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

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 mu m, 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 mu m, 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 mu m in size) within the walls of considerably bigger ones (22 mu m 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. (C) 2015 Elsevier Ltd. All rights reserved.