Poly(lactic acid) green composites using oilseed coproducts as fillers

Poly(lactic acid), PLA, is a biodegradable polymer made from renewable resources with similar mechanical properties to polypropylene. PLA is more expensive than petroleum-based plastics, and the use of low-cost fillers as extenders is desirable. Agricultural coproducts of the alternative oilseed crops, cuphea (C), lesquerella (L) and milkweed (M), were collected after the oil was recovered. PLA and various levels of coproduct (0-45%, w/w) were compounded by twin-screw extrusion and injection molded. As coproduct content increased, tensile strength for all PLA composites decreased consistent with the Nicolais-Narkis model. PLA-C exhibited increased stiffness. In contrast, the modulus of PLA-M and PLA-L decreased slightly. Unexpectedly, PLA-M showed extensive stress-cracking under tensile stress and exhibited an elongation value 50-200% greater than the PLA control. Acoustic emission showed ductile behavior of the PLA-M composite.