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Jay Gonzalez
Figure 1. Γ = 0.2, Subjects/Patients=5, Trials=1,000
Renewable Carbon-based Citric acid-polyol- Cellulose composite materials Jay Gonzalez
Mentor: Ananda S. Amarasekara Department of Chemistry
Introduction: The current interest in the use of renewable resources based monomers and feedstocks for the preparation of polymeric materials is due to depleting fossil resources as well as climate change concerns. There are two basic approaches in this area; the first is the development of synthetic methods for the preparation of current monomers from renewable carbon and the second is the synthesis of new generation polymers based on renewable monomers. The second route is more attractive as it avoids the complex synthetic steps required in the conversion of biomass based compounds to current monomers [1]. As a continuation of our research in development of novel renewable polymeric and composite materials we have studied poly esterification of citric acid (CA) with erythritol (ER). Polycarboxylic alcohol CA can react with ER in several reaction modes, where the -OH and -CO2H groups can undergo inter and intra molecular esterifications [2] [3]. We have used the CA : ER 2 : 1 stoichiometric ratio in these experiments expecting complete reactions of all hydroxyl and carboxylic functional groups. The polymerizations were studied by heating with zinc(II)acetate as a catalyst at 120-160 °C. During these attempts in cross linking carboxylic acid groups with hydroxyl groups from citric acid and erythritol it was found that there were incomplete polymerizations. In an attempt to complete the esterification process, we have added 10-20% (w/w) Sigmacell cellulose (DP ~ 100) as a second hydroxyl group source, as shown in figure 1. FT-IR analysis of cellulose added samples showed a decrease in carboxylic acid peaks and improved esterification type cross linking reactions, producing hard composite materials.
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Figure 1. Synthesis of citric acid-erythritol-cellulose composite Materials and Methods: A mixture of citric acid (8.00 mmol), erythritol (4.00 mmol), Sigmacell cellulose (DP ~ 100) 1020% (w/w relative to citric acid) and zinc(II)acetate catalyst (0.025 - 0.10 mol % relative to citric acid) was gradually heated from room temperature (23 °C) to 160 °C in 1 h, and then at 160 °C for 24-48 h. The reaction mixture was cooled to room temperature, washed with methylene chloride (3 x 5 mL), water (3 x 5 mL) to remove any unreacted staring material, catalyst and dried in an oven at 90 °C for 24 hr to give citric acid-polyol- cellulose as a hard pale yellow composite. The new composite material was characterized by FT-IR and thermogravimetric analysis. Results and Discussion: The experiments using Zn(II) acetate as the catalyst and cellulose as a cross-linker for unreacted carboxylic groups produced a hard, pale yellow poly(citric acid-erythritol)-cellulose composite material. It was also found that even without a water medium as a solvent, the reaction still works and instead produces water as a by-product which needs to be removed by evaporation during cross-linking. FT-IR analysis showed that the addition of Sigmacell cellulose (DP ~ 100) 10-20% (w/w relative to citric acid) as a polyol cross-linker reduced the unreacted carboxylic acid group content in the polymer. Thermogravimetric analysis showed that new composites are thermally stable up to about 260 °C. Conclusions: We have shown that Zn(II) acetate catalyzed condensations with the additional cross-linker cellulose with citric acid and erythritol gives poly(citric acid-erythritol)-cellulose. This method provides a simple process for the production of a new all renewable carbon-based, cross-linked, thermo-plastic composite from inexpensive biomass-derived monomers with potential applications in the fabrication of packaging materials and household items.
Reference
[1] F.D. Pileidis, M.M. Titirici, Levulinic Acid Biorefineries: New Challenges for Efficient Utilization of Biomass, ChemSusChem, (2016). [2] A.S. Amarasekara, M.A. Animashaun, Acid-Catalyzed Competitive Esterification and Ketalization of Levulinic Acid with 1,2 and 1,3-Diols: The Effect of Heterogeneous and Homogeneous Catalysts, Catalysis Letters, (2016) 1-6. [3] A.S. Amarasekara, S.A. Hawkins, Synthesis of levulinic acid–glycerol ketal–ester oligomers and structural characterization using NMR spectroscopy, European Polymer Journal, 47 (2011) 2451-2457.
