Mechanical and Morphological Characterization of PVA/SA/HNTs Blends and Its Composites1

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Mechanical and Morphological Characterization of PVA/SA/HNTs Blends and Its Composites1 N. Thayumanavan1 1 – Jawaharlal College of Engineering and Technology, Palakkad, Kerala, India DOI 10.2412/mmse.13.26.681 provided by Seo4U.link

Keywords: polyvinyl alcohol (PVA), sodium alginate (SA), halloysite nanotube (HNTs).

ABSTRACT. Halloysite nanotube (HNTs) filled polyvinyl alcohol (PVA)/sodium alginate (SA) blend and its composites films were prepared by solution casting. It was found out, that SA a biopolymer act as a modifier that improves the dispersion of HNTs in composites by establishing the interaction between the HNTs and SA established through FTIR and solution experiments. Morphological observation indicates the improved dispersion of HNTs in presence of SA for PVA/SA/HNTs composite film as compared with PVA/HNTs composite film, which results in a remarkable improvement in mechanical properties.

Introduction. Halloysite nanotubes (HNTs) filled polymer blends and its composites are under intense investigations for various applications [1], [2]. The incorporation of small concentration of HNTs in polymer blend matric result in an enhancement in mechanical and thermal properties [1], [2]. HNTs as a reinforcing material is more attractive as compared to carbon nanotubes due to its lower cost [3], [4]. In this work, polyvinyl alcohol (PVA) as a matrix material is used and HNTs as a filler material. PVA is a biodegradable polymer used in biomedical, coatings and fuel cells applications [5], [6]. Filler material is added to improve mechanical and thermal properties of PVA composites. The properties of PVA composites depends on the dispersion of filler in PVA matrix.

Sodium alginate (SA) has been utilized which will intercalate into interlayer space of HNTs to overcome the aggregation of HNTs in polymer matrix. The aim of this paper is to develop PVA/HSA/NTs blends and its composites by solution processing route with an aim to achieve improved mechanical properties which can be exploited for several potential applications.

Materials and Experimental procedure. Halloysite nanotube (HNTs) were received from Imerys Tableware and PVA (99% hydrolyzed, Mw ~ 89,000~98,000) purchased from Aldrich. The procedure for preparing PVA/SA/HNTs nanocomposite films are as follows. HNTs was dissolved in 10 mL of water and treated with ultrasound for 45 min to make a homogeneous dispersion (1 mg/mL). PVA powder was dissolved in distilled water at 90oC and the solution was subsequently cooled to room temperature. The HNTs aqueous dispersion was gradually added to the PVA solution, sonicated at room temperature for 15 min, and stirred to obtain homogeneous PVA/HNTs solutions. Finally, the above solutions were cast into polystyrene petri dishes at room temperature for film formation until its weight equilibrated. The weight contents of HNTs in the nanocomposite films described above were controlled to be 0.5, 2.5, 5 and 10 wt%. In addition SA powder was dissolved in distilled water at room temperature and subsequently added to PVA solution and aqueous dispersion of HNTs for the preparation of PVA/SA blend film and PVA/SA/HNTs nanocomposite blend film.

Characterization. Mechanical properties of films were tested using Tensiometer (Kudale Instrument, India) at 10 mm/min having sample size of 60x10x1 mm for at least 10 samples. The data reported here are average of 5 tests for each composition; the standard deviation is less than 5%.

Fourier transform infrared spectroscopic analysis (FTIR) was performed on the samples with Mettler 1

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Taldeo FTIR in the scanning range of 400–4000 cm-1. Optical microscopy was performed on film using Karl Zeiss optical microscope.

Results and discussion.

a)

c)

b)

Fig. 1. Optical micrograph of PVA/HNTs composites having concentration of (a) 5 wt% HNTs, (b) 10 wt% HNTs, (c) PVA/SA/HNTs composites having 5 wt% of 1:1 ratio of HNTs and SA.

a)

b)

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Fig .2. Optical micrograph of PVA/SA/HNTs composites having fixed concentration of HNTs with varying SA content (a) 10 wt%, (b) 20 wt%, (c) 30 wt% of SA.

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b)

Fig. 3. Photograph of PVA/HNTs and PVA/SA/HNTs solution.

PVA/HNTs nanocomposite optical micrograph is shown in Figure 1a,b. It is to be noted that HNTs has been dispersed in the form of granules all over the matrix which suggests the aggregation of HNTs (Figure 1a,b). In order to reduce the aggregate nature of HNTs in PVA matrix, SA a biopolymer has been utilized. It can be clearly seen that SA helps in HNT to disperse in the PVA/SA matrix (Figure 1c). With an increase in SA concentration from 5 to 10 wt% result in the formation of matrix-droplet morphology in case of PVA/SA/HNTs composites (Figure 2). In addition, SA phase consist of less aggregates of HNTs as compare to PVA phase as shown in Figure 2a,b,c, which is due the possible

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

interaction between the HNTs and SA which is confirmed with the help of solution experiments and FTIR spectroscopy.

