Modeling of the sheet-molding process for poly(methyl methacrylate)

The sheet-molding process for the production of poly(methyl methacrylate) ( PMMA) involves an isothermal batch reactor followed by polymerization in a mold (the latter is referred to as a "sheet reactor"). The temperature at t he outer walls of the mold varies with time. In addition, due to finite rat es of heat transfer in the viscous reaction mass, spatial temperature gradi ents are present inside the mold. Further, the volume of the reaction mass also decreases with polymerization. These several physicochemical phenomena are incorporated into the model developed for this process. It was found t hat the monomer conversion attains high values of near-unity in most of the inner region in the mold. This is because of the high temperatures there, since the heat generated due to the exothermicity of the polymerization can not be removed fast enough. However, the temperature of the mold walls has to be increased in the later stages of polymerization so that the material near the outer edges can also attain high conversions of about 98%. This wo uld give PMMA sheets having excellent mechanical strength. The effects of i mportant operating (decision) variables were studied and it was observed th at the heat-transfer resistance in the mold influences the spatial distribu tion of the temperature, which, in turn, influences the various properties (e.g., monomer conversion, number-average molecular weight, and polydispers ity index) of the product significantly. (C) 2001 John Wiley & Sons, Inc.