Preparation And Temperature Stability Of Thermosetting Resin-based Carbon Fiber Conductive Composites

Resin-based conductive composites are new functional materials which have been extensively studied in recent years.It not only maintains the basic characteristics of polymer materials such as easy molding,corrosion resistance,light weight and durability,but also has many new characteristics,such as easy-to-adjust electrical conductivity and mechanical properties.Carbon fibers have excellent mechanical properties as well as good electrical conductivity,so they are often used to prepare resin-based conductive composites.For the study of carbon fiber reinforced conductive composites,most researchers discussed from the perspective of carbon fiber fillers,so the research is not thorough enough.Therefore,the stability of carbon fiber conductive composites is studied in depth from non-functional fillers and resin matrix in this paper.The idea of this paper is to form hybrid fibers by introducing non-functional filler short glass fiber(SGF)and short carbon fiber(SCF),and then compounds hybrid fibers with thermosetting resin matrix to prepare conductive composites.The internal conductive mechanism was analyzed from the macroscopic point of view by resistivity test and volt-ampere characteristic test.The effects of non-functional fillers and resin matrix on the conductivity and temperature stability of thermosetting resin-based carbon fiber conductive composites were also studied.This work set foundation for preparation of conductive composites with high temperature stability and wide service temperature range.The results are as follows:(1)SCF-SGF/VER conductive composites with different SGF content were prepared on the premise of fixing SCF content.The test results show that the addition of SGF improved the dispersion of SCF.Within 14.5wt%,increasing SGF content can increase the conductivity of the material and improve the relationship between voltage and current,while excessive addition can weaken the conductivity.Temperature stability test shows that increasing SGF content can reduce resistance variation of composites in different temperature environments and increase the stability.On the premise of fixing the content of SCF and SGF,SGF length also affects the conductivity.When SGF is powdered,the dispersion effect of SCF is not obviously improved,and the conductivity of the composite is general.When SGF length is greater than or equal to 12 mm,the increase of SGF length will increase the difficulty of fiber dispersion,which is not conducive to the construction of conductive network and weaken the conductivity of composites.In isothermal environment,increasing the length of SGF can improve the stability of the composites.However,when the length of SGF is 3-6 mm,the stability of the composites is the best under variable temperature.(2)SCF-SGF/UPR conductive composites with different resin matrix contents were prepared on the premise that the ratio of SCF to SGF was fixed in hybrid fibers.The experimental results show that reducing the content of resin matrix can increase the conductivity of the composite.But the content of resin matrix has little effect on the ohmic properties and isothermal stability.In variable temperature environment,before glass transition temperature(T_g)of resin matrix,the stability of conductive composites with different resin matrix content has little difference;when the temperature exceeds T_g,reducing the content of resin matrix can increase the temperature stability of composite.On the premise of fixing the amount of hybrid fibers and resin matrix,the stability of composites prepared by different kinds of resin matrix has little difference in isothermal environment of 70?,while the conductive composites using thermosetting resins with better thermomechanical properties as matrix have better stability in variable temperature environment.(3)Through the study of SGF content and length parameters,it is found that when SGF content is 27.3 vol%,SGF length is 3-6 mm,the composite has better comprehensive properties.For example,when 27.3vol%6mm SGF was used to prepare the composite,the resistance of the composite decreased by 46%compared with that of the composite without SGF.The maximum change of resistance of the composite decreased from 2%to about 0.1%in the isothermal test at 70?and from70%to 2.2%in the temperature test at 20-165?and the composite showed good cyclic stability.Through the study of the content and types of resin matrix,it is shown that reducing the content of resin matrix in conductive composites and using thermosetting resins with better thermodynamic properties as the matrix can increase the conductive stability and broaden the range of using temperature of composites.For example,the composite prepared with 55.7wt%bisphenol E cyanate ester(CE)not only has good conductivity and volt-ampere characteristics,but also has excellent temperature stability.During the isothermal test at 70?,the resistance changes within 0.1%and about 1%during the temperature test at 30-165?.