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

Abstract

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 the outer walls of the mold varies with time. In addition, due to finite rates of heat transfer in the viscous reaction mass, spatial temperature gradients 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 that 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 cannot 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 would give PMMA sheets having excellent mechanical strength. The effects of important operating (decision) variables were studied and it was observed that the heat-transfer resistance in the mold influences the spatial distribution of the temperature, which, in turn, influences the various properties (e.g., monomer conversion, number-average molecular weight, and polydispersity index) of the product significantly.

Bulk free radical polymerizations of methyl methacrylateunder non-isothermal conditions and with intermediate additionof initiator: Experiments and modeling

“…Good agreement with model predictions is observed for a wide variety of experimental conditions. The correlation developed is, we believe, very general and can be used under almost any other experimental conditions, as well as under conditions used industrially [36].…”

Use of Agitator Power as a Soft Sensor for Bulk Free-Radical Polymerization of Methyl Methacrylate in Batch Reactors

“…In fact, in an industrial reactor where the Trommsdorff effect is encountered (e.g., the manufacture of polystyrene using the tower process 12 ), the temperature is increased during later stages of polymerization to suppress the gel effect. A similar action is taken in the case of the sheet molding of PMMA, where the temperature of the furnace is increased as the gel effect sets in.

4 Experimental data on agitator current for near-isothermal (Table ) conditions at three different temperatures ( I 0 = 15.48 mol/m 3 ).

…”