Study On The Process Optimization Of Carbon Nanotubes Uniformly Growing On Carbon Fiber Fabrics Surface And Their Composites

In this paper,the preparation of carbon nanotubes/carbon fiber fabrics(CNTs/CFFs)was completed by first modifying CFFs and then growing CNTs on the surface by chemical vapor deposition(CVD).The process optimization of uniform growth of CNTs on CFFs surface and the preparation of high-performance composites were achieved by studying the following contents:(1)Three different modification schemes were used to pretreat the surface of desized CFFs.The effects of these modifications on the surface properties of CFFs,the growth morphology and yield of CNTs,the tensile strength of CNTs/CFFs and the interlaminar shear strength(ILSS)of composites were researched by using related characterization methods.(2)Different catalytic parameters were used to optimize the growth of CNTs on the surface of modified CFFs.The effects of catalyst type,impregnation time of catalyst precursor,reduction temperature and reduction time on the morphology and properties of CNTs/CFFs and their reinforced composites were studied.(3)Different CVD parameters were used to further optimize the growth of CNTs on the modified CFFs.The effects of growth temperature,growth time and hydrogen ratio on the morphology,and properties of CNTs/CFFs and their reinforced composites were studied.Different pretreatments could produce different effects.It was found that PyC pretreatment only deposited a small amount of carbon particles on CFFs,and did not form a uniform layer of PyC,which adversely affected the growth of CNTs;NaOH pretreatment resulted in a small amount of active groups on CFFs,the surface wrinkles were etched,and the groove depth and distribution tend to be uniform,which promoted the uniformity of the CNTs distribution;CFFs were oxidized by H2O2 pretreatment,resulting in a large number of oxygen-containing functional groups,and the surface grooves became more uniform and slender,thus achieving uniform and efficient growth of CNTs.After modification with H2O2 CNTs were anchored to the surface of CFFs,and the tensile strength of CNTs/CFFs was increased by 3.6%compared with that of desized CFFs.Moreover,due to the uniform coating of fine CNTs,the specific surface area of CFFs was increased,and the wettability of resin was improved,which led to an increase in the ILSS of CNTs/CFFs composites.Therefore,H2O2 modification is the best pretreatment method for CNTs growth on CFFs surface.Through studying the effects of catalytic parameters on the morphology and properties of CNTs/CFFs and their composites,the obtained conclusions are as follows:with the increase of catalyst immersion time,the reinforcement effect of CNTs increased gradually,however,after excessive impregnation,the severely entangled CNTs were not conducive to the wettability of resin.Finally,the best performance was obtained at 10min.In terms of catalyst type,the yield of CNTs catalyzed by Co was higher than that catalyzed by Fe,the diameter of the tube was larger but the graphitization degree was lower.The catalytic activity of bimetals was higher than that of monometals,and the diameter distribution of catalyzed CNTs was wider.Unlike Fe2-Co,which had a too fast catalytic rate,Fe-Co showed the better catalytic activity.In terms of reduction process,the CVD one-step method weakened the disadvantage of the two-step method,that is,the catalyst easily aggregated toward the direction of particle enlargement during heating process,which had greater potential in the preparation of high-performance composites.Through studying the effects of CVD parameters on the morphology and properties of CNTs/CFFs and their composites,we optimized the process of uniform growth of CNTs on CFFs surface,and combined the experimental results to establish a theoretical model to reveal the reinforcement mechanism of CNTs.The results showed that the damage of catalysts to CFFs was greatly reduced under 500?,and the interlaminar bonding of composites was obviously enhanced due to the rapid growth of short and uniform CNTs.Accordingly,the tensile strength was increased by 7.52%and the ILSS was increased by 5.48%as compared with the desized CFFs.When the growth temperature gradually increased to 600?,the activity of catalyst increased,but the diffusivity increased accordingly,resulting in a gradual decrease in the tensile strength of CNTs/CFFs.However,when the temperature rised to 650?,excessive growth temperature shortened the catalyst life,which was not conducive to the efficient growth of CNTs.With the increase of growth time,the distribution of CNTs became more uniform,and the length became longer,which led to entanglement of CNTs after 20min growth.Therefore,after only 10min,the uniformity of CNTs was the highest,and the reinforcement of tensile strength and ILSS was the greatest.When the H2 ratio was 2:1,CNTs with stable growth at low speed and high quality made up for the defects on the surface of CFFs,which was formed by catalysts.The roots of CNTs were further crosslinked adjacent carbon crystals,increasing crystal size,which limited the crack propagation under external forces.So the tensile strength showed the highest value,which was 8.64%higher than that of the desized CFFs.At the same time,CNTs improved the wettability of CFF and resin,the ILSS increased by 12.27%compared with the initial value.