Submitted to: Journal of Biobased Materials and Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 16, 2007
Publication Date: December 3, 2007
Citation: Felker, F.C., Biresaw, G. 2007. Rheology and morphology of extruded blends of polystyrene with biodegradable polyesters. Journal of Biobased Materials and Bioenergy. 1:401-408. Interpretive Summary: Blending newly available biobased polymers with synthetic polymers such as polystyrene provides an opportunity to create new biodegradable materials with improved properties while increasing demand for agricultural commodities. Successful development of useful blends requires an understanding of the compatibility and interaction of biobased and synthetic polymers. In this study, model blends were made by combining polystyrene with three biobased polyesters in various ratios using melt extrusion. The flow properties and microscopic structure of the blends were examined. The results, combined with those of previous studies, help explain the compatibility and performance of the blends, and indicate areas in which further research would be fruitful. Small amounts of polystyrene significantly decreased the viscosity of one of the biobased polyesters. This information will enable scientists, processors, and manufacturers to further refine processing techniques and open new markets for the agricultural products used to produce the biobased polymers.
Technical Abstract: Zero-shear viscosity (zsv) of polycaprolactone (PCL)/PS, polylactic acid (PLA)/PS, and poly(tetramethyleneadipate-co-terephthalate (EBU)/PS blends at 25/75, 50/50, and 75/25% (w/w) ratios was determined and transmission electron microscopy (TEM) of embedded, sectioned samples was performed. Except at 25% PS, zsv of blends were between those of PS and the corresponding polyesters. At 25% PS, PCL displayed the highest, and PLA the lowest zsv of any blend. The blends with 25% PS displayed increasing zsv in the order: PLA/PS < EBU/PS < PCL/PS, which was the reverse in the trend of domain size of PS in the blends obtained by TEM. The trend in domain sizes correlates with the melting point of the polyester component and can be attributed to better mixing of a polyester with lower melting point than that with a higher melting point.