Preparation Of Short Carbon Fibers Continuous Mats With High Fiber Alignment Degree And Properties Of Mat-based Composites

Carbon fiber reinforced composites are widely used in various fields,such as aerospace,energy,transportation and industries,owing to its outstanding characteristics such as light weight,high strength,high module,good chemical stability,and excellent heat resistance.Due to high performance retention rate,high resistance to degradation under natural conditions,increasing amount for carbon fiber applications and its waste,and high economic benefits of recycling carbon fiber,the problem of carbon fiber recycling has become the focus of public concerns.Using recycled fluffy state short carbon fibers(SCF)to prepare SCF aligned mats reinforced composites with excellent properties,which maximizing develop its mechanical properties,is the most ideal and most valuable way to use recovered carbon fiber.A complete set of continuously preparing technology for SCF aligned mats with high alignment,high volume friction and high performance was developed,based on using water as dispersing medium and carboxymethyl cellulose(CMC)as dispersant.An optimal process for preparing high performance SCF aligned mats reinforced composites were established,providing data support,theoretical guidance and technical support for large-scale preparation of recycled carbon fiber reinforced high performance composites,the main work is as follows:The effective way to realize the stable dispersion of SCF in large-scale were studied.The effect of surface morphology of SCF,rheological characteristics of carboxymethyl cellulose and the agitation type and mechanism on the dispersion of SCF were studied.Dispersion coefficient ? was used to quantitative characterization the dispersion of SCF.It is found that the surface morphology of SCF has a great influence on the wettability of SCF,T800s SCF showed a lower surface tension and better wettability,which makes it more suitable for the dispersion of SCF in large-scale.Based on the study of the rheological characteristics of carboxymethyl cellulose,the industrial grade carboxymethyl cellulose,which is most suitable for large-scale dispersion,has been matched,and the optimum applicable concentration range,the upper limit of temperature and time during dispersing have been obtained.By studying the type and mechanism of agitation dispersion,the agitator type most suitable for large-scale dispersion was obtained,and data support and theoretical guidance were provided for the design of a large-scale stirring dispersion device.Based on the self-designed and manufactured alignment nozzle,the corresponding self-gravity orientation mechanism is proposed.The main factors that influence the orientation of carbon fiber are systematically studied,including fluid viscosity(?),slit width of orientation device(w),angle between orientation device and receiving belt(0),operating speed of receiving belt,concentration of SCF,length of SC(w).The alignment degree of SCF was quantitatively characterized by alignment angle statistics and alignment tensor calculation,and A theoretical evaluation method for the dispersion and alignment of SCF is established by calculating the crowding factor.SCF aligned mats with a width of 300 mm,a length of more than 200 m,a relative orientation of more than 80%and a carbon fiber mass fraction of more than 85%has been successfully prepared.The composites with good properties were obtained by combining the SCF aligned mats with epoxy resin with different molding processes.By comparing the characteristics of different molding processes,the optimal process method for preparing composites using SCF aligned mats was established.The SCF aligned mats reinforced composites with 25%carbon fiber mass fraction were prepared by semi-prepreg molding process,the mechanical properties of the composites were excellent.Tensile strength and modulus increased by 175%and 65%compared with random carbon fiber reinforced composites with the same carbon fiber mass fraction.The tensile strength and modulus of 50%carbon fiber composites reach 900MPa and 45GPa.The mechanical properties of the composites reinforced by SCF aligned mats are much higher than the aluminum and the composites reinforced by continuous glass fiber and.It can completely replace some continuous fiber reinforced composites as secondary structure materials.In addition,the composite reinforced by SCF aligned mats also has excellent electromagnetic shielding performance,the electromagnetic shielding efficiency in the 1-18GHz range is up to 60 dB.By using recycled carbon fiber as raw material,the prepared composite has excellent mechanical and electromagnetic shielding properties,and has a high ratio of performance to price,which has an important guiding significance for the secondary reuse of recycled carbon fiber.