Bulk graft modification of polyolefin membranes by combining pre-irradiation-induced graft and supercritical CO2-swelling polymerization

Uniform bulk graft modification of vinyl monomers to polypropylene or polyethylene membranes was achieved by combining gamma (γ)-ray pre-irradiation-induced graft copolymerization and supercritical carbon dioxide (scCO2)-swelling polymerization techniques. In the first step, the polymer membranes were irradiated with γ-rays originated from cobalt-60 resource under oxygen or air atmosphere at ambient temperature, and thus potential active sites, hydroperoxides and diperoxides, were uniformly formed on the polymer backbone. Then, graft copolymerization of vinyl monomers such as styrene, N-vinylpyrrolidone (N-VP), methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) impregnated into polymer substrates with the aid of scCO2 was initiated thermally within the host polymer by the polymer radicals (PO) resulting from the decomposition of peroxides uniformly distributed in the irradiated polymer samples. The process parameters were controlled by the properties of the fluid phase (CO2/monomer mixture) and experimental conditions, such as monomer concentration, temperature and time. The bulk graft modification of polyolefin membranes was confirmed by element analysis, spectroscopy and microscopy.