Preparation and Characterisation of Poly (Acrylic Acid) Starch Polyblends

The preparation of a poly(acrylic acid) starch graft copolymer polyblend was achieved by polymerisation of acrylic acid monomer using hydrolysed starch thiocarbonate-potassium bromate as a redox initiation system. The influence of polymerisation time and temperature, concentration of potassium bromate, acrylic acid, and thiocarbonation components (CS ₂ and NaOH) as well as partial pre-neutralisation of acrylic acid on total conversion, graft yield, homopolymer and grafting efficiency were extensively studied. The viscosity of the poly(acrylic acid) starch graft copolymer polyblend, produced under a variety of reaction conditions, was also studied. The results indicated that the polymerisability of acrylic acid molecules, expressed as % total conversion (i.e. counting both grafting and homopolymerisation), is enhanced greatly by increasing the concentrations of the thiocarbonation components (i.e. concentrations of CS ₂ and NaOH, from 0.5% to 4%, based on weight of starch), KBrO ₃ (from 0.25% to 1.5%, on weight of starch), and acrylic acid (from 30% to 50%, on weight of starch). However, the polymerisability of acrylic acid decreases substantially as the extent of pre-neutralisation of acrylic acid increases from 25% to 75%. The apparent viscosity of poly(acrylic acid) starch graft copolymer polyblend paste, on the other hand, increases with increasing polymerisation temperature and extent of pre-neutralisation, and decreases with increasing concentrations of acrylic acid and potassium bromate. Tentative mechanisms, signifying various chemical events that probably occur throughout the whole course of the thiocarbonation and polymerisation reactions along with the hydrolysed starch, are reported.