Study On Modification Of Polyurethane Membranes

In this paper,blending SiO₂ and specific additives,and PVB or PVC in addition,the PU hybrid or hybrid blend membranes were respectively prepared by means of immerged phase-inversion process.The performance of PU hybrid membranes were enhanced significantly based on improved the microporous structure.It were analyzed that the mechanism of the phase separation by testing the thermodynamic phase diagram and kinetic curves of phase separation,meanwhile,combined with NMR and SEM analysis. The compatibility of the PU hybrid systems were investigated by DMA.In addition,by using the UV grafting method,performance of PU hybrid membranes was modified.The properties of PU hybrid membranes were investigated separately.The method of NMR relaxation time T₁ value of PU was used to determine effects of SiO₂,LiCl,PEG6000,PVB and PVC respectively.The results showed that blending SiO₂ or others mentioned above with PU,the T₁ values could be down in a certain degree and the PU molecular chains entanglement was decreased.Adding the specific additives to the PU/SiO₂ system could improve the speed of phase separation.The retention of PU hybrid membrane with PEG or LiCl were improved substantially,however,the flux and retention of the PVP system were both decreased a little bit.Comparison with PU/SiO₂/PEG6000 hybrid system,the flux and retention of PU/SiO₂/PEG10000 hybrid membrane were smaller.Blending PVB with different viscosi could improve the performances of the PU/PVB/SiO₂(abbreviated PU/PVB) hybrid membranes.The kinetic curves of phase separation indicated that the PVB could obviously accelerate speed of phase separation process,and the speed of phase separation of PU/PVB-1 system was faster than that of PU/PVB-2.The DMA diagram showed that the PVB was all but incompatible with PU.The flux of the PU/PVB hybrid membranes were decreased when using PVB with higher viscosity,while the retention improved.When the concentration of PVB-2 was 20%in the PU system,the retention of PU/PVB-2 could be up to around 85%.Blending PVC could also improve the performances of the PU/PVC/SiO₂(abbreviated PU/PVC) hybrid membranes.The DMA diagram showed that the PVC was compatible with PU.The retention of the PU/PVC hybrid membranes were enhanced with the increasing the quantity of PVC.Blending PEG into the PU/PVC system,it could increase the retention of PU/PVC hybrid membranes but decrease the flux.With the adding MPC, the flux of PU/PVC hybrid membranes could increase slightly and the retention increase in a certain concentration range of MPC.When the content of MPC was 5%in the PU system, the flux of PU/PVC hybrid membranes could get a higher level.It was prepared that the HEMA grafted PU hybrid membranes were prepared by means of UV grafting method.In addition,the effects of technical settings were evaluated.The results showed that the flux of PU hybrid membrane could enhance significantly by the aid of grafting modification,which could be up to 132.36 L/m²h.In the application of treatment papermaking black liquor,comparison with PU/SiO₂ membrane,the PU/PVB hybrid membranes showed better effects under the condition of continuous treating operation.By using fractal theory to analyze the SEM photos,the results indicated that the fractal theory analysis could be used to quantification morphology and microporous structure of PU hybrid membranes.The results of SEM analysis were coincident with achieved performances of PU hybrid membrane.