PROCESSING OF BIODEGRADABLE BLENDS OF WHEAT GLUTEN AND MODIFIED POLYCAPROLACTONE

Different compositions of wheat gluten (65% and 75%) and polycaprolact one (PCL) were melt blended in a twin screw extruder. PCL was modified to incorporate a functional group that could interact with the functi onal groups on the protein. These samples were then injection moulded to obtain test samples whose tensile and flexural properties were obta ined. Results indicate that a small amount of anhydride modified polyc aprolactone in the blend improved the physical properties of these ble nds over those of simple mixtures of wheat gluten and polycaprolactone . These blends have a narrow window of processability. Up to 75% by we ight of wheat gluten could be incorporated into the blends without adv ersely affecting the tensile properties. However, elongations decrease d significantly at these levels of gluten. Weldline strengths ranged b etween 50 and 75% of the non-weldline strengths and decreased with inc rease 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 mechani cal spectroscopy was used to obtain information on the respective phas es and the significance of G' and G '' as a function of temperature an d frequency are discussed. Both G' and G '' for the compatible blends were an order of magnitude higher than blends containing simple mixtur es. Morphology of the blends using an optical microscope indicate a tw o-phase system with PCL as the continuous phase and gluten as the disp ersed phase. At such high gluten content the moulded samples absorbed around 40% by weight of water within 7 days. The mechanism of water up take is discussed. Average oil absorption was less than 0.5% for a 20- day period. The samples were found to be biodegradable under aerobic c onditions. (C) 1998 Elsevier Science Ltd. All rights reserved.