Submitted to: Journal of Applied Polymer Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/1/1996
Publication Date: N/A
Citation: Interpretive Summary: Scientists are exploring ways to use cornstarch as a replacement for petroleum-derived polymers in an effort to generate new markets for surplus corn and to increase the biodegradability of plastic articles. Combining starch with synthetic polymers through graft polymerization is one of the best approaches for achieving these goals. Graft polymerization of methyl acrylate onto starch gives materials that can be processed into tough, flexible plastic articles. Graft copolymers can also be added to starch- based compositions. As part of a study aimed at reducing production costs for starch graft copolymers, we have examined the use of an initiating system that is less expensive than the current initiator. We have found that the new system can be used for these graft polymerizations. These results are useful to other researchers in the area of starch utilization.
Technical Abstract: Graft polymerizations of methyl acrylate (MA) onto granular cornstarch were carried out in water with both ferrous ammonium sulfate/hydrogen peroxide (FAS/H2O2) and ceric ammonium nitrate (CAN) initiation. Starch concentrations were 10, 20 and 30% in water, and the amount of MA used was either 0.5, 1 or 2 moles per AGU of starch. Two concentrations of FAS/H2O2 were used: 1 mole each of FAS and H2O2 per 100 AGU of starch, and 1 mole per 1000 AGU. Significant amounts of acetone-extractable PMA homopolymer were produced, and homopolymer formation was especially high at the 1:100 ratio. Sharp exotherms were observed, and reaction mixtures reached maximum temperature within 2 min or less. Total conversions of MA to PMA were higher at the 1:100 ratio, and conversions in some polymerizations were nearly quantitative. CAN-initiated polymerizations were run under the same conditions used for FAS/H2O2; however, the amount of CAN used was limited to 1 mole per 100 AGU because of low conversions at the 1:1000 ratio. Compared with FAS/H2O2, CAN gave more moderate exotherms; and longer time periods were required for reaction mixtures to reach maximum temperature. CAN gave quantitative conversions of MA to PMA, but only low percentages of PMA homopolymer were observed. High levels of homopolymer produced on starch granule surfaces with FAS/H2O2 could be seen in scanning electron micrographs and was also apparent in infrared spectra obtained with an attenuated total reflectance (ATR) cell. ATR spectra of acetone extracted products indicated that the amount of PMA actually grafted to starch granule surfaces was similar with both initiating systems. Tensile properties of extruded ribbons prepared from these polymers did not vary greatly with the initiator used.