Preparation And Properties Of Epoxy Resin Modified By Polyimide Microspheres

Epoxy resin(EP)and its modified material play an extremely important role in the national defense industry and the electronics manufacturing industry.It has always been critical and challenging task to achieve the synergistic improvement of the mechanical properties,thermal properties and dielectric properties of epoxy resin.In order to solve these problems,monodisperse preformed polyimide(PI)microspheres and PI hollow microspheres were synthesized and used in EP,and modified EP with high temperature resistance,high modulus and low dielectric properties was prepared,which is of great significance to promote the application of high-performance engineering plastics in modified EP.The main research contents of this paper are as follows:PI microspheres with good dispersion were successfully prepared through the inverse microemulsion method,and the influence of surfactant concentration on the size and particle size distribution of PI microspheres was discussed.Then the structure,morphology and thermal properties of PI microspheres were studied.The curing kinetics and gel time of EP matrix were studied by non-isothermal DSC method,and the curing process of EP was determined.The PI microsphere modified EP was prepared,and the mechanical and thermal properties of the PI microsphere modified EP were systematically studied.The results showed that PI microspheres can not only enhance the mechanical strength of epoxy resin,but also significantly improve the toughness;when filled with 3 wt%PI microspheres,the tensile strength of modified EP was increased by 47%,the fracture toughness K_IC and impact strength of modified EP were increased by 92%and 200%,respectively.The cross-sectional morphology of the modified EP was analyzed using a scanning electron microscope system,and the mechanism of strengthening and toughening was revealed.In addition,studies have also shown that the addition of PI microspheres can give EP excellent thermal stability and heat resistance.PI hollow microspheres were successfully prepared through the o/w/o multiple emulsion method,and the structure,particle size distribution,glass transition temperature and thermal stability of PI hollow microspheres were studied.Compared with PI solid microspheres,the prepared PI hollow microspheres have a smaller particle size and higher heat resistance.After adding the PI hollow microspheres to EP,the prepared modified EP was more lightweight,the water absorption rate of modified EP was further reduced,and the modulus and the rigidity were also enhanced.The introduction of 1 wt%and 3 wt%of PI hollow microspheres can significantly improve the mechanical properties of EP,the tensile strength has reached more than 100 MPa,the fracture toughness K_IC and the critical strain energy release rate G_IC have reached 1.96 Mpa·m^1/2 and 2.33 KJ/m²,respectively.In addition,the thermal stability of PI hollow microsphere modified EP was significantly improved.The PI hollow microsphere modified EP has excellent dielectric properties,the high-frequency(10⁵?10⁷ Hz)dielectric constant is 3.6?3.8,and the dielectric loss is about 0.03.