Characterization of microporous ECTFE membrane after exposure to different liquid media and radiation

Changes in the properties of microfiltration (MF) membranes exposed to acids, bases and organic solvents used in semiconductor processing are of interest. Microfiltration membranes used for sterilization in beverage, biotechnology and pharmaceutical industries are sterilized by gamma radiation among others. Irradiation-induced degradation in membrane properties should be known. Microporous membranes of ethylene chlorotrifluoroethylene (ECTFE) membranes subjected to caustic soaking, organic solvent soaking and γ-irradiation were characterized extensively and compared with widely-used polyvinylidene fluoride (PVDF) membranes for selected properties. ECTFE membrane swellings by seven solvents including tri-n-octylamine (TOA) were much larger than those of nonporous ECTFE films. Scanning electron microscopy, atomic force microscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicated significant defects in TOA-soaked membranes. Thermogravimetric analysis (TGA) and DSC confirmed TOA presence in membrane pores. Solvents THF (tetrahydrofuran), toluene, acetonitrile and TOA decreased Young's modulus by 6-30%. ECTFE membranes resisted plasticization by these solvents: glass transition temperature variations were limited. In TOA-treated membranes, XRD indicated more significant defects in PVDF membranes. Treatment with NaOH solutions showed no effect on contact angle and bubble point pressure (BPP). Only 3 M caustic solution reduced liquid entry pressure by 13.8 kPag. ECTFE membranes showed greater hydrophobicity, stronger wetting resistance and better ability to maintain hydrophobicity vis-à-vis PVDF membranes. ECTFE membranes subjected to γ-radiation (up to 45 kGy) showed almost no effect on morphology, porosity and Young's modulus. Slight variations were observed in BPP, melting enthalpy obtained via DSC and energy loss measured in dielectric relaxation spectroscopy.