Characterization of microporous ECTFE membranes exposed to different liquid media and ?-radiation and nanoparticle microfiltration through such membranes

Microporous polymeric membranes are used in a variety of applications for separations, purification as well as barrier function. A major application is for microfiltration (MF). Changes in the properties of MF membranes exposed to acids, bases and organic solvents are of interest in semiconductor processing as well as in membrane contactor applications. 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. A variety of fluoropolymer-based microporous membranes are available with varying properties. Ethylene chlorotrifluoroethylene (ECTFE) membranes are a new addition and are of potential interest. Microporous membranes of 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 (SEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicated significant defects in TOA-soaked membranes. Bubble-point-pressure (BPP) based maximum pore diameters of selected solvent-soaked ECTFE membranes are in good agreement with the pore size distribution estimated from AFM. Fourier transform infrared and Raman spectroscopies were used to study the solvent-membrane interactions: TOA introduced C-H stretching and deformation. Thermogravimetric analysis (TGA) and DSC confirmed TOA presence in membrane pores. Solvents tetrahydrofuran, toluene, acetonitrile and TOA decreased Young’s modulus by 6 to 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. ...