FOAMING POLYSTYRENE USING BLENDS OF HFC: SOLUBILITY AND PROCESSING BEHAVIOUR

摘要

With the increasing concern over global climate change, there is a continuing need to develop and understand more environmentally acceptable blowing agents useful in the production of extruded polystyrene (XPS) foam for thermal insulation. Most manufacturing processes of extruded XPS foam insulation boards are currently based on HFC-134a (1,1,1,2-tetrafluoroethane). Neat HFC-134a has a relatively low solubility in polystyrene. This is translating into processing difficulties and inadequate foam properties. Extrusion operation must then be conducted at larger operating pressures and foams blown from neat HFC-134a have higher densities, very small cell size and significant open cell content. In addition, HFC-134a has a large global warming potential; approaches enabling to mitigate its environmental impact would be highly desirable. This paper investigates various blowing agent formulations based on mixtures of HFC-134a with HFC-32 (difluoromethane) or HFC-152a (1,1-difluoroethane). Investigations focused on the rheological (plasticization) and degassing (solubility) behaviour of the formulations, as measured on-line during foam extrusion. Rules of mixing for such blends of HFCs are proposed based on the relative contribution of each component to the overall processing behaviour.