Richard T. Fox

Assessment of hydrofluoropropenes as insulating blowing agents for extruded polystyrene foams

Thermally insulating extruded polystyrene foams are currently produced with hydrofluorocarbon blowing agents. Hydrofluorocarbons have zero ozone depletion potential but rather high greenhouse warming potential. Various unsaturated fluoropropenes, with greenhouse warming potential values <15, have been assessed as HFC-134a replacements for styrenic extrusion foaming. The screening is first based on the modeling of solubility and diffusivity properties, followed by foaming experiments with a conventional extrusion process. Some fluoropropenes appear to be excellent blowing agents for extruded polystyrene foams and can be used alone for making very low-density foams with regular and large cell sizes, while some others require the use of a co-blowing agent for processing good quality foam. A few others are not suitable as a blowing agent for extruded polystyrene foams due to their toxicity or their very poor transport properties.

Large-celled extruded foams with zero-ozone depletion potential for insulating billet applications

Phase out of specific refrigerant use within extruded polystyrene foam requires reformulation to meet ever-evolving regulatory considerations; elimination of hydrochlorofluorocarbon-based blowing agents is one such example. While this transition has been applied to insulation sheathing addressing the bulk of extruded polystyrene use, large-celled formulations intended for billet applications can differ considerably from these. Reformulation, however, cannot result in unacceptable changes which impact desired performance. Further, the differences inherent to hydrochlorofluorocarbon and hydrofluorocarbon blowing agents require additional attention around appropriate co-blowing agent and resin selection strategies. The unique approaches for large-celled foams to balance the often competing needs and relationships between material selection, processing conditions, expansion behavior and end-use properties are described. Large-celled hydrofluorocarbon-based foams with zero-ozone depletion potential that can perform in a manner consistent with hydrochlorofluorocarbon predecessors are demonstrated.