THERMAL-DEGRADATION OF FOAMED POLYMETHYL METHACRYLATE IN THE EXPENDABLE PATTERN CASTING PROCESS

The thermal degradation of foamed polymethyl methacrylate (PMMA) patte rns in the expendable pattern casting process has been studied, Variou s physical transitions that may occur during the degradation of PMMA h ave been determined using scanning electron microscopy, differential s canning calorimetry, and thermogravimetric analysis, and the effects o f polymer density on the degradation characteristics have been investi gated, The results indicate that, when exposed to elevated temperature s, the polymer beads collapse at about 140 to 200 degrees C. The colla psed beads melt at 260 degrees C and begin to volatilize, Peak volatil ization temperatures are on the order of 370 degrees C, The end temper ature for volatilization is between 420 and 430 degrees C. The initial density of the polymer does not have a significant effect on the tran sition temperatures associated with degradation.