, N. (2002). Safety and quality of food contact materials. Part 1: evaluation of analytical strategies to introduce migration testing into good manufacturing practice. Food Additives and Contaminants, 19(2), 184-201 http:// dx.doi.org/10.1080/02652030110053002 PMid:11820501.
51 Vera, P., Canellas, E., Barknowitz, G., Goshawk, J., & Nerín, C. (2019). Ion-mobility quadrupole time-of-flight mass spectrometry: a novel technique applied to migration of nonintentionally added substances from polyethylene films intended for use as food packaging. Analytical Chemistry, 91(20), 12741-12751 PMid:31502827.
52 Helmroth, I. E., Dekker, M., & Hankemeier, T. (2002). Influence of solvent absorption on the migration of Irganox 1076 from LDPE. Food Additives and Contaminants, 19(2), 176-183 http:// dx.doi.org/10.1080/02652030110066198 PMid:11820500.
53. Liang, R., Hu, Y., & Li, G. (2020). Monodisperse pillar[5] arene-based polymeric sub-microsphere for on-line extraction coupling with high-performance liquid chromatography to determine antioxidants in the migration of food contact materials. Journal of Chromatography. A, 1625, 461276 http:// dx.doi.org/10.1016/j.chroma.2020.461276 PMid:32709328.
54 Abrantes, S. M. P. (1998). Uso da eletroforese capilar para a determinação da migração química em alimentos em contato com embalagens (Doctoral thesis). Universidade Federal do Rio de Janeiro, Instituto de Química, Rio de Janeiro
55 Gnanasekharan, V., Floros, J. D., & Glacin, J. R. (1997). Migration and sorption phenomena in packaged foods. Critical Reviews in Food Science and Nutrition, 37(6), 519-559 http:// dx.doi.org/10.1080/10408399709527788. PMid:9404993.
56 Baner, A., Bieber, W., Figge, K., Franz, R., & Piringer, O. (1992). Alternative fatty food simulants for migration testing of polymeric food contact materials. Food Additives and Contaminants, 9(2), 137-148 http://dx.doi.org/10.1080/02652039209374056 PMid:1499771.
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Mesquita, M. S., & Abrantes, S. M. P.
58 U.S. Food and Drug Administration. (1995). Recommendations for chemistry data for indirect food additive petitions Silver Spring: U.S. Food and Drug Administration
59 Pop, A., Kiss, B., & Loghin, F. (2013). Endocrine disrupting effects of butylated hydroxyanisole (BHA - E320). Clujul Medical, 86(1), 16-20 PMid:26527908.
60 Van Battum, D., Rijk, M. A. H., Verspoor, R., & Rossi, L. (1982). Draft eec method for the determination of the global migration of plastics constituents into fatty-food simulants: applicability to lacquers, plastics and laminates. Food and
Chemical Toxicology, 20(6), 955-959 http://dx.doi.org/10.1016/ S0015-6264(82)80236-8 PMid:6891682.
61 Brasil Resolução da Diretoria Colegiada - RDC nº51/2010 (2010, November 30). Dispõe sobre migração em materiais, embalagens e equipamentos plásticos destinados a entrar em contato com alimentos Diário Oficial da República Federativa do Brasil, Brasília
Received: Aug. 23, 2022
Revised: Jan. 24, 2023
Accepted: Jan. 25, 2023
Mercedes Puca Pacheco1* , Oscar Rafael Tinoco Gómez2 , Gonzalo Canché Escamilla3 , Santiago Duarte Aranda3 and María Guadalupe Neira Velázquez4
1Facultad de Ingeniería, Carrera de Ingeniería Industrial y Comercial, Universidad San Ignacio de Loyola, Lima, Perú
2Facultad de Ingeniería Industrial, Universidad Nacional Mayor de San Marcos, Lima, Perú
3Unidad de Materiales, Centro de Investigación Científica de Yucatán A.C., Yucatán, México
4Centro de investigación en Química Aplicada, Coahuila, México
*mpucap@gmail.com
Obstract
Currently there is a great trend towards cleaner, more sustainable and green production, based on a circular economy. Therefore, in the present work the study of the effect of the concentration of potato starch, aloe vera and graphene on the mechanical properties, water vapor permeability, biodegradability and structural properties of bioplastics is reported. These bioplastics could replace conventional synthetic plastics that currently produce high environmental pollution. According to the statistical analysis of a 2˄3 factorial design, a biodegradable bioplastic with improved mechanical properties was obtained, with a high maximum stress of 2.49 ± 0.28 MPa at high concentration levels of starch, aloe vera and graphene (10% w/w starch, 24% w/w of aloe and 0.045% w/w of graphene). A minimum value of permeance and permeability to water vapor of 5.35 kg/h.kPa.m2 and 0.001839 kg/h.kPa.m, respectively, was found at a graphene concentration of 0.005%; aloe concentration, 24%; and starch concentration, 10%.
Keywords: graphene, bioplastic, biodegradable, mechanical properties, starch.
How to cite: Puca Pacheco, M., Tinoco Gómez, O. R., Canché Escamilla, G., Duarte Aranda, S., & Neira Velázquez, M. G. (2022). Obtaining and characterization of bioplastics based on potato starch, aloe, and graphene. Polímeros: Ciência e Tecnologia, 32(4), e2022037. https://doi.org/10.1590/0104-1428.20220084
Currently, interest has arisen in developing new materials to replace synthetic polymers that pollute the environment[1]. To date, more than 8 billion tons of plastics have been produced in the last 70 years and an increase in non-biodegradable plastic waste is expected to exceed 25 billion metric tons by 2050[2,3]. The waste produced causes very severe damage to the environment and biodiversity[4,5]; since they contaminate the oceans by 85% and are even ingested by living organisms causing damage and death[6,7]
Currently, the main strategy of the plastic industries is to adopt a circular economy instead of a linear economy. The circular economy consists of zero-waste manufacturing, which allows conventional plastic products to be remanufactured, reused, and recycled at the end of their useful life[8,9]. Given this situation, biodegradable biopolymers can put an end to the problem of environmental pollution, since after their useful life, they degrade and are transformed into biomass again without harmful effects on the environment[10,11].
The advantage of using biopolymers is that they do not pollute the environment, they are chemically versatile, sustainable, biocompatible, biodegradable, non-toxic,
renewable, not intrinsically functional and ecological[12] However, there is a need to improve the mechanical properties, transport properties (vapor and gas permeability), and poor processability among others. For this reason, there are other studies on the incorporation of cellulose nanoparticles, zinc, magnesium, copper and gold nanoparticles to obtain polymeric nanocomposites with better thermal and mechanical properties and biodegradability[13,14]
Starch is the second most abundant carbohydrate in the biosphere after cellulose. In this work, Yungay potato starch was selected, due to its performance, processability and costs, which are the greatest challenges for the production of biodegradable polymers to be effective and fulfill the functions required during their useful life and final disposition of the product. Aloe vera gel has been used for the formation of the bioplastic since it is rich in mucilage, which is the source of polysaccharides containing galacturonic, glucuronic, and sugar-linked acids as glucose, galactose and arabinose; and phenolic compounds with great antioxidant power and act as an antibacterial agent in films[15]. Aloe vera improves compatibility between starch and glycerin, preventing phase separation[16]
On the other hand, graphene is a two-dimensional (2D) carbon nanostructure, with sp2 hybridization, which was discovered by Geim and Novoselov[17], they used scotch tape to peel graphene sheets from graphite. The important characteristics of graphene are its high thermal conductivity[18], Young’s modulus of 1 Terapascal, being 100 times stronger than steel and 6 times lighter than steel, also present good thermal and optical properties[19], among other, for which it has created interest to be used in energy storage materials[20], drug delivery systems[21], biosensors[22], polymeric compounds[23], and in other areas.
In the present research work, a biodegradable bioplastic material based on yungay potato starch, aloe vera gel and graphene with better physicochemical and mechanical properties has been obtained at laboratory level, to be considered as an alternative material to synthetic plastics.
For the synthesis of graphene, graphite from SigmaAldrich was used. Sulfuric acid at 98% w/w, potassium permanganate, concentrated hydrochloric acid at 36.5% w/w and ascorbic acid were also used and were acquired from Merck (Peru). Triple distilled, deionized and filtered water was used. Yungay potato tubers (Solanum tuberosum) from the department of Huánuco in Peru were used. Aloe vera (barbadensis Miller) from Lima was used. Venturo brand vinegar and glycerin acquired from Laboratory Alkofarma EIRL were used.
The extraction of the starch was carried out at the laboratory level by means of a manual process. For this, the Yungay potato was harvested, washed and peeled, after which they were chopped into approximately 3 cm sizes and blended with cold boiled water in a proportion of 1: 1 to facilitate starch extraction. Then the starch was decanted and the supernatant liquid was then removed. The starch obtained was dried at 50 °C for 15 hours. Finally, the starch was pulverized and stored at a temperature of 20 °C[24]. Thus, starch granules of 5 to 10 microns were obtained.
To obtain the aloe vera gel, the aloe leaves collected were washed to remove all impurities. They were then placed for 2 days in a bucket containing drinking water to remove the iodine. Then the bark was separated, to only keep the pulp (aloe vera). The separated pulp was chopped and subsequently liquefied for 5 minutes to obtain a good homogeneity.
The following procedure was used to obtain graphene: 0.5 g of graphite was weighed and poured into a 250 mL erlenmeyer flask, and then the flask, was placed in an ice bath, then 23 mL of concentrated sulfuric acid was slowly added, keeping the solution at a temperature below 20 °C and stirring for 4 hrs. Then 3 g of solid KMnO4 were added
slowly and the stirring was maintained for 1 hour more in an ice bath. The solution was then heated to 35 °C, removing it from the ice bath, and keeping it under stirring for 1 hour more. Next, 45 mL of distilled water was added and then heated at 95 °C; keeping it under stirring for 2 hours. Then 10 mL of 30% hydrogen peroxide solution was added, and it was stirred for 1 hour more. Then 200 mL of a 5% m/v ascorbic acid solution was added to achieve the reduction of the graphene oxide and the solution was kept under stirring for 2 hours. In this stage, topological defects and vacancies produced during the elimination of functional groups can be created[25]. Then, the graphene obtained was washed with distilled water and finally dried at 50 °C for 2 days.
For the preparation, potato starch was poured into the water, heated to 40 °C, and mixed for 10 minutes. Then 7 g of vinegar (5% w/v acetic acid) was added and stirred for 15 minutes to produce acid hydrolysis of starch and to remove amylopectin branches. Aloe vera gel was added and after 10 minutes of stirring, graphene (previously sonicated in 30 mL of distilled water for 30 minutes) was also added, and agitation was continued for another 15 minutes. Then 5 g of glycerin was added to provide flexibility to the bioplastic and the mixture was stirred for 10 minutes. The solution was heated between 60 °C and 70 °C and stirred for approximately 5 minutes until the mixture acquired a certain viscosity at the gelatinization temperature and then was poured into a 20 × 20 cm glass mold. Finally, the viscous mixture was dried in an oven at 60 °C for 10 hours. The amounts of starch, aloe vera and graphene used in the preparation of the films, were according to Table 1.
To evaluate the effect of the concentrations of Yungay potato starch, aloe vera gel, and graphene on the mechanical properties, and biodegradability of the films, an experimental design was proposed through a factorial design 2˄3 with three factors: the starch concentration (%w/w), the aloe concentration (%w/w) and the graphene concentration (%w/w), of two levels for each factor: high level (+) and low level (-) as shown in Table 1. A 2˄3 design was chosen since it allows estimating the effects of the independent variables and the combination of them, on the response variables with fewer experiments, it is cheaper and with the same precision than studying them separately[26]. The range of graphene
Obtaining and characterization of bioplastics based on potato starch, aloe, and graphene
concentration was considered from 0.005 to 0.045%w/w since at graphene concentrations above 0.045%w/w formed brittle films and were not homogeneous.
In each run, the glycerin concentration was maintained at 5% w/w, vinegar concentration at 7% w/w and the rest distilled water was used until completing 100% in the formulation.
For the structural characterization, a Nicolet model protege 8700 equipment with an ATR accessory and ZnSe crystal was used, making 6 scans from 4000 to 650 cm-1, and a resolution of 4 cm-1
For the film’s biodegradability study, aerobic biodegradation was performed, which produces the complete oxidation of the bioplastic. To do this, they were measured by placing the films inside farmland prepared to be degraded by the natural action of microorganisms, decomposing into carbon dioxide, water and/or methane and biomass, and the bioplastic films were weighed every 7 days for 1 month. To calculate weight loss, a test was carried out for a period of a month. The following Equation 1 was used:
vapor transmission (WTV) and water vapor permeance values were calculated from the following expressions:
Water Vapor Transmission Rate, WVT:
/ Gt WVT A = (3)
where:
G = weight change, in grams (from linear graph G/t); t = time, hours;
A = exposure area, m2 (canopy area: 0.0025 m2).
Permeance:
where:
∆p = S (R1 – R2),
S = mmHg (Absolute saturated vapor pressure at a temperature of 23 °C., 21.068 mmHg) *
R1 = Relative humidity of the crown, that is, 1
R2 = Relative humidity at normal laboratory conditions (0.5)
* Value reported per ASTM D1653-1 standard (Standard Test Methods for Water Vapor Transmission of Organic Coating Films).
Permeability:
In this work, the water solubility of the bioplastic was determined according to the methodology proposed by Gontard et al.[27] The bioplastics were cut in a circular shape with a diameter of 2 cm, weighed, and then immersed in 50 mL of distilled water contained in glass beakers. The samples were kept in water and stirred for 24 hours at 25 °C. The samples were dried (105 ± 2 °C for 24 hours) in a drying oven, and then the dry weight of the bioplastic that was not solubilized was determined. The solubility is expressed according to Equation 2:
PermeabilityPermeance*Thickness = (5)
The bioplastic films evaluated had an average thickness of 0.3437 mm.
