Construction Of Hierarchical Composites Reinforcement And Study On Its Enhancement Mechanism

Polymer matrix composites have excellent properties such as high specific strength,high specific modulus,low density,high and low temperature resistance,corrosion resistance and fatigue resistance,which are of great value in military applications such as aerospace.However,there are few polar groups and active groups on the surface of carbon fiber.The wettability and adsorption between polymer matrix and carbon fiber are poor,which makes the surface energy low.These factors lead to the poor interface strength of carbon fiber composite,hinder the load transfer from matrix to fiber,and the excellent properties of carbon fiber-reinforced polymer matrix composite cannot be fully developed.At the same time,the uneven dispersion of the reinforcement in the polymer also becomes the bottleneck of the performance improvement of the composite.In order to improve the interfacial strength,solve the problem of dispersion and improve the properties of the composite,carbon nanotube/carbon fiber hierarchical and natural wood/epoxy composite were designed and prepared.Carbon nanotubes were grafted onto the surface of carbon fiber by chemical assembly method.Carbon nanotubes were evenly distributed on the surface of carbon fiber.The mechanical meshing ability between carbon fiber and polymer matrix was improved,and the interface strength of composite was enhanced.XPS results showed that CNTs were grafted onto the surface of carbon fiber by high-strength chemical bond with PPI dendrimers as the media.The results of FESEM show that the grafting of CNTs onto the surface of carbon fiber is of high density and uniformity.The results of surface energy test show that the wettability between carbon fiber and polymer matrix is improved after grafting carbon nanotubes.At the same time,the grafting of CNTs also provides the mechanical interlock effect between carbon fiber and polymer matrix.The crack propagation at the interface is further hindered,and the final interface strength is increased by 109%.Natural wood has a natural multi-scale structure,and from the micro point of view,the lignin removed from the wood will leave holes,which will facilitate the entry of epoxy resin.A large number of oxygen-containing groups will be introduced into the surface of the inner pipe of the wood treated by chemical method to further improve the wettability of the wood surface and the epoxy resin and improve the interface strength.The bending strength of the longitudinal wood / epoxy multi-scale reinforced composite reached 180 MPa,36% higher than that of the original wood and 100% higher than that of the epoxy resin;the bending strength of the transverse wood / epoxy multi-scale reinforced composite was 108% higher than that of the original wood;the tensile strength of the transverse wood / epoxy multi-scale reinforced composite was 107% higher than that of the original wood.Based on the excellent electrical conductivity of wood after carbonization,the natural wood derived carbon materials were further prepared and their electromagnetic shielding properties were studied.The electromagnetic shielding test results show that in the range of 8-12 ghz,the average electromagnetic shielding effectiveness of wood derived carbon / epoxy composite is 15 d B,and the maximum is 32 d B.After calculation,the transmission coefficient is about 0,and the reflection coefficient is about 0.7.This result shows that there is almost no electromagnetic wave passing through the material,and nearly 80% of the electromagnetic wave is reflected on the sample surface,which proves that the material has excellent electromagnetic shielding efficiency.The electromagnetic shielding effectiveness of wood derived carbon / RGO composite is up to 32 d B,and that of wood derived carbon / mxene composite is up to 27 d B.