Interface Design And Performance Of Epoxy Resin-based/carbon Fiber Composites

In order to solve the problems of high brittleness and poor impact toughness of resin matrix composites used in aerospace with the need of high performance and low cost,using high viscosity epoxy and porous expanded graphite（EG）as raw materials,GNPs with high aspect ratio was obtained by continuous exfoliating EP with three-roller milling technology（TRM）,and the GNPs and EP mixtures after exfoliating were heated and cured by curing system to obtain in situ reinforced epoxy carbon fiber composites with GNPs.The functionalized granular magnesium aluminum spinel（MA）prepared by molten salt method was used to modify CF,and then the high-performance GNPs-EP/MA-CF composite was further prepared.The main findings are as follows:（1）Using loose porous EG as raw material,continuous exfoliated by TRM technique in EP medium,the exfoliated product uniformly mixed in EP was obtained,and the structure,surface morphology,number of layers and thickness of the exfoliated product were characterized by XRD,SEM and HRTEM.The results showed that the exfoliated products were graphite nano-platelets（GNPs）with a thickness of 4-20 nm,an average aspect ratio of 400-1200.（2）The exfoliated GNPs were uniformly dispersed in EP to prepare GNPs/EP composites.The thermal stability,structure and surface morphology of the GNPs/EP composites were characterized by TG-DTA and SEM.The mechanical properties such as flexural strength,flexural modulus,tensile strength and tensile modulus of GNPs/EP composites were tested.The results showed that when the mass ratio of expanded graphite in epoxy resin was 1%,the flexural and tensile properties of the composite were the strongest,compared with pure epoxy resin,the flexural strength was increased by 31.9%,and the tensile strength was increased by 53.4%.The water absorption rate was tested of the GNPs/EP composites,the water absorption rate was tested.The GNPs/EP composites with GNPs of 0%,1%,2%,3%,4%and 5%were all stable and low water absorption,and comparing the water absorption in different pH solutions,it was found that the acid-base environment had little effect on GNPs/EP materials.（3）The GNPs was uniformly dispersed in EP,then compounded with CF by laminating method,and cured in autoclave at high temperature and high pressure to obtain EP/CF composite.The thermal stability,structure and surface morphology of the EP/CF composites were characterized by TG-DTA and SEM.The results showed that the prepared EP/CF composite had good thermal stability before 250°C and had good wettability between CF reinforcement and EP matrix.The mechanical properties such as flexural strength,flexural modulus,tensile strength and tensile modulus of EP/CF composites were tested,when the mass ratio of EG in epoxy resin was 1%,the flexural and tensile properties of this EP/CF composite were the strongest,reaching 471.21 MPa and 496.37 MPa,respectively,compared to EP/CF composites without GNPs.The flexural strength increased by an average of 26.1%,the tensile strength increased by an average of 12.01%,and the overall performance improved.（4）MgAl₂O₄（MA spinel）was synthesized by molten salt method at 1150℃using nanometer alumina grains（Al₂O₃）and magnesia particles（MgO）as raw materials and lithium chloride（LiCl）as molten salt.Then the CF was modified by MA spinel,which was then compounded with the mixture of GNPs and EP by layer-layer method,and cured in an autoclave under high temperature and high pressure to obtain GNPs-EP/MA-CF composite.The structure,surface morphology and properties of the composites were characterized by SEM.The results showed that GNPs were uniformly dispersed in the EP matrix and existed in the EP matrix in the form of platelets,and there was no agglomeration.The GNPs and the EP matrix were tightly bound.The CF surface was adhered with MA,which had the effect of preventing CF from being pulled out in the EP matrix,the bonding between the CF and EP substrates was also very close,and the EP substrate adhered firmly to the surface of the carbon fibers without defects such as bubbles.The mechanical properties such as flexural strength,flexural modulus and tensile strength of the composites were tested by means of flexural and tensile tests.When the mass ratio of EG in the epoxy was 1%,the content of EG was 1.5 wt.%,the flexural strength and tensile strength of the EP/CF composites prepared with CF modified by MA were 672.43 MPA and 513.97 MPA,respectively,which were 20.2%and 14.6%higher than that of the samples with 0%MA.Therefore,it is feasible to obtain GNPs by grinding and stripping EG with TRM technology,and to obtain more excellent composites than pure EP by doping EG into EP.