Graft polymerization of acrylonitrile onto starch-coated polyethylene film surfaces

Starch-coated polyethylene (PE) films were prepared by immersing PE in a hot, jet cooked solution of starch. They were allowed to react with acrylonitrile (AN) in the presence of ceric ammonium nitrate initiator, and the graft polymerization that occurred produced starch-g-polyacrylonitrile (PAN) coatings that contained about 25 wt % grafted PAN. The starch-g-PAN coatings tightly adhered to the PE film surfaces. When grafted starch coatings were wetted with water and the surfaces vigorously rubbed, less than 20% of the coating was removed. The fact that PAN-grafted coatings were not removed with boiling water provided further evidence for their strong adherence. When starch was removed from the coating by acid hydrolysis, the residual grafted PAN still remained adsorbed on the PE surface. Because the grafted coating was completely removed by treatment with refluxing 0.7N sodium hydroxide, there is apparently no chemical bonding between starch-g-PAN and PE. The dimensional changes associated with the evaporation of water from these PAN-grafted coatings caused the films to curl during drying. Because the final shape of these coated films depends upon the presence or absence of water in the surrounding environment, these films may be considered to be a type of stimulus-responsive polymer. Attempts to graft polymerize methyl methacrylate and methyl acrylate onto starch-coated PE surfaces, under conditions similar to those used with AN, were unsuccessful. (C) 2003 Wiley Periodicals, Inc.