Gf. Fanta et Rl. Shogren, MODIFICATION OF STARCH-POLY(METHYL ACRYLATE) GRAFT-COPOLYMERS BY STEAM JET COOKING, Journal of applied polymer science, 65(5), 1997, pp. 1021-1029
Starch-g-poly(methyl acrylate) containing 12.3, 31.9, 51.7, and 58.3%
PMA, by weight, were prepared by eerie ammonium nitrate-initiated poly
merization of methyl acrylate onto granular cornstarch. The granular s
tructures of these graft copolymers were not disrupted by steam jet co
oking at 140 degrees C. At most, only 13% of the polymer was dissolved
, and this soluble fraction was comprised largely of starch. The proba
bility of crosslinking within these graft copolymer granules was consi
dered. Physical properties of extruded ribbons depended upon whether o
r not granular graft copolymers were jet cooked prior to extrusion. Al
though tensile strengths were not greatly affected by steam jet cookin
g, cooked samples showed significant increases in both percent elongat
ion and tear resistance. The effects of jet cooking upon the propertie
s of extruded ribbons can be explained by gelatinization of starch wit
hin the grafted starch granules. Although jet-cooked granules still re
main intact, gelatinization of the starch moiety causes these granules
to be less rigid, more deformable, and more easily plasticized by sma
ll amounts of water. Loss of starch crystallinity after steam jet cook
ing was proved by both differential scanning calorimetry and X-ray dif
fraction. (C) 1997 John Wiley & Sons, Inc.