New Route for Novel Polycarboxylic Starch Hybrid

Abstract

Starch was polymerized with methacrylic acid (MAA) to different magnitudes of poly (MAA) using potassium persulphate/sodium thiosulphate redox initiation system. The polymerization products are referred to as “ composite ” . The latter consists of poly (MAA)-starch graft copolymer, poly (MAA) in the form of homopolymer, oxidized starch brought about under the influence of the initiator and intact starch. At this end, the composite, the copolymer, and the untreated (native) starch were subjected to carboxymethylation under different conditions and the rheological properties of these starch — based on products before and after carboxymethylation examined. Results obtained disclosed that the susceptibility of these products toward carboxymethylation follows the order: native starch > Copolymer > composite. Meanwhile, these products exhibit non-Newtonian thixotropic behavior before carboxymethylation; and their rheology signifies the order: Composite > copolymer > native starch whereas after carboxymethylation these products are char acterized by non-Newtonian Pseudoplastic behavior. For a given rate of shear, the apparent viscosity follows the order: native starch > composite > copolymer > carboxymethyl composite > carboxymethyl starch > carboxymethyl copoly mer, in contrast with p seudoplasticity which reveals an opposite order. It was also shown that the apparent viscosity increases by increasing poly (MAA) in the copolymer and composite and that redrying of the copolymer and the com posite after normal precipitation and drying causes a considerable enhancement in the apparent viscosity of these prod ucts.