Study Of IPDI Tvpe-modified Waterborne Polyurethane Pervaporation Membranes' Preparation And Properties

Pervaporation has been widely developed as a novel membrane separation technology.Thus,preparation of high-performance pervaporation membranes is especially crucial for the rapid progresses of pervaporation.Polyurethane with soft and hard segments alternatively arranged structures,shows the feature of phase separation,which is a fascinating base material in the field of pervaporation.In our work,we modified waterborne polyurethane(WPU)by incorporating silane moieties,grafting polymerization methacrylate monomers,and performing sol-gel with polyvinyl alcohol(PVA).1.A series of WPU were firstly synthesized using isophorone diisocyanate(IPDI)as the hard segments and poly ether or polyester diols with a molecular weight of 2000 as the soft segments,named as WPU-PPG,WPU-PTMG,WPU-PHA,WPU-PBA and WPU-PEA,respectively.The flux and separation factor of these membrane were evaluated carefully.WPU-PPG and WPU-PTMG exhibit a separation factor of 2.00 and 2.10,and the flux is 5.00 kg·m-2·h-1 and 3.10 kg·m-2·h-1 respectively.For the three membranes of WPU-PHA,WPU-PBA and WPU-PEA,WPU-PEA gives the highest separation factor of 6.45,while WPU-PHA gives the highest flux of 0.58 kg·m-2·h-1.WPU-PBA was chosen as the representative membrane to perform the separation between benzene and cyclohexane.To reach ideal separation properties,the membrane thickness,the downstream vacuum,the concentration and temperature of feed and the membrane surface flow velocity were carefully optimized.The results demonstrated that both of benzene and cyclohexane exhibit the absorption-swelling-diffusion process to achieve mass transport,and dry phase show relatively large influences on the resulting separation results.2.The WPU-PPG was further modified using y-Glycidyloxypropyltrimethoxysilane(GPTMS)through hydrolysis and condensation reactions.The incorporated amounts of GPTMS obviously influenced the chemical compositions and physical micro-structures.Typically,when the molar ratio of GPTMS and-COOH derived from the WPU-PPG is 1 to 3,the effective cross-linking structure of Si-O-Si was gained.When such molar ratio varies from 4 to 6,GPTMS self-polymerized to form particles evenly distributed into the membrane matrix.Then,when such molar ratio increases to 7,the continuous inorganic phase originating from GPTMS occurred.When those membrane' properties were checked,it has been found that as increasing amounts of GPTMS,the permeation flux decreases from 5.00 to 1.02 kg·m-2·h-1 and the separation factor increase from 2.00 to 2.43.3.The WPU was modified using methacrylate with different alkyl chain structures,termed as WPU-MMA,WPU-BMA and WPU-DMA.As the length of alkyl chain increases,the flux shows an increasing trend,while the separation factor shows a decreasing trend.For the benzene and cyclohexane mixture,WPU-MMA,WPU-BMA and WPU-DMA show a separation factor of 3.2,3.2,2.6,and a flux of 0.43,0.62,1.04 kg·m-2·h-1,respectively.Taking butyl methacrylate(BMA)as modified agents for example,the optimized emulsion polymerization parameters are listed as below:the reaction temperature is 80 ?;the reaction time is 5 h;the initiator ratio is 0.6%.The resulting product shows the core-shell structure,where the core comes from BMA and the shell comes from GPTMS.With added amounts of BMA increase,the micro-phase separation in modified WPU decreases,and the separation factor increases.The highest separation factor can reach 3.3.The amounts of BMA show tiny influences on the flux.4.The WPU prepolymers end capped by y-aminopropyltriethoxysilane(APTES)were functionalized with PVA through the sol-gel process to get access to organic-inorganic hybrid membranes(WPU/PVA-APTES).When the weight ratio for WPU and PVA is 1:2 and the amount of APTES is 1.78%,WPU/PVA-APTES gives a separation factor of 38.42,and a flux of 0.128 kg·m-2·h-1(the alchol/H2O system).Then,GPTMS was chosen as the end capping agents,and the as-prepared membranes show better separation properties.For this membrane(WPU:PVA = 1:2(weight ratio),GPTMS:-COOH(WPU)= 2(molar ratio)),the highest separation factor is 89.9 and the flux is 0.114 kg·m-2·h-1.