Research On Carbon Fiber Composites Based On The Intercalation Method For Synergistic Toughening And Resistance Reduction

The carbon fiber reinforced resin matrix composite has light weight,high strength and excellent comprehensive performance and is favored by the aviation industry at home and abroad.However,due to the intrinsic brittle matrix of the epoxy resin and the characteristics of the hierarchical structure,the interlaminar fracture toughness is insufficient to be easily damaged by the impact of foreign objects.Besides,its electrical conductivity cannot meet the performance requirements of electromagnetic shielding and lightning protection.The interlaminar toughening method is an effective method to improve the interlaminar fracture toughness by introducing a high toughness thermoplastic resin into the interlayer region where the composite material is easily delaminating,under the thermodynamic induction of the epoxy resin during the curing process.The formation of a double continuous phase interlayer structure significantly improves the impact resistance of the laminate without affecting its own thermal stability and static mechanical properties.Although the interlaminar toughening method increases the interlaminar fracture toughness,it hinders the contact of carbon fibers and further reduces the electrical conductivity in the thickness direction.Most of the studies reported so far have only improved the interlaminar mechanical properties of composites.We hope to fabricate the composite laminate with good structural and functional properties.In this paper,considering the two aspects of toughening and reduce resistance.Based on the interlaminar toughening method,a series of carbon nanotube hybrid conductive films are first prepared as a carrier for reinforcing the toughness and electrical conductivity of carbon fiber resin matrix composites.The structure and electrical conductivity were characterized.Then,the prepared film was laid flat between the prepreg layers,and the sandwiched carbon fiber composite laminate with hybrid film interleaves was prepared by hot pressing method.The Mode ? and ? interlaminar fracture toughness,as well as electrical conductivity of interleaved laminates were tested.The effect of the carbon nanotubes and the thermoplastic matrix synergistically toughening the composite material and reducing the volume resistance of the laminates is achieved.The main research work and results of this paper are as follows:(1)Preparation of CNT hybrid thermoplastic resin conductive film:Multi-walled carbon nanotubes(MWCNTs)are used as conductive nano-fillers.One-dimensional carbon nanotubes have low specific gravity,high aspect ratio and superior mechanical and electrical properties.They are considered to be ideal for functional and toughening filler.Thermoplastic polyurethane elastomer(TPU)and nylon 12(PA 12)are used as the film matrix.Both thermoplastic polymers have excellent properties such as high strength,high toughness and good processing properties.Two different mass fractions of MWCNTs/TPU and MWCNTs/PA12 hybrid films were prepared by solution casting.The conductivity test results show that the conductivity changes of the two films show a significant percolation behavior with different CNT mass fractions.The structure of the film conductive network was investigated by the percolation theory.The results show that the MWCNTs/TPU film has a percolation threshold of about 0.6 wt%and a critical index of about 3.36,which is a typical three-dimensional conductive model.The MWCNTs/PA 12 flm is percolated.The threshold is about 0.2 wt%,indicating a lower critical filler concentration.The critical index is around 1.26,which is combined with a typical two-dimensional conductive network structure.And the MWCNTs/PA12 film has higher conductivity than the MWCNTs/TPU film at the same carbon nanotube mass fraction.(2)Preparation of MWCNTs/TPU film intercalation low temperature curing epoxy/carbon fiber composite laminate:The film is laid flat between the prepreg layers,and the laminate is prepared according to a prepreg curing process.The results of conductivity test show that the conductivity of samples TC-5,TC-10 and TC-15 in the transverse(Y)and thickness(Z)directions are 9.35 S/m,0.14 S/m,20.8 S/m and 0.32 S/m,25.75 S/m and 0.41 S/m.The TC-15 improvement was most pronounced in the sample,which was approximately 13-fold and 16-fold higher,respectively,compared to the control sample,and the total weight fraction of carbon nanotubes in the TC-15 sample was only 1.02 wt%.The reason is mainly attributed to the excellent electrical conductivity of the carbon nanotubes,and the resistance of the inter-layer resin-rich region is reduced.The results of Mode-I interlaminar fracture toughness test show that the initial interlaminar fracture toughness values(Gic)of samples TC-5,TC-10 and TC-15 are 0.39 kJ/m2,0.42 kJ/m2,0.30 kJ/m2,respectively.Compared with the control samples,TC-5 and TC-10 increased slightly,which increased by 11.4%and 20%,respectively,but the initial interlaminar fracture toughness of sample TC-15 decreased slightly The interlaminar fracture toughness resistance(GIR)values of the three samples were slightly reduced,which were 0.34 kJ/m2,0.51 kJ/m2,and 0.36 kJ/m2,respectively.The Mode-?interlaminar fracture toughness test results show that the Mode-? interlaminar fracture toughness values(G?c)of samples TC-5,TC-10 and TC-15 are significantly improved compared with the control samples,which are 2.48 kJ/m2?3.15 kJ/m2?2.5 kJ/m2 respectively.They increased by 65.3%,110%and 66.7%respectively.Among them,the toughening effect of sample TC-10 was the most obvious.(3)Preparation of MWCNTs/TPU film intercalation high temperature curing epoxy/carbon fiber composite laminate:the MWCNTs/PA12 film was laid in the same mehtod between the prepreg layers to prepare a laminate.he conductivity test results of the laminate show that there is a significant improvement in the transverse and thickness directions.As the content of carbon nanotubes in the film increases,the electrical conductivity of the laminate also increases.The improvement of the sample PC-15 was most significant,with electrical conductivity of 30.4 S/m and 0.17 S/m in the transverse and thickness directions,respectively,which was increased by about 155%and 1600%compared to the control sample.The mass fraction of carbon nanotubes in sample PC-15 was only about 1.05%.The interlaminar fracture toughness test results show that the intercalation film has a negative effect on the interlaminar fracture toughness,and the interlaminar fracture toughness values of the Mode I and II are lower than the control samples.This reason is attributed to the compatibility between the hybrid film system and the CF/EP system is poor according to SEM,which affects the flow of epoxy and the process of co-melting with the film during the curing process,resulting in low interfacial interaction force.In order to improve the compatibility with CF/EP system,the film was modified by low temperature plasma treatment,and then to prepared interleaved laminate.The experimental results show that the fracture toughness of both the Mode ? and ? is significantly improved.Among them,the sample PC10-M was the most obvious improvement,and its initial interlaminar fracture toughness value(Gic)was 0.51 kJ/m2,which was 59.3%higher than that of the control sample.The interlaminar fracture toughness resistance(GIR)was 0.83 kJ/m2,which was 112.8%higher than that of the control sample.The Mode ? interlaminar fracture toughness(Giic)value is 0.56 kJ/m2.Compared with the control sample,it increased by 86.7%.Interestingly,the conductivity of the laminate was further improved.The conductivity values of the samples PC15-M in the transverse(Y)and thickness(Z)directions were 38.8 S/m and 0.18 S/m,which were 226%and 1700%higher than the control samples.