Processing of biodegradable blends of wheat gluten and modified polycaprolactone

Different compositions of wheat gluten (65% and 75%) and polycaprolactone (PCL) were melt blended in a twin screw extruder. PCL was modified to incorporate a functional group that could interact with the functional groups on the protein. These samples were then injection moulded to obtain test samples whose tensile and flexural properties were obtained. Results indicate that a small amount of anhydride modified polycaprolactone in the blend improved the physical properties of these blends over those of simple mixtures of wheat gluten and polycaprolactone. These blends have a narrow window of processability. Up to 75% by weight of wheat gluten could be incorporated into the blends without adversely affecting the tensile properties. However, elongations decreased significantly at these levels of gluten. Weldline strengths ranged between 50 and 75% of the non-weldline strengths and decreased with increase in gluten content. Storage at high humidity and low temperature (freezer), or dry and elevated temperature conditions (oven), did not affect the physical properties of the blends. They could be re-ground and reused without any appreciable loss in properties. Dynamic mechanical spectroscopy was used to obtain information on the respective phases and the significance of G′ and G″ as a function of temperature and frequency are discussed. Both G′ and G″ for the compatible blends were an order of magnitude higher than blends containing simple mixtures. Morphology of the blends using an optical microscope indicate a two-phase system with PCL as the continuous phase and gluten as the dispersed phase. At such high gluten content the moulded samples absorbed around 40% by weight of water within 7 days. The mechanism of water uptake is discussed. Average oil absorpnon was less than 0.5% for a 20-day period. The samples were found to be biodegradable under aerobic conditions.