Competing with chemical blowing agents, Physical Blowing Agents (PBAs) offer an interesting alternative with its advantages, notably concerning environment for some of them, but also its limitations concerning ease of processing for most of them and safety and/or environmental requirements for some others.
CBAs as already seen in a previous paper are used with conventional machines needing modified tools only. Unlike that, Physical Blowing Agents, generally need specific processes and machines.
However PBAs are used for mass produced foams such as polystyrene, polyethylene etc.
Physical blowing agents are:
* High-pressure gases such as nitrogen or carbon dioxide absorbed and finely dispersed into the polymer to be foamed and then expanding when returning to atmospheric pressure.
* Volatile liquids such as pentane or water absorbed and finely dispersed into the polymer to be foamed and then expanding when heated to produce a high volume of vapour.
* Gases, often air, emulsified in a liquid form of the polymer: latex, plastisols, prepolymers, solutions.