Preparation And Properties Of Carbon Fiber Networks Reinforced Anionic Polymerized Nylon 6 Composites

Compared with fiber-reinforced thermosetting composites,fiber-reinforced thermoplastic composites have better impact resistance,self-lubricity and recyclability,and have a short manufacturing cycle,and are widely used in aerospace,automotive,sports and transportation industries.In situ anionic polymerization can fully infiltrate the fiber reinforcement due to its low monomer viscosity,which solves the problem that the melt of thermoplastic resin is difficult to infiltrate the reinforcing material due to its high melting viscosity.However,APA6 has strong water absorption,poor thermal stability and dimensional stability,and insufficient mechanical properties,which limits its wide application.APA6 is usually modified by glass fiber and carbon fiber.With the increasing awareness of environmental protection,using ramie-based carbon fiber or chopped PAN-based carbon fiber as a reinforcing material has become hot.Using phenolic resin as binder and ramie fiber as raw material to prepare stable and rigid carbon-bonded carbon fiber network reinforcement(CFNR).The RCFNR/APA6 composite was prepared using a vacuum assisted resin transfer molding process(VARTM).The physical and chemical changes of ramie fiber before and after heat treatment were studied comprehensively.The mechanical properties,impact section and thermal stability of RCFNR/APA6 composites were systematically characterized.The results show that the ramie fiber after high temperature heat treatment has completely carbonized,but the phenolic resin has left a small amount of residue.The micro-holes are formed inside the carbonized ramie fiber,and the mechanical properties are decreased,therefore,the tensile properties of the RCFNR/APA6 composite are not significantly improved,but the flexural and impact properties are improved.The carbonized ramie fiber has no effect on the thermal stability of the composite,and the residual phenolic resin significantly increases the thermal decomposition temperature of the composite.In view of the fact that RCFNR has no obvious reinforcing effect on APA6,SCFNR/APA6 composites were prepared by short cut PAN-basedcarbon fibers(SCF)with length of 1 mm.Through the characterization,the short carbon fibers are joined by carbon bonding points to form a three-dimensional network reinforcement(SCFNR).Although the tensile properties of the SCFNR/APA6 composites have not been significantly improved,the flexural properties and impact properties are significantly improved.The addition of SCFNR provides a large number of nucleation sites for the anionic polymerization of CL,APA6 is more prone to form stable ? crystal forms,so the thermal stability of SCFNR/APA6 composites is significantly improved.In order to further study the effect of carbon fiber length on the reinforcing effect of composites,carbon-bonded long carbon fiber network(LCFNR)reinforcing materials were prepared with PAN-based carbon fibers with the length of 10 mm.LCFNR/APA6 composites were prepared by in situ anionic polymerization of CL.It has been found that the long carbon fiber dispersion in LCFNR is more orderly,and the network reinforcement is formed by the carbon bonding points and face bonding and overlapping.The tensile and flexural properties of LCFNR/APA6 composites increase with the increase of LCFNR volume fraction,while the impact properties show a trend of first increasing and then decreasing.The addition of LCFNR acts as a physical barrier to the thermal decomposition of the composites,and the maximum thermal decomposition temperature of the composites moves towards high temperature.Because the way of bonding carbon fibers in LCFNR is different from SCFNR,the three-dimensional structure and reinforcement mechanism of the two composites are significantly different.Finally,the tensile and flexural properties of LCFNR/APA6 composites are better than those of SCFNR/APA6 composites.