Design Of Rigid-and-flexible Interphase And Study On Interfacial Properties Of Carbon Fiber Composites Based On Star-like Copolymer

Modulus difference between carbon fiber and resin matrix is the frontiers research problem of interphase engineering for carbon fiber reinforced composites(CFRP).The optimal design of interphase requires not only increasing the interfacial modulus to improve low load-transfer efficiency,but also introducing appropriate flexibility to alleviate the interfacial stress caused by the discrepancy in volume between the shrinkage of resin matrix and the expansion of carbon fiber under curing condition.To mitigate the problem,the construction of modulus transition layer by conjugated organic molecules and rigid-and-flexible interphase by "rigid-flexible" star-like copolymer were proposed in this paper.The formation and strengthening mechanism of rigidand-flexible interphase was researched then compared with modulus transition layer.The interphase reinforcement of CFRP were achieved.(1)Tetraaminophthalocyanine(TAPc)was synthesized via the design of molecular and used to configure the appropriate sizing agent to modify CFdesized for the preparation of CF-TAPc.Compared with CF-desized,the surface roughness and chemical activity of CF-TAPc were increased.According to the distribution of chemical structure,transition of modulus and change of deformation of the interphase characterized by Raman mapping and AFM-force,the formation mechanism of modulus transition layer constructed by TAPc was proposed as follows:TAPc was attached onto carbon fiber surface by chemical bonding,coordination bonding and ?-? stacking,and connected with epoxy matrix by the diffusion and crosslinking between TAPc and epoxy matrix;the stiffening interphase was achieved by TAPc with high rigidity and crosslinkability?(2)The star-like copolymer with different ratio of rigid/flexible segments was synthesized based on TAPc,including TAPc-connected poly(glycidyl methacrylate)(Pc-PGMA)composed of one TAPc core and four PGMA arms,and Pc-PGMA/Pc consisted of one TAPc core and four PGMA/Pc branches.CF-(Pc-PGMA)and CF-(Pc-PGMA/Pc)were prepared during sizing with Pc-PGMA and Pc-PGMA/Pc.Compared with CF-(Pc-PGMA),the surface roughness and chemical activity of CF-(Pc-PGMA/Pc)were improved.The relative distribution of TAPc and PGMA at interphase,transition of modulus and change of deformation were analyzed by Raman mapping and AFM-force,based on which the formation mechanism of rigid-and-flexible interphase constructed by Pc-PGMA and Pc-PGMA/Pc was proposed:the rigid inner layer with suitable stiffness was formed by TAPc preferentially attached on carbon fiber surface and PGMA subsequently deposited on the surface via the dragging effects due to the chemical bonding of TAPc and PGMA,while the flexible outer layer was mainly contributed by the interdiffusion and crosslinking between PGMA and epoxy matrix,which allowed the interfacial slippage.(3)The Interfacial properties and surface microtopography of CFdesized/EP,CF-TAPc/EP,CF-(Pc-PGMA)/EP and CF-(Pc-PGMA/Pc)/EP bundle and monofilament composites were compared.The TFBT strength and IFSS ofCF-desized/EP?CF-TAPc/EP?CF-(Pc-PGMA)/EP and CF-(PcPGMA/Pc)/EP were improved gradually.The adhesive failure severely occurred in CF-desized/EP,while the growth paths of crack propagation were partially transferred into the interphase in CF-TAPc/EP composite.The crack might be partially propagated along carbon fiber surface due to the low cohesive strength in CF-(Pc-PGMA)/EP composite,and the cohesive failure was triggered by the balance between enhanced interfacial adhesion and increased energy absorption capacity from the rigid-and-flexible interphase in CF-(PcPGMA-Pc)/EP composite.The strengthening mechanism of rigid-and-flexible interphase was proposed:the rigid inner layer served as a "shielding layer" to prevent the cracks from directly touching fiber surface,while the flexible outer layer allows plastic deformation to alleviate stress concentration.