Hydrothermal Carbon Modification Of Carbon Fibers For Interfacial Enhancement Of Carbon Fiber Composites

The interface interaction of carbon fiber(CF)composites plays an important role in the mechanical properties of CF composites.A vast number of valuable reports focused on the surface modification of carbon fibers by varied methods,including sizing,oxidation,vapor deposition,electrophoresis chemical grafting and so on.But there are still some problems in composite fabrication practices,such as the decrease of the CF strength after oxidation,decrease of the CF wettability after sizingIn chapter 2,the thermoplastic polyetherimide(PEI)microemulsion sizing agent was prepared by solution evaporation method,for interfacial interaction enhancement of CF/polyetherimide ketone(PEEK)composites.The results indicate that the PEI emulsion improves the interfacial interaction of the composite obviously,but it cannot form a complete coating on the surface of carbon fibers.The dewetting of the thermoplastic polymers on the CFs was observed and discussedIn chapter 3,a new CF modification method for composite fabrication is explored.The multiscale hydrothermal carbon layer(MHTCL)was introduced into the carbon fiber modification research and CF composite fabrication.The MHTCL CFs have ultrarobust surface,high surface energy,good wetting ability and abundant functional groups on the surface.Owing to the CFs serving as nucleation centers in the hydrothermal processing,the MHTCL CFs were prepared at a very low glucose concentration,which is much lower than the critical concentration in hydrothermal carbonization reaction.The MHTCL CF's BET specific surface area was increased by 150%and the advancing contact Angle in water was reduced by 30%,compared with that of unsized CFs.The total surface energy was increased by 13%,and the polar component of surface energy was increased by 600%.The oxygen content on the MHTCL CF surface was increased by over 100%.The structure of hydrothermal carbon layer is certified a polyfuran carbon substance with abundant ketone and ether functional groups.The formation mechanism of hydrothermal carbon layer and the decisive role of the nucleation in the process of hydrothermal carbonization were supposedIn chapter 4,carbon dots(CDs)was introduced in CF sizing research Fabrication of massive and deep-carbonized CDs by hydrothermal treating the glucose aqueous solution in the monolithic methyl silicone hydrogel at 200? was introduced.It is well known that carbon substances with polycyclic aromatic hydrocarbons(PAHs)structures only form at high temperature.But the resultant CDs have large size PAH inner structure,far different to the polyfuran hydrothermal carbons prepared by normal hydrothermal processes.For the composite fabrication,the large size PAH inner structure of CDs and graphite microcrystals in the CF surface have a strong ?? interaction;abundant organic functional groups of carbon dots can form chemical bonds,hydrogen bonds and strong van der Waals forces with resins in the CF composites.A high interfacial energy methyl-silicate hydrogel was designed as a nanometer reaction vessel for the glucose hydrothermal carbonization The glucose aqueous solution is enclosed in the nano-pores of methyl-silicate hydrogel with a size range of 2-20 nanometers and an average size of 7.8 nanometers to avoid the formation of large-size hydrothermal carbon spheres caused by collisions and aggregations.The carbon dot size is 2-5 nmIn chapter 5,the large size PAH structure in the carbon dots was confirmed by experiments,comparations and calculations.In the mild hydrothermal carbonization,aromatization is impossible for common senses,experiences and literatures.The formation mechanism of large size PAH structure in the mild hydrothermal processing was discussed.Pre-wetted super-hydrophobic methyl-silicate aerogel(hydrogel)has high interfacial energy and strong adsorption of hydrothermal intermediate,which leads to the self-assembly of the hydrothermal intermediates on the super-hydrophobic surface,forming a two-dimensional adsorption layer.It is easier to form large size PAH structure in two-dimensional adsorption layer than in three-dimensional crosslinked polymer particles.The carbon dot has 19 wt.%carboxyl groups.The carbon dots with abundant functional groups have good solubility in polar solvents and water-solubility dependence of pHIn chapter 6,the interface interaction between carbon fiber and polymers in the composites was evaluated.For the MHTCL modification,high roughness enhances mechanical locking action;high surface energy and high wettability enhance carbon fiber adsorption of the polymers;the van der Waals force and hydrogen bond of the CF/matrix interface are enhanced by high oxygen content and multi-functional groups.The interface interactions of CF/PEEK composite,CF/PEI composite and CF/epoxy composite were significantly improvedThe carbon dots improve the interlaminar shear strength of the CF/epoxy composite obviously,due to the strong ?? interacions of the carbon dots and CFs While the epoxy emulsion and CD solution were mixed in sizing,the interlaminar shear strength of the resultant samples was increased by 72%.The large size PAH inner structure and abundant polar functional groups in the CDs endow the interfacial activities of the carbon dots,which self-assemble on the interface of carbon fiber and epoxy and improve the composite interfacial interaction.The carbon dot sizing process is suitable for continuous production of carbon fibers.