Preparation Process Optimization Of High-performance CNTs/CF Multi-scale Reinforcement And Their Structure And Performance Characterization

CNTs/CF multiscale reinforcers can effectively enhance the interfacial bonding strength between carbon fiber and resin,and improve the comprehensive properties of carbon fiber and its composites.In this paper,the electrochemical treatment process of carbon fiber surface and CNTs growth process has been explored,by using the own chemical vapor deposition(CVD)equipment in laboratory,there are four main aspects being carried on the experiment:(1)the impact of carbon fiber surface pretreatment on the carbon fiber surface morphology and adhesion(2)the influence of optimizing catalyst system using vertical quasi CVD vacuum furnace to explore the catalytic effect of double metal Fe-Ni catalyst(3)the impact of continuous equipment CVD process parameters on the CNTs/CF multi-scale graphitization degree and increasing body monofilament tensile strong teams.(4)Characterization of other properties and microstructure of CNTs/CF multiscale enhancers.In terms of surface pretreatment of carbon fiber:electrochemical anodic oxidation(EAO)was selected as the surface pretreatment process of carbon fiber by comparing three surface treatment methods.The chemical composition of carbon fiber surface was changed by electrochemical anodic oxidation.Compared with desized carbon fiber,the content of O element on the surface of EAO sample increased from 20%to 50%,and 1.5%oxygen element appeared.At the same time,two oxygen-containing functional groups,-C=O and-COOH,appeared at the bond energies of 286.7eV and 289.5eV.Then EAO optimized process selected 50 C/g,100 C/g,150C/g and 200C/g power intensity for desizing carbon fiber pretreatment and loads of CNTs,measuring four current strength under the preparation of CNTs/monofilament tensile strength of CF,and testing of the four samples by SEM tests,of which 100c/g 150c/g surface topographical effects appeared best,the growth of CNTs distributed evenly.In terms of catalyst system optimization:the catalytic effect of Fe-Ni bimetallic catalyst is better than that of single metal catalyst at the same temperature.After analyzing the reduction products of Fe-Ni bimetallic catalyst,it was found that Fe-Ni alloy composition did exist,which has the possibility of catalytic CNTs in low temperature.The effect of Fe-Ni catalyst on the preparation of CNTs/CF was investigated in a quasi-vacuum CVD furnace.Three groups of catalysts with concentrations of 0.015Fe-0.15Ni,0.025Fe-0.025Ni and 0.035Fe-0.035Ni(mol/L)were used to prepare CNTs/CF.It was found that with the increase of catalyst concentration,the density and length of CNTs growing on the surface of carbon fibers also increased.When the concentration of catalyst was low,the number of catalyst particles could not be concentrated on the surface of carbon fiber,and the number of catalytic growth CNTs on the surface after the CVD process was small,which could not effectively improve the surface morphology of the sample.While excessive use of catalyst would lead to severe etching effect of catalyst particles,excessive number of CNTs on the surface of carbon fiber,and local catalyst particles agglomeration deactivation phenomenon,so the concentration ratio of 0.025Fe-0.025Ni is more appropriate.In terms of the influence of CVD process parameters,CNTs/CF were prepared by Fe-Ni bimetallic catalysts at 350?,400?,450?,500? and 550? using vertical CVD furnace equipment.Studies show that the catalyst activity would increase with the rising of temperature.There is a lower catalytic activity at 350?and stopping growing CNTs on the carbon fiber surface,and at 550? the carbon source separates rapidly and catalyst speed starts below C atomic deposition rate,with surface impurities increasing.The sample of the surface topography is good at 450?,500? with the tensile strength of 4.46 GPa,4.41 GPa.Fe-Ni bimetallic catalyst can significantly improve the graphitization degree of the sample surface,and CNTs/CF with good surface morphology can be prepared at lower temperature.For large-scale industrial production,CNTs/CF were prepared by one-step process in an open CVD furnace.The process was optimized for the speed of wire running and the CVD atmosphere.The growth time of CNTs was determined by the spinning speed.When the spinning speed was faster,the number and length of CNTs growing on the surface of carbon fibers were smaller and shorter,showing budding appearance.The density of CNTs on the surface of carbon fiber increases and the graphitization degree increases with the decrease of the velocities.When the spinning speed is too slow,the long CVD time leads to partial deactivation of the catalyst,and a large number of active carbon atoms are deposited on the surface of the carbon fiber in the form of amorphous carbon impurities.Therefore,the appropriate spinning speed is 3.5cm/min.The different proportion of growth atmosphere has different effects on the catalytic growth of CNTs.The cracking of C2H2 is a reversible reaction.When the proportion of H2 is too large,the cracking of carbon source is inhibited,the surface CNTs are sparse,and the catalyst etching is serious.When the H2 ratio is too low,the carbon source will crack violently,and a large amount of carbon impurities would be deposited on the surface of the sample.The effect is best when the H2 flow rate is slightly faster than that of C2H2.In terms of other properties and microstructure of CNTs/CF multiscale reinforcers,the tensile strength of monofilament samples produced by the two CVD production devices under the optimal process is 4.55 GPa and 4.49 GPa,respectively,which is increased by 6.5%and 5.1%compared with that of desized carbon fiber.The thermogravimetric curve showed that the growth of CNTs changed the thermal stability of the material as a whole,at the same time,both CNTs and CF showed two weightlessness phenomena,indicating that the thermal stability of CNTs and amorphous carbon under loading was low.The growth of CNTs increases the specific surface area of carbon fibers,improves the surface roughness,and improves the wettability of multi-scale reinforcers to the resin.In the CVD process,most CNTs grow in the apical growth mode,and the etching effect of catalyst particles on the material is low in this mode.The CNTs grown by the best process have clear structure,good coaxiality and great tube wall uniformity,which can effectively improve the performance of CNTs/CF.