Solid Phase Graft Polymerization Of Starch With Methyl Methacrylate By γ-Irradiation And Chemical Initiation

In this work , using cornstarch as trunk polymer, and methyl methacrylate as grafting monomer, cornstarch-g-MMA(methyl methacrylate) copolymers were synthesized by semi-dry process with gamma irradiation , eerie ammonium nitrate(CAN) and potassium persulphate(KPS), respectively. The effect of reaction media such as water, glycol and glycerol etc., atmosphere, irradiation dose , initiators , reaction time , reaction temperature and monomer-to-starch ratio on the grafting parameters like grafting ratio(G), grafting efficiency(GE) and monomer conversion(C) was investigated .The structure of starch-g-MMA copolymers were characterized by means of infrared spectroscopy , X-ray diffraction, differential scanning calorimetry, thermogravimetry and polarized light microscopy. The thermoplasticity , mechanic properties and water resistance of copolymer were studied primarily. The main results were obtained as follow:In comparison with traditional wet process, semi-dry process have advantages of without gelatinization , lower consumption of initiator, higher grafting ratio , grafting efficiency and monomer conversion , lower moisture of reaction mixture and simple post treatment.With respect to graft polymerization of MMA onto cornstarch by simultaneous irradiation at room temperature, The higher grafting ratio ,grafting efficiency and monomer conversion were obtained at 4~5kGy of irradiation dose, and 0.3-0.5 of water/dried starch ratio or glycol/dried starch ratio. Graft polymerization conducted under vacuum was of advantage of higher grafting ratio, grafting efficiency and monomer conversion , meanwhile, it was proved that effect of elimination of inhibitor on graft polymerization was negligible.It was not need to purge oxygen by nitrogen and to gelatinize starch during graftpolymerization by semi dry process using eerie ammonium nitrate and potassium persulphate as initiators. The optimum condition of graft polymerization initiated by CAN was at 40~50 of reaction temperature and approx SOmin of reaction time. The optimum condition of graft polymerization initiated by KPS was 60-65 "C of reaction temperature and about 45min of reaction time. The semi dry process had some advantages such as high efficiency , low cost and without pollution over wet process .The graft polymerization initiated by gamma irradiation , CAN , and KPS could be effectively promoted when either certain water or glycol was added, but glycerol had little effect on graft polymerization.It was proved that the linkage of grafted PMMA and trunk polymer was chemical bonding by infrared spectra analysis and hydrolysis of modified starch. The crystal of starch was destructed and thermal stability , thermoplasticity of starch were improved because of grafting reaction , it was demonstrated not only by analysis of graft copolymers by XRD, TG ,DSC and PLM, but thermoplasticity of graft products improved. Water resistance of starch was improved markedly via garft polymerization , this result had been proved to determine water absorption of grafted starch soaked in water.