Thermal Degradation of Foamed Polymethyl Methacrylate in the Expendable Pattern Casting Process

The thermal degradation of foamed polymethyl methacrylate (PMMA) patterns in the expendable pattern casting process has been studied. Various physical transitions that may occur during the degradation of PMMA have been determined using scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis, and the effects of polymer density on the degradation characteristics have been investigated. The results indicate that, when exposed to elevated temperatures, the polymer beads collapse at about 140 to 200 ~ The collapsed beads melt at 260 ~ and begin to volatilize. Peak volatilization temperatures are on the order of 370 ~ The end temperature for volatilization is between 420 and 430 ~ The initial density of the polymer does not have a significant effect on the transition temperatures associated with degradation.