Preparation And Properties Of Wear-resistant Shape Memory Polyimide/Boron Nitride/Carbon Black Materials

Shape memory polyimide（SMPI）is a type of smart polymer material with good comprehensive properties,such as high thermal stability,high strength,high modulus and radiation resistance,etc.It has wide range of application prospects.In the severe environment in which SMPI operates,friction will damage the material or even shorten the service life of the material,so it is necessary to improve the friction and wear resistance of the material.Hexagonal boron nitride（h-BN）has a layered structure similar to graphite,with good lubricity,high thermal conductivity,and high temperature resistance.It has been used in material modification for many years.Carbon black（CB）has the advantages of low cost,light weight,good shielding ability,and high chemical stability.This paper combines shape memory polyimide with boron nitride and carbon black in order to maintain the good comprehensive performance of polyimide while effectively improving the wear resistance of polyimide composite materials,broadening the application scope of SMPI in aerospace,microelectronics and other frontier fields.In this paper,in-situ polymerization was used to prepare shape memory polyimide.In order to enhance the interface between the inorganic and the organic phase,h-BN was modified with 3-aminopropyltriethoxysilane（APTES）.The modified boron nitride（M-BN）disperse polymerization in PAA precursor,after high temperature curing and cross-linking,prepare SMPI/M-BN composite material and perform performance analysis.The results show that the glass transition temperature Tg of SMPI prepared with 4,4-（hexafluoroisopropylene）phthalic anhydride（6-FDA）and 2-（4-aminophenyl）-5-aminobenzoxazole（AAB）as monomers is 363 ℃,which is higher than that of other homopolymer SMPIs reported so far.After the modified boron nitride（M-BN）is added,the thermal stability and thermomechanical properties of SMPI/M-BN composites are significantly improved,and the shape memory response time is significantly shortened.The composite material has excellent wear resistance,and the wear rate drops from7.5×10^-9 g·N^-1·r^-1 of the original SMPI to 0.83×10^-9 g·N^-1·r^-1 of SMPI/10% M-BN,a decrease of 88.9%,the wear mechanism gradually evolves into slight adhesive wear.In this paper,modified micron boron nitride and nano carbon black are mixed according to the ratio（M-BN:CB=6:4）to prepare binary filler,and SMPI prepared with3,3,4,4-biphenyltetracarboxylic dianhydride（BPDA）and 2,2-bis [4-（4-aminophenoxy）phenyl] propane（BAPP）as monomers is used as matrix material to prepare SMPI/M-BN/CB ternary composite material.Analysis results show that as the contentof M-BN/CB increases,the T_g value of the material tends to increase.The thermo-mechanical properties of composite materials are enhanced.This paper proves that the joint addition of M-BN/CB can more effectively improve the wear resistance of the polymer.When the M-BN/CB content is 15 mass%,the degree of surface wear of the composite material is significantly weakened.After 3600 s of friction,the wear rate decreased from 13.3×10^-9 g·N^-1·r^-1 of the original SMPI to 0.84×10^-9 g·N^-1·r^-1 of15mass% of the mixed filler,the reduction range is 93.68%.The friction mechanism changes from severe fatigue and adhesive wear to slight adhesive wear,which is of great significance for reducing energy consumption and improving equipment reliability.