|St Lawrence, Sterling|
Submitted to: Polymer Processing Society
Publication Type: Abstract Only
Publication Acceptance Date: February 1, 2001
Publication Date: N/A
Technical Abstract: Starch is a low cost, renewable material which has received considerable interest as a filler in biodegradable polymers. It is available in a wide range of particle sizes, from approximately 1 micron (amaranth) to 30 microns (potato). The stress-strain behavior of starch-filled materials is dependent on the degree of adhesion between the starch and the polymer matrix, as well as the properties of the matrix. For most polymers studied, the degree of adhesion is poor; the yield strength or tensile strength decrease with increasing starch volume fraction. Starch- poly(hydroxybutyrate-valerate) (PHBV) materials are in this category. Surface treatment of the starch to form starch-g-poly(glycidyl methacrylate) improves the properties compared to untreated starch. In poly(ester-amide)s, however, the yield strength increases with starch volume fraction. Yield strength in these materials also increases with strain rate, and the effect is more pronounced with increasing starch content. Despite the presence of voids from debonding, these materials may show considerable ductility for starch volume fractions up to approximately 0.40. When blended with starch, poly(hydroxyester-ether) (PHEE) polymers display a transition from ductile to brittle behavior at relatively low starch content. Scanning electron microscopy of starch-PHEE shows that, in contrast to starch-PHBV and starch-poly(ester-amide) materials, most starch granules are fractured rather than debonded. Loading-unloading tests of starch-PHEE materials show no significant loss of modulus after pre- loading, while starch-PHBV shows significant modulus loss. In addition, starch-PHEE materials show little if any strain rate dependence or particle size effect on tensile properties.