3.1 Structural characterization of starch and aloe vera.
Table 2 shows the yield and composition chemical of Yungay potato starch. A starch yield of 8.13% was obtained with respect to the dry weight of the potato. The content of amylose (linear polymer) and amylopectin (branched polymer) was 25.67% and 74.32% respectively.
where:
PI: Initial weight of bioplastic (g);
PF: Final weight of dry bioplastic that was not solubilized in water (g).
The morphology analysis of the cross section of the bioplastics was observed using a JEOL 6360LV SEM scanning electron microscope operated at 20 kV.
To carry out the mechanical tests of the films with an average thickness of 324 microns, the samples were conditioned at a temperature of 25 °C and relative humidity (RH) of 66 ± 4% RH for 24 hours prior to the mechanical tests. The tests were carried out on a Shimadzu AGS-X universal machine with a 100 N load cell. The speed of the test was 3 mm/min, according to the ASTM D 882 standard.
For the determination of the water vapor transmission (WVT) and the permeance in the starch/aloe vera/graphene films, the standard ASTM E96/E96M-14: Standard Test Method for Water Vapor Transmission of Materials was used, using the desiccant method or dry cup method. The water
Aloe vera leaves are made up of a gel and a bark that represent 60.2 and 39.8% of the weight of the fresh leaf, respectively. The aloe vera gel is mainly made up of water (99.1%) and the 0.9% remaining are mucilage and other carbohydrates[31,32]
The infrared spectrum of dry aloe vera gel (Figure 1) shows the functional groups of these compounds. The broad absorption band centered at 3424 cm-1 is due to the stretching of -OH groups, a characteristic of carbohydrate monomers, such as mannose and uronic acid[33,34]. The absorption band at 2922 cm-1 can be assigned to symmetric and asymmetric C-H stretching of aliphatic -CH and -CH2 groups. The absorption band at 1743 cm-1 is a characteristic of C=O stretching, which indicates the presence of carbonyl groups in aloe vera samples, which is not seen in the infrared spectrum of starch and allows them to be differentiated. The absorption reaches its maximum point at 1634 and 1418 cm-1, these signals are associated, respectively, with the asymmetric and symmetric stretching of carboxylate compounds -COO- in aloe vera. The absorption peak at 870 cm-1 is due to outof-plane C−H deformation of the carbohydrate monomers. These absorption peaks indicate the presence of mannose and uronic acid, as well as their carbohydrate polymers[35,36]
Figure 2 shows the infrared spectrum of graphene synthesized by the modified Hummer method, showing a band around 1600 cm-1, which corresponds to the stretching vibration of the C=C bond, another peak located around 1100 cm-1 due to the vibration of the ether group (C-O-C), and also other peaks associated to the stretching and bending
vibration of the O-H bond around 3000 - 3500 cm-1 and at 1400 cm-1, are shown[37]
Figure 3 shows the FTIR spectra corresponding to the samples with the high level (F1G) and the lower level (F2G) of the components (see the factorial design in Table 1). In the region from 400 to 1250 cm-1 considered the fingerprint region[38], there were four characteristic peaks in the spectra between 925 and 1150 cm-1, which are attributed to the stretching of the CO bond[39]. The peak located at 1467 cm-1 is assigned to the bending of the CH2 group and the broad peak between 2900 and 2950 cm-1, is characteristic of the C-H stretches associated with the glucopyranose ring[40] The broad peak between 3000 and 3700 cm-1 is due to the hydrogen bonding of the hydroxyl groups that contributes to the stretching vibrations associated with the inter and intramolecular free bonding of the hydroxyl group, and this group being a characteristic of the structure of the starch[41]
Table 3 shows the results of the % biodegradability after 30 days of exposure, which are between 75.61 and 94.37%. Graphene is chemically inert since it does not corrode or degrade in the presence of atmospheric agents such as light, humidity and pH[42,43], so the film decomposition is mainly
Obtaining and characterization of bioplastics based on potato starch, aloe, and graphene
due to organic matter such as starch and organic compounds present in aloe gel. The degradation capacity of bioplastics is due to the hydrophilic nature of starch, which is increased by containing glycerin, which produces greater adsorption of water, which favors the cultivation of starch-degrading bacteria and fungi. The biodegradation is catalyzed by the action of enzymes that break the bonds between the anhydroglucose molecules of the starch chains[44]
Table 3 shows that the bioplastic films have a solubility in water between 41.00 ± 0.11 and 59.93 ± 0.67%, which can be attributed to the glycerin present in the film. The remotion of compounds soluble in water, such as glycerin and oligomers, increases because water has a high affinity with the starch matrix which results in the acceleration of the diffusion of water through the polymeric film. It was found that increasing the content of graphene in the formulation, results in a higher solubility of the films.
Figure 4 shows the images obtained by SEM of the cryogenic fracture zone of the graphene-reinforced films with a higher concentration of graphene (0.045% w/w) at different magnifications. It can be observed that all samples show the presence of several stacked graphene sheets with a dense, wrinkled and folded morphology (indicated by the arrow in Figure 4b) and this is more notorious when the high level of starch was used in the films (F1G and F4G). These films show the presence of starch granules in one face of the films, and the films can be appreciated in the cross section of an irregular fracture of the film.
According to Table 4, it is important to point out that the maximum stress was higher in the high level of starch, aloe and graphene concentration compared with the low level.
According to the results shown in Table 4, the maximum stress was between 2.49 ± 0.28 and 1.09 ± 0.10 MPa and the % elongation at break was between 63.67 ± 6.26 and 29.06 ± 2.15%.
A decrease in Maximum stress from 1.93 MPa to 1.36 MPa and an increase in % elongation at break from 29.06 to 63.67% was observed when the weight ratio of glycerin and starch was increased from 5:10 to 5:6 in run F4G and F6G respectively (see Table 1). Similar behavior to that reported by Meneses et al.[45] who pointed out that the increase in the dose of glycerin reduces the intermolecular forces, such as internal hydrogen bonds, causing the bioplastic to be flexible and less resistant, increasing the intermolecular spaces, and avoiding cracks in the bioplastic during its manipulation and storage.
For the ANOVA analysis of the results obtained the Minitab Statistical Software Version 21.1. 0 was used. Table 5 shows the analysis of variance for maximum stress and elongation at break (%). According to the study of the principal effect, a significant effect of the starch concentration on maximum stress, and strain at break was obtained with a p-value of 0.0000. Also, there was a significant effect of aloe concentration on maximum stress, and elongation at break (%) with a p-value of 0.0024 and 0.0139 respectively. Finally, there was a significant effect of graphene concentration on maximum stress, and elongation at break (%) with a p-value of 0.0005 and 0.0141 respectively.
According to the main effects, a direct effect of the concentration of starch, aloe and graphene on the maximum resistance was found. However, an inverse effect of starch concentration on elongation at break(%) and a direct effect of aloe and graphene concentration on elongation at break were found.
Table 6 show the result of permeance and permeability of bioplastic film for design 2˄3 with two central points.
Table 7 shows the analysis of variance of the permeability results, which was obtained using the statistical software Minitab 21.1.0 and it was found that the concentration of starch and the concentration of graphene had a significant effect with p values of 0.029 and 0.044 (p-value ˂ 0.05). However, the concentration of aloe had no significant effect. It was shown that the permeability to water vapor depends not only on the concentration of graphene (filler) and the concentration of starch, but there is also an interaction between the concentration of starch and graphene, which determines the dispersion, the affinity of the permeant gas molecule - membrane and the morphology of the nanoparticle.
A biodegradable bioplastic material based on starch, aloe vera, and graphene using an experimental design 2˄3 with
Obtaining and characterization of bioplastics based on potato starch, aloe, and graphene
improved mechanical properties was obtained, with a high maximum stress of 2.49 ± 0.28 MPa at high levels of starch, aloe and graphene concentration (10%w/w starch, 24%w/w aloe and 0.045%w/w graphene).
Therefore, the use of aloe, starch and graphene is convenient to obtain better mechanical properties. Likewise, using graphene and aloe vera, maximum stress is improved, and the strain at break is increased, that is, it gives flexibility to the bioplastic.
A minimum permeance and permeability value of 5.35 kg/h.kPa.m2 and 0.001839 kg/h.kPa.m, respectively, was found at a graphene concentration of 0,005%; aloe concentration, 24%; and starch concentration, 10%.
For future studies, the antimicrobial properties in the bioplastic film will be measured. Also, other reinforcing materials will be used, such as nanocellulose fibers, in order to further improve the mechanical properties.
5. Author’s Contribution
• Conceptualization – NA.
• Data curation – NA.
• Formal analysis – Mercedes Puca Pacheco; Oscar Tinoco Gómez.
• Funding acquisition – NA.
• Investigation – Mercedes Puca Pacheco.
• Methodology – Mercedes Puca Pacheco.
• Project administration – NA
• Resources – Mercedes Puca Pacheco; María Guadalupe Neira Velázquez; Gonzalo Canché Escamilla; Santiago Duarte Aranda; Manuel Aguilar Vega.
• Software – NA.
• Supervision – NA.
• Validation – NA.
• Visualization – NA.
• Writing – original draft – Mercedes Puca Pacheco.
• Writing – review & editing – Mercedes Puca Pacheco; Gonzalo Canché Escamilla; María Guadalupe Neira Velázquez.
The authors thank María Isabel Loría Bastarrachea (CICY) for her support in running the water vapor permeability tests.
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Received: Sept. 04, 2022
Revised: Nov. 17, 2022
Accepted: Nov. 25, 2022
Jefferson Renan Santos da Silva1 , João Christian Paixão Fonseca1 , Thais da Silva Santos1 , Josiel Bruno de Oliveira1 , Thiago Monteiro Maquiné2 , Bruno Mello de Freitas1 , Raimundo Nonato Alves Silva1 , Nayra Reis do Nascimento1 , João Martins da Costa1 , Roger Hoel Bello1 and José Costa de Macedo Neto1*
1Departamento de Engenharia de Materiais, Universidade do Estado do Amazonas – UEA, Manaus, AM, Brasil
2Programa de Pós-graduação em Ciência e Engenharia de Materiais – PPGCEM, Universidade Federal do Amazonas – UFAM, Manaus, AM, Brasil *jmacedo@uea.edu.br
Obstract
Solid residues from agroindustry often accumulate and cause environmental imbalance. An alternative to this is to use this residue as a reinforcement in polymers. The achievement of this work was to characterize a composite with a polystyrene matrix reinforced with Brazil nut shells residues. The residues were cleaned and ground to then produce the samples via injection molding with the proportions of 0%, 2.5% and 5% of load. The specimens were characterized using mechanical tensile testing and thermogravimetric analysis (TGA). The mechanical test showed that the composite with 2.5% of filler had greater stiffness and strength was improved by 5%. Thermal analysis showed an increase in the temperature for the beginning of the degradation of the M2.5 composite. The results confirm a potential application in the automotive industry for the polystyrene composite reinforced with Brazil nut shells.
Keywords: residues, polystyrene, HIPS, characterization.
How to cite: Silva, J. R. S., Fonseca, J. C. P., Santos, T. S., Oliveira, J. B., Maquiné, T. M., Freitas, B. M., Silva, R. N. A., Nascimento, N. R., Costa, J. M., Bello, R. H., & Macedo Neto, J. C. (2022). Polymer composite produced with Brazil nut residues and high impact polystyrene. Polímeros: Ciência e Tecnologia, 32(4), e2022038. https://doi. org/10.1590/0104-1428.20220013
The Brazil nut (Bertholletia excelsa), one of the tree species of greatest economic importance in the Amazon region, has excellent quality wood, but felling of these trees is prohibited. Its fruit, which is a husk with the nuts inside, has natural rigidity and is part of the extractive activities of the Amazon[1]. Brazil nut trees have great economic value due to the exploration of their nuts (which have about 60 to 70% lipids and 15 to 20% proteins)[2]
In Brazil, the state of Amazonas stands out for being the largest producer of Brazil nuts, and production was 11,707 tonnes in 2020, which is equivalent to 35.3% of the total produced in the country[3]. However, studies show that, for every ton of shelled nuts, 1.4 tons of residues are produced, which are composed of the shells and the husks[4] One of the solutions to the problem of the accumulation of residues that is currently being investigated is the use of plant waste as a filler in polymeric composite materials and other so-called traditional engineering materials[5]. In this context, the management of residues benefits organizations and society through the commercialization of these materials and the generation of income through the practice of recycling and sustainability[6]. In addition, the alternative
use of lignocellulosic materials, such as Brazil nut shells, either as particles or fibers in polymer composites, has been studied due to factors such as increased elastic modulus and mechanical strength, in addition to reducing the weight and cost of the final product[7].
Polystyrene (PS) at room temperature is an amorphous glassy polymer and has low energy absorption under impact due to the absence of local mobility of chain segments, since its Tg occurs between 90 and 100 C. Obtaining rubber-PS results in the product known as high impact polystyrene (HIPS), which under impact has mechanical properties that are superior to PS. This improvement is mainly due to the introduction of a flexible amorphous component (Tg ≤ - 40 °C) in the rigid matrix of PS[8] .
