Lawrence S. Hood

Advances in Thermal Insulation of Extruded Polystyrene Foams

Since their discovery in the early 40s extruded polystyrene foams (XPS) have been produced with various organic and inorganic blowing agents, and are now widely used as thermal insulators in building and construction. Blowing agent regulations have forced foam suppliers to look for new polymer - blowing agent - additive combinations. These must deliver high performance insulation, but must not compromise on high mechanical strength, foam integrity, and moisture resistance. This paper focuses on the thermal resistance of XPS blown with zero-ODP blowing agent (hydrofluorocarbon HFC-134a) and with carbon dioxide. IR-blockers such as carbon black and graphite reduce the thermal conductivity of CO2 blown XPS between 1 and 3×10-3 W/m.K depending on the concentration of IR-attenuators. Properties of a new XPS product using CO2 with IR blockers are presented. This product is CE certified and fulfills the requirements of the European XPS product standard DIN EN 13164.

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.