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Extrusion processing of granular starch‐ g ‐poly(methyl acrylate): Effect of extrusion conditions on morphology and properties
Author(s) -
Trimnell D.,
Swanson C. L.,
Shogren R. L.,
Fanta G. F.
Publication year - 1993
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1993.070480917
Subject(s) - extrusion , ultimate tensile strength , materials science , methyl acrylate , copolymer , granule (geology) , starch , polymer chemistry , reactive extrusion , composite material , polymer , chemical engineering , chemistry , organic chemistry , engineering
Starch‐ g ‐poly(methyl acrylate) copolymers (S‐ g ‐PMA) containing 10, 30, 46, and 58% PMA, by weight, were prepared by ceric ammonium nitrate‐initiated polymerization of methyl acrylate onto granular cornstarch. Graft copolymers were extrusion‐processed through a strand die with water contents of 10 and 30% (based on starch) and at temperatures of 140 and 180°C, and the resulting strands were then pelletized. Properties of ribbons prepared from extrusion‐processed S‐ g ‐PMA depended on the combined effects of processing temperature, PMA level in the graft copolymer, and water content during extrusion. Ribbon formation was poor at the lowest PMA level of 10%, and extruded ribbons did not have sufficient continuity for tensile testing. Ribbons with smooth surfaces were obtained with 10% water in the polymer, whereas a water content of 30% produced extrudates that were rough and pebbly. When processed with 10% water, graft copolymers containing 46 and 58% PMA exhibited the highest values for both ultimate tensile strength (UTS) and % elongation at break (% E ) when the extrusion was performed at 180°C. UTS was reduced and % E was increased when the water content during processing was increased to 30%. At the highest grafting level (58%), discrete granules of S‐ g ‐PMA were still apparent in scanning electron micrographs of extruded ribbons. More granule disruption occurred when the PMA level was reduced to 46%, and virtually none of the original granule structure remained after extrusion with 30% water. The effect of water content during processing was especially apparent at the grafting level of 30%, and extrudate properties were consistent with the formation of starch as the continuous phase under high moisture conditions. The behavior of S‐ g ‐PMA granules during extrusion can be explained by cross‐linking within the starch matrix during the graft polymerization reaction. DSC data were consistent with this theory. © 1993 John Wiley & Sons, Inc. This article is a US Government Work and, as such, is in the public domain in the United States of America.