Submitted to: Journal of Food Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/5/2005
Publication Date: 6/1/2006
Citation: Mohamed, A., Gordon, S.H., Carriere, C.J., Kim, S. 2006. Thermal characteristics of polylactic acid/wheat gluten blends. Journal of Food Chemistry. 29(3):266-281. Interpretive Summary: The main objective of this work is to develop new uses for excess agricultural products. The nature of interactions between natural and synthetic polymers (components) in different systems is not addressed adequately in the literature. The key to understanding these interactions is to understand the effect of these polymers on each other. The interaction between proteins and plastics is the determining factor that governs the use of proteins and other components in different biodegradable plastic formulas. This project is designed to produce a blend of agricultural products (i.e., soy proteins) and by-products (corn, and wheat proteins) with plastic material to produce a biodegradable blend. The major benefits of this project are economical and environmental.
Technical Abstract: The interaction between polylactic acid (PLA) and wheat gluten (gluten) has been studied using differential scanning calorimetry (DSC) repeated heating and cooling cycles between 0 - 200ºC. The primary DSC thermogram of wheat gluten showed a glass transition (Tg). 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 the 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 by means of heating and cooling cycles, but the 80:20 PLA:gluten blend needed 35 cycles for the Tg and the Crys or Mel transitions to fade away, while the 50:50 blend required 11 cycles, and the 20:80 needed 5 cycles. 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 and hydrolyzed gluten molecules, appeared at 1750 cm-1.