Preparation And Properties Of EVOH EVOH Tablets By Thermally Induced Phase Separation

Membrane separation technology is simple, energy-saving, high-effective, no secondary pollution, operational in room temperature, and has been applied in various fields. At present, membrane materials used in water treatment are polypropylene (PP), polyethylene (PE), et al. Membranes made of such polymers have good thermal stability and chemical resistance. However, the relatively poor hydrophilicity of this type of membranes limits its applications, for the loss of permeation flux caused by adsorptive fouling of biological molecules. Poly(ethylene-co-vinyl alcohol) (EVOH) is a semi-crystalline random copolymer..Because EVOH has hydrophilic vinyl alcohol segment, it has superior properties over other hydrophobic polymers for the prevention of membrane fouling. Recently, EVOH membranes have been the subjects of significant research interest for water treatment applications. In this paper, EVOH porous membranes were prepared via thermally induced phase separation (TIPS). The effects of membrane forming conditions on structures and performance were studied.First, EVOH flat membranes were prepared via thermally induced phase separation, glycerin and polyethylene glycol (PEG600) as mixed diluents. When the PEG600 and glycerin were 7:3,5:5, the cross section of the membrane were sponge-like structure; when the PEG600 and glycerin were 3:7, the cross section of the membrane were spherulitic crystal structure. With the increase of glycerol content, the pure water flux (PWF) reduced, the retention rate of BSA increased.Then, EVOH flat membranes were prepared via thermally induced phase separation, glycerin and PEG600 as mixed diluents, polyvinyl pyrrolidone (PVP) as porogen. The scanning electron microscopy (SEM) was employed to observe the morphological structure. Permeation and separation performances were evaluated by the PWF and BSA rejection. The results showed that the cross section of the membrane were sponge-like structure. With the increase of polymer content, the pore size of the surface and the cross section increased. At the same time, with increase of polymer content, the porosity decline, the PWF reduced, the retention rate of BSA increased to 89%. As the PVP content was 0.5wt%, the PWF was increased, the mean pore size and the porosity and the retention rate of BSA were no obvious change.Finally, EVOH flat membranes were prepared via thermally induced phase separation, glycerin and PEG600 as mixed diluents, nano-silica (SiO2) as additives. The morphologies of the membranes were observed by a SEM. Corresponding performance was characterized by mercury injection apparatus, PWF, BSA rejection and mechanical strength. And effects of the additives on the membrane morphologies and performance were analyzed and discussed. The results showed that, with the increase of SiO2 content, the mean pore size and porosity first increased then decreased, the tensile strength and elongation at break decreased. As the SiO2 content was 0.5wt%, the porosity was 74.0%, the mean pore size was 0.5μm, the PWF was 511 L·m-2·h-1, the retention rate of BSA was 88%, the tensile strength was 3.5MPa and elongation at break was 21.7%.