Study On The Mechanism Of TIPS-Stretching Process And The Performance Improvement Of UHMWPE Microporous Membrane

Due to their unique properties,microporous membranes are widely used in wastewater treatment,lithium battery separators,medical fields,etc.With the rapid development of technology and economy,the demand for high-performance microporous membranes has been increasing.Ultra High Molecular Weight Polyethylene(UHMWPE)has become an important material for high-performance microporous membranes in recent years studies due to its excellent mechanical properties,chemical stability and thermal stability,but its extremely high viscosity and low critical shear rate make it difficult to process and limit its application.In this paper,UHMWPE was used as the polymer and Liquid Paraffin(LP)was used as diluent.And UHMWPE microporous membranes were prepared by TIPS-Stretching process(TIPS-S),which not only solved the problem of material processing,but also realized the regulation and optimization of the pore structure,laying a foundation for the research and preparation of high-performance microporous membranes.Thermally induced phase separation method(TIPS)was applied to prepare the UHMWPE/LP precursor films to solve the processing difficulties of UHMWPE.And during TIPS process,phase separation behavior of the system directly affects pore structure and performance of the microporous membrane.In this paper,polarizing microscope was used to study the phase separation mechanism of UHMWPE/LP system and phase separation behavior during cooling process.And then the effects of cooling rate on the phase separation behavior and membrane pore structure of UHMWPE/LP system were systematically studied,and the relationship between the above factor and the pore size,porosity,crystallinity and water flux of the microporous membrane was obtained by DSC,SEM and wide-angle XRD tests.Based on the study of phase separation behavior of UHMWPE/LP system,in order to further explore the influence mechanism of process conditions on the structure and performance of the UHMWPE microporous membrane.By SEM,XRD,SAXS and other testing methods,the relationship between melt draw ratio(DR)and crystal morphology,pore structure,crystallinity,orientation,and periodicity of the UHMWPE microporous membrane was described.And the effects of different structures produced by different melt draw ratios on the performance of UHMWPE microporous membranes such as heat shrinkage properties and tensile properties were studied by mechanical tensile and thermal shrinkage testing,got the best DR parameters.Subsequent hot-stretching process is applied to the UHMWPE/LP precursor films obtained by TIPS method,which is helpful to obtain microporous films with more uniform pore structure.In this paper,the effects of the two kinds of hot-stretching process,stretching first then extraction process(SF process)and extraction first then stretching(EF process),on the pore structure and performance were compared under the same hot stretching condition.And by TGA curves,crystallinity,microporous membrane surface structure and the porosity characterization methods,the effects of hot stretching ratios on pore structure were discussed,and the optimal stretching parameters were determined.