Influence of polyamide-imide concentration on the cellular structure and thermo-mechanical properties of polyetherimide/polyamide-imide blend foams

Abstract

The present work considers the preparation of medium-density polyetherimide (PEI)/polyamide-imide (PAI) blend foams by means of water vapor-induced phase separation (WVIPS) and their characterization. While pure polymer foams showed homogeneous cellular structures with average cell sizes of 10-12 µm, PEI/PAI blend foams presented two distinctive closed-cell structures depending on the composition of the blend. At the lowest concentration of PAI (25 wt%) foams showed a very fine homogeneous microcellular structure with an average cell size of 1.4 µm, consequence of good miscibility between both polymers, while at the highest studied concentration of PAI (50 wt%) foams presented a dual cellular structure formed by small cells (around 1 µm in size) within the walls of considerably bigger ones (22 µm in size) due to polymer phase separation. The blend foams presented a thermal decomposition behavior similar to that of pure unfoamed polymers, with the foam with 25 wt% PAI showing a slightly higher thermal stability. Furthermore, this particular foam presented an improved specific storage modulus compared to pure PEI foam and to the one with 50 wt% PAI. X-ray diffraction (XRD) analysis indicated that no polymer crystallization was induced by foaming.