Grafting acrylic acid onto starch and poly(vinyl alcohol) by photolysis

Abstract

Grafting Acrylic Acid onto Starch and Poly( vinyl Alcohol) by Pho tolysisAcrylic acid graft polymerizes onto starch with low add-on in chemically initiated free radical systems such as ceric ion or ferrous iron-hydrogen peroxide.'Higher add-on is obtained using y radiation or electron beam preirradiation.2Irradiation of an aqueous monomer solution in a thin layer has been shown to be effective in maximizing conversion of monomer to p ~l y m e r .~We find that we can graft acrylic acid onto granular starches and poly(viny1 alcohol) by photolysis in a novel cyclic process whereby a slurry of the material in water is pumped continuously past a quartz cell and irradiated while adding acrylic acid.The cell is wrapped with a polyethylene sheet transmitting light a t wavelengths longer than 250 nm.This sheet prevents homopolymer from sticking to the quartz element and facilitates good recovery of product.Acrylic acid is added dropwise to minimize homopolyber formation by providing a maximum initial starchmonomer ratio.The method is applicable to ordinary, high-amylose, thin-boiling, oxidized, acid-modified, and hydroxyethylated starches as well as granular poly(viny1 alcohol).Graft copolymers with up to 20% add-on of poly(acry1ic acid) are obtainable.Monomer goes 40-66% to graft copolymer and 19-36% to homopolymer.The graft copolymers give clear, thick pastes when heated in aqueous alkali.