An important polymer that can be used in composite materials with shell residues as a filler is high impact polystyrene (HIPS). This polymer consists of a multiphase copolymer in which rubber particles of polybutadiene (PB) are dispersed in the rigid matrix of polystyrene (PS). HIPS has a melting temperature (Tm) of 180-270 °C, and is usually processed via injection at 210 to 260 °C, and its main application is in electronic components[9]. In addition to its temperature
not being high during processing, these characteristics make HIPS of great interest for applications in composites with lignocellulosic materials, since the optimization of the balance of rigidity and impact properties can be achieved by controlling the morphology and formulation of the composite[10]
In the literature, studies using Brazil nut shells have already obtained promising results[11]. Some other studies have produced polymeric composites using lignocellulosic fillers obtained from agricultural tailings and HIPS matrix and polystyrene. Zafar and Siddiqui[12] produced polymeric composites by in situ polymerization with a polystyrene matrix using rice husk, wheat husk and mustard husk as fillers. In this study, the husks were ground to 250-355 µm, 355-500 µm, and 500-710 µm. The authors performed the tensile test in which composites with a wheat husk and mustard husk filler of 250-235 µm at 10% load achieved better results, while the composite with rice husk of 355-500 µm achieved a better result with a 5% load. Siregar et al.[13] produced a composite with HIPS and pineapple fiber with and without alkaline treatment. The composites were prepared using an intensive mixer and then the mixture was hot pressed in a compression mold. The fibers were ground and passed through a sieve with a 10-40 mesh. The authors tested the melt flow index (MFI) and observed that the melt flow index of the composite with untreated fiber was 0.316 g/10 min, while that of neat HIPS was 4.0 g/10 min.
Saber et al.[14] produced a composite by compression molding using a HIPS matrix and filler made up of sugarcane bagasse in the quantities of 10, 20, 30, 40, 50% with treatments in water, HCl, NaOH solution and oil. The results were interpreted by bar graph comparison. All composites using water-treated fibers reduced tensile strength and increased elastic modulus in relation to pure HIPS. Composites with 10 to 20% wt/wt fibers reduced 32% tensile strength, those with 30 to 40% wt/wt reduced 40% and 50% wt/wt showed a 60% reduction. Additionally, all composites increased the elastic modulus above 20% in relation to pure HIPS, and the composite with 50% wt/wt fiber showed an increase of 250%. The treatments of the composites with 5% HCl, 5% NaOH and oil increased Young’s modulus by an average of 20% for all the composites relative to pure HIPS. The tensile strength was reduced by an average of 55% for all composites compared to pure HIPS. In our work, we show the mechanical and thermal performance of a HIPS composite with a Brazil nut shell filler obtained from Amazonian agro-industry. For this, the materials were produced via injection molding, and is one of the very few works on HIPS with Brazil nut shells.
Thus, the objective of this work was to produce a polymeric composite material using a HIPS matrix and Brazil nut shells as the lignocellulosic filler. Obtaining this material aims at possible applications in the automotive industry since it combines lower weight and high rigidity. Due to this application, it is necessary to understand the fracture mechanism of this composite, as HIPS presents deformation by microfibrillation or crazing and the shell acts as a filler that increases rigidity. A large majority of the literature shows the crazing in a two-dimensional manner with a large shortcoming since the propagation of the crazing is not shown in 3 dimensions, but this is addressed
in this work. For this, a detailed study of the basic fracture mechanism of the tensile test was performed using optical and scanning electron microscopy (SEM). Finite element simulations were also performed to obtain the thermal transient behavior in the material, in addition to the characterizations using FT-IR, TGA and DSC.
The Brazil nut shells were obtained from a producer in the Amazonas state, Brazil. Figure 1a shows the tree that provides the nut shells that can be used as a filler in plastics. Figure 1b-1c show the fruit, in this case, the open husk and inside it the nuts can be seen. Inside the shells are the white-colored nuts. Figure 1 d shows the shells left after removing the nuts. These residues were used to obtain the polymeric composite materials.
After collection, manual scraping and dry brushing were performed to remove any residue[10]. Subsequently, the shells were ground using a knife mill (MA048 Marconi). Finally, the ground shells were sieved through a 20 mesh sieve (Tyler/ ABNT). The particle dimensions were measured using a digital optical microscope (VHX-100, Keyence, Japan) and presented dimensions (between 1.0-2.39 mm). The HIPS used as the matrix was donnated by INNOVA, Manaus.
The sample was obtained using injection moulding in which the HIPS was weighed and separated into two different quantities, taking as a reference the value of 0.7500 kg as the maximum amount of material. The proportion was defined in relation to its weight being 2.5% (M2.5) and
Polymer composite produced with Brazil nut residues and high impact polystyrene
5% (M5) of residue. A storage container was used to mix the shells in particulate form and the HIPS in pellet form. Mixing was performed manually by preparing the container, seeking to ensure the best mixing of the polymer matrix and filler. This method was used because it is practical and fast, and is economical because it does not add another process, such as extrusion, in order to mix the polymer and filler[15]. For the production of samples according to the ASTMD 638-2010 standard, an injection moulding machine (300/1400/390 CL, Krauss Maffei, Germany) was used. The temperatures of the zones were 200 °C (T1), 228 °C (T2), 225 °C (T3) and 238 °C (T4). For the injection process, a speed of 75 mm/s was used, and injection pressures of 900 bar, relief pressure of 800 bar, injection time 5 s, relief time of 15 s and cooling time of 30 s.
For the characterization, an FT-IR spectrometer (Nicolet 6700 Madison, Thermo Scientific, USA) was used. The measurements were made in ATR (germanium crystal) mode using the FT-IR Imaging Microscope (Nicolet Continuun Madison, Thermo Scientific, USA). The ranges used were between 4,000-675 cm-1 and the resolution was 4 cm-1 and the SCAN number was 64. The samples were analyzed via tensile testing on the universal testing instrument (Series 5980, Instron, USA). Tensile testing was carried out according to the ASTMD 638-2010 standard with type I sample dimensions, 150 kN cell, test speed 5.0 mm/s, and 3 samples were tested. Scanning electron microscopy (SEM) (Vega3, Tescan) with a voltage of 10 kV was used to analyze the faces of the fractures obtained in the tensile tests. The TG analysis was performed in a TGA-DSC thermogravimetric analyzer (TGA-50M Shimadzu, Japan), with the aid of a microanalytical scale (MX5, MetllerToledo, Switzerland). The method used was the TGA021, which consists of heating from 25 °C to 600 °C, at the rate of 10 °C/min, under an inert atmosphere of nitrogen (50 mL/min). This analysis was applied to the residue, the HIPS and the composites. The glass transition temperature is the temperature at which the polymeric chains of the amorphous phase acquire mobility. To determine the glass transition (Tg) temperatures, a differential scanning calorimeter (DSC) (DSC1, Mettler Toledo, Switzerland) was used in the temperature range from
-30 to 300 °C, heating rate of 10 K/min, under an atmosphere of N2 with a flow rate of 50 mL/min. To study the thermal transient and predict some of the mechanical properties of the composites and HIPS, finite element analysis (FEA) was used. For this analysis, Ansys Workbench® software was employed. In this simulation, heat was applied to the end of the sample, as seen in Figure 2. The simulation started at 25 °C and an external temperature of 50 °C, which, according to Saber et al.[14], is the maximum operating temperature for HIPS, for 8 h in the transient regime.
The material type, explicit dynamic mode and characteristics of a quasi-static test were obtained from the Ansys® software library. The contour parameters used in the software for the HIPS analysis were a) displacement of |100| mm (tensile), b) analysis time of 7x10-4 s, c) mesh size of 3 mm, d) 257 knots, e) 219 elements and f) Poisson coefficient of 0.407. The outline properties for the HIPS were a density of 1.021 kg.m3, thermal expansion coefficient of 84 C-1, elastic modulus of 737.17 MPa, melt modulus of 8.19 x 108 Pa, shear modulus of 2.73x108 Pa, flow voltage of 14.22 MPa, isotropic thermal conductivity of 0.12 W.m-1.C-1 and specific heat of 0.23 J.g-1.K-1. The specific heat (Cp) represents the energy required to change the temperature of a unit of mass of the material by one degree. The following Equation 1 was used in the thermal transient simulation (temperature and time variation)[16].
Where:
heat generation as a function of time; q = thermal diffusivity of the material;
== thermal conductivity of the material; k = specific mass;
= specific heat;
= temperature variation over time;
Figure 3 illustrates the infrared spectrum for the Brazil nut shell residue, HIPS polymer (0%) and the polymer composites of the HIPS matrix containing 2.5% (M2.5) and 5% (M5) of Brazil nut shells. According to Figure 3, it is possible to observe that the spectrum of the Brazil nut has two intense absorption bands at 3,424 cm-1, which are related to O-H bond stretching. Close to 1,742 and 1,615 cm-1, the stretching bands (C=O) are observed, which are attributed to carboxylic acids and esters. For lignin, these stretchings have been associated with aliphatic ketones and substituted aromatic ketones, respectively. Additionally, the band at 1,615 and 1,374 cm-1 corresponds to aromatic skeleton vibrations, which are characteristic of lignin, while the bands at 1,453, 1,374 and 1,315 cm-1 are related to deformation (C-H). Finally, close to 1,160 cm-1, the C-O stretching occurs and, at 1,104 and 1,056 cm-1, the deformation of OH of the C-OH group occurs[17]
In relation to the spectrum of the HIPS polymer, it is possible to observe five main bands in Figure 3. The bands between 3,400-2,700 cm-1 are related to axial deformation in the hydrogen atoms attached to the carbon, oxygen
and nitrogen atom (C-H, C-O and N-H). In the regions between 3,080-3,020 cm-1, it is possible to observe the bands representing the C-H vibrations of the alkenes. In addition, the two absorption bands of the region between 2960-2850 cm-1 represent aliphatic C-H (primary and secondary carbons). The absorption bands between 1,600-1,450 cm-1 are the vibrations of the C=C band of aromatic carbons[18]
In relation to the composites using the HIPS polymer with the reinforcement of 2.5 (M2.5) and 5% (M5) Brazil nut shells, it is possible to verify the presence of all the main bands of the neat HIPS polymer, as previously reported. It was not possible to verify significant alterations in the spectra; however, it is important to note in Figure 3 that there is an increase in the band close to 1,500 cm-1 (C=C aromatic symmetric stretching for lignin), which may be associated with an increase in the lignin content present in composites[19]
The results of the tensile test can be seen in Table 1, while the image of the sample after the tensile test is shown in Figure 4. It is observed that, after adding the residues, the material showed a considerable increase in the properties of average maximum stress, yield stress and elastic modulus compared to the neat polymer, thus making it more rigid.
HIPS has a glassy matrix of polystyrene that is rigid due to its chemical structure that it contains aromatic rings as a pendant group. The incorporation of a second elastomeric phase in a PS vitreous matrix has as a main objective the increase in its toughness, i.e., its impact resistance[20] . The addition of a rigid material tends to increase the rigidity
Polymer composite produced with Brazil nut residues and high impact polystyrene
of the composite because, when there is a greater amount of reinforcement, up to a limit value so that it can be covered by the matrix, it will contribute to the greater strength of the composite. Furthermore, fillers reduce the free movement of polymer chains, thus resulting in an increase in their elastic modulus[21,22]. According to Table 1, the tensile strength of M5 was higher (21.64 MPa±0.07) compared to M2.5 (20.51 MPa±0.54). This occurred because as the fiber content increases, the stresses become more evenly distributed and the composite strength increases[23,24] However, M5 had a higher elastic modulus (0.89 GPa±0.02) than M5 (0.85 GPa±0.02). The values of the means of the elastic modulus are close, and the difference between them is not statistically significant.
A study was carried out of the fractures of the test samples tested after the tensile test, and is illustrated in Figure 4a-4b Figure 4a shows the behavior of the stress deformation curves for HIPS and the composites. It can be observed in Figure 4b that the behavior of the fractures showed it to be brittle and all the fractures occurred in the useful area of the samples. HIPS is composed of two immiscible phases of polybutadiene and polystyrene. The introduction of an elastomeric phase in the rigid PS matrix, as expected, promotes a decrease in the elastic modulus value, which means that the tenacified material deforms at stresses lower than those verified for the PS homopolymer[25].
The presence of blanching in all the samples is also observed. This blanching is called microfissuring or crazing and ais formed by 50% of the highly oriented polymers and 50% of the voids, which causes the process of dilatational deformation[26]. These microfissures occur in amorphous polymers, such as polystyrene, and are characterized by a whiteness of the amorphous region, due to differences in the refractive index that causes light scattering of the fibrils in the crazing[27]. It is observed in Figure 4b that the presence of crazing is perpendicular to the main stress in the tensile test. The stress at the tip of the crazing is greater than the average stress of the tension in the material; thus, the crazing tends to grow in the direction that is perpendicular to the uniaxial main stress in the tensile test[28].
Although the crazing is formed in all the samples, it can be observed in Figure 4b that the crazing formed in HIPS is less intense than that formed in the composites. This implies that the rubber microparticles in the HIPS induced the formation of crazing around them[29]. The growth of crazing is interrupted and restarted when it finds another rubber particle providing the emergence of smaller crazes[30]. These smaller cracks allowed a greater dissipation of applied energy before the catastrophic cracks and this caused a greater elongation in relation to the composites[26]
Figure 5b reveals that the composites demontrated a lower elongation than the HIPS, and the M5 composite showed a lower elongation when compared to M2.5.
The shell particles acted as stress concentrators and, as M5 has a greater amount of shell, therefore it became more fragile and has less elongation[31]. Another reason is that the rubber particles influenced a weakening in the adhesion of the fiber-matrix interface, thus preventing the mechanical anchoring of the polystyrene molecules on the surface of the shells, further weakening the composites[32].
Figure 5a-5c shows the fracture faces of the HIPS, and the M2.5 and M5 composites, respectively. Figure 5a shows the presence of micro fissures in the fracture of the HIPS. In Figure 5b, it can seen that the Brazil nut shell particles act as a stress concentrator at the end of the propagation of the elliptical-shaped crack[33]. However, in Figure 5c, it is observed that the greater amount of shell increased the stress concentrators, further weakening the composite, which is proven by the reduction of elongation.
