Preparation And Properties Of PH Switch EVAL Membrane With Controlled Grafting Site

Poly(ethylene-co-vinyl alcohol) (EVAL) separation membrane with pH-switchable property was prepared by grafting 2-(Dimethylamino)ethyl methacrylate (DMAEMA) onto porous EVAL membrane using the UV sequential grafting method. The grafting sites were controlled by regulating BP concentration and the facing light side of EVAL membrane based on the absorption property of BP. The effect of graft site regulation on switch property of EVAL membrane was investigated and the pH-switchable EVAL membrane based on site-controlled graft polymerization was prepared successfully.The results showed that the PDMAEMA chains were detected both on the surfaces and pores of EVAL membrane. The degree of PDMAEMA in membrane pore increased with grafting degree (GD) and improved the switch property of membrane. The distribution of grafted chains and switch property of the membrane were significantly affected by BP concentration. With BP concentration increasing from 20 g L-1 to 100 g L-1, the quantity of pore-grafting relatively decreased and the quantity of surface-grafting relatively increased. When BP concentration is 60 g L-1, the hightest amount of surface-grafting and pore-grafting were obtained, meanwhile the pH-switchable property was good and the switch coefficient was 5.1. When BP concentration was 100 g L-1, the amount of pore-grafting was close to zero, and the switch coefficient was 2.9.In the study of graft site regulation, the quantity of the grafted chains to the light side was obviously higher than that back light side and the micro topography and roughness of the light side changed significantly in surface-grafting controlled membrane (EVAL-T) and pore-grafting controlled membrane (EVAL-B). The graft chains showed gradient descending from the light side to backlight side within the overall membrane. The GD had little effect on the distribution trend of graft sites. The contact angle of EVAL-T and EVAL-B membranes to the light side showed obvious pH response, and the values were 80.9° and 84.4° respectly under pH 11,71.3° and 76.5° respectly under pH 3,whereas the contact angle of back light side was similar to that of original membrane and had no pH responsive. The pH-switchable property of EVAL-B membrane was significantly superior to that of the EVAL-T membrane. When the GD of EVAL-B membrane was 8.7%, the switch coefficient reached 17.2.