Foaming of thermoplastics is today widely used in the polymer industry, not only to reduce the weight of final products but also to achieve certain properties. But producing thermoplastic foams is a critical process and processing windows tend to be very small. This paper aims to give a better understanding of the mechanisms of foaming. This will give a better understanding of production problems and how to avoid them. The basic chemical foaming agents and their chemistry will be discussed as well as the action of chemical foaming agents as nucleating agents in physical foaming. Some examples of typical chemically foamed thermoplastics produced by extrusion, injection moulding, plastisol processes or even rotomoulding will be given.
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