Preparation And Properties Of Cork/Epoxy Resin Composites

Cork is a characteristic resource in China,which has many natural characteristics such as high elasticity,heat insulation,wear resistance and flame retardancy.Due to the problems of production quality and process,the utilization rate is low in the processing process.The excellent properties of cork can be used to improve the defects of high brittleness and poor toughness of epoxy resin after curing.Therefore,in order to improve the flexibility of epoxy resin,cork/epoxy resin composites were prepared by blending cork particles with high resilience,and nanocellulose was introduced to improve the stiffness and toughness of epoxy resin composites.In order to solve the problem of weak interface between polar epoxy resin and non-polar cork particles,the surface of cork was modified by chemical reagent pretreatment and atom transfer radical polymerization(ATRP)respectively.The surface wettability and chemical structure of cork before and after treatment were studied,which provided a theoretical basis for the interface construction of cork/epoxy resin composites.The cork particles modified by different pretreatment methods were blended with epoxy resin to prepare composites.The influence mechanism of cork surface reconstruction on the mechanical properties and microstructure of composites was explored,and the interface structure with good compatibility was constructed.In addition,due to its special cell structure and chemical composition,cork particles can improve the toughness of epoxy resin while improving its heat resistance and flame retardancy.Therefore,this paper further studies the effect of cork particles on the heat resistance and flame retardancy of epoxy resin,and analyzes the flame retardant mechanism.The main results are as follows:(1)The introduction of cork particles can toughen the epoxy resin.When the cork particle content is 4%and the particle size is 40-100 mesh,the impact toughness of the two-phase composite reaches the maximum value of 10.57 KJ/m~2,which is 95.74%higher than that of pure epoxy resin.Cork particles and nanocellulose have synergistic toughening effect on epoxy resin.The impact toughness of CNF(NCC)/cork/epoxy three-phase composites is much higher than that of CNF(NCC)/epoxy two-phase composites without cork particles.When the content of CNF is 1%,the content of cork particles is 3%,and the particle size is 40-100 mesh,the impact toughness of the composite reaches the maximum value of 13.35 KJ/m~2,which is 147.22%higher than that of pure epoxy resin.At the same time,cork particles and nanocellulose have a synergistic effect on the thermal stability of epoxy resin.The introduction of the two can increase the initial decomposition temperature and carbon residue rate of the composite.(2)The pretreatment of Na OH solution can improve the hydrophilicity and wettability of cork surface.The contact angle of untreated cork is 106.98°,which is a hydrophobic material.After dipping in Na OH solution,the contact angle of cork surface decreased.Na OH solution can dissolve part of lignin and hemicellulose in cork,reduce the cohesion of cork fiber,cause cork fiber to swell,so as to improve the wettability of cork surface.The pretreatment of Na OH solution can enhance the bending resistance and impact toughness of cork/epoxy resin composites.The optimal treatment conditions of Na OH solution are temperature 25℃,concentration 5%and time 30 min.(3)ATRP technology is an effective means to improve the interfacial compatibility between cork and epoxy resin composites.Cork graft copolymer(Cork-g-PGMA)was successfully prepared by ATRP technology.Compared with the untreated cork,the intensity of the carbonyl characteristic peak was significantly increased,the intensity of the O1 s peak and the O/C element ratio were significantly increased,that is,the grafting of GMA introduced more epoxy groups and double bonds,increased the relative content of C2 and C4 peaks in the modified cork,enhanced the surface activity and surface tension of the cork,so the interfacial compatibility of the composite was effectively improved.(4)The peak heat release rate(PHRR)of pure epoxy resin was 1051.8 k W/m~2,and the total heat release(THR)was 140.7 MJ/m~2.Both cork particles and silica aerogels can improve the flame retardancy of epoxy resin,and the improvement effect of silica aerogels is more obvious.The PHRR and THR of silica aerogel/cork/epoxy resin composites were730.7 k W/m~2and 103.5 MJ/m~2,respectively,which were 30.5%and 26.4%lower than those of pure epoxy resin.At the same time,the carbon residue rate of the composites increased from 3.2%to 22.6%.The surface of the composite forms a complete and dense expanded carbon layer,and the flame retardant performance is significantly improved.