ABSTRACT
Polymeric foam is generally characterized by blowing agent indwelling and expansion within the polymeric matrix. Unstable foaming like boiling occurs and must be sustained by the surrounding polymeric material to form a stable cellular product. In most cases, blowing agent is virtually indispensable in the polymeric foaming process. There are a great variety of organic and inorganic blowing agents suitable for the process. From the nature of gas formation, it can be classified as physical blowing agent (PBA) and chemical blowing agent (CBA). The former is generally referred to as a variation of state, such as saturated liquid to liquid/vapor, vapor, then supercritical fluid state, in the processing of the blowing agent. The blowing agent never changes its composition, except the state. However, CBA is known by its formation path, such as heat-induced chemical decomposition. It begins in solid state, then evolves into gas when heat-activated decomposition occurs. In general, inorganic volatile gases, nitrogen and carbon dioxide, are evolved as the main components. In short, both PBA and CBA have been well established for specific foaming processes.
