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.
In this study, starch foams are obtained by melt extrusion
in which water is used as blowing agent as it turns into steam
under temperature and pressure conditions of the extrusion.
To enhance the number of cells and to homogenise the
cellular microstructure, additives such as nucleating agents,
that is, talc, are used. PLA foams are obtained by melt
extrusion using a chemical blowing agent (called CBA) which
decomposes at the PLA melting temperature.
The foaming capacity of the polymer materials was
assessed by the measurement of the void content of the
final product after extrusion. The experimental results allow
defining an optimum set of extrusion conditions (screw profile
and speed, cooling temperature, extrusion temperatures
along the screw...) and material formulations (CBA content,
fibre content and nature...) to improve void content and
foams properties. The cell morphology (number, dimen-
sions, shape...) and the mechanical properties (tensile,
bending...) are analyzed.