Modification of Poly(vinilydenefluoride) Porous Membranes by Grafting of Acrylic Acid Assisted by Supercritical Carbon Dioxide

Aim of this work is to study the preparation of pH sensitive membranes for biomedical applications via thermally induced graft polymerization of acrylic acid (AA) on poly(vinilydenefluoride) (PVDF) assisted by supercritical carbon dioxide (scCO2). Using scCO2 as a solvent and swelling agent, the monomer and the initiator (benzoyl peroxide) could diffuse faster into the polymer matrix, distribute more uniformly and allows a better control of the final molecular architecture promoting grafting reactions rather than chain degradation processes. As polymer matrixes we are using commercial hydrophobic porous PVDF membranes. Grafted polymers are characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and water permeability test at different pH values. Collected results indicate that the grafting degree can be tuned by controlling the monomer concentration and the carbon dioxide density. Moreover, the water permeation of grafted membranes decreases considerably as pH increases from 1 to 7, contrary to virgin membranes that were characterize by an almost pH independent water permeation. Research activity is going on to study the microstructure of the membrane and to optimize the level and distribution of poly(AA) grafts.