| A novel process for grafting vinyl acetate and styrene onto poly(vinyl chloride) in a supercritical CO{dollar}sb2{dollar} medium has been developed. The advantages of the developed process can be found in the nature of the process, which eliminates the need for expensive solvents or costly recovery systems required by conventional solution grafting technology. The process feasibility and the effects of various process variables have been investigated in this study. The free radical graft copolymerization in a supercritical CO{dollar}sb2{dollar} medium was performed in a high pressure micro-pilot plant and was operated at a temperature and pressure above the critical point of the monomer-CO{dollar}sb2{dollar} mixture. The supercritical CO{dollar}sb2{dollar} medium serves as a solvent for the monomer as well as a swelling agent for the polymer in the process. The weight percentage of vinyl acetate needed to establish supercritical conditions at the reaction temperature and pressure was calculated from a computer simulation using the Soave equation of state (EOS). The binary interaction parameter {dollar}ksb{lcub}ij{rcub}{dollar} for the Soave EOS was regressed to experimentally measured vapor-liquid equilibrium data for the CO{dollar}sb2{dollar}-vinyl acetate system. The critical loci for the styrene-CO{dollar}sb2{dollar} mixture were obtained from literature and used when determining the reaction conditions. The successful grafting was qualitatively confirmed by FTIR, GPC, DSC, and TGA. An IR absorbance ratio technique was applied for quantitative determination of graft levels. Thermal analysis showed that the PVC-g-PS is more stable than homopolymer PVC, but PVC-g-PVAc has less thermal stability than PVC. The effects of reaction time, monomer concentration, initiator concentration, temperature and pressure were investigated. The weight percent of grafting increased with temperature, monomer concentration, and initiator concentration, but the increase in pressure resulted in a decrease in grafting yield, which could be explained by the decreased sorption of monomer in the polymer phase with pressure. The process has good potential for the production of other chemically modified polymers as well. |
