Study On Preparation And Properties Of Para Aramid Fiber Composite Membrane

Aramid fiber(PPTA fiber)is a high performance fiber,its strength and modulus are very high,and its thermal stability,heat resistance and solvent resistance is excellent.The decomposition temperature of the fiber is 550 centigrade.The fiber has been widely used as a high performance fiber.In this paper,the lithium ion separator,polyurethane/PPTA nano fiber composite film and polyacrylic acid/PPTA nano fiber composite film were prepared by using para-aramid nanofibers respectively.The structure and properties of the prepared materials were analyzed.The specific contents are as follows:(1)In this experiment,low temperature solution polycondensation method was carried out to prepare PPTA,then aramid nanofibers of uniform size was prepared under the condition of adding solvent and high shear.Finally,the aramid nanofiber film was prepared by vacuum assisted filtration.Aramid membrane was used as a separator to assemble the battery,and a series of tests and characterization were carried out according to the requirements of the lithium ion battery separators.Compared with the commercial membrane polypropylene,the aramid membrane has excellent mechanical properties,the tensile strength of PPTA separator is about 50 MPa.It has good wettability to the electrolyte,contact angle results show that the PPTA nano fiber membrane has good hydrophilicityand.The thermal stability of PPTA separator is good and it began to decompose at around 400 degrees celsius.It also can still maintain the integrity of the size at high temperatures.The films were heat treated under the condition of 150 degrees celsius and 200 degrees celsius for 30 min,PP separator has serious deformation and PPTA nano fiber membrane is still intact.(2)The aramid nanofibers were blended with the polyurethane and then the PPTA-PU composite films were prepared by vacuum assisted extraction.The relationship between the structure and properties of the composite films was analyzed.The results show that the mechanical properties of the composite films were significantly improved.The maximum strength of the composite film can reach 79.2MPa,which is 4.6 times higher than that of pure PU(17.3MPa).Infrared spectrum analysis shows that hydrogen bonds formed betweenPPTA and PU,both of which have strong interaction with each other and leads to the improvement of mechanical properties.(3)Aramid nanofibers were blended with polyacrylic acid solution,then the nano-reinforced transparent composite thin film material with certain flexibility was prepared by vacuum assisted extraction.The hydrophilicity of the composite films were enhanced by the introduction of aramid nanofibers,the contact angle decreased from 55.6 degrees to 35.0degrees.Infrared spectroscopy shows that the formation of hydrogen bonds between polyacrylic acid and aramid nanofibers can greatly improve the mechanical properties of the composite membrane.The maximum strength of the composite membrane can reach85 MPa,the composite membrane with excellent mechanical properties and hydrophilic properties is successfully prepared in this paper.