Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2010
Publication Date: 12/5/2010
Citation: Mohamed, A., Finkenstadt, V.L., Gordon, S.H., Palmquist, D.E. 2010. Thermal and mechanical properties of compression-molded pMDI-reinforced PCL/gluten composites. Journal of Applied Polymer Science. 118(5):2778-2790. Interpretive Summary: In this work, we showed that wheat gluten and synthetic polymer can interact and produce a new biodegradable product with better properties and faster degradability. This is important because most polymer composites are difficult to recycle or incur substantial cost for disposal. Preparation of bio-based composites is possible only when the biodegradable polymers are compatible with the bio-fillers. Compatibility can be determined by measuring the degree of intermolecular interactions between the biodegradable polymers and bio-fillers. We achieved the necessary degree of interaction in polymer composites containing natural biodegradable polycaprolactone (PCL) and vital wheat gluten or wheat flour by including a compatibilizer – another polymer material used to help the other two polymers blend together. This result is significant because it allows new biodegradable composites to be introduced as an alternative to petroleum based polymers and also creates new markets for industrial by-products. This work could benefit wheat growers, wheat wet-milling and wheat-starch industry by offering new non-food applications for vital gluten, a by-product of wheat wet-milling. Researchers in industry and academia involved in testing new biodegradable plastics would also benefit.
Technical Abstract: Polycaprolactone (PCL) and vital wheat gluten or wheat flour composites were prepared and compatibilized with polymeric diphenylmethane diisocyanate (pMDI) by blending and compression-molding. The thermo-mechanical properties of the composites were determined by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Instron, while molecular interactions were assessed by Fourier-transform infrared spectroscopy (FTIR) analysis. After it was cooled down to -70ºC and heated to 150ºC, the glass transition (Tg) of blended neat PCL/pMDI emerged at -67ºC. Vital wheat gluten showed Tg at 63ºC, whereas no Tg was recorded for wheat flour. The delta-Cp of PCL and gluten were 0.20 and 0.45 (J/g/ºC) respectively. Although Tg was unmistakable for either PCL and gluten, all composite exhibited one Tg, which is strong indication for interaction between PCL and the fillers. Several samples amongst the blended or compression-molded composites exhibited no Tg signifying another confirmation for interaction. The delta-H of the endothermic (melting) and the exothermic (crystallization) for PCL was decreased as the percentage of gluten or flour increased, while the overall delta-H was higher for all composites compared to the theoretical value. The presence of pMDI appeared to strengthen the mechanical properties of the composites by mostly interacting with the filler (gluten or flour) and not as much with PCL. The FTIR analysis ruled out any non-covalent interaction between PCL, pMDI, or the fillers, but proposed the occurrence of physical interactions.