Graft Copolymerization of some acrylic acid derivative onto Starch: synthesis and physical properties

Abstract

Grafting of N-tert-Butylacrylaide (BAM), tert-Butylacrylate (BAC), and n-Butylacrylate (n-BAC) onto maize starch in aqueous medium initiated by ceric ammonium nitrate (CAN) has been studied under N2 gas. The optimum conditions with respect to monomer concentration, initiator concentration, polymerization temperature, polymerization time and material to liquor ratio were studied in terms of percentage grafting efficiency (%GE) and percentage grafting yield (%GY). The optimum conditions obtained for the grafting of BAM, BAC and n-BAC on 1.0g starch where [BAM], [BAC] and [n-BAC] were 0.02 mol/L, [CAN]=0.91×10-3 mol/L, Temperature=30C, 20 C, and 30 C respectively and a time of 4,3 and 3 hours to produce 33.5, 80 and 88% as maximum %GE for Starch-g-BAM, Starch-g-BAC, and starch-g-n-BAC copolymers were characterized by FTIR, TGA for thermal stability, x-ray diffraction (XRD) for their crystallinity and scanning electron microscope (SEM) for surface morphology. Acid hydrolysis and viscosity average molecular weights (Mv) were determined to be in the range of 105, 106, 106. Hydrogels were also prepared by grafting of BAM, BAC, and n-BAC onto gelatinized maize starch to show a maximum water uptake and moisture retention of (162%, 63%) for BAM, (68.49%, 30.27) for BAC and (533%, 246%) for n-BAC respectively. Activation energy was also calculated for Starch-g-BAM to be 5.56 KJ/mol and 8.3×10-7 KJ/mol for the Starch-g-BAC and the values of activation energies were supported by conductivity measurements which also used to investigate the dielectric behavior of the above graft copolymers.