Effects of supercritical extraction on the plasticization of poly(vinyl butyral) and dioctyl phthalate films

Supercritical extraction of organic phases from films containing poly(vinyl butyral) (PVB) binder and dioctyl phthalate (DOP) plasticizer was performed with CO2 and C2H4 at 35–75 °C and 10–40 MPa for cycle times of 3 h. For films containing 60:40 wt.% PVB:DOP, extraction efficiencies near 50% were observed with either fluid at 75 °C and 40 MPa, which suggests nearly complete removal of the plasticizer. The degree of plasticization of the PVB+DOP films before and after supercritical extraction was characterized by using differential scanning calorimetry. For films containing 60:40 wt.% PVB:DOP, no thermal transitions were observed from −15 to 110 °C before supercritical extraction, whereas multiple thermal transitions were seen after supercritical extraction. The glass transition temperatures, Tg, of the films after extraction were between 24 and 45 °C, as compared to the Tg∼72.5 °C for the as-received PVB.