Figure 5d-5f shows the scanning electron microscopy image of a fracture in the composite M5. Figure 5d shows the face of the fracture side by side after the tensile test. In the image, it is possible to observe that the shells tended to agglomerate in the matrix of HIPS and become stress concentrator points[11]. It is also possible to observe the smooth regions (black arrows) that propagated towards the clusters by shear and are perpendicular to the tensile stress[31]. Few elliptical regions (red arrow) are observed[34].
Figure 5f shows the presence of unstuck shells and regions that derive from the weak interaction of the matrix and the shell. In Figure 5f, a roughness is observed on the surface of the region that pulled the shell out of the matrix. This roughness is a result of the small rubber balls that are scattered in the HIPS matrix. In the figure, it is also possible to observe a fibrillar region (white arrow), which is characteristic of
a catastrophic fracture. It is also possible to observe the division (white arrow) of the region that presented a fast and a slow craze propagation speed[35].
In Figure 6a-6b, the thermogravimetric curves of the Brazil nut shells and the HIPS are presented. While in Figure 6c-6d, the thermogravimetric curves of the composites M2.5 and M5 are presented. Additionally, in Table 2, there is a summary of the temperatures and respective weight loss of the samples studied, i.e., filler (Brazil nut shells), neat polymer and its composites. It is important to note that the average mass of the samples was 10.20±0.11 mg.
The DTG curve of the residue showed that, at a temperature of 73.56 °C, there was a 1.391 mg loss of moisture (13.7%) due to the lignocellulosic materials having a hydrophilic character, as already cited by Viana et al.[10]. Subsequently, there was a considerable weight loss of about 5.39 mg (53.08%) at 371.8 °C, which is related to the decomposition of the cellulose through the endothermic process. Finally,
Polymer composite produced with Brazil nut residues and high impact polystyrene
the weight loss at the end of the analysis was 6.78 mg (66.79%), which can be attributed to lignin degradation[36]
The HIPS curves showed a single stage of mass loss at approximately 444.88 °C, which is also the level observed in the works of Cordeiro et al.[37] and Agung et al.[38]; in this case 415 °C. The curves of the composites showed that the addition of the residue provided a slight increase in the temperature at the beginning of degradation of the M2.5 composite, i.e., 444.68 °C (Figure 6c), but for the M5 composite this temperature dropped to 275.94 °C (Figure 6d).
After the analysis of TGA, it was observed that the shells presented a residue of 33% by weight. Neat HIPS presented a residue of 0.1% by weight. While the composites M2.5 and M5 obtained a residue of 1.444% and 6.262%, respectively. The HIPS sample almost totally decomposed in the analysis (about 0.1%). The addition of filler in the HIPS polymer matrix of resulted in residues at the end of the analysis for both compositions, which were more expressive at 5% of filler, indicating the presence of the Brazil nut shells.
Figure 7 illustrates the DSC thermograms for neat HIPS polymer and the composites. According to Figure 7, peaks
around 90 °C are attributed to moisture absorbed by the shells[39]. Additionally, it can be observed that the Tg of the composites did not show significant alterations in relation to the neat HIPS, and varied between 100 and 103 °C. This small alteration in the Tg can be attributed to the restriction imposed by the shells to the molecular movement of the HIPS matrix[40] Figure 7 also shows the specific heat (Cp) reduction for composites. This behavior was caused by the shells, which reduced heat transfer[38]. The shells of Brazil nuts consist of the exotesta regions, central mesotesta region, mesotesta vascular region and tegmen that present structures with voids such as long and porous cells, porosities and vascular exchanges[41,42]. These voids can be filled with air and moisture that act as resistance to heat transfer reducing the Cp for composites[43,44]
In order to verify the thermal transient behavior of the composites with M2.5, M5 and the HIPS, a simulation was performed using Ansys® Workbench software. The parameters used in the simulation, such as specific heat Cp of composites M2.5, M5 and HIPS were obtained from the DSC analysis (Figure 7), i.e., CpM2.5: 0.16J/g.K, CpM5: 0.12 J/g.K and CpHIPS: 0.23 J/g.K.
After the simulations, the software provided the images of the thermal transient behavior of the composites and HIPS and these can be seen in Figure 8a-8c. From the images, it is possible to observe that the composites obtained a higher thermal resistance than the HIPS during the period of 8 h (288 s). The addition of the lignocellulosic shells and the lack of a coupling agent effectively slowed the heat transfer in the HIPS matrix[44,45]
Figure 9 shows the graph obtained from the final minimum temperature after simulation for neat HIPS polymer and the composites. According to Figure 9, it is possible to observe that the HIPS left the initial equilibrium state after 288 s at 25.001 °C and, after 8 h in operation, the minimum temperature in the sample was 44.831 °C. The M2.5 composite, tested under the same conditions as the HIPS, showed greater resistance at the initial temperature
of 25.005 °C and, at the end of the 8 hours in operation, the minimum temperature in the sample was 47.215 °C. This represents a higher temperature; approximately 5% higher when compared to HIPS. The M5 composite started the thermal transition at 25.014 °C, and showed a higher initial thermal resistance when compared to the other two materials (HIPS and M2.5), however, at the end of the 8 hours, the minimum temperature in the sample was 48,400 °C. This implies an approximately 8% higher temperature when compared to the HIPS and the M2.5 composite.
The technique of producing the composite using the injection molding process has shown that it is possible to obtain the products quickly. The values for tensile strength and elastic modulus of HIPS and composites were close, but the elongation reduced for composites in relation to HIPS. The addition of filler in the HIPS caused an increase in thermal resistance (thermal insulation). This behavior has shown that the application in the production of automotive parts is possible.
In this study we investigated the role of Brazil nut shells in the thermal and mechanical properties of high impact polystyrene polymer (HIPS) and HIPS-based composites. According to the mechanical properties, it can be said that, after the addition of 2.5 and 5% by mass of the Brazil nut residues, there were no significant changes in the values obtained for the elastic modulus and tensile strength. The values were similar to those obtained for the pure HIPS polymer of 0.85 GPA and 23 MPa, respectively. However, for ductility, there was a progressive decrease in values after the increase in the amount of residues. The residues have high values of lignin and hemicellulose that hinder adhesion with the polymer matrix, justifying a superficial chemical treatment. Additionally, the results of the scanning electron microscopy corroborate the presence of agglomerates in the composites. Regarding the thermal properties, it is important to emphasize that the Brazil nut residues did not affect the thermal stability as well as the glass transition temperature values, as the values of both composites (M2.5 and M5) were similar to the pure polymer. Finally, the results demonstrated the potential suitability of the HIPS composite reinforced
with Brazil nut residues, which could be a use for a residue that has little utility.
5. Author’s Contribution
• Conceptualization – NA.
• Data curation – NA.
• Formal analysis – NA.
• Funding acquisition – NA.
• Investigation – Jefferson Renan Santos da Silva; João Carlos Martins da Costa; Roger Hoel Bello; José Costa de Macedo Neto; Raimundo Nonato Alves Silva; Nayra Reis do Nascimento.
• Methodology – Jefferson Renan Santos da Silva; João Carlos Martins da Costa; José Costa de Macedo Neto; João Christian Paixão Fonseca; Thais da Silva Santos; Josiel Bruno de Oliveira; Thiago Monteiro Maquiné; Bruno Mello de Freitas.
• Project administration – Jefferson Renan Santos da Silva; José Costa de Macedo Neto.
• Resources – NA.
• Software – NA.
• Supervision – José Costa de Macedo Neto.
• Validation – NA.
• Visualization – NA.
• Writing – original draft – Jefferson Renan Santos da Silva; João Martins da Costa; Roger Hoel Bello; José Costa de Macedo Neto.
• Writing – review & editing – Jefferson Renan Santos da Silva; João Martins da Costa; Roger Hoel Bello; José Costa de Macedo Neto.
We would like to thank the Amazonas State University (UEA), the Federal University of Amazonas (UFAM), the Research and Development Laboratory at UEA, and TESCAN Group for SEM images.
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Received: Feb. 16, 2022
Revised: Aug. 15, 2022
Accepted: Dec. 02, 2022
1Department of Forestry and Forest Products, Artvin Çoruh University, Artvin, Turkey
2Department of Forest Industrial Engineering, Artvin Çoruh University, Artvin, Turkey
3Department of Forest Industrial Engineering, Karadeniz Technical University, Trabzon, Turkey
*peker100@artvin.edu.tr
Obstract
In this study, the hybrid Entropy-TOPSIS method is applied to the problem of selecting an optimal impregnation material with maximum performance requirements. Swelling, shrinkage, bending strength, modulus of elasticity, compressive strength and shock strength values were used to rank the impregnation materials. Barite, boric acid, borax and their mixture were used to impregnation material. The impregnation materials used in the study generally increased the physical and mechanical properties of the spruce specimens, except swelling. The impregnation materials reduced the swelling of the specimens. According to the entropy method, the most important factor affecting the success of the impregnation process was the modulus of elasticity. According to the TOPSIS method, the most successful impregnation material was a mixture of barite and boric acid. Moreover, the proposed method was compared with other Multi-Criteria Decision-Making (MCDM) approaches and it can be used to ranking of impregnation materials with reliable accuracy.
Keywords: TOPSIS, entropy, decision making, impregnation.
How to cite: Ersen, N., Peker, H., & Akyüz, İ. (2022). Selection of materials with entropy-topsis by considering technological properties of impregnated wood. Polímeros: Ciência e Tecnologia, 32(4), e2022039. https://doi. org/10.1590/0104-1428.20220067
Wood material is used in many industries such as paper and cellulose, board, furniture because of its light weight, its easy to process, its resistance to mechanical and physical impacts, its good electrical and thermal insulation, its renewable. Dimensions and volume of wood material change due to the fact that it is a hygroscopic material. In addition, it may burn and it be destroyed by biotic and abiotic factors. It is not possible to completely eliminate the undesirable properties of wood. However, the wood can be protected by impregnating the wood with suitable impregnation materials[1-3]
Today, boron compounds as an impregnation material are considered one of the safest chemicals. Boron compounds are seen as the most important impregnation material of the future because they are less toxic than other heavy metal containing impregnation materials. Moreover, they have advantages such as eco-friendly, low cost, easy penetration into the wood depending on the steeping time, high performance against biological pests. Boric acid and borax, which are boron compounds and used as impregnation in the study, are the most common fire retardants in wood protection[4-8].
Barite, which is used as an impregnation material in this study, is the main source of barium. Barite is used as both a cost-reducing and functional filling material in the paint, paper, glass and ceramic industries. It has advantages such as insulation against sound and radiation, very good
chemical resistance, resistance to weather conditions and UV, stability against high pressure and heat, easy and inexpensive production from various sources. Also, powdered barite particles are easily dispersed in water and oil[9,10].
In order to determine whether the impregnation material is successful, it is necessary to evaluate more than one criterion at the same time, instead of evaluating the physical and mechanical properties (criteria) of the wood material one by one. This process can be possible with multi-criteria decision making (MCDM) methods. MCDM techniques are techniques that select and classify among alternatives by evaluating factors[11]. There are various MCDM techniques used in the literature. In some studies, MCDM techniques have been used alone or in combination[12-19]. In this research, two-stage hybrid MDCM technique, which is formed by combining entropy and technique for order preference by similarity to ideal solution (TOPSIS) methods, was used. In multi-criteria decision making techniques, the weights of the criteria are of great importance. In the entropy method, the weight of each criterion is calculated based on the observation values. The low entropy value of the criterion indicates that the criterion is important and the weight value is high[20-22] The TOPSIS is the most used of the MCDM methods due to its good performance in different fields. TOPSIS is used to rank alternatives. TOPSIS allows direct application on the obtained data and the method needs very little subjective
input. Moreover, this method has advantages such as simple and understandable, computationally efficient, and ability to measure the relative performance of alternatives in a simple mathematical form[23,24]
There are many studies on the effect of impregnation materials on the physical and mechanical properties of wood. There are no studies on the effect of impregnation materials on the properties of wood using multi-criteria decision making methods. In this study, it has been tried to determine which impregnation material is more successful in the effect of impregnation materials on the physical and mechanical properties of wood. To achieve this objective, Entropy and TOPSIS methods, which are one of the multicriteria decision-making methods and are used the most in practice, were implemented.
Spruce (Picea orientalis Link.) wood obtained from Artvin region of Turkey was used as wooden material.
Barite, boric acid, borax and their mixture (1:1; weight/ weight or 1:1:1; weight/weight/weight) was used in the impregnation process as 1.00% aqueous solutions.
Test specimens were cut in dimensions of 20 x 20 x 360 mm according to TS EN 2474 (1976) standards for tests of bending strength perpendicular to the grain and modulus of elasticity in the bending[25]. Test specimens were cut in dimensions of 20 x 20 x 30 mm according to TS 2595 (1977) standards for tests of compression strength parallel to the grain[26]. Test specimens were cut in dimensions of 20 x 20 x 300 mm according to TS 2477 (1976) standards for tests of shock strength[27]. A total of 210 test specimens, 70 of which were test specimens, were used for each test.
Impregnation process of the samples was carried out according to ASTM D 1413-76 (1976) standards[28] In the impregnation process, the pre-vacuum equivalent to 60 cm of Hg was applied at 60 minute. Then, the samples were dipped in the barite, boric acid, borax, and their mixture solution at atmospheric pressure for 60 minute. After impregnation process, the impregnated specimens were kept at the temperature of 103 ± 2°C until fully dry. The amounts of retention (kg.m-3) were calculated by the following Formula 1[29]. The impregnation test setup was shown in Figure 1 103 GxC Rx V = (1) 21GTT =−
Where:
G : the amount of solution absorbed by test specimen;
T1: weight of test specimen before impregnation (g);
T2: weight of test specimen after impregnation (g);
V: volume of test specimen (cm3);
C: the solution concentration as percentage.
