Development of Copolyamide-66/6 Cross-Linked Foams by a One-Step Reactive Extrusion Process

Abstract

The simultaneous chemical cross-linking and foaming of aliphatic copolyamide by one-step reactive extrusion using a bifunctional trialkoxysilaneimidazoline additive is studied. The aim was to reach efficient melt strength enhancing the cell growth without coalescence. From liquid NMR analyses, the cross-linked foam synthesis was evidenced resulting from both imidazoline ring opening (further reacting with the polyamide carboxylic acid end-groups) and alkoxysilane hydrolysis–condensation reactions (leading to cross-linking reaction and ethanol formation). From these chemical modifications, ethanol concomitantly released lead to the expansion of the cross-linked copolyamide. From the knowledge of this chemical mechanism, various extruder and formulation parameters have been modified and their impact scrutinized to optimize the foam morphology. With our optimized conditions, it was possible to synthesize rigid foam with mean pore size mainly below 90 μm and a density around 0.36 kg·m–3 while reaching reasona...