2. General Aspects on Polymer Foams
Polymer foams are made of a solid and a gas phase mixed
together upon processing. Foams with air bubbles or cells being either closed-cells or open-cells are obtained, opencell
foams being usually more flexible than closed-cell foams.
The gas used as blowing agent is either a chemical or a
physical blowing component. Chemical blowing agents react
in the extruder to give off the foaming gas, mainly through
thermally induced decomposition reactions. Physical blowing
agents are gases that do not chemically react during the
foaming process and are therefore inert towards the polymer
matrix.