Synthesis and characterization of cassava strach grafted poly[acrylamide-co-(itaconic acid)] superabsorbents

Abstract

Biodegradable superabsorbent polymers were synthesized by graft copolymerization of acrylamide (AM)/itaconic acid (IA) onto cassava starch via a redox initiator system of ammonium persulfate (APS) and N,N,N’,N’-tetramethylenediamine (TMED), N,N’-methylene bisacrylamide (N-MBA) crosslinking agent, sodium bicarbonate foaming agent, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The acrylamide-to-itaconic acid ratio, starch-to-monomer ratio, crosslinking agent, initiator, reaction temperature and agitation rate on the water absorption of the product were investigated. By-products of the reaction, the free polymer of the homopolymer and the copolymer, were removed by water extraction. The functional groups of graft copolymer were investigated by Fourier transform infrared spectroscopy, surface morphology by scanning electron microscopy, and thermal properties by thermal gravimetric analysis technique, which is utilized as a technique for determining the percentage of grafting. Biodegradation of the polymer was carried out using α-amylase to degrade the starch grafted copolymer. The highest water absorption (379±10 g g⁻¹) of the graft copolymer was produced by the starch-to-monomer ratio of 1:2, AM-to-IA ratio of 90:10 by mole, 1.0 % wt. of APS, 2.0 % wt. of N-MBA at 250 rpm and 45°c for 30 min. After the α-amylase hydrolysis of the graft copolymers, the degradation was monitored by measuring the amount of reducing sugar by DNS method. The hydrolyzed solution gave a negative test with iodine solution and positive test by Benedict’s solution, an indication of the existence of glucose units. The water absorption of the product in salt and buffered (pH) solutions were measured. Moreover, the surface morphologies of the product were revealed by SEM technique, which indicated that the flexible structure was found in the graft copolymer with the higher water absorption.