Preparation Of Tertiary Amine Containing Amphiphilic Copolymer Blended Membrane For Adsorption During Filtration

The pollution of environmental, especially the pollution of water has become great troubles to the whole society with the rapidly expanding of the social productive forces and population explosion. Among these, negatively charged molecules, especially hexavalent chromium, has also become threatens to the water resource. As a new and efficient separation technology, membrane technology is considered as one of universal technique to solve these troubles in resources and environments. Basically, membrane materials are regarded as the core of this technology. Thus, to prepare a proper membrane with the ability to remove these negatively charged molecules is considered to be the key to solve these problems. Blending is an efficient and application potential method to prepare functional polymeric membranes. However, the elution of additives during the membrane preparation process and the application process seriously influences the stability of membrane composition which further influences its performance. Therefore the present study synthesized functional copolymers with different sequence structures and prepared functional membranes with stable morphologies, composition and performance by blending method. After that a novel separation approach, a process that removal negatively charged molecules by adsorption during filtration, was developed. The research details and results are as follows.Tertiary amine groups containing amphiphilic copolymers with similar composition but different sequence structures were designed and synthesized by free radical polymerization. Three tertiary amine groups containing amphiphilic copolymers with different sequence structures, such as diblock, triblock and four-armed diblock, were synthesized using dimethylamino-2-ethyl methacrylate (DMAEMA) as functional monomers and methyl methacrylate (MMA) as hydrophilic monomers by atom transfer radical polymerization (ATRP). These copolymers were characterized and confirmed by hydrogen nuclear magnetic resonance (’H-NMR) and gel permeation chromatography (GPC). The mechanism of this living polymerization was confirmed by researching the impact of reaction times on the DMAEMA content in the final copolymer. And finally the method to control the DMAEMA content in copolymer was obtained. Tertiary amine groups containing amphiphilic copolymers with random structures were synthesized by solution free radical polymerization. The impact of monomer ration in reaction solution on the DMAEMA content in the final copolymer was investigated and characterized by’H-NMR and GPC. Finally the way to control the DMAEMA content in copolymer by free radical polymerization was obtained.Tertiary amine block copolymer containing ultrafiltration (UF) membranes were design and prepared, the properties of these membranes were studied. Diblock copolymer P(MMA-b-DMAEMA) was used to fabricate the tertiary amine block copolymer containing blend membranes with poly(vinylidene fluoride) (PVDF) via a non-solvent induced phase separation (NIPS) process.’H-NMR and X-ray photoelectron spectroscopy (XPS) were used to characterize the bulk and the surface layer compositions of the prepared membranes. It was found that P(MMA-b-DMAEMA) stably retained in the blend membranes and greatly enriched onto the surface layers. The pH-dependent performances of the membranes were investigated in details. With the change of pH values, the surface hydrophilicity, water permeation, dextran sieving behaviors and hexavalent chromium (Cr(VI)) adsorption properties varied greatly. And the membrane performed obviously reversible pH-dependent property. From the results, a feasible method could be inferred for fabricating UF membranes with tunable filtration, macromolecule sieving and anion adsorption properties under different pH conditions.The impact of amphiphilic copolymer structures on the morphology, composition and performance stability of the blend membranes was investigated. Four tertiary amine based amphiphilic copolymers with similar composition but different sequence structures in terms of diblock (P(MMA-b-DMAEMA)), triblock (P(DMAEMA-b-MMA-b-DMAEMA)), four-armed diblock (P(MMA-b-DMAEMA)4) and random (P(MMA-r-DMAEMA)) were used for fabricating functional porous membranes by blending method. The retention ratios and surface enrichment ratios of the copolymers in blend membranes were determined by 1H-NMR and XPS. The composition of the formed membranes was investigated and the durability was experimentally tested. The hydrophilicity of the membranes was evaluated by water contact angle measurement. The performance of membranes under different conditions including water fluxes at different pH and various ionic strength, the adsorption capabilities for Cr(VI) and negatively charged dye sunset yellow at different pH was studied. The results showed that tertiary amine based amphiphilic copolymers with block and multi-armed sequence structures endowed the blend membranes with higher copolymer retention ratios, more surface tertiary amine groups contents and better composition stability as well as more sensitive to the variation of pH, ionic strength, higher equilibrium anions, and negatively charged dyes uptakes.Cr(VI) removal by adsorption during filtration process on a quaternary ammonium based UF membrane (QA membrane) was studied. A QA membrane was prepared by surface quaternization on the tertiary amine based UF membrane (TA membrane), using CH3I as the quaternization regent. The surface quaternization was confirmed by attenuated total reflectance fourier transform infrared (ATR/FTIR) and XPS. Scanning electron microscopy (SEM) images suggested the quaternization had little effect on the membrane morphology. By measuring the contact angle, surface charge, water permeation properties at different pH or different ion strength, Cr(VI) adsorption and desorption properties as well as the Cr(VI) removal performance in filtration, QA membrane and TA membrane were compared. The results showed that compared with the TA membrane, the QA membrane displayed enhanced hydrophilicity, permeation stabilities and wide Cr(VI) removal pH scopes, indicating the potential application in low concentration Cr(VI) removal.The random structure amphiphilic copolymer blended membrane with stable tertiary amine groups containing surface was designed and fabricated. The random structure amphiphilic copolymer P(MMA-r-DMAEMA) was partly cross-linked by xylene dichloride (XDC) during the blending process. Then the PVDF blended membranes were prepared via NIPS process. The retention ratios and surface enrichment ratios of the copolymers in blend membranes were determined by element analysis (EA) and XPS. The results showed that the copolymer retention ratio increased from 73.57% to 89.59% when the additive amounts of XDC increased from 0%to 3% according to the copolymer additive amounts, while the surface DMAEMA contents decreased slightly simultaneously. The performance durability of theses membranes were experimentally tested. It was found that the more XDC added the more stable of the membrane performances were. In addition, the blend membrane performed obviously pH-dependent negatively charged molecular sunset yellow adsorption properties by electrostatic interaction. At lower pH, the blend membrane could remove sunset yellow from aqueous solution by adsorption during filtration process. And at higher pH, the adsorbed sunset yellow could be washed out. Sunset yellow was concentrated in the elution solution, the concentration factor was as high as 428.76%. Moreover, the blend membrane could adsorb bivalent copper and bivalent cadmium by complexation.