New grades of low-density, high melt-strength polypropylene (PP) foams are increasingly challenging older polymer foams made of polyurethane, polyethylene and PVC. Compared to these existing foams, the PP materials offer such additional benefits as high heat resistance, excellent chemical resistance and superior insulation properties. The new PP foams are also noteworthy for their light weight, high stiffness, low-temperature impact resistance, and easy recyclability. Applications for these foams are emerging in the automotive, food, packaging and construction sectors.
The high melt-strength of the new PP grades, along with their enhanced extensibility (stretching properties) , are the key features that allow them to compete in demanding foam markets. In the past, pure PP could not be foamed because any bubbles that formed would collapse as a result the polymer's low melt strength. Moreover, the low extensibility of ordinary PP hindered formation of the cells in the first place.