ARS | Publication request: Kinetics of Poly(lactic Acid) and Transglutaminase-Crosslinked Wheat Gluten Blends

Submitted to: North American Thermal Analysis Society Meeting
Publication Type: Proceedings/Symposium
Publication Acceptance Date: September 21, 2005
Publication Date: September 21, 2005
Citation: Mohamed, A. 2005. Kinetics of poly(lactic acid) and transglutaminase-crosslinked wheat gluten blends. In: Proceedings of North American Thermal Analysis Society Meeting, September 17-21, 2005, Universal City, California. p. 75.

Technical Abstract: Wheat gluten (10g) was crosslinked (XL) using 10 units of Transglutaminase in a 2L Tris-HCl buffer (pH 7.5). The reaction lasted 24 hours at 40ºC. The suspension was then freeze-dried. Different blends of XL gluten and Poly(Lactic acid) (PLA) were prepared and mixed in a Brabender mixer at 180ºC for 10 minutes. Neat PLA components and blends were tested using Modulated Differential Calorimetry (MDSC), where 40-50 mg of the sample were scanned from 20 to 250ºC with a 10ºC/min heating rate. The onset, peak temperatures, and delta-H were recorded. Neat PLA displayed a glass transition (Tg), and a exothermic transition (Cry), followed by endothermic (Mel) transitions. The plot exhibited a Tg of 0.46 Jg/ºC, Cry of 29.9 J/g, and Mel of 28.7 J/g. XL wheat gluten demonstrated one Tg with 0.45 J/g/ºC. Samples were subjected to repeated heating and cooling cycles in order to show the level of interaction between the two polymers. An isothermal DSC experiment was used to determine activation energy (Ea) and pre-exponential factor (Z) (assuming reaction rate n=1) according to the Borchardt and Daniels (B/D) kinetics approach. The blends showed reduced Ea values with an increase in the amount of XL gluten. In the presence of 5% and 20% XL gluten, the Ea of PLA increased from 150 to 200 (kJ/mol) respectively. A higher number of cycles caused an increase in Ea. The Z value showed a significant increase in the presence of XL gluten indicating higher PLA molecular mobility.