Submitted to: American Chemistry Society Abstracts
Publication Type: Proceedings
Publication Acceptance Date: December 20, 2006
Publication Date: March 21, 2007
Citation: Onwulata, C.I., Tomasula, P.M. 2007. Biopolymers from polylactic acid and milk proteins. American Chemistry Society Abstracts. Technical Abstract: Polylactic acid (PLA) is a commercially available biodegradable polymer derived from lactic acid and is used in many nonfood products as an alternative to petrochemical-derived polymers. However, its physical properties limit its use in many applications. Using dairy proteins to substitute for portions of PLA in a formulation may extend its use. This work reports on the thermal properties of composites made from PLA substituted with starch-whey concentrates and casein blends (DPB). The blends were extruded under the following conditions: mass flow rates (27 to 102 g/min), solids feed rates (0.43 to 2.85 g/sec), moisture (30 to 75%); extrusion melt profiles were: 75, 90, 100, 100, 90, 80 deg C; and molding conditions at 200 deg C and 12,000 psi. The physical properties of the extruded DBP were moisture 14 – 18%, peak tensile strength 4.5 mPa, thickness 3.9 mm, elongation at break 45%, and storage modulus 5.0 mPa. Injection molded product peak melt temperature as measured by Differential Scanning Calorimetry shifted down in the order: PLA 132.8 deg C, DBP/PLA (10/90%) 149.4/130.3 deg C, DBP/PLA (20/80%) 148.8/128.2 deg C, indicating softening of PLA when combined with DBP. Dairy proteins, whey and casein, may provide an advantage by lowering the molded product peak temperature of PLA allowing for more biomaterials to be used in a formulation; however, some scorching of the molded blends was noted. Further work is needed to improve the extrusion compounding and miscibility of these high temperature- melting PLA – DBP blends.