Effects of water on starch‐<i>g</i>‐polystyrene and starch‐<i>g</i>‐poly(methyl acrylate) extrudates

Abstract

Abstract Polystyrene and poly(methyl acrylate) were grafted onto wheat starch by gamma radiation and chemical initiation, respectively. The respective percent add‐on values were 46 and 45;68% of the polystyrene formed was grafted to starch, and the corresponding proportion of poly(methyl acrylate) was 41%. The molecular weight distributions of the homopolymer and graft portions were characterized, and extrusion conditions were established for production of ribbon samples of starch‐ g ‐PS and starch‐ g ‐PMA. Both copolymer types were considerably weakened by soaking in water, and this effect was more immediate and drastic for starch‐ g ‐poly(methyl acrylate). Both graft copolymers regained their original tensile strengths on drying, but the poly(methyl acrylate) specimens did not recover their original unswollen dimensions and retained high breaking elongations characteristic of soaked specimens. Tensile and dynamic mechanical properties of extruded and molded samples of both graft polymers are reported, and the plasticizing effects of water are summarized.