Fabrication Of Microcellular Polysulfones Using Batch Foaming Technique With Supercritical CO₂ As Blowing Agent

Polysulfone（PSU）and Polyphenylsulphone（PPSU）are high temperature materials with excellent mechanical properties,chemical resistance abilities and flame retardant properties which can meet the requirement of many special application fields.Green preparation of their light-weight materials using supercritical CO₂ foaming polymer technology is important for their low-cost application.First,a solid-state batch temperature-rising foaming process was used to prepare PPSU foams with microcellular and nanocellular structure.PPSU foams withll cell sizes from200nm to 2μm,cell density ranging from 10¹¹ to 10¹³ cell/cm,and expansion ratio ranging from 1.10 to 2.45 were obtained by controlling the saturation pressure in the range of 8-25MPa and foaming temperature 160-220℃.The mechanical property of foamed samples with different cell sizes at a density of 0.6g/cm³ was measured,and it was indicated that both compression strength and tensile strength improved with the decreasing of cell size.The compression strength increased 256.1%and the tensile strength increased 106.1%when the cell size decreased from 1920nm to 206nm.Then,both PPSU and PSU foams were prepared through a batch rapid depressurization foaming process.The solubility measurement indicated that CO₂ solubility in PSU is higher than that in PPSU.The foamable temperature window was 200℃-260℃ for PPSU and 180℃-240℃ for PSU.Higher foaming pressure and depressurization rate is beneficial to smaller cell size and larger cell density.Expansion ratio had a maximum with the temperature rising.PPSU and PSU foams had the average cell size in the range of 2 to 14μm,cell densities in the order of 10⁹-10¹⁰ cells/cm³,and expansion ratio in the range of 1.10 to 3.30.Finally,four solvents were chosen as co-blowing agent to improve expansion ratio of PPSU and PSU foams.The effect of different solvents on increasing expansion ratio was in sequence of ethanol>water>aceton≈ethyl acetate.The maximum expansion ratio can reach to 5.02 for PPSU and 6.54 for PSU with the addition of 10wt%ethanol in CO₂.Moreover,the foamable temperature window is extended with the addition of co-blowing agent,PPSU can be foamed at 150℃ and PSU can be foamed at 110℃.