Preparation And Electromagnetic Shielding Properties Of Recycled Carbon Fiber Oriented Felt Composites Based On Electro-magnetic Double Loss Effect

The increasing demand and waste volume of carbon fiber have brought people’s attention to the problem of recycling carbon fiber.The recycled carbon fiber(rCF)has properties comparable to that of the virgin carbon fiber(vCF).Therefore,how to maximize the value and performance of rCF in the secondary utilization is a very important topic in the recycling ecology of carbon fiber.A recycled short carbon fibers(rSCFs)reinforced composite material with excellent mechanical properties can be prepared by the fluffy rCF orientation.rSCFs have great potential in electromagnetic shielding materials due to its excellent conductivity,low radiation absorption,excellent vibration damping,creep resistance,and fatigue resistance.In this paper,a carbon nanotube(MWCNT)conductive network was constructed on the rSCFs skeleton(MWCNT@rSCFs)by freeze drying technology,and a high magnetic recovery carbon fiber oriented mat(FeNPs@rSCFs)was prepared by loading citric acid nanoparticles(FeNPs)onto rSCFs by citric acid sol.On this basis,multi-scale recycled carbon fiber oriented felt(FeNPs-MWCNT@rSCFs)with magnetic core and conductive wall double loss structure was prepared by two step method.The electromagnetic shielding performance and shielding mechanism of rSCFs,MWCNT@rSCFs,FeNPs@rSCFs and FeNPs-MWCNT@rSCFs composites were systematically discussed,which provided theoretical basis and basic data for the controllable preparation of rSCFs electromagnetic shielding materials and the realization of high electromagnetic shielding performance.The main work of the study is as follows:(1)The effects of rSCFs’ content and orientation structure on the electromagnetic shielding effectiveness of the composites were discussed.It is found that the electrical conductivity of rSCFs composites shows obvious percolation behavior under the influence of rSCFs content.When rSCFs content is less than 11.26 wt.%of percolation threshold,the electromagnetic wave absorption of rSCFs composites is dominant in the electromagnetic shielding mechanism,and when rSCFs content is greater than the percolation threshold,the reflection dominates.The total electromagnetic shielding effectiveness of the vertical structure 31%higher than that of the parallel structure.The influence mechanism of the orientation structure on the electromagnetic shielding performance of the material is explored.(2)High conductive recycled carbon fiber oriented felt(MWCNT@rSCFs)were prepared by freeze-drying technology.The correlation between MWCNT conductive network and electrical properties and electromagnetic shielding performance of materials was discussed.The morphology of MWCNT conductive network and its structure retention in composite materials were characterized by scanning electron microscopy(SEM)and contact angle test,which shows that the MWCNT conductive network can maintain stable network structure in epoxy resin impregnation.The electromagnetic shielding performance of MWCNT@rSCFs with different MWCNT content is tested by vector network analysis(VNA).It is found that with the increase of MWCNT content,the total electromagnetic shielding effectiveness of MWCNT@rSCFs is increased from 31 dB to 46 dB,and the shielding effectiveness is increased by 48%.When the mass fraction of carbon nanotubes reaches 1 wt.%,the reflection efficiency of MWCNT@rSCFs reaches the maximum value.The influence mechanism of MWCNT conductive network on the electromagnetic shielding effectiveness of MWCNT@rSCFs is explored.It is proved that MWCNT conductive network can significantly improve the electromagnetic waves reflection ability of materials.(3)The high magnetic recycled carbon fiber oriented felt(FeNPs@rSCFs)with different FeNPs load were prepared by the citric acid sol method.The influence of different FeNPs loading on the electromagnetic shielding effectiveness and electromagnetic shielding coefficient of FeNPs@rSCFs was discussed.It was found that the absorption efficiency of FeNPs@rSCFs increased with the increase of FeNPs load,from 23 dB to 33dB,which increased by 43%,and the electromagnetic wave absorption coefficient increased to about 0.2.The influence mechanism of FeNPs on improving FeNPs@rSCFs absorption efficiency is explored.It is found that FeNPs is the enhancement of electromagnetic wave loss inside the material.(4)The FeNPs-MWCNT@rSCFs with magnetic core and conductive wall double loss structure was prepared by two step method.The influence of dual loss structure on electromagnetic shielding effectiveness,electromagnetic shielding coefficient,and electromagnetic relaxation quantity was discussed.It was found that by double loss design,the total shielding effectiveness of the material increased from 31dB to 56dB,increased by 80%,and the reflection efficiency increased from 8 dB to 23 dB,up 187%;The absorption efficiency increased from 24 dB to 35 dB,increased by 46%.It’s improved that the reflection and absorption properties of rSCFs composites to electromagnetic wave is improved at the same time.The synergistic mechanism of dual loss structure in electromagnetic shielding was explored.The core sheath structure composed of FeNPs and MWCNT conductive network greatly increased the number of electric relaxation and magnetic relaxation phenomena,and the method of using rSCFs to prepare electromagnetic shielding materials with high reflection and high absorbability was established.