Thermal Decomposition Studies of EPS Foam, Polyurethane Foam, and Epoxy Resin (SLA) as Patterns for Investment Casting; Analysis of Hydrogen Cyanide (HCN) from Thermal Degradation of Polyurethane Foam

Abstract

Thermal and chemical characteristics of three different polymer pattern materials for investment casting were investigated: expandable polystyrene foam (EPS), polyurethane (PU) foam at three densities, and epoxy resin (SLA). Thermal degradation behaviors and glass transition temperatures (Tg) of polymers were examined by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively. The TGA results indicated that both EPS foam and SLA were degraded more readily than the PU foam, which was decomposed completely at 700 °C under air atmosphere while there was about 20% residue remaining at 800 °C under N2 atmosphere. The PU foam showed two Tgs at 56 and 140 °C. The EPS foam and SLA demonstrated single Tg at 106 and 55 °C, respectively. The generation of toxic gas, hydrogen cyanide (HCN) from thermal degradation of the PU foam was examined by a laboratory-built heating system. The HCN level depended on decomposition conditions, higher oxidant level, and longer residence time in the hot zone of furnace could reduce the HCN level.