Characterization of membranes prepared from blends of poly(acrylic acid)-graft-poly(vinylidene fluoride) with poly(N-isopropylacrylamide) and their temperature- and pH-sensitive microfiltration

Molecular modification of ozone-pretreated poly(vinylidene fluoride) (PVDF) via thermally-induced graft copolymerization with acrylic acid (AAc) in N-methyl-2-pyrrolidone (NMP) solution was carried out (the graft-copolymerized PVDF (PAAc-g-PVDF) copolymer). pH- and temperature-sensitive microfiltration (MF) membranes from blends of the PAAc-g-PVDF copolymer and poly(N-isopropylacrylamide) (PNIPAAM) in NMP solution were prepared by phase inversion in water at 25 °C. The bulk and surface compositions of the membranes were obtained by elemental analysis and X-ray photoelectron spectroscopy (XPS), respectively. XPS analyses of the blend membranes revealed a substantial surface enrichment of the grafted AAc polymer and blended PNIPAAM. The thermal stability of the PAAc-g-PVDF/PNIPAAM blend membranes was investigated by thermogravimetric (TG) analysis. The miscibility of the PAAc-g-PVDF/PNIPAAM blend membranes was studied by differential scanning calorimetry (DSC) analysis. The polycrystallinity of the blend membranes was evaluated by X-ray diffraction (XRD) analysis. The pore sizes of the blend membranes were measured using a Coulter® Porometer II apparatus. The morphology of the membranes was studied by scanning electron microscopy (SEM). The copolymer blend membranes exhibited both pH-dependent and temperature-sensitive permeability to the aqueous solutions, with the most drastic change in permeability being observed at permeate pH between 2 and 4 and temperature around 32 °C.