Renewable Polylactide / Polymerized Soybean Oil Blends Compatibilized by Block Copolymers

Megan Robertson, University of Minnesota

In recent years, there has been an increasing emphasis on finding alternatives to replace traditional non-degradable petroleum-based plastics. Of great interest and environmental importance are renewable feedstocks for polymeric raw materials. Polylactide is one of the most extensively studied polymers derived from an annually renewable resource, due to its biocompatibility and biodegradability for biomedical applications as well as its competitive physical properties. The brittleness of the polymer is one of the main impediments to its use in many traditional petroleum-based polymer applications. One method of toughening a brittle polymer is to blend it with a rubbery material, creating micron-sized rubber particles in the brittle polymer matrix. In this study, all-renewable blends of polylactide and polymerized soybean oil (polySOY) were prepared with melt blending. Free radical polymerization was used to prepare crosslinked polySOY samples with a variety of molecular weight distributions and gel fractions. The conjugation of the double bonds on the soybean oil triglyceride molecule greatly reduced the concentration of crosslinking agent required for the polymerization. The polySOY samples were melt blended with polylactide, and polymerizing the soybean oil eliminated soybean oil loss and phase inversion, both of which occur when unmodified soybean oil is melt blended with polylactide. The particle size and tensile toughness of the blend were found to strongly depend on the gel fraction (fraction of insoluble material) of the polySOY. The tensile toughness was increased to as high as four times that of neat polylactide.

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