Preparation And Electromagnetic Shielding Properties Of Bio-based Carbon Fibers

Carbon fiber is a national strategic emerging material with excellent electrical and thermal conductivity and mechanical properties.It is widely used in wind power generation,aerospace,sports and leisure and automotive fields.The key to the performance of carbon fiber depends on the quality of the original filament,because the internal defects of the original filament are completely"inherited"into the carbon fiber after carbonization,so that the performance of carbon fiber decreases;the second is the carbonization process,in which high temperature is the main factor affecting the degree of graphitization.Therefore,this project intends to study bio-based carbon fibers and prepare flame retardant raw yarn by adding flame retardant to cellulose solution through electrostatic spinning method to reduce fiber defects,while using flame retardant to increase carbonization temperature,so as to obtain high performance carbon fibers.Following that,it was compounded with PMMA to prepare high-performance electromagnetic shielding carbon fiber materials to explore the relationship between structure and performance.The research work and the results of this study show that:(1)Prepare flame retardant fiber raw yarn by electrostatic spinning process.Through the orthogonal experimental method,it was determined that the concentration of cellulose solution was the main factor affecting the spinning process and cellulose diameter,and voltage and spinning distance were secondary factors.The results show that the optimal spinning process conditions are spinning voltage 20 k V,cellulose spinning solution concentration 4 wt%,spinning distance 8 cm,the right amount of flame retardant does not affect the smoothness and roundness of the raw fiber,when the flame retardant is 15%of the mass of cellulose,the average diameter of 10 um flame retardant cellulose raw silk can be prepared under the optimal spinning conditions.(2)Pre-treatment of flame retardant cellulose raw yarn followed by high temperature carbonization to prepare bio-based carbon fiber;SEM morphological characterization,XRD characterization,BET specific surface area,mechanical properties,and electrical conductivity tests were performed.The results of the study showed that the best carbonization process conditions for the preparation of flame retardant cellulose carbon fibers were pretreatment of the raw cellulose yarn in 3%ammonium chloride solution,pre-oxidation at 200℃ for 60 min,and high temperature carbonization at 1200℃ for 20min.The specific surface area of the resulting carbon fiber FRC5#-1200 under these conditions was 112.31 m~2/g;resistivity was 8.816Ω·cm;tensile strength of 0.54 GPa.The addition of flame retardant causes the formation of continuous and uniformly distributed nano-spherical bumps on the surface of carbon fiber,which increases the specific surface area of carbon fiber;the flame retardant enhances the carbonization temperature of cellulose carbon fiber,which results in a high degree of graphitization and a reduction of internal defects,forming a microporous carbon fiber material.(3)PMMA/CF electromagnetic shielding composites were prepared by twin-screw extrusion with PMMA as matrix and cellulose-based carbon fiber as filler;the mechanical properties,electrical conductivity and electromagnetic shielding properties of the composites were tested.The results showed that the mechanical properties,electrical conductivity and electromagnetic shielding properties of the composites increased with the increase of carbon fiber content in the composites,and when the carbon fiber content is1.5%,the tensile strength of the composites is 75.4 MPa,Young’s modulus is 3.01 GPa,and the electromagnetic shielding effectiveness of the composites in the high frequency range of 30 MHz-1500 MHz is 20 dB-71 dB,which meets the requirement of 20 dB for general commercial use.The idea of adding flame retardant into the stock solution of carbon fiber raw yarn is proposed for the first time in this subject to prepare high performance bio-based carbon fiber through electrostatic spinning and carbonization route.The method reduces the defects of the original filament,increases the carbonization temperature,and obtains carbon fiber microporous materials with uniformly distributed nano-spherical projections on the surface,which solves the key technical problems in the production process of bio-based carbon fiber and provides technical support for the preparation of high-performance bio-based carbon fiber and its electromagnetic shielding composites,with great theoretical and practical significance.