Study On Modification And Performance Of Polyurethane Microporous Membranes

In this paper,the polyurethane(PU)microporous membranes were prepared by wet membrane forming process.The effects of different PUs(polyether type 1180-PU,polyether type 1190-PU,polyester type 5280-PU,polyester type 5290-PU),nonsolvents(water,methanol,ethanol,isopropanol)and modifiers(graphite oxide,4,4'-dihydroxyazobenzene,PVC)on membrane structure,the rate of membrane formation,porosity,moisture absorption,air permeability,hydrophilicity,water vapor permeability and mechanical properties were discussed.The ternary phase diagram was used to qualitatively characterize the polymer-solvent-nonsolvent ternary system,and molecular simulation was used to analyze the mechanism of performance modification in the micro-scale.For different PUs,the rate of membrane formation of pure PU was related to the diffusion coefficient of water molecules in the PU membrane,and the moisture absorption of PU membrane was related to the free volume fraction.The position of bimodal line of the ternary phase diagram of four different PUs closed to PU-DMF axis increased in order of 1180-PU,1190-PU,5280-PU and 5290-PU.Adding the same amount of graphite oxide to the four different PUs,respectively,could greatly reduce macroporous structure and increase the number of interface micropores.The rate of membrane formation,porosity,moisture absorption,permeability,tensile strength and elongation at break of four different types of PU membrane were improved.When the proportion of soft segment of polyether-PU was higher(1180-PU),the modification effect of PU membrane was the best.For different nonsolvents,the rate of membrane formation was closely related to the hydrogen bond strength between solvent and nonsolvent,but the pore size of PU membrane was related to reaction energy difference of the solvent-nonsolvent complex formed in the solvent and nonsolvent,respectively.The position of bimodal line of the ternary phase diagram of four different nonsolvents closed to PU-DMF axis went from water to methanol and then down to ethanol and finally to isopropanol.The asymmetric structure of PU.membrane obtained under the water system.The porous structure of PU membranes prepared in alcoholic coagulant was more uniform compared to those prepared in water coagulant,and the permeability,tensile strength and elongation at break of these membranes were higher.4,4'-dihydroxyazobenzene was prepared via azo-coupling reaction and added to the PU membrane.Molecular simulation results showed that-OH in 4,4'-dihydroxyazobenzene most easily formed hydrogen bonds with-NH-in PU.The experimental results show that the rate of membrane formation of PU slowed down with the increase of consumption of 4,4'-dihydroxyazobenzene.The macroporous shape of the membrane became irregular.The number of interface micropores increased.The thermal stability increased slightly.The porosity,moisture absorption,air permeability and mechanical properties were significantly improved.However,the properties of the membrane tended towards stability when 4,4'-dihydroxyazobenzene supplementation exceeded 0.6%.When PVC was used as a modifier,molecular simulation results showed that the compatibility between PU and PVC was the best with 90/10 mass ratio.The position of bimodal line of the ternary phase diagram of five different PU/PVC mass ratios closed to PU/PVC-DMF axis increased in order of 90/10,70/30,80/20,60/40 and 100/0.The better of the compatibility of PU and PVC,the slower of the rate of membrane formation and the better of the thermal stability.When the mass ratio of PU/PVC was 90/10,the air permeability increased from 0.1561L·cm-2 min-1 to 2.600L·cm-2 min-1,the water vapor permeability increased from 0%to 25.18%,the elongation at break increased from 414.26%to 430.96%,the PU/PVC blend membrane achieved optimal comprehensive performance.