Preparation of pH sensitive poly(vinilydenefluoride) porous membranes by grafting of acrylic acid assisted by supercritical carbon dioxide

Free radical grafting of acrylic acid (AA) on poly(vinilydenefluoride) (PVDF) porous membranes was studied at 65°C using supercritical carbon dioxide (scCO 2) as a solvent and delivery agent. The process was initiated by the thermal decomposition of benzoylperoxide (BPO). Spectroscopic analyses confirmed the presence of poly(AA) chains linked to treated membranes. The mass fraction of grafted AA increased with grafting time and BPO concentration while it decreased when the density of the fluid phase was enhanced. A not-monotonic trend was obtained when the effect of the initial AA concentration was studied. The grafting process was accompanied by a reduction of the crystallinity of the PVDF matrix. Flow measurements and caffeine release experiments performed using PVDF membranes with proper grafting degree exhibited a pH dependent behaviour. © 2011 Elsevier B.V.