| Proton exchange membrane fuel cell(PEMFC) is recognized as one of the new ideal energy fit to the future environmental requirements, because of its high efficiency, low pollution and high power density. Bipolar plate is an important part in PEMFC, which directly affects the cell stack cost, volume size, service life and output power. Therefore, the research for bipolar plate material of low cost and superior performance is one current subject of PEMFC. In this subject we adapted inexpensive phenolic resin, epoxy resin and graphite, which were mixed by dry power milling, hot pressing in low temperature to prepare milled carbon fiber reinforced resin/graphite composite. Hope to reduce material cost through suitable selection of raw materials and preparation process, while in the protection of resin/graphite composite performance.The performance of milled carbon fiber reinforced resin/graphite composites is not only affected by the used raw materials, and the corresponding ratio, but also the process condition. First of all, to determine reliable processing conditions, so we set up two single-factor tests to fix the important parameters of the curing temperature and curing time in process condition. Then a uniform test was used to determine raw materials and their appropriate ratio. Also the main factor which further affected the performance was made a comparison using single-factor tests. Considering the flexural strength and electrical conductivity, the conductive filler of milled carbon fiber reinforced resin/graphite composite was determined as natural flake graphite of 80 to 120 mesh particle size and synthetic graphite of 160 to 200 mesh, and their content was 45wt% and 33wt%. Using the blend of epoxy resin and phenolic resin as binder, whose functional group molar ratio was 1:3, and the total resin content was 17wt%. In the addition of 5wt% milled carbon fiber as reinforcement, at this time the flexural strength and the conductivity of composite were 50.9MