Microcellular foams from high performance miscible blends based on PEEK and PEI

• Microcellular low density foams from high performance PEEK/PEI polymer blends.
• Sub-micron sized, closed cell morphologies were obtained.
• PEEK50/PEI50 blend showed the best performances at all foaming temperatures.

The foamability of miscible blends based on semicrystalline Poly(ether ether ketone) – PEEK and amorphous Poly(ether imide) – PEI have been investigated for their potential outstanding mechanical, thermal and chemical-physical specific properties with the aim to produce high performance foams with a microcellular or sub-microcellular morphology and low density. Foams have been obtained by using supercritical carbon dioxide as blowing agent and were prepared by means of the solid state foaming technique, which uses a fast temperature increase to induce bubbles nucleation and growth in samples previously solubilized with the blowing agent. The role of blend composition, solubilization pressure, and crystallinity on density and morphological parameters of the resulting foams has been investigated. A closed cell microcellular morphology, with average cell size between 0.9 and 2.3 μm, was obtained and nucleated bubbles up to 1012 cells cm−3 were detected. Higher CO2 uptake allowed a decrease of the foam density at each foaming temperature (down to 0.13 g cm−3), while a complex relationship between foaming temperature and cellular morphology (in terms of nucleated cells and mean cell size) emerged.

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