| Polysulfone (PSF) and polypropylene (PP) are common organic polymer membrane materials, but due to the hydrophobic properties, they are easily to be polluted in application, resulting in attenuation of membrane flux, reduction of membrane efficiency and the membrane service life, and increasing of the membrane cost. Thus, developing hydrophilic membrane or hydrophilic modification of the existing membrane is of crucial importance. Ultraviolet irradiation (UV) method has mild reaction condition, simple process and continuous adjustable wavelength and the reaction induced by UV can only occur in the material surface. UV treatment is a commonly used method of membrane surface modification. In order to improve the anti-fouling performance of the common organic polymer membranes, in this paper, effect of photosensitizer, molecular weight of the monomer, and the number and distribution of the hydrophilic groups on grafting and the membrane structure and properties were studied, and the performance of the membranes were characterized. Hollow fiber membranes with substantial raise in hydrophilicity and anti-fouling performance were successfully prepared. The main contents and conclusions are as follows:First, acrylic acid (AA) and hydroxy ethyl acrylate (HEA) were grafted on the surfaces of PSF and PP hollow fiber membranes by intermittent UV irradiation, the effect of photosensitizer (BP) on the membrane structure and performance were studied. Results showed that the surface structure of the membrane was greatly influenced by BP. Monomers can be grafted on the PSF membrane surface after UV irradiation when there was no BP, but the membrane structure was damaged and the pores of the membrane were enlarged and the rejection rates were reduced, and the monomers can’t be grafted on the PP membrane without BP.While in presence of BP, the monomers can be grafted on the PSF and PP membrane surface successfully after UV irradiation, the surfaces were regulated and the hydrophilicity and anti-fouling performance of the membranes were improved.Secondly,2-hydroxypropyl acrylate (HEA),3-Hydroxypropyl acrylate (3HPA), 4-hydroxybutyl acrylate (4HBA) and 2,2-Bis(hydroxymethyl)butylacrylate (TMPAA) were grafted on PSF membrane by intermittent UV irradiation, and the influence of the monomer molecular weight on the membrane structure and performance were studied. The results showed after irradiation, all of the monomers were successfully grafted and the hydrophilic hydroxyl group was introduced on on the membrane surfaces, the surface structures were changed and the hydrophilicity and anti-fouling performance of the modified membrane were all better than the original PSF membrane. The grafting density and the increasing range of the hydrophilicity and anti-fouling performance of the membrane decreased with the increasing of the molecular weight, but improvement of the number of -OH groups can effectively improve the hydrophilicity and anti-fouling performance of the membranes. When the grafting density of TMPAA was 3.02 mmol.m-2, the water contact angle decreased from 80° to 46°, the pure water flux increased from 115 L.m-2.h-1 to 173 L.m-2.h-1, the retention of BSA increased from 88.6% to 93.4%, and the flux recovery rate after cleaning was increased from 68.6% to 90.5%.Thirdly, in order to further achieve industrialization and improve the practical application value,2-hydroxypropyl acrylate (HEA),2,3-Dihydroxypropyl acrylate (GA), and 3-hydroxy-2,2-bis(hydroxymethyl)propyl acrylate (PEA) were grafted on the PP membrane by continous UV irradiation, and the effect of the number and distribution of the hydrophilic groups of the monomers on the membrane structure and performance were studied. Results showed that modified PP hollow fiber membranes with different number and distribution of -OH can be prepared after continous UV irradiation, and the chemical structure and morphology were all effectively improved. Furthermore, the modification of the membranes were more evenly with continous UV irradiation, and to design the surface structure of the modified membrane by using different monomers, surface hydrophilicity and pollution resistance of the membranes can be greatly improved. The hydrophilcity and anti-fouling performance of membrane surface increased with increasing the number of -OH groups on the membrane surface when other conditions renained the same; the distribution of the -OH groups on the two properties of the membrane was a bit complicated. When the grafting density was low, the more concentrated the-OH distribution, the better hydrophilicity and anti-fouling properties the modified membrane had; while the influence of -OH distribution on the two properties of the modified membrane was not so obvious when the grafting density was high. When the grafting density of PEA on the membrane surface was 0.838 mmol.m-2, the water drop on the membrane surface disappeared in 6.3 s, and the pure water flux of the modified membrane was about 4.5 times higher than that of the original membrane, the flux reduction decreased from 56% for the original membrane to 21% for the modified membrane, and the flux recovery rate after cleaning was increased from 34% of the original membrane to 85% of the modified membrane, the hydrophilicity and pollution resistance improved significantly after modifing.The research of this paper showed that the membrane surface structure can be regulated by grafting of hydrophilic monomers by UV irradiation in presence of BP, and the hydrophilcity and pollution resistance of the membrane surfaces can be effectively improved without damage of the membrane substrate. In addition, the structure of the membrane surface can be effectively controlled by changing the molecular weight and the number and distribution of the hydrophlic groups of the monomers. This results provided a theoretical basis for the structure design of the hydrophilic membrane surface and had guiding significance for the preparation of new type of hydrophilic membranes.
|
PDF Full Text Request