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We have studied a foam preparation by using an innovative method in 2 steps developed by Solvay since 2002. This concept consists, in a first step, in preparing expansible PA 6,6 pellets by extrusion, then, in a second step, in initiating the foaming thermally in a standard process (injection moulding or extrusion). The foaming reaction which generates CO2 involves an additive with switchable isocyanate functions (polyurethane), the water molecules which are present in polyamide and carboxylic acid polyamide chain ends. Foams with a density reduced by about 25% as compared to standard, bulk polyamide have been obtained thanks to the presence of glass fibers acting as nucleating agents. 

Two joint patents between Solvay and CNRS have been granted.