Foamed thermoplastics provide excellent insulating properties because of their very low thermal conductivity, good shape retention, and good resistance to moisture pickup. As such, cylindrical shapes are extruded for pipe insulation, and sheets for building panel insulation. Chemical blowing agents are usually solid powders that can be incorporated into molten plastics without reacting to release their by-product gases until subsequently heated to a higher temperature. Physical blowing agents are dissolved and held in solution by the pressure developed in the extruder. As the molten thermoplastic exits the extruder die, the pressure release causes instantaneous foaming. The chlorinated fluorocarbons formerly used as blowing agents have been replaced with more environmentally friendly substitutes, such as hydrochloroflurocarbons (HCFCs) or low molecular weight hydrocarbons such as butane or isopentane. For some thermoplastics, carbon dioxide, nitrogen, or argon can be used as blowing agents. Critical to the success of most foaming extrusion operations is cooling of the melt just prior to entry to the die. Cooling is most effectively accomplished with a tandem arrangement of two extruders, wherein the first extruder ensures complete dissolution of the blowing agent, and the second extruder is operated at slow speed for optimum cooling.
The Dow Chemical Company (Dow) products listed below are well-suited to meet your needs in this fabrication process.