Shrinkage and swelling ratios of test samples were determined according to TS 4083, 4084, 4085 and 4086 standards[30-33]
The bending strength and modulus of elasticity tests were carried out in accordance with the principles of TS 2474 (1976)[25]
The compression strength parallel to grain test was determined according to the TS 2595 (1977) standard[26]
The shock strength test was performed according to the TS 2477 (1977) standard[27].
The symbolizations of the impregnation materials (alternatives) used in this study are given as:
Alternative-1 (A-1): non-impregnated material
Alternative-2 (A-2): barite-impregnated material
Alternative-3 (A-3): boric acid-impregnated material
Alternative-4 (A-4): borax acid-impregnated material
Alternative-5 (A-5): barite and boric acid mixtureimpregnated material
Alternative-6 (A-6): barite and borax mixture-impregnated material
Alternative-7 (A-7): barite, boric acid and borax mixtureimpregnated material
The evaluated physical (shrinkage, swelling) and mechanical (bending strength, modulus of elasticity, compressive strength, shock strength) properties were taken as a criterion in the ranking process of the impregnation materials. The implications of the selected criterion are given as:
Selection of materials with entropy-topsis by considering technological properties of impregnated wood
Criterion-1 (C-1): Shrinkage (Volume-%, Lower-isbetter)
Criterion-2 (C-2): Swelling (Volume-%, Lower-is-better)
Criterion-3 (C-3): Bending strength (N.mm-2, Higheris-better)
Criterion-4 (C-4): Modulus of elasticity (N.mm-2, Higher-is-better)
Criterion-5 (C-5): Compressive strength (N.mm-2, Higher-is-better)
Criterion-6 (C-6): Shock strength (N.mm-2, Higher-isbetter)
In this study, a hybrid Entropy-TOPSIS technique was used to rank the best alternatives of impregnated materials. The architecture of the hybrid Entropy-TOPSIS approach was presented in Figure 2. The process is concerned with determining the attribute weight using the Entropy and the best alternatives using the TOPSIS method.
Entropy, one of the most used methods for weight calculation, was proposed by Shannon and Weaver[34] and formulated using probability theory. The steps of the entropy method are listed below[21,35];
Step 1: Creating the decision matrix
The decision matrix consists of the alternatives and the evaluation criteria.
Step 2: Normalization of the decision matrix
The data was subjected to normalization using Formula 2.
Where: aij is the benefit value, and pij is the normalized value.
Step 3: Calculating the entropy value
The entropy value (ej) was calculated according to Formula 3. The ej value takes a value between 0 and 1. The k value was the inverse of the natural logarithm of the total number of alternatives (k =1 / ln(m)).
Where: pij is the normalized value, ej is the entropy value and k is the entropy coefficient.
Step 4: Calculation of weight value
The weight value (wj) is calculated via Formula 4.
Where: ej is the entropy value, wj is weight value.
The TOPSIS method was first proposed by Hwang and Yoon[36] and developed by Yoon[37] and Hwang et al. [38]. The basic principle of the TOPSIS method is to choose the alternative closest to the positive ideal solution and the farthest from the negative ideal solution. This method consists of 6 steps. The stage of creating the decision matrix is explained in the steps of the entropy method, and the other steps are listed below[39];
Step 2: Normalization of the decision matrix
The data was subjected to normalization using Formula 5.
Where: J is the maximization value, J ′ is the minimization value
Step 5: Calculation of the distances to the positive (S+) and negative (S-) ideal solution
Using Formulas 9 and 10, distances to the positive and negative ideal solution are calculated.
Where: rij is normalized value.
Step 3: Creation of weighted and normalized decision matrix
The weighted and normalized decision matrix is formed via Formula 6.
Step 6: Calculation of relative closeness to the ideal solution (C*) and ranking of alternatives
S+ and S- values are used to calculate the relative closeness of each alternative to the ideal solution. The relative closeness of each alternative to the ideal solution is calculated using Equation 11. Alternatives are ranked so that the alternative with the higher C* value is in the first place.
Where: Vij is weighted normalized value, is weighted normalized value, wj is weight value.
Step 4: Determination of positive (V+) and negative (V-) ideal solution values
V+ and V- values are determined using weightednormalized values. Formulas 7 and 8 are used to calculate the V+ and V- values.
Properties of the materials used in the impregnation process were given in Table 1. According to Table 1, there was no important change in the pH value and density of the solutions before and after the impregnation.
Table 2 shows the effects of different chemicals (barite, boric acid, borax) on the physical (shrinkage and swelling ratios) and mechanical (bending strength, modulus of elasticity, compressive strength, and shock strength) properties of spruce wood. While the impregnation process generally increased the shrinkage ratio of spruce wood, it decreased the swelling ratio of the wood. Compared to the control (alternative A-1), the shrinkage ratios of the test specimens treated with boric
acid (alternative A-3) and the mixture of barite, boric acid and borax (alternative A-7) were decreased by 3.6% and 10.7%, respectively. The highest shrinkage was obtained after the test specimens were impregnated with borax (alternative A-4) and the ratio of increase was 13.7% compared to the control. The alternative A-7 (Barite + Ba + Bx) had the lowest swelling (9.32%). Compared to the control, the swelling ratio of the test specimens treated with the mixture of barite, boric acid and borax (alternative A-7) were decreased by 16.5%. The control group (alternative A-1) had the highest swelling (11.16%). Baysal et al.[40] stated that water absorption levels of aqueous solutions of Ba+Bx were much higher than that of control specimens. Baraúna et al.[41] reported that boron compounds at different concentrations (4% and 8%) significantly influenced tangential, radial and volumetric shrinkage of eucalyptus wood.
When Table 2 showing the mechanical properties of alternatives was examined, the impregnation materials used in the study generally increase the bending strength, modulus of elasticity, compressive strength and shock strength of spruce wood. Compared with the control (alternative A-1) test specimens (0.27 Kpm.cm-2), only the shock strength of the test specimens treated with boric acid (alternative A-3) was low (0.24 Kpm.cm-2). The highest bending strength determined was in the test specimens treated with borax (alternative A-4). The alternative A-6 (test specimens treated with mixture of barite and boric acid) had highest modulus of elasticity (9696 N.mm-2). The highest compressive strength was in the alternative A-5 (test specimens treated with mixture of barite and borax). The shock strength of wood specimens treated with barite and a mixture of barite and boric acid (alternatives A-2 and A-6) were the highest (0.35 Kpm.cm-2).
These findings are similar to other studies; for example, LeVan and Winandy[42] reported that Bx has an increasing effect on bending strength in scotch pine and beech wood specimens. Keskin et al.[43] stated that Borax increases the mechanical properties of Rowan wood and boric acid decreases only bending strength of Rowan wood. Perçin et al.[44] reported that borax slightly increases the bending strength, modulus of elasticity and compressive strength parallel to the grain of the oak wood specimens, and boric acid slightly decreases the bending strength and modulus of elasticity of the wood specimens. In addition, they said that boric acid slightly increases the compressive strength parallel to the grain of the oak wood. Tan et al.[45] investigated the effects of barite on the bending strength, modulus of elasticity and shock strength of scotch pine and
eastern beech woods. They found that the barite material increases the bending strength, modulus of elasticity and shock strength. Sen et al.[6] stated that the compressive strength parallel to the grain of Scotch pine test samples impregnated with boric acid, borax and a mixture of boric acid and borax had higher than untreated test specimens. In addition, they found that that boric acid increased the elastic modulus of scotch pine wood, even at different concentrations and compared to the control group, the bending strength of the test specimens impregnated with boron compounds is generally low. Wang et al.[7] detected that the bending strength and modulus of elasticity of Chinese fir wood treated with BA+BX (2% boric acid + 4% borax) to compared untreated Chinese fir wood were higher.
For recommending the best impregnation material, the results of the evaluated properties were analyzed using the combined Entropy-TOPSIS methodology. As seen in Table 2, the decision matrix consists of seven alternatives and six criteria. Generally, the criteria (tests) in this study are used to determine whether the wood material is suitable for the place of use. Kaymakci and Bayram[46] used the same criteria (tests) to measure the success of the heat treatment and to determine the optimum parameters.
To rank the alternatives, the weights of the criteria must first be calculated. The weight values of the criteria were determined using the Entropy method. After the decision matrix was created to determine the weight values of the criteria, the data were normalized via Formula 2. After normalization, the entropy value of each criterion and the weight value of each criterion via Formulas 3 and 4 were determined, respectively (Table 3).
According to calculations, the order of criterion weight was obtained as C-4 (0.2866) > C-6 (0.2303) > C-5 (0.1996) > C-3 (0.1706) > C-1 (0.0707) > C-2 (0.0423). Therefore, the impregnation treatment may have the greatest effect on the modulus of elasticity of the wood. The effect of the impregnation treatment on the swelling and shrinkage of
the wood was quite low. It is seen that there is no significant difference between the importance levels of the mechanical properties.
After the calculation of weights via Entropy method, the ranking of the test samples was determined using the TOPSIS method. In the TOPSIS method, the decision matrix (Table 2) used in entropy method was used. Firstly, the decision matrix was normalized via Formula 5. The matrix formed by the normalized data was given in Table 4.
Then, the weighting normalized decision matrix were obtained (Table 5). To get this matrix, the normalized data were multiplied by the weight values of the criteria.
By using weighted normalization matrix values, positive-ideal solution (V+) and negative-ideal solution (V-) values were obtained. Positive-ideal solution (V+) values were determined by choosing the highest value from each criterion (column) value, and negative-ideal solution (V-) values were determined by choosing the lowest value. The positive and negative ideal solution values were given
in Table 6. The assessed criteria play a decisive role in determining the positive ideal solution and negative ideal solution. The implications of the selected criterion in section 2 are specified. For example, lower experimental values are desirable for criteria like shrinkage, swelling, whereas higher values are desirable for bending strength, elastic modulus, compressive strength, shock strength.
Using weighted normalization matrix values and Formulas 9 and 10, the distance of each alternative (row) from the positive-ideal solution (S+) and the distance of each alternative from the negative-ideal solution (S-) were calculated. Finally, the relative closeness (C*) values of each alternative to the ideal solution were obtained via Formula 11. The alternatives (test samples) were ranked so that the alternative with the higher C* value is in the first place and the S+, S-, and C* results were given in Table 7 and the ranking of alternatives illustrated in Figure 3.
In this investigation, it was observed that ranking of impregnation materials are in descending order as A-5 >
Selection of materials with entropy-topsis by considering technological properties of impregnated wood
A-4 > A-6 > A-2 > A-7 > A-3 > A-1. It is seen that the C* value of the alternative A-5 (barite and boric acid mixtureimpregnation material) is the highest (0.9262), whereas the C* value of the alternative A-1 (non-impregnated material) is the lowest (0.1086).
Furthermore, the ranking results of the proposed entropyTOPSIS methodology were compared to those of other common MCDM methodologies to validate its applicability. The ranking results obtained by the entropy-TOPSIS approach were compared with VIKOR (Visekriterijumska optimizacija kompromisno resenjemeaning)[47], ARAS (Additive ratio assessment)[48], GRA (Grey relation analysis)[49], PROMETHEE II (Preference ranking organization method for enrichment evaluation II)[50], MOORA (Multiple objective optimization
on the basis of ratio analysis)[51], COPRAS (Complex proportional assessment)[52] approaches and ranking results are given in Table 8 and Figure 4 Table 8 demonstrates that the alternative A-5 highest of all other alternatives and the alternative A-1 lowest when solved with all the methods. Therefore, it can be reported that the proposed EntropyTOPSIS can be used to ranking of impregnation materials with reasonable accuracy.
The effects of impregnation materials were investigated relative to the physical and mechanical properties of spruce wood with the Entropy and TOPSIS methods. According to the obtained data, the following results were obtained:
The impregnation process generally increased the shrinkage ratio of the spruce specimens and decreased the swelling ratio of the specimens. The highest shrinkage (12.91%) and swelling (11.16%) ratios were found in borax treated specimens and untreated (control) specimens, respectively. The lowest shrinkage (10.14%) and swelling (9.32%) ratios were found in the specimens treated with a mixture of barite, boric acid and borax.
Compared with the control specimens, it was determined that there was an improvement in the mechanical properties of the test samples treated with the impregnations used in the study. It was obtained that the highest bending strength was in the specimens treated with borax with 79.11 N.mm-2, the highest modulus of elasticity was in the samples treated with a mixture of barite and boric acid with 9696 N.mm-2, and the highest compressive and shock strengths were in the samples treated with a mixture of barite and borax with 47.74 N.mm-2 and 0.35 Kpm.cm-2
The modulus of elasticity emerged as the most important factor affecting the success of the impregnation process. The effect of physical properties (shrinkage and swelling) on the success of the impregnation process was quite low.
According to the TOPSIS method, the best results among the impregnation materials were obtained in the specimens impregnated with barite and boric acid. The worst result was obtained in the non-impregnated specimens.
Moreover, the results of the proposed method proved to be reliable by comparing with other decision making approaches. Therefore, the study shows that the Entropy-TOPSIS method is a robust tool in the selection of impregnation material.
In this study, seven alternatives (barite, boric acid, borax, their mixture and control) and six criteria (shrinkage,
Ersen, N., Peker, H., & Akyüz, İ
swelling, bending strength, modulus of elasticity, compressive strength, and shock strength) were discussed. This is a limitation of the study. More alternatives and criteria may be added to this study.
