Process Monitoring of Rigid Polyurethane Foams for Automotive Composites 970245
Process temperature profiles of a two-component rigid poly(urethane-isocyanurate) foam system were studied and compared with the predictions of a one-dimensional numerical simulation. This model is based on experimentally determined thermophysical properties including thermal diffusivity, enthalpy of reaction, and rate of reaction. Temperature profiles were measured at three positions within the foam and at the foam surface for mold temperatures of 25°C and 55°C. High rate of reaction and heat of reaction, along with low thermal diffusivity, cause temperatures near the foam center to be insensitive to mold temperatures for thick samples. Thermal analysis and spectroscopic methods were used for determination of thermophysical properties. Temperature dependent heat capacity was evaluated using dynamic DSC. Reaction kinetics were studied using FTIR and isothermal DSC measurements. Heat of reaction was measured by dynamic DSC, and thermal conductivity was analyzed from steady state heat profiles. The system reaction kinetics, measured by FTIR, are based on NCO (isocyanate) absorbance. FTIR spectroscopic measurements indicated much faster kinetics than reflected by process cure temperature profiles made using thermocouples. The simulations accurately predict experimental results allowing determination of demold time dependence on process conditions including feed temperature, mold temperature programming, and sample thickness.