Study On Synthesis Of Polyimide And Properties Of High Strength Membrane

Polyimide(PI)has excellent mechanical properties,high and low temperature resistance,chemical corrosion resistance,insulation and flame retardant due to the existence of imide structure and benzene ring.It can be applied to aerospace,battery,microelectronics industry and rail transit in the form of membrane,fiber,adhesive,battery diaphragm,coating and composite materials.In recent years,the preparation and application of high-performance polyimide membrane materials have attracted extensive attention.With the development of science and technology and the increasing demand for membrane materials,the application of universal methods to prepare high performance polyimide membrane materials has become the focus of research.This paper mainly focuses on the research of high strength PI membrane and nanofiber membrane.The first part of the work has system research for PI by focusing on the structural regulation,controlled synthesis and thermal imidization temperature,successfully developing the universal preparation technology and the fabricating the high strength PI membrane.In the above research process,it is found that the research ideas can be introduced into the research work of PI nanofiber membrane to solve the problem of poor mechanical properties of PI nanofiber membrane.Therefore,the second part focuses on exploring the influence of PI synthesis on the mechanical properties of PI nanofiber membranes.Combining PI synthesis and preparation as well as in-situ strengthening and modification technology,high strength PI nanofiber membranes are prepared,and its application prospect in the field of lithium electric diaphragm is studied.Specific work is as follows:(1)Preparation and properties of high strength PI membranes.Firstly,the influence of the synthesis conditions of P/O foundation system on the mechanical properties of the membrane was explored.Based on the above synthesis conditions,the PI structure was regulated(P/O/P and B/P)to explore the importance of structural units for improving the mechanical properties.The PAA solutions of B/P/H and B/P/B copolymerization systems were prepared by combining the preliminary structural regulation and the optimized conditions in the synthesis process.The influence of thermidization temperature on the mechanical properties of PI membranes was further investigated.The results show that the performance of B/P/B copolymerized PI membrane is the best.When the thermidization temperature is 390℃,the tensile strength of PI membrane with 0.5%BI content is up to408.5 MPa,the temperature is 586.2℃,the T_g is 472.0℃,the storage modulus is 7963 MPa when the weight loss is 5%,the CTE is 9.28 ppm/K,the water absorption rate is 1.78%and the membrane density is 1.49 g/cm~3.(2)Preparation and properties of high strength PI nanofiber membrane.Firstly,PAA solution with high intrinsic viscosity is obtained by adjusting polymerization temperature,and high performance initial PI nanofiber membrane was prepared by electrospinning and thermidization process.Then,the dilute solution of PAA was used as the reinforcing agent to bond initial PI nanofiber membrane to obtain high strength PI nanofiber membrane,and the nanofibers were functionalized by using thermoplastic polyether imide.Finally,high-strength functional PI nanofiber composite membranes(PIE)with shutdown function is prepared.The results showed that the strength of initial PI nanofiber membrane was 64.1MPa,and the tensile strength of the enhanced and modified PIE nanofiber membrane was95.7 MPa,showing good flame retardant,heat resistance(5%weight loss at 491.5℃),wettable(electrolyte contact Angle 17.7°)and high ionic conductivity.In particular,the specific power capacity at 0.1 and 10 C is 168.4 and 111.3 m Ah/g.In addition,the shutdown function,flame retardant and heat resistant of PIE nanofiber membrane can effectively improve battery safety.