2.1 Introduction

A substance that produces a cellular structure in a polymer mass is defined as a blowing agent. Alternatively, the gaseous phase in most polymeric foam material derives from the blowing agent(s) used in the foam manufacturing process. Blowing agents include gases that expand when pressure is released, liquids that develop cells when they change to gases, and chemical agents that decompose or react under the influence of heat/catalyst to form a gas.

The blowing agent plays a very important role in both the manufacturing and performance of polymer foam. The blowing agent is the dominant factor controlling density of the foam. Besides density, it affects the cellular microstructure and morphology of the foam, which in turn define the end-use performance. In some applications, such as insulation, the blowing agent properties play a central role in the overall long-term performance of the foam. In these and many other cases, the foam is closed cell and the blowing agent is retained in the cellular structure of the foam, at least until it diffuses out, which in some cases can be decades. In many others, such as packaging and cushioning, the cellular structure of the foam is such that the blowing agent escapes almost immediately after the foam is formed. In such cases, referred to as open cell foam, though the cellular structure and morphology imprint of the blowing agent impact on the performance of the foam, the blowing agent per se does not. Of course there...