Synthesis and Characterization of Starch-Poly(vinyl Acetate) Graft Copolymers and their Saponified Form

A redox initiation system based on potassium persulfate/acetone sodium bisulphite (KPS/ASBS) was developed to initiate the graft copolymerization of vinyl acetate (VAc) monomer onto corn starch in aqueous solution. The grafting reaction was studied with respect to grafting yield (GY), grafting efficiency (GE) and total conversion (TC) and results obtained were compared with those a well-established redox initiation system namely potassium persulfate/sodium bisulphite (KPS/SBS). The effect of reaction variables such as redox initiator concentration, liquor ratio, reaction time and temperature as well as VAc concentration were investigated. The GY, GE and TC increased significantly with increase of the redox initiation concentration up to 8/16 mmol/l irrespective of the initiation system used. Moreover, optimal grafting was obtained at 60 ^○C for KPS/ASBS redox system and 70 ^○C for KPS/SBS redox system. Saponification of poly (vinyl acetate)-starch graft copolymers were effected using NaOH in three different bath media (n-hexane, acetone or methanol) to convert starch-g-poly(vinyl acetate) to starch-g-poly(vinyl alcohol). Higher extent of solubility in hot water of the saponified form was achieved by using a bath containing n-hexane/sodium hydroxide; however, increasing the graft yield higher than 26.3% decreases the solubility. The structures and thermal stability of starch, grafted starch copolymer and saponified grafted starch copolymer were characterized by infrared spectroscopy and thermogravimetric analysis. Moreover, the rheological behavior as well as sizing performance of the saponified grafted starch copolymers were evaluated and compared with the native starch and commercial polyvinyl alcohol.