The MCDM can be recommended as an alternative method for non-destructive, cost-effective and rapid analysis of success of wood materials.
5. Author’s Contribution
• Conceptualization – Hüseyin Peker; Nadir Ersen; İlker Akyüz.
• Data curation – Nadir Ersen.
• Formal analysis – Hüseyin Peker; Nadir Ersen.
• Funding acquisition – NA.
• Investigation – Hüseyin Peker; Nadir Ersen; İlker Akyüz.
• Methodology – Hüseyin Peker; Nadir Ersen; İlker Akyüz.
• Project administration – NA.
• Resources – Hüseyin Peker; Nadir Ersen; İlker Akyüz.
• Software – NA.
• Supervision – NA.
• Validation – NA.
• Visualization – NA.
• Writing – original draft – Nadir Ersen; Hüseyin Peker.
• Writing – review & editing – Hüseyin Peker; Nadir Ersen; İlker Akyüz.
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Received: July 28, 2022
Revised: Oct. 07, 2022
Accepted: Nov. 18, 2022
Wenderson da Silva do Amaral1 , Milton Thélio de Albuquerque Mendes1 , João Victor Frazão Câmara2* , Josué Junior Araujo Pierote3 , Fernando da Silva Reis4 , José Milton Elias de Matos4 , Ana Cristina Vasconcelos Fialho1 and Walter Leal de Moura1
1Departamento de Patologia e Clínica Odontológica, Centro de Ciências da Saúde, Universidade Federal do Piauí, Teresina, Brasil
2Klinik für Zahnerhaltung, Parodontologie und Präventivzahnmedizin, Universitätsklinikum des Saarlandes, Homburg, Saar, Deutschland
3Universidade Santo Amaro, São Paulo, Brasil
4Departamento de Química, Centro de Ciências da Natureza, Universidade Federal do Piauí, Teresina, Brasil
*jvfrazao92@hotmail.com
Obstract
To analyze the surface topography and mechanical properties of a polyurethane derived from castor oil reinforced with hydroxyapatite (PU–HA) for bone fixation. The surface analysis was performed by Scanning Electron Microscopy (SEM) and the mechanical properties by Vickers microhardness and tensile tests. The SEM images showed that the PU surface presented important characteristics for materials intended for bone fixation, such as an irregular and porous surface. The analysis showed a surface with alternating areas with depressions and elevations of approximately 80±100 µm, presence of pores of 12 µm in size. The microhardness analysis showed values of 0.42±1.01 HV for PU–HA plates, lower in relation to the poly lactic-co-glycolic acid (PLGA) plate (control group). The elastic modulus and ultimate tensile strength of 317.4 MPa, and 35.57 MPa for PLGA sample, 1.187 MPa, and 0.29 MPa for PU–HA sample. The PU produced showed good surface properties, however demands better mechanical properties.
Keywords: biocompatible materials, castor oil, fractures, bone.
How to cite: Amaral, W. S., Mendes, M. T. A., Câmara, J. V. F., Pierote, J. J. A., Reis, F. S., Matos, J. M. E., Fialho, A. C. V., & Moura, W. L. (2022). Surface and micromechanical analysis of polyurethane plates with hydroxyapatite for bone structure. Polímeros: Ciência e Tecnologia, 32(4), e2022040.
Bone fracture fixation with metal plates and screws (titanium, stainless steel, and Fe-Cr-Ni-Mo alloys) represents the gold standard because these materials present high rigidity and strength, helping to keep approximate bone fragments in a safe and stable position[1]. However, disadvantages, such as not following bone growth in pediatric patients, have encouraged the development of fixation systems with resorbable materials.
Resorbable systems are mainly used in pediatric patients in the bone growth phase because resorption occurs over time, usually from six to eight weeks. These materials are indicated for clinical use, promoting surfaces with gradual osteoconductive properties[2]. However, resorbable devices have limitations, such as high cost, the possibility of fracture, the development of foreign body-type reactions, and material-specific complications, including the need for a wider dissection due to the size of devices and complications in molding the plates in the desired shape[1,2]
In this sense, biopolymers of plant origin have been used for developing products to the biomedical field, including
polyurethane[3-8]. Polyurethane from castor oil is a compound that consists of a prepolymer and a polyol extracted from the seed oil of the Ricinus communis plant, which does not exude toxic vapors and is a biocompatible material[9,10]
The amount and composition of the isocyanate and polyol used in the synthesis directly affect polyurethane properties and such material can be prepared for specific applications by varying parameters such as length, distribution of flexible and rigid segments, molar mass, and degree of branching or crosslinking of chains[11]. For a safe clinical application, polyurethane must have a rigidity that allows an internal fixation with an initial force that meets the biomechanical needs. Besides roughness and porosity, some characteristics are relevant for bone fixation devices[12]. This study highlights the use of hydroxyapatite (HA), a bioactive and osteoconductive component for developing bioactive materials that simulate bone tissue composition. Such simulation occurs because of the chemical and structural similarities to the mineral phase of vertebrate bones and teeth[3], inducing bone tissue growth due to a porous structure similar to the porous bone[4].
Thus, the present study aimed to analyze surface topography and mechanical performance of polyurethane from castor oil with hydroxyapatite, intended as a bone fixation material.
The production method followed the protocol by Moura et al.[12]. The composite production sequence occurred at the Material Physics Laboratory of the Federal University of Piauí (Fismat/UFPI). After preparing monoacylglycerol (MAG) from castor oil, it was mixed for polymerization with hexamethylene-1, 6-diisocyanate (1,6 - HDI, SigmaAldrich Brasil Ltda™) and poly (ethylene glycol) (PEG) in the proportion of 30% relative to MAG mass, at a controlled temperature and time (the stoichiometric ratio of monomers MAG: 1,6-HDI = 3:1). Hydroxyapatite (HA) was gradually added to the mixture until obtaining PU-HA at a 3% concentration. In the “gel point” phase, the mixture was deposited and closed in a bipartite rectangular container (mold). PEG (62000-6400) was used as a plasticizing agent to improve the mechanical and surface properties of the polymer[13].
The FTIR spectra for the synthesized materials were obtained in a Thermo Fisher SCIENTIFIC spectrophotometer, model Nicolet iS5, with a purge pump, wavelength between 400 cm-1 and 4000 cm-1, in a transmittance module.
Micrographs were captured in a scanning electron microscope with a field emission gun, brand FEI, model Quanta FEG 250, with accelerating voltage from 1 to 30 kV, and equipped with SDD EDS (Silicon drift detectors), brand Ametek, model HX -1001, Apollo X-SDD detector. The conditions (energy, spot, and magnification) are recorded at the bottom of each photo as scale and magnification (Notation: SE - ETD-SE secondary electron detector).
The samples were fixed on an aluminum substrate (stub) using double-sided carbon adhesive tape, grounded with carbon paint, and coated with Au in a metallizer, Quorum, model Q150R, for 30 seconds at 20 mA, with plasma generated in an argon atmosphere. The micrographs were treated with ImageJ software (open source, free), considering the algorithms used by Paulo et al.[14] and Johner and Meireles[15]
The samples, in triplicate, were analyzed in a microvicker ISH-TDV2000 automatic digital microhardness tester from the mechanical testing laboratory of the Federal University of Piauí at a load of 10 gf. Five measurements were taken in different areas from each of the analyzed samples, as standardized by the ASTM E92 (Standard Test Method for Vickers Hardness and Knoop Hardness of Metallic Materials) and the ASTM E384 (Standard Test Method for Microindentation Materials).
The samples were analyzed in a universal mechanical testing machine, model Emic DL20000, trd cell 24, and analyzed in Tesc 3.04 software to determine the mechanical properties of the material. The study evaluated the parameters of elasticity, ultimate tensile strength, and deformation at which the materials were analyzed in the equipment at a continuous speed of 10 mm/min.
The descriptive analytical statistical analysis was performed with Bioestat™ open source software, version 5.3, at 95% CI and p<0.05.
The composition of the produced polyurethane (PU) was confirmed by analyzing the infrared spectra (Figure 1). The transmittance band in the 3315 cm-1 region is compatible with the presence of N-H bonds of urethanes and stretching in the 2939 cm-1 and 2852 cm-1 regions related to asymmetric and symmetric CH3 stretching, respectively. A stretch band at 1700 cm-1 corresponding to the carbonyl functional group (C=O), a CO-O bond (urethane) corresponding to the band at 1250 cm-1, and a hydroxyapatite (HA) phosphate radical peaking at 1150 cm-1 are compatible with the molecular structure of a castor oil PU composite with HA.
The photomicrographs obtained at different magnifications (Figure 2A-2C) show the sample surface characteristics, with porosity areas, projections, depressions, and granular structures distributed across the viewing area in the micrograph. The darker zones represent low areas such as pores and depressions, and the lighter ones represent granulation or surface projection areas. The histogram shows that the highest pixel concentrations are between 50 and 123, peaking at 106, demonstrating a homogeneous distribution between high and low areas of the castor oil-based polymer surface (Figure 2D-2E).
The “Interactive 3D Surface Plot - Spectrum LUT” algorithm allowed the reproduction of the castor oil-based
and micromechanical analysis of polyurethane plates with hydroxyapatite for bone structure
PU surface in a 3D image, considering the color variation associated with low and high areas of the analyzed sample surface. The three-dimensional reconstruction (Figure 2F) revealed the alternation between peak regions (blue to red color areas) representing high surfaces and valley regions (green to red colors) representing low areas such as depressions, fissures, and pores. Figure 2G represents the graph produced with the “Plot” algorithm of ImageJ™ software, explaining the distribution of pixel values according to the total surface space of micrograph 10b. The lowest area value is close to 80 µm, and the highest value is close to 130 µm, showing little difference between these regions.
Figure 3A represents the photomicrograph of a porous surface area. This image was treated with the “Interactive 3D Surface Plot” algorithm, which allowed visualizing the depth level of this structure based on the values of pixels represented in a color range. Yellow is the deepest observable point of the pore (40 µm), considering that the surface area circumscribed to the edge differs between high and low structures of approximately 80 to 100 µm.
The ImageJ circular algorithm, followed by commands “Analyze>measure”, calculated the mean perimeter of depression and pore areas recorded in the images (Figure 3C). Measurements were performed in four flatter areas, and Bioestat 5.3 calculated the mean of these records. The 3D reconstruction (Figure 3B and 3D) shows blue areas representing
the pores and low texture regions and the reddish or orange areas illustrating greater superficial height.
Moreover, there was a crack on the polymer surface in an image magnified at 500x, and 3D reconstruction showed its path across the sample surface (Figure 4A). The histogram (Figure 4B) shows that the highest pixel values are between 80 and 100, presenting little difference between them and a surface with little differences between the lowest and highest areas. Regarding the crack path (Figure 4C), a depth of around 40 µm was reconstructed in 3D, represented by the yellow color. The histogram (Figure 4D) corresponds to the mean of 73 pixels.
Microhardness was analyzed on samples of castor oil PU and PLGA plates (Inion™) sold commercially (Control group). The analysis was performed by calculating the diagonals of the impression produced with the microdurometer indenter. Student’s t-test was applied to two independent samples with unequal variances, in which p<0.05 suggests a statistically significant difference between the mean microhardness values for the analyzed samples (Table 1).
The PLGA samples supported 317 Mega Pascal (MPa) before undergoing irreversible deformation and failed under an applied load of 183 Newtons (N), with approximately
25% of their structure deformed. For castor oil-based PU, the elastic modulus was 1.19 MPa, and it fractured under an applied load lower than 1 N. Considering that failure occurred at low values, there was no record of a specific
strain value for this sample. Thus, the value differences indicated in the graphs show that castor oil-based PU could not withstand the required loads for a bone fixation material, considering that the control sample (PLGA) was used as
a parameter for defining properties for the test sample (PU-HA) (Figure 5A). The effect of HA addition resulted in poorer mechanical properties of the composite. Moreover, the Young’s modulus (E) value is strongly affected by the magnitude of the porosity in a material and high porosity values may lead to E values close to zero[1-4]. Our results corroborate the findings of Nasrollah et al., in which higher porosity due to HA addition impairs the mechanical properties and consequently reduces strength, which, in turn, favors the potential for increased cell adhesion and proliferation[4] In this study, the elastic modulus value was lower than that by Nasrollah and collaborators, but the author also reports divergent results from other studies[4]
Stress-strain curves are commonly used to represent material behavior in tensile tests, representing the behavior of PLGA (Figure 5B) and PU-HA (Figure 5C) samples. The absence of a plastic zone in both materials shows that both groups are fragile in a ductility analysis, meaning that they undergo small deformations until rupture but with higher resistance of the PLGA plate than the PU-HA.
Several types of isocyanates are used for PU production, such as toluene diisocyanate (TDI)[16], dicyclohexylmethane diisocyanate (HMDI)[17], and isophorone diisocyanate[18]. This study used hexamethylene diisocyanate (HDI, Sigma-Aldrich Brasil Ltda™), an aliphatic molecular chain isocyanate (C8H12O2N2, 168.2 g/mol) with OCN(CH2)6NCO structure that is less reactive than other isocyanates, less volatile, less toxic, and with a flexible, linear, and symmetric molecular structure.
Diisocyanates can have different structures, such as aromatic, aliphatic, cycloaliphatic, or polycyclic. The most reported systems in the literature are based on dihydroxylated polyether or polyester and aliphatic diisocyanates[19]. These compounds are responsible for the so-called rigid segment in the PU structure, giving polymers properties such as hardness, shear strength, and elastic modulus in traction and/or compression[20].
