Graft Copolymerization of Methyl Methacrylate on Corn Starch Surface in an Aqueous Medium for Preparation of a Processable Bioplastic

In this study, a graft copolymer of Methyl MethAcrylate (MMA), on Corn Starch (CS) backbone, by slurry polymerization was carried out in order to the preparation of a bioplastic. The effect of temperature, MMA/ Starch weight ratio and amount of the initiator on the percentage of grafting was investigated. A maximum grafting (34%) was obtained using the weight ratio of MMA/starch (80%), initiator/starch (2.5%) and temperature (75˚C). Results showed that increase in polymerization temperature up to optimum temperature (75˚C) causes to increase in the percentage of grafting, percentage of homopolymer and the total monomer conversion and after that just the percentage of homopolymer increases. Results showed that by increasing monomer weight percent up to optimal percent (80%), the percentage of grafting increased. Beyond the optimal weight ratio of the monomer, percentage of grafting was decreased, amount of the homopolymer increased and the total conversion almost remained constant. Effect of the weight ratio of the initiator on the percentage of the grafting and amount of homopolymer was similar to the effect of the weight ratio of the monomer, with the difference that the total conversion of the monomer was increased with the weight ratio of the initiator beyond the optimal amount (2.5%). FT-IR spectra of extracted samples showed a peak at 1730 cm-1 as evidence on the grafting of PMMA on starch. SEM micrographs illustrated the presence of patches of PMMA on the surface of bulk starch. The Melt Flow Index (MFI) measurements were carried out in order to evaluate the processability of the copolymer and the results showed that by increasing the percentage of grafting, MFI of the copolymer was increased and the processing properties of samples were improved, consequently.