Study On Preparation And High Temperature Resistance Of Boric Acid Modified Phenolic Epoxy-GO Microcellular Foam Composites

Epoxy foam materials have been widely concerned in aerospace,rail transportation,new energy vehicles and other industries due to their advantages of high specific strength,low density,low thermal conductivity and good corrosion resistance.However,the low high temperature resistance of traditional epoxy resin limits its further application in extreme high temperature environment.How to improve the high temperature resistance of epoxy foam materials while maintaining high mechanical strength is an important problem to be solved at present.Based on the integration of material structure and performance of design thought,to carry out the boric acid modified phenolic epoxy resin（BEPN）and BEPN grafted oxidized graphene（BGO）synthesis preparation research,through exploring and optimize synthesis process got the curing activity is moderate,good mechanical properties and high glass transition temperature（Tg）BEPN resin material.The dispersion state of BGO in BEPN resin matrix and the reinforcement law of mechanical properties of BGO nanocomposites were studied.Taking BEPN and BEPN/BGO nanocomposites as substrates,foaming materials with low cell size,high cell density and high heat resistance were finally obtained by optimizing foaming conditions,which provided feasible scientific methods for modification of high heat resistance epoxy resin and preparation of foaming materials.Details are as follows:（1）The problem of epoxy group loss and boric acid surplus caused by high activity of benzyl hydroxyl group was solved effectively by using weak base type catalyst.A homogeneous BEPN with high epoxy value（0.47mol/100 g）was successfully synthesized by step heating method.The activation energy of BEPN reaction（52.6 k J/mol）was calculated by Kissinger method based on differential scanning calorimetry（DSC）test results.Compared with traditional bisphenol A epoxy resin（EP）,dynamic mechanical analysis（DMA）confirmed that BEPN has a more complete cross-linking network resulting in higher Tg.The thermo-gravimetric analysis（TGA）showed that the temperature of 10%weight loss(T_10%)of BEPN resin in nitrogen atmosphere decreased by 10%increased by 76℃.The results of mechanical properties test show that the tensile strength and modulus of BEPN resin are increased by 16.3%and 26.2%respectively.（2）In order to improve the compatibility between GO and BEPN resin,the preparation of BEPN grafted GO was studied,and the successful preparation of BGO was confirmed by fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The dispersion of BGO in resin matrix was investigated by optical microscope（OM）.The tensile strength and modulus of BEPN/BGO increased by 28.1%and 28.4%,respectively,compared with the resin matrix without BGO.（3）Three kinds of foam materials（EP-foam,BEPN-foam,BGO-foam）were successfully prepared using EP,BEPN and BGO/BEPN as foaming resin matrix.The influence of pre-curing temperature and time,post-curing temperature on the size and density of cell was systematically studied,and the best foaming process was optimized.The mechanism of improving foaming effect by BGO was revealed.Compared with EP-foam,the average cell cell of BGO-foam was 83.9%（81μm）lower,and the cell density of BGO-foam was91.6 times higher（2.5*10⁶cells/cm³）.By testing the stability of foam size,fragility and compression performance,the evolution law of cell diameter,cell density and foam compressive and deformation resistance was revealed.The introduction of BGO can improve the stiffness of cell wall,and lower cell size and higher cell density can produce more energy dissipation.Based on thermal infrared imaging test,the mechanism of heat insulation of foam was verified.Finally,the short time flame resistance of the foam was tested by butane flame,and the graphitization degree of the carbon layer of the foam was analyzed by Raman spectroscopy.The flame resistance mechanism of BGO-foam material was proposed:the synergistic carbon fixation of boron element and GO,which effectively improved the ability of the foam to resist flame burning.