Hydroxyapatite (HA) bioceramic was used at a 3% concentration to improve the mechanical properties of PU, considering the vast literature on its biological properties, biocompatibility, biodegradability, osteoconductive, and osseointegrated characteristics[2,17]. The PU was polymerized using monomeric condensation with CO2 release, responsible for expanding the material during setting and forming reticular areas inside the polymeric structure. The material remained closed with a tray lid in the curing period of 72 hours to reduce this expansion[12]
Spectroscopy in the infrared region was used because it is the most suitable technique for the qualitative
determination of the products formed, as it is based on the vibrational energies of the bonds in the sample and one of the most important techniques for identifying and/or determining structural characteristics of polymers, especially regarding the functional groups and bonds in the sample[21] The transmittance band in the 3315 cm-1 region is compatible with the presence of N-H bonds of urethanes and stretching in the 2939 cm-1 and 2852 cm-1 regions related to asymmetric and symmetric CH3stretching, respectively. Such results corroborate those by Sathiskumar and Madras[22]. A stretch band at 1700 cm-1 corresponding to the carbonyl functional group (C=O), a CO-O bond (urethane) corresponding to the band at 1250 cm-1, and a hydroxyapatite phosphate radical peaking at 1150 cm-1 are compatible with the molecular
structure of a castor oil-based PU and HA, corroborating the results by Cardoso and Balaban[21]
SEM provided high-resolution images and the amplification of a sample surface. SEM images are threedimensional and suitable for analyzing and evaluating the surface area of polymer samples[23]. This tool investigates the fracture zone and tries correlating the topographical features of the sample surface[24,25]. Thus, the resulting photomicrographs characterized the surface topography aspects of castor oil-based PU with HA. The images were analyzed with ImageJ™ software algorithms for treating micrographs from electron microscopy. In this software, binary images (8 bits) map grayscale values from 0 (applied to the darkest areas) to 255 (corresponding to the lightest images). Our research group used this technique based on the study by Paulo et al.[14] to visualize the surface topography of a nanoporous alumina membrane. The image treatment performed with the “Interactive 3D Surface Plot - Spectrum LUT” algorithm was also used by Johner and Meireles[15] in their validation study of a production method with imagecoupled thin layer chromatography.
The presence of pores on the material surfaces favors a higher physical adhesion between the bone tissue and the fixation system. Hence, the produced castor oil-based PU presents this favorable characteristic for bone fixation[26] Pore size also affects bone growth. Our study reports approximate pore sizes between 50 and 125 μm, corroborating the findings of Itälä et al.[27]
The fracture observed on the polymer surface had a relatively flat surface, with a fracture pattern called brittle, usual in polymeric bodies. These results were also reported in the study by Rocha et al.[28], which described this fracture type. The method for obtaining the specimens from gel pressing[7] and the presence of solid particles of HA dispersed throughout the internal material structure can explain the irregular and rough material surface. These findings are similar to those by Sousa et al.[29] involving polyhydroxybutyrate membranes with hydroxyapatite. The appearance of cracks on the polymer surface may relate to sample preparation. Pacheco et al.[30] also reported cracks in advanced cementitious composites verified in scanning microscopy images, justifying that this crack is linked to material cutting for analysis.
Material hardness is associated with the capacity to resist elastic deformation, usually by penetration, and is mainly related to atom bonds in material compositions[31]. According to Tan et al.[7], PU from ricinoleic acid has low crosslinking density, hypothesizing the mechanical fragility of our polymer at low microhardness values.
For Gürbüz et al.[32], microhardness can be affected by the type of monomer, filling, morphology, volume, and weight of composites. The values of the different groups show that castor oil-based PU with HA has a lower hardness than the commercially available plate, which implies that the polymer produced at UFPI is more likely to wear and deteriorate. The production technique of specimens is significant for establishing their properties. The method used in this study was compression molding, in which the mold cover was screwed and maintained in place for 72 hours[12]
For Ligowski et al.[33], extrusion is the most suitable method for producing composites. It converts the appropriate raw material into a given product with semi-continuous production in which the material is forced through a matrix, thus acquiring a predetermined shape under controlled conditions. Different authors[34-37] have used this method to produce composites with satisfactory properties, but the literature does not provide comparisons for material properties using other production methods.
According to Callister[31], fragile bodies rupture soon after reaching the proportionality limit, and the plastic phase is virtually non-existent. Thus, the two tested polymers show brittle behavior. The negative sign for flow values indicates contraction and stretching during force application, which is common in such a test performed on polymers. The low polymer value of this parameter is linked to the low deformation resistance of this material[38].
Ductility was analyzed by evaluating the behavior of the stress-strain graphs produced in the test. Fragile bodies undergo reversible deformation proportional to the applied stress up to the breaking point, and ductile bodies undergo reversible deformation up to the proportionality limit but with permanent deformation even after ceasing load application, promoting a plastic behavior that characterizes material ductility[31]
The mixture of two polymers in the PLGA composition (polylactic acid and resorbable trimethylene carbonate copolymer) may explain the resistance of this material[39]. Moreover, the high degree of crystallinity of PLGA provides a high mechanical performance level, unlike the produced PU, which has a semi-crystalline appearance[12]. Tan et al. [7] suggest that the low mechanical performance of the produced PU may also be due to glycerol percentage. In their research, the mechanical properties improved as glycerol concentrations increased, showing their highest module at 60%. In our study, glycerol percentage was 30% relative to MAG mass.
The tensile test also allowed defining the material’s ductile or brittle behavior, characterized by the ability to absorb forces before fracture[31]. This is a desirable property for bone fixation devices because, during bone healing, the fracture area receives different forces and must be partially absorbed by the fixation material. Thus, the PU-HA and the PLGA plate showed fragile mechanical behavior, although the PLGA plate performed better than PU.
According to our findings, castor oil-based polyurethane with hydroxyapatite showed interesting characteristics required for bone fixation procedure, however regarding the mechanical properties need reassessing.
• Conceptualization – Wenderson da Silva do Amaral; Walter Leal de Moura.
• Data curation – Wenderson da Silva do Amaral; Milton Thélio de Albuquerque Mendes.
Surface and micromechanical analysis of polyurethane plates with hydroxyapatite for bone structure
• Formal analysis – Wenderson da Silva do Amaral.
• Funding acquisition – Walter Leal de Moura.
• Investigation – Wenderson da Silva do Amaral; Fernando da Silva Reis.
• Methodology – Wenderson da Silva do Amaral; Ana Cristina Vasconcelos Fialho.
• Project administration – Wenderson da Silva do Amaral; José Milton Elias de Matos.
• Resources – Wenderson da Silva do Amaral; Josué Junior Araujo Pierote.
• Software – Wenderson da Silva do Amaral; Fernando da Silva Reis.
• Supervision – Walter Leal de Moura.
• Validation – Walter Leal de Moura.
• Visualization – Walter Leal de Moura.
• Writing – original draft – Wenderson da Silva do Amaral.
• Writing – review & editing – João Victor Frazão Câmara; Walter Leal de Moura.
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28. Rocha, G. B. T., Pereira, L. M. M., Farias, L. D. P., Gandur, N. L., Flores, P. M., Oliveira, R. M., & Silva, M. H. P. (2016). Análise fractográfica em MEV: fratura dúctil x fratura frágil. Revista Militar de Ciência e Tecnologia, 33(2), 85-87. Retrieved in 2023, January 18, from https://rmct.ime.eb.br/arquivos/ RMCT_4_tri_2016_web/PICM_2016_B3_final.pdf
29. Sousa, W. J. B., Barbosa, R. C., Fook, M. V. L., Filgueira, P. T. D., & Tomaz, A. F. (2017). Membranas de polihidroxibutirato com hidroxiapatita para utilização como biomaterial. Revista Matéria, 22(4), e-11902 http://dx.doi.org/10.1590/s1517707620170004.0236
30 Pacheco, F., Christ, R., Gil, A. M., & Tutikian, B. F. (2016). SEM and 3D microtomography application to investigate the
distribution of fibers in advanced cementitious composites. Revista IBRACON de Estruturas e Materiais, 9(6), 824-841 http://dx.doi.org/10.1590/s1983-41952016000600002
31 Callister, W. D. C. (2007). Materials science and engineering New York: John Wiley & Sons.
32 Gürbüz, Ö., Cilingir, A., Dikmen, B., Ozsoy, A., & Eren, M. A. (2020). Efeito do selante de superfície na rugosidade superficial de diferentes compósitos e avaliação de sua microdureza. European Oral Research, 54(1), 1-8 http://dx.doi.org/10.26650/ eor.20200020. PMid:32518904.
33 Ligowski , E. , Santos , B. C. , & Fujiwara , S. T. (2015 ). Materiais compósitos a base de fibras da cana-de-açúcar e polímeros reciclados obtidos através da técnica de extrusão. Polímeros: Ciência e Tecnologia, 25(1), 70-75 http://dx.doi. org/10.1590/0104-1428.1605
34 Santos, E. F., Moresco, M., Rosa, S. M. L., & Nachtigall, S. M. B. (2010). Extrusão de compósitos de PP com fibras curtas de coco: efeito da temperatura e agentes de acoplamento. Polímeros: Ciência e Tecnologia, 20(3), 215-220 http://dx.doi. org/10.1590/S0104-14282010005000036
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Received: Aug. 05, 2022
Revised: Jan. 17, 2023
Accepted: Jan. 18, 2023
1Chemistry Laboratory, Department of Chemical Sciences, Afe Babalola University, Ado-Ekiti, Ekiti, Nigeria
2Chemistry Laboratory, Department of Chemistry, Federal University of Technology, Akure, Ondo, Nigeria
*adewumidf@abuad.edu.ng
Obstract
This analysis studied the effects modification on the properties of starch-based polymer grafted with acrylonitrile (copolymers). Starch was extracted from bitter yam. The starch was modified by heating the solution above 70 °C and then esterified with phthalic anhydride to produce a pregelatinized phthalated derivative. Acrylonitrile was grafted onto natural and pregelatinized phthalated starch at 120 °C using calcium oxide from snail shell as the initiator. The grafting reaction of starch with poly(acrylonitrile) and the phthalation of the starch were both confirmed by Fourier transform infrared (FTIR). Scanning electron microscopy analysis revealed changes in the morphology of the pregelatinized phthalated grafted copolymers. The X-ray diffractogram showed that native starch grafted copolymer displayed broad diffraction peaks (amorphous), but the phthalated bitter yam starch grafted with acrylonitrile had prominent diffraction peaks (crystalline). Thermogravimetry analysis revealed that the phthalated grafted copolymer has better thermal stability than the native grafted copolymer.
Keywords: acrylonitrile, biopolymers, bitter yam, copolymers, phthalic anhydride.
How to cite: Adewumi, F. D., Lajide, L., Adewole, E., & Johnson, J. A. (2022). Synthesis and characterization of native and modified bitter yam starch grafted with acrylonitrile. Polímeros: Ciência e Tecnologia, 32(4), e2022041. https://doi.org/10.1590/0104-1428.20220020
Because plastics are flexible, light, resilient, inexpensive, and readily available, they are used in a wide range of industries and everyday materials[1]. These petroleum-based polymers are non-biodegradable, and their use and disposal have major effects on the environment. The use of biopolymers to partially or totally replace petroleum-based polymers may provide a solution to environmental contamination problems[2]. Biopolymers, also known as bio-based polymers, are environmentally benign, biodegradable, and renewable polymers that can be used to replace petroleum-based polymers[3]. Many biodegradable polymers are currently available, including polyester amide (PEA), polybutylene adipate terephthalate (PBAT), polyhydroxy alkanoates (PHAs), polyhydroxy butyrate (PHB), polycaprolactone (PCL), and polylactic acid or polylactide (PLA), but they are uneconomical due to the high cost of production[4]. Even still, the cost of making biodegradable polymers prevents them from being used as a substitute for synthetic polymers in some cases[5]. Natural raw resources such as starch, keratin, lignin, cellulose, gelatin, collagen, and chitosan could be used to make biopolymers instead of petroleum-based polymers[5] Among the natural polymers, more emphasis is placed on starch. Because of its low cost, renewability, non-toxicity, and availability, as well as complete biodegradability, starch is a high molecular weight naturally occurring substance with extensive applications in food, chemical industry, and as a raw material in industrial processes[6-8]. Despite the
fact that starch has always been used as a food ingredient, it has also been shown to be a reliable alternative in a variety of industries, including pharmaceuticals, textiles, papers, adhesives, plastics, and cosmetics[9]. It is utilized as a stabilizer, bulking agent, thickener, and viscosity booster, among other things[10]. Enzymatic or chemical hydrolysis of starch yields compounds such as maltose, glucose, cyclodextrins, and maltodextrins[11]
However, starches in their natural state have drawbacks such as strong hydrophilicity, high water solubility, low miscibility with hydrophobic synthetic polymers, poor heat stability, processability issues, and weak mechanical qualities, which limit their utilization in a variety of fields[12,13] As a result, there is a need to change these natural starches in order to increase and improve their industrial use for a variety of purposes[14]. A great deal of work has been done on starch modification using chemical, physical, and enzymatic methods[15]. Among all the chemical modification procedures, esterification can simply and effectively enhance the flexibility and hydrophobicity of starch[16]. Although aliphatic anhydrides such as octene succinic anhydride, octene succinic anhydride, and acetic anhydride have been used to alter starch[17-20], aromatic anhydrides such as phthalic anhydride have received less attention in starch esterification than aliphatic anhydrides[21]. When an aromatic group of esters is added to starch, however, it can improve
flexibility, hydrophobicity, and diminish hydrogen bonds between starch molecules. Grafting is another important way for changing the characteristics of polymers. Grafting allows synthetic polymer and starch to adhere together after graft copolymerization rather than physically combining them[22] Multiple studies have shown that chemical initiators such as potassium permanganate/citric acid[23], ceric ammonium nitrate[24], potassium bromate-thiourea, and ammonium persulfate[25,26] can graft several vinyl monomers onto starch. Despite the fact that graft polymerization of starch has several advantages, some chemical initiators pollute the environment and are also expensive to produce, making grafted copolymers competitive with petroleum-based polymers. To replace these chemical initiators, it is critical to develop an environmentally acceptable and low-cost heterogeneous catalyst for copolymer synthesis.
