Chemical and Physical Blowing Agents

Microcapsule foams are a currently more expensive alternative to chemical and physical blowing agents. These small thermoplastic bubbles added into the melt do not release gas, but rather expand to an optimum size as they are heated, through the expansion of the hydrocarbon gas inside them [13-12]. 

Both chemical and physical blowing agents (PBA) are used to expand extruded plastics. The choice of blowing agent depends somewhat on the product being made. 

Furthermore, extrusion allows the use of both chemical and physical blowing agents, which need specific treatments to be correctly handled. The most critical operations for producing thermoplastic foams by extrusion are summarized in the following. 

The most important thermoplastic foams are based on thermoplastic polystyrene and on the polyolefins PE, PP and PVC. The foaming process generally involves expansion resulting from use of chemical or physical blowing agents (Table 6). 

TPEs can readily be via foamed extrusion to lower their macroscopic hardness and density. Closed-cell foamed tubing, sheeting, and profiles with a thin, solid skin are now routinely fabricated by extruding TPEs with a chemical or physical blowing agent. 

The cellular structure of synthetic foams is created by so-called blowing agents. Additives are also often required, particularly nucleation agents and stabilisers. Depending on the process and desired foam density, either chemical or physical blowing agents are applied. 

---