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.