Preparation And Application Of Carbon Fiber Composite Conductive Papers

As a kind of multi-functional papers,carbon fiber composite papers can be prepared by distributing short carbon fibers in the cellulose fiber matrix using papermaking technique.Due to the excellent conductivity of carbon fibers,composite papers with different conductivities can be gained by controlling the carbon fiber fraction in the insulting matrix.Aside from the adjustable conductivity,carbon fiber composite paper also present other good properties like high flexibility,good thermal conductivity and excellent electro-thermal performance,so that it can be applied in a wide range of applications such as EMI shielding materials and heating elements.Carbon fiber composite papers are gaining growing importance in both military industry and residential areas due to the combination of shape conformability and multi-functional applications.With a wide range of potential applications,carbon fiber composite conductive papers have been commercially marketed by a few companies via papermaking process.Nevertheless,many problems still remain to be solved as listed below:(1)the unevenly distributed carbon fibers in the cellulose matrix result in electrical inhomogeneity of the obtained conductive papers;(2)the resistivity of carbon fiber papers prepared by papermaking process is found to fluctuate when exposed to an open environment;(3)it is an urgent to obtain a controllable and stable resistivity for carbon fiber composite paper around the percolation threshold;(4)as most conductive composites studied are of continuous phase matrix like plastics and cements,the electrical behavior of conductive composites in fibrous discontinuous phase matrix remains to be further investigated.In this work,proper dispersing agent for carbon fiber aqueous suspension was selected and the carbon fiber dispersing process was optimized.Via hot-melting fiber modification,the electrical performance of the composite conductive paper was stabilized and the resistivity fluctuation phenomenon can be eliminated.The structure,mechanical and electrical performance of both modified and unmodified conductive papers were characterized by SEM,tensile test and four-probe measurement.The electrical percolation behavior of the obtained conductive papers was further investigated by theoretical modelling.Moreover,electrical heating elements based on the modified conductive papers were successfully prepared and the electro-thermal performance was also discussed.The main conclusions of this work are summarized as follows:(1)Adding APAM as fiber dispersing agent,carbon fiber aqueous suspension can be obtained with high dispersion as well as good stability.Conductive papers with good carbon fiber dispersion and electrical homogeneity can be prepared under this dispersing process.(2)The resistivity fluctuation phenomenon is caused by the swelling and shrinking of cellulose fibers.By introducing the "substrate method",hot-melting fiber modified carbon fiber composite papers were successfully prepared,presenting enhanced resistivity stability.(3)The tensile test results showed that carbon fiber fraction and matrix composition are both important influencing factors to the mechanical performance of carbon fiber composite papers.And the tensile breaking strength can be increased from 5MPa to 9MPa by hot-melting fiber modification.(4)The resistivity of the composite paper with discontinuous fibrous matrix was found to obey the percolation behavior.And K-Z model and FC model were used to describe the percolation behavior of the conductive papers and both were in good agreement with experimental results.The results also showed that the critical parameter of dc/d in the FC model is not a constant and dc is also influenced by the contact pressure of adjacent conductive fibers.(5)The modified conductive paper showed excellent electro-thermal performance and proved to be practical in deicing and heating applications by self-designed experiments.