MECHANICAL-PROPERTIES OF LDPE GRANULAR STARCH COMPOSITES

The mechanical properties of composites of granular starch and low den sity polyethylene (PE) have been studied as functions of starch volume fraction phi, granule size, and presence of compatibilizer. Property- volume fraction relationships were interpreted using various theories of composite properties. The dependence of elongation (epsilon similar to phi(1/3)) and tensile strength (sigma similar to phi(2/3)) agree w ith theoretical predictions, although the proportionality constants ar e less negative than theoretic al values. The addition of compatibiliz er (ethylene-co-acrylic acid copolymer, EAA) did not significantly aff ect the elongation or tensile strength, but significantly increased th e composite tensile modulus. The cornstarch/PE moduli could be describ ed by the Kerner or Halpin-Tsai equations. Analysis of the composite m oduli data using the Halpin-Tsai equation allowed the estimation of th e modulus of granular starch. The value obtained, 15 GPa, is considera bly greater than most unfilled synthetic polymers of commercial import ance, but significantly lower than the modulus of cellulose. It is als o greater than a previously reported value of 2.7 GPa. (C) 1994 John W iley and Sons, Inc.