Evaluation of HFC-245fa as an Alternative Blowing Agent for Extruded Polystyrene

The need for replacing conventional CFCs with alternative blowing agents has led to the development of many candidates. Among those, HFC-245fa is targeted as one of the most promising for the replacement of HCFC-141b in polyurethane foams. However, the low thermal conductivity of HFC-245fa and its interesting near room-temperature boiling point may render it suitable for other applications such as polystyrene insulating foam board manufacturing. This work investigates the use of HFC-245fa as a potential physical blowing agent for extruded thermoplastic foams. The process was monitored using ultrasonic probes, which reveals information on the solubility behavior of the gas in the molten state. Results showed that at 190°C, HFC-245fa could be incorporated in molten polystyrene up to about 7 wt.% and generate homogeneous solutions. Higher concentrations revealed evidence of heterogeneous conditions as seen in the attenuation signal. Three concentrations of blowing agent (5, 6 and 7 wt.%) were used to produce foam samples at lower extrusion temperatures. Increasing the concentration of blowing agent or nucleating agent greatly affected the expansion profile of the foam samples. Thus, lower densities could be achieved by using an optimal combination of both.