The use of a waste heterogeneous catalyst has the potential to lower the grafted copolymer’s current high cost of production, making it competitive with petroleum-based copolymer. Ca(NO3)2, CaCO3, or Ca(OH)2 are the most common basic materials used to make CaO catalysts[27] CaO catalyst can be made from a variety of natural calcium sources, including mollusk shell, eggshell, and bone waste. In fact, using waste-derived CaO catalyst could reduce catalyst costs and make the copolymer environmentally friendly.
The purpose of this study is to extract starch from bitter yam and use phthalic anhydride to make pregelatinized starch phthalate bitter yam starch. Using CaO from the snail shell as an initiator, the native and pregelatinized starch phthalates were grafted onto acrylonitrile. The thermal stability, structural qualities, and morphological aspects of natural and modified composites were studied.
Bitter yam (Dioscorea dumetorum) tubers were purchased in the Ago Aduloju market in Ado–Ekiti, Ekiti State, Nigeria in 2019. CaO was produced using the Hadiyanto approach as described in 2.5. All other reagents were of analytical grade and purchased from Sigma Aldrich.
In preparation for starch extraction, the tuber yams were peeled, washed with distilled water, and cut into smaller pieces (about 1 - 2 cm2) with a sharp knife.
Wet extraction method was used to extract the starch[28]. The cut tubers were blended in a blender for five minutes. The slurry was collected using a muslin cloth and putdown into a bucket filled with distilled water. The starch was ejected into the bucket of water by continually squeezing the contents. The starch was allowed to settle overnight, and the supernatant was decanted, the product was being rinsed regularly to remove soluble contaminants until the supernatant was clear. The completed product was spread on a flat substrate and air-dried.
Gelatinization and esterification were involved in this process[29]. The gel was gelatinized by heating the starch solution to 70 °C, then oven-dried, grinded and sieved. The esterification reaction was carried out by mixing 10% pregelatinized starch with 16.7% solution phthalic anhydride in 96 percent ethanol in distilled water. Throughout the reaction, 10 M NaOH was continuously injected to keep the pH between 8 and 10. To absorb surplus moisture, anhydrous sodium sulphate was applied. Stirring was carried out at a speed of 1000 rpm for 30 minutes before being left alone for 24 hours. HCl solution was used to modify the pH of the mixture to 6.5-7.0. To wash the unreacted phthalate, 50 percent ethanol was added to the neutralized solution. To make pregelatinized Dioscorea dumetorum starch phthalate powder, the final precipitate was dried, crushed, and sieved.
The Hadiyanto approach was applied to prepare the CaO catalyst[30]. Snail shell was bought from a restaurant in Ado-Ekiti and cleansed carefully with tap water until dust and filth were removed. The clean samples were then dried for 24 hours in a hot air oven at 105 degrees Celsius. It was calcined for 4 hours at 800 °C in a muffle furnace. Calcined snail shell ash (CSSA) was crushed to a fine powder (CaO) and filtered through a stainless steel sieve of 60 mesh before being stored in a covered utensil to prevent air reaction.
The method reported by Pourjavadi et al.[31] for graft copolymerization of acrylonitrile onto starch was used. In 300 ml of distilled water, 20 g of starch was dispersed, and 1 g of calcined snail shell powder was added. For 15 minutes, the calcined snail shell was allowed to interact with the starch while being constantly agitated. The combination was then given a dose of acrylonitrile (20 ml). A graft copolymerization of acrylonitrile on starch was performed at 120 °C for 6 hours with constant agitation. The pH of the reactant was adjusted to 7, and the solution was rinsed to precipitate the polymer. The precipitate was centrifuged at 6000 rpm for 15 minutes, and the supernatant was decanted.
To eliminate any leftover acrylonitrile, the residue was rinsed again with water. The residue was air dried and weighed after the product was filtered. The degree of percentage grafting (%Gr) was calculated as described in Equation 1, and the yield (% Y) was calculated by dividing the weight of the grafted polymer by the weight of the monomer and multiplying by 100 (Equation 1).
Where Gr, Y, Wgp, Ws and Wm represent grafting, yield, weight of bitter yam starch grafted with acrylonitrile, weight of bitter yam starch and weight of monomer (acrylonitrile), respectively.
Synthesis and characterization of native and modified bitter yam starch grafted with acrylonitrile
All analyses were carried out in triplicate, and the results were statistically analyzed using SPSS for Analysis of Variance (ANOVA) (IBM Statistics 21). The results are the standard deviations of the means of replicates (calculated on a dry weight basis), which are substantially different at p < 0.05.
2.8 The native and modified composite characterization
Thermo Nicolet FT-IR spectrophotometer (Model JASCO FT-IR-5300) was used to determine the IR spectra of native and phthalated grafted copolymers in solid state utilizing the KBr pellet method. The IR spectra were measured in the 4000-400 cm-1 range.
Energy-dispersive X-ray spectroscopy (EDX) with a 6742A/ Thermo-Scientific equipment linked to a JSM6510/JEOL scanning electron microscope was used to qualitatively analyze the chemical composition of the grafted copolymers.
X-ray diffraction (XRD) was used to characterize the physical structure of the grafted copolymers (crystalline and/ or amorphous) using a Shimadzu XRD6000 diffractometer (Shimadzu, Kyoto, Japan) with CuKa radiation, from 10° to 80°, at 20 min-1
The grafted copolymers’ thermal analysis (TGA) was performed in a TA Q500 thermal analyser (TA Instruments, New Castle, DE) using a synthetic air atmosphere and a 60 ml/cm flow rate. The samples were heated at a rate of 10 oC/min from ambient temperature to 600 oC.
Scanning electron microscopy (SEM) was used to examine the morphology of the native and phthalated copolymers using a JSM6510/JEOL model microscope (JEOL instrument, Austin, EUA). Using a SCD 0050/LEICA metallizer, the samples were mounted on SEM stubs with double-sided adhesive tape and coated with a 20 nm gold layer (LEICA instrument, California, EUA).
Table 1 shows the percentage yield (%Y) and grafting (%Gr) of native and phthalated grafted copolymer. The percentage yield (38.00%) and percentage grafting (54.23%) of phthalated grafted copolymer were found to be higher than the native grafted copolymer’s percentage yield (35.95%) and percentage grafting (50.62%). The increase observed in percentage grafting of phthlated bitter yam grafted with acrylonitrile (PBGC) when compared with the native bitter yam grafted with acrylonitrile could be due to the addition of phthalic anhydride to the hydroxyl groups of the starch[32]
Results are expressed as means ± standard deviations (n = 3). NBGC = native bitter yam grafted copolymer; PBGC phthalated bitter yam grafted copolymer.
The FT-IR spectra of native bitter yam starch grafted with acrylonitrile and phthalated starch grafted with acrylonitrile are shown in Figures 1-2. For the native starch grafted with acrylonitrile (Figure 1), peaks at 3436 cm-1 and 2937 cm-1 corresponded to O-H stretch and C-H stretching, respectively, whereas the peaks at 2375 cm-1, 1442 cm-1, and 1007 cm-1 corresponded to CN stretch, C-H bend, and C-O stretch, respectively. For phthalated starch grafted with acrylonitrile (Figure 2), peaks at 3415 cm-1, 2923 cm-1, and 2324 cm-1 were assigned to O-H stretch, C-H stretch, and C-N stretch respectively, whereas peaks at 1646 cm-1, 1421 cm-1, and 1022 cm-1 were assigned to C=O, C-H bend, and C-O stretch, respectively. There was a decrease in vibrational frequency from 3436 cm-1 in the native starch to 3415 cm-1 in the phthalated starch and this decrease could be due to weakening effects on the O-H bond from the hydrogen bond in the glycosidic ring thereby causing a shift in the absorption band[33]. Also, an increase was observed in vibrational frequency of the carbonyl group from 1582 cm-1 in the native starch to 1646 cm-1in the phthalated starch grafted with acrylonitrile. Evidence of acrylonitrile grafting on both native and phthalated bitter yam starch was revealed by the presence of CN- peak at 2375 cm-1 and 2324 cm-1, respectively. The FTIR report of ungrafted native and phthalated starch of bitter yam was reported earlier[34]
A micrograph of the native bitter yam starch grafted with acrylonitrile is shown in Figure 3. The native starch grafted with acrylonitrile had a smooth, fractured surface and a continuous matrix that was homogenous. Figure 4 shows a micrograph of phthalated bitter yam grafted with acrylonitrile with a rough, nonuniform surface and a gel-like bulk. The observed changes in morphological structure could be due to the phthalation process in the grafted phthalated copolymer. Starch grafted with acrylonitrile was shown to have a similar loss of uniformity[35]. By displaying a good adhesion characteristic, phthalation improved the incorporating behavior of acrylonitrile in bitter yam starch, also, the mechanical properties of phthalated bitter yam starch grafted with acrylonitrile are expected to improve.
The native bitter yam starch grafted with acrylonitrile XRD pattern (Figure 5) showed a broad diffraction peak at 21o(2θ)), indicating its amorphous character. For native cassava starch grafted with acrylonitrile, similar observations of only
one large broad peak were reported[35].The phthalated bitter yam starch grafted with acrylonitrile (Figure 6) exhibited prominent peaks at 8°, 19o, 20o, 23o, 27o, 32o, and 45o(2θ). The higher crystallinity in the phthalated bitter yam grafted with acrylonitrile could be due to additional alterations that occurred during the grafting process.
Figures 7-8 showed the thermogram curves of the grafted copolymer of native and phthalated starches. At temperatures below 100 oC, native biter yam copolymer began to lose weight, which could be related to the reduction of moisture content in the granules. At 310 oC, the second weight loss was
detected, which could be attributed to C-O-C[36] glycosidic bond breakage. At 420 oC, the weight of the native bitter yam starch copolymer was further reduced in the third stage. The native bitter yam starch grafted with acrylonitrile structural matrix broke completely at 480 °C, leaving only the residues. Figure 8 shows the TGA curve of phthalated bitter yam starch grafted with acrylonitrile. The initial weight loss occurred at temperatures below 100 oC, indicating that water content in the starch was being removed. At 320 oC, the second weight drop was seen. At 550 oC, the weight of the phthalated bitter yam starch grafted with acrylonitrile was further reduced in the third stage. The phthalated bitter yam starch grafted with acrylonitrile structural matrix broke completely at 650 oC, leaving the residues. The thermal stability of phthalated grafted with acrylonitrile was significantly higher than that of native grafted copolymer.
The thermal stability of the grafted copolymers was improved by phthalation because the phthalated starch copolymer’s structural matrix broke completely at 650 °C as compared to the native starch which broke completely at 480 °C (indicated by blue arrow in Figure 8). The improved thermal stability of the phthalated starch grafted with acrylonitrile could be related to the copolymer’s crystallinity, which requires a greater temperature to destroy the ordered arrangement in crystalline materials. Heat exchanger parts, vehicle polymer parts (bumpers, dashboards, stirring cases, etc.), wire insulators, pump casing, curing containers, and sterilizable containers in medical applications are all examples of polymers that demand higher temperatures.
Starch was considered in the development of biodegradable polymers to solve the solid waste problems caused by petroleum-derived plastics (synthetic polymer) which are not readily biodegradable because of their resistance to microbial degradation. In this study, bitter yam starch modification was carried out using phthalic anhydride before grafting with acrylonitrile to produce grafted copolymers. The surface morphology of the graft copolymers studied by SEM revealed that phthalated starch grafted with acrylonitrile displayed a good adhesion characteristic. Thermal stability of phthalated grafted sample was higher in comparism to native starch. X-ray diffractogram showed that there was increase in
crystallinity of phthalated starch grafted with acrylonitrile. Grafting of phthalated starch resulted in the creation of novel materials with improved characteristics compared to grafted native starch. The properties of the phthalated starch grafted with acrylonitrile may make it a more promising material for reducing petroleum-based polymers and hence it could be considered as bio- films for packaging industries.
• Conceptualization – Funmilayo Deborah Adewumi; Labunmi Lajide; Ezekiel Adewole.
• Data curation – Funmilayo Deborah Adewumi; Labunmi Lajide; Jonanthan Abidemi Johnson.
• Formal analysis – Funmilayo Deborah Adewumi.
• Funding acquisition – Funmilayo Deborah Adewumi; Labunmi Lajide.
• Investigation – Funmilayo Deborah Adewumi; Labunmi Lajide; Ezekiel Adewole.
• Methodology – Funmilayo Deborah Adewumi.
• Project administration – Labunmi Lajide.
• Resources – Funmilayo Deborah Adewumi; Labunmi Lajide; Jonanthan Abidemi Johnson.
• Software – Jonanthan Abidemi Johnson.
• Supervision – Labunmi Lajide.
• Validation – Labunmi Lajide.
• Visualization – Funmilayo Deborah Adewumi.
• Writing – original draft – Funmilayo Deborah Adewumi; Labunmi Lajide.
• Writing – review & editing – Funmilayo Deborah Adewumi; Labunmi Lajide; Ezekiel Adewole.
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Retrieved in 2022, December 8, from https://www.ajol.info/ index.php/csj/article/view/158485
Received: June 09, 2022
Revised: Dec. 01, 2022
Accepted: Dec. 08, 2022