To check the solubility of HNTs in PVA and PVA/SA blend, aqueous solution of HNTs has been mixed with PVA solution and PVA/SA solution followed by 1 hour sonication and kept for seven days at room temperature without disturbance. Figure 3a shows the addition of HNT in PVA solution result in sedimentation of HNTs occurs at the bottom of the mixture after seven days of mixing. This is due to the aggregated nature of HNTs in PVA solution suspended at bottom of the mixture. While the addition of HNT in PVA/SA solution exhibit translucent, dense solution without any sedimentation at the bottom of the mixture suggesting the formation of stable solution (Figure 3b) which is possibly due to establishment of an interaction between HNTs and SA. Similar strategies were employed for the dispersion of carbon based nanoparticle like carbon nanotube (CNT) and graphene in polymer matrix by covalent grafting of a suitable polymer with CNT and utilizing the πelectron cloud of CNT for improved dispersion by establishing π- π interaction or cation- π iterations [7], [8].

Figure 4 shows the FT-IR spectroscopy of PVA/SA and PVA/SA/HNT composite films. The PVA/SA films exhibit characteristic peak at 1740 cm-1 that is formed due to the formation of hydrogen bonding, as reported in the literature [9]. In the other case, PVA/SA/HNT films exhibit complete absence of a characteristic peak as seen in case of the PVA/SA film, which shows the appearance of peak, is due to the HNTs. This shows that there is an interaction between HNTs and PVA/SA phase.

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b)

Fig. 4. FT-IR graph comparisons of PVA/SA and PVA/SA/HNT composite films (a) PVA/SA, (b) PVA/SA/HNT.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

a)

9

Modulus (GPa)

8

7

6

5

4 2

0

4

10

8

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Weight % of HNTs

50

Tensile Strength (MPa)

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45

40

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20 0

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Weight % of HNTs

Fig. 5. Mechanical properties of PVA and PVA/HNTs composites (a) Modulus, (b) Tensile strength.

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Modulus (GPa)

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PVA/SA/HNTs PVA/SA

9

8

7

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80

Tensile Strength (MPa)

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PVA/SA/HNTs PVA/SA

70

60

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5 30

4 20

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Weight % of SA

10

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Weight % of SA

Fig. 6. Mechanical properties of PVA/SA films and PVA/SA/HNTs composites films (a) Modulus, (b) Tensile strength.

Tensile testing was performed on the PVA, PVA/SA and PVA/SA/HNTs composite films.

Mechanical properties of the PVA, PVA/SA, PVA/HNTs and PVA/SA/HNTs composites were calculated using stress strain curves. With an addition of HNTs in PVA matrix results in an increase in tensile properties of PVA/HNTs composite film as shown in Figure 5. It has been observed that with an increase in HNTs concentration in PVA result in an increase in tensile strength and tensile modulus of PVA/HNTs composites (Figure 5 a, b). In addition, by addition of SA in PVA results in an increase in tensile properties of PVA/SA blend film (Figure 6,b). However tensile modulus and the tensile strength of the PVA/SA blend films increases considerably till 20 wt % of SA. With further increase the concentration of SA in the PVA/SA blend films to 30 wt %, there is a drop both in the tensile modulus as well as the tensile strength of the PVA/SA blend. This drop is due to the brittle MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

nature of SA [9]. By addition of SA and HNTs in PVA matrix results in a remarkable improvement in tensile properties of PVA/SA/HNTs composites. This remarkable increase in the tensile modulus (GPa) and tensile strength (MPa) in case of the PVA/SA/HNTs composite films is due to the interaction between the matrix and the HNTs (as established by FTIR spectroscopy) as well as due to the better dispersion of HNT’s in the PVA/SA matrix (as established by the solution experiment).

Here, mechanical properties increases in case PVA/SA/HNTs composite up to the SA concentration of 20 wt% of SA and when SA concentration increases more than 20 wt% result in a decrease in mechanical properties as expected due to the brittle nature of SA. Summary. PVA, PVA/SA, PVA/HNTs and PVA/SA/HNTs composites has been prepared by solvent processing method. It was observed that with an addition of SA and HNTs result in an increase in mechanical properties of blend and composites respectively. However, remarkable increase in mechanical properties was observed in case of PVA/SA/HNTs composites due to the interaction between the matrix and the HNTs as well as due to the better dispersion of HNT’s in the PVA/SA matrix.

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