Study On The Growth Of Carbon Nanotubes On Carbon Fibers And Its Reinforcement In Epoxy Composites

The excellent mechanical properties of carbon fibers（CFs）reinforced polymer composites depends on interfacial bonding between reinforcement and polymer matrix.The poor interfacial bonding between the untreated CFs and matrix is presented because of the excessive smoothness,chemical inertness and less reactive functional groups of CFs.Surface treatment（chemically or physically）of CFs is employed to improve the interfacial bonding for stress transfer at the interface.In this paper,catalyst precursor coated on CFs were prepared through a solvothermal reaction,where iron（III）acetylacetone（nickle acetylacetone）as catalyst source and polylol as solvent.The effect of different solvents on composition of catalyst prercursor and dispersion were investigated.On the basis of optimum solvent of TREG,the effects of solvothermal reaction temperature,reaction time and catalyst source concentration on catalyst precursor composition and morphology were investigated.Compared with morphologies of catalyst precursor prepared in different catalyst sources.The iron（III）acetylacetone was chose to prepare catalyst precursor coated on CFs,reducted to iron nanoparticles using mixed nitrogen and hydrogen gas flow at certain temperature and subsequently,chemical vapor deposition（CVD）method was employed to grow carbon nanotubes（CNTs）on short-cut CFs.The effects of reduction temperature and time on catalyst and CNTs were investigated.The effects of growth temperature,growth time and gas flow ratio on morphologies of CNTs were discussed.Then,CNTs grown on CFs were used as reinforcement in epoxy（EP）to improved its flexural strength.The effects of CNTs grown at different catalyst concentrations and CNTs-CFs mass ratios on composites flexural strength were investigated.The main conclusions are described as followed:（1）The experimental results indicate that the preparation of particle size of about 10 nm Fe₃O₄ nanoparticles only in TREG and PEG200 solvent reaction system,which are of uniform particle size and no obvious aggregation of particles observed.With the increase of reaction temperature or the extension of time,the reaction degree increases.The nanoparticles became dense on CFs even appeared stack with complete crystal shape on CFs surface,but the contour of nanoparticles are still clear.It indicates that Fe₃O₄ formed in TREG solvent system with better dispersion.（2）Catalyst precursor of 50 nm coated on CFs through solvothermal reaction（283℃ for 60 min under N2 atmosphere）,where nickle acetylacetone as catalyst source and TREG as solvent.The changing morphology of catalyst precursor with increasing temperature during the reduction process was investigated.Multi-layer catalyst coated on CFs melted together,which is not favorable for growing uniform CNTs.（3）Fe₃O₄ coated on CFs was prepared using iron（Ⅲ）acetylacetone as catalyst source,which can be directly reducted to Fe at 415℃ under hydrogen and nitrogen atmosphere.The diameter of catalyst particles is related to reduction temperature and time.With the extension of reduction time and the increase of temperature,the nanoparticles coated on CFs in single layer with obvious increased diameter due to amalgamation.（4）In order to ensure high interfacial bonding of CNTs-CFs/EP composites,the morphology of CNTs grown on CFs surface needed to be in good control.Results indicate that the optimum growth temperature is of 750℃;the optimum growth time is of 30min ensure the enough time for carbon source to propagate to surface of sample,thus catalytically growing uniform CNTs;the optimum gas volume rate is of V（N2）:V（H2）:V（C2H2）=50:10:10 cm3/min.Appropriate density of carbon source ensure the growth of CNTs and no excessive carbon source coated on catalyst particles leads to inactivation.（5）The CNTs-CFs/EP isotropic composites were fabricated successfully by using short-cut CFs as primary reinforcement and CNTs as secondary reinforcement.When the CNTs grown on CFs at catalyst source concentration of 1.5 mmol/L,the flexural strength of CNTs-CFs/EP composites increased by 19.2%to 102.5 MPa in comparison to that of EP reinforced by acetone cleaned CFs.（6）0.8 wt%addition of CNTs-CFs in EP enhanced the flexural strength of composites from 80.0 MPa of pure EP to 102.5 MPa.Appropriate mass ratio of CNTs-CFs ensures its good dispersion in matix without defect to reinforce matrix flexural strength.