Preparation of pH sensitive 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 thermal 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 initiator (benzoyl peroxide) could diffuse faster and distribute more uniformly into the polymer matrix. A better control of the final molecular architecture should be achieved because bimolecular grafting reactions are accelerated with respect to chain degradation processes. Commercial hydrophobic PVDF porous matrixes were selected as model membranes. Grafted polymers were characterized by FT-IR spectroscopy, field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA) and water permeability test at different pH values. Preliminary 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 whose water permeability was substantially pH independent. Research activity is going on to study the microstructure of the membrane and to optimize the level and distribution of poly(AA) grafts.