Graft copolymers of polysaccharides with thermoplastic polymers. A new type of filled plastic

Abstract

AbstractA series of starch graft copolymers and one cellulose graft copolymer were prepared containing 40‐50 percent synthetic polymer. The monomers used (styrene, methyl methacrylate, methyl acrylate, and butyl acrylate) were chosen to give grafted synthetic polymers with varying glass transition temperatures (Tg). These graft copolymers were extruded, in the absence of any added thermoplastic homopolymer, to give strong, continuous polysaccharide‐filled plastics which are biodegradable and which exhibit little or no die swell. Properties of plastics varied with the Tg of the thermoplastic portion. Starch‐g‐polystyrene and starch‐g‐poly(methyl methacrylate) were hard and brittle, while graft copolymers prepared from methyl and butyl acrylate were more flexible and leathery. The graft Uopolymers with lower Tg grafts required less torque and could be extruded at lower temperatures. In the methyl acrylate series, a graft copolymer prepared from gelatinized starch was more easily extruded than one prepared from granular starch, and addition of water produced a water‐filled extrudate of excellent quality. The surprising feature of these results is that the matrix polymers, starch and cellulose, are rigid, nonsoftening materials. Grafting of a thermoplastic polymer to these matrix polymers would not be expected to give an extrudable product. The results are explained as powder flow followed by fusion or sintering of the graft polymers under the temperature and pressure conditions in the die.