Synthesis And Tribological Properties Research Of Carbon Fiber Reinforced Poly(hexahydrotriazine)s Composite

With the popularization of the concept of "Green" and the urgent demand for efficient lubrication system equipment in aerospace,military,marine and other cutting-edge fields,the application of carbon fiber reinforced resin matrix composites is increasing,which benefits from the advantages of low density,high strength,high wear resistance and recyclability.However,due to the low surface roughness and poor chemical activity of carbon fiber,its wettability and mechanical anchoring effect with resin matrix are poor,resulting in the interfacial debonding failure between carbon fiber and resin matrix under harsh conditions such as high speed and heavy load.In addition,carbon fiber reinforced resin matrix composites are composed of carbon fiber and thermosetting resin,its threedimensional cross-linked molecular chain structure endows thermosetting resin with high performance,also leading to two major bottlenecks:(1)The contradiction between strength and toughness;(2)The non-recoverable technical challenges.In view of surface inertia of carbon fiber,low strength and toughness of thermosetting resin matrix,poor wear resistance and non-recyclability,based on the theoretical knowledge of multi-scale interface and dynamic molecular bond of composite materials,this subject combines multi-scale carbon fiber,solid lubricant with low melting point and cation-π crosslinked indolyl-based PHT thermosetting resin to build a polymer based self-lubricating composite with high strength and toughness,high wear resistance and recyclability.The main research contents are as follows:(1)In order to improve the surface roughness and wettability of carbon fiber,the multi-scale rigid nano-interface layers of one-dimensional linear CNT and two-dimensional lamellar ZnO were grown on the carbon fiber surface through vapor deposition and electroplating oxidation,respectively.Although the linear structure of CNT alleviates the difference of interface modulus,its’ inert surface leads to poor wettability.The two-dimensional ZnO nano-sheet with "shield"structure obtained good interface compatibility,which endowed the carbon fiber surface with greater specific surface area and stress bearing capacity,and the composite obtained more stable wear resistance.Under dry conditions,compared with PHT/CFC,the friction coefficient of PHT/ZnO@CFC was reduced by 57%.Due to the improvement of interfacial property,the tensile property of PHT/ZnO@CFC was improved,and the tensile strength increased to 212.87MPa.(2)In order to endow PHT matrix with self-lubricating characteristics,carbon based lubricating materials and polytetrafluoro wax(PEW)lubricating materials were selected as PHT matrix lubricating additives,and the doping amount of lubricating phase was adjusted to further improve the wear resistance and service life of the composite.According to the analysis of friction and wear test results,the best ratio of graphene/carbon nanotube hybrid carbon-based lubricating material modified by ionic liquid crystals was 1:3,but the wear resistance of composite improved significantly when only adding modified CNT.However,under the long-term wear condition,the rigid tubular lubricating additive has certain limitation in the bearing capacity,so the soft PEW lubrication has more advantages on the extension of the service life of the material.Under the longterm wear condition,the friction coefficient of composite with 3%PEW was still stable at about 0.12.In addition,the composite also acquired self-healing performance,which was due to the low melting point of PEW.Three cyclic friction tests in different environments had proved that the self-healing process at 120℃has no adverse effect on the wear resistance of the composite.In addition,the flexible transition layer constructed by soft PEW also greatly alleviated the stress concentration between interfaces,and increased the tensile strength to 287 MPa.(3)In order to improve the toughness of PHT matrix and adjust the structure of rigid chain segment,the PHT matrix containing indole branched chain(In-PHT)was prepared by high temperature closed-loop reaction.The GO loaded with K+and Zn2+were selected as the reinforcing phase.The non-covalent bond was constructed through the cation-π interaction between metal ions and In-PHT matrix.The effect of two non-covalent bonds on the wear resistance of the composite was investigated.With the assistance of good bearing capacity of ZIF8@GO,the wear mark width of composite was reduced to 0.2 μm.In order to reduce the friction coefficient,PEW was selected as the lubricating phase,and the friction coefficient of composite was lower than 0.17(300 min)under long-term friction condition.In addition,due to the introduction of PEW,the composite was given the self-healing performance,and the friction coefficient of composite before and after self-healing remained around 0.2.The construction of cation-πendowed the interface with both physical reinforcement and chemical bonding,and designed a new scheme for the strength and toughness improvement of the matrix.(4)Due to the lack of dynamic bonding between fiber and matrix interface in the above modification schemes,a rigid transition layer of FeOOH nanorods with stable structure was grown on the carbon fiber surface by hydrothermal method,and Fe3+ was loaded on the surface,thus forming an effective cation-π noncovalent bond with indole group at the interface.The results showed that the friction coefficient of composite with stable rigid transition layer was still stable at about 0.25,even in alkaline corrosion environment.Then,the PEW lubricating phase was introduced to form a flexible transition layer between interfaces.The interface microstructure was characterized by SEM and EDS,and the reinforcement mechanism of rigid and flexible interface structure was analyzed.The tensile test results showed that the tensile strength of composite increased to 322 MPa,which due to the synergistic toughening of the rigid and flexible interface layer,and its average friction coefficient decreased to 0.15 under the long-term wear condition(600 min).In addition,the composite also obtained selfhealing performance,and the friction coefficient after self-healing in various environments was also stable at about 0.15.This durable In-PHT-CFRPs with efficient self-healing capability is expected to adapt to wear resistant applications in more severe environments.