Microcellular foams from polyethersulfone and polyphenylsulfone: Preparation and mechanical properties

Polymeric foams having microcellular structures were successfully prepared from some high-performance thermoplastics, specifically polyethersulfone and polyphenylsulfone. A two-stage batch foaming process was used and the resulting materials had average cell sizes in the range 2-13 μm, and cell densities the order of 10¹⁰-10¹¹ cells/cm³. The foam densities (relative to those of the unfoamed polymers) were in the range 0.90-0.35. Average cell sizes increased with foaming temperature and foaming time; on the other hand, cell densities and relative foam densities decreased slightly with foaming temperature but remained almost constant with foaming time. Experimental values of Young’s modulus in compression and the elastic collapse strength were higher than theoretically predicated at high relative densities, but the discrepancies became small at lower densities. In contrast, Young’s moduli in tension were in very good agreement with theory, but the relative strengths were somewhat lower than predicated.