Study On Forming Mechanism And Process Control Of UHMWPE Nanocomposite Microporous Membrane

Microporous membrane has won the high recognition in the industry process with its unique separation performance.It is widely used in various fields,such as desalination,sewage treatment,gas separation,biotechnology,battery diaphragm and so on.With continuous development of industrial production,the requirements for the performance of microporous membrane are increasing.Ultra-high molecular weight polyethylene（UHMWPE）,with its strong corrosion resistance,low temperature resistance,wear resistance and excellent impact resistance,is one of the ideal matrix materials for preparing high performance microporous films.However,due to high melt viscosity of UHMWPE,its processing performance is poor.In this thesis,through reasonably controlling rheological properties of materials,UHMWPE nanocomposite microporous membrane was fabricated via thermal induced phase separation（TIPS）method combined with film casting process successfully.The effects of nanoparticles on phase separation and pore structure of microporous membranes were systematically studied.After that,the pore structure was further regulated by post-tensile process.This work can provide important guidance for preparation and process control of high-performance nanocomposite microporous membranes.Firstly,systematic studies were conducted in terms of rheological properties of substrate materials in this thesis.By analyzing parameters change of viscosity,storage modulus and loss modulus of UHMWPE/LP system under different conditions,the effects of polymer concentration,polymer molecular weight,temperature,shear rate and content of nanoparticles on rheological properties of the system were discussed.Further,optical microscopy and DSC were used to analyze turbidity temperature and crystallization temperature.Phase separation mechanism of UHMWPE/LP/TiO₂ system was studied,so as to guide the selection of matrix materials and some process parameters.On the basis above,UHMWPE/TiO₂ nanocomposite microporous membranes were fabricated by combining TIPS method with film casting process.DSC,WAXD,SAXS,SEM and other test methods were used to systematically analyze crystallization properties,crystal structure,microporous morphology and porosity of different nanocomposite systems to explore the relationship between structure and properties of nano-composite microporous membranes.The structure and property evolution of UHMWPE/LP/TiO₂ system within flow molding process was studied.The influence of draw ratio on the crystal structure,pore structure and performance of nanocomposite microporous membrane was analyzed by WAXD,SAXS,SEM and other methods.In order to further improve the performance of UHMWPE/TiO₂ nanocomposite microporous membrane,post-tensile treatment method was used to control the pores of the nanocomposite microporous membrane.By studying tensile deformation behavior,pore morphology and porosity evolution,the effects of stretching ratio and stretching temperature on the pore structure of the nanocomposite microporous membrane were analyzed.