Thermal Characteristics of Poly-lactic acid / Wheat Gluten Blends

摘要

The interaction between poly-lactic acid (PLA) and wheat gluten (gluten) has been studied using DSC repeated heating and cooling cycles between 0 -200℃. The primary DSC thermogram of wheat gluten showed a glass transition (Tg) while PLA also showed a Tg around the same temperature range and crystallization (Cry) followed by a melting (Mel) transition during the heating cycle. The different blends of PLA/gluten (20:80, 50:50, 80:20) showed one Tg. The Tg was followed by PLA crystallization and immediate melting transitions. However, subsequent cycling of the same sample demonstrated a decrease in the values of the Cry and Mel transitions depending on the ratios of the blends. Only at the 50:50 and 20:80 PLA:gluten ratios, a second Tg appeared following disappearance of Cry and Mel transitions indicating some form of miscibility and interaction between the two polymers PLA and gluten. The number of cycles needed for the disappearance of the transitions varied with the amount of PLA in the blend. Neat PLA showed no sign of change with heating and cooling cycles, but 80:20 PLA:gluten needed 35 cycles, 50:50 1 lcyies, and 20:80 took 5 cycles for the Tg, the Cys and Mel transitions to fade away. The crystallization of PLA was prevented by wheat gluten indicating compatibility of the two polymers. Solid state FTIR showed that amide Ⅰ and Ⅱ peaks are significantly decreased as a result of heating. A strong peak, corresponding to ester formation between gluten hydrolyzed gluten molecules, appeared at 1750 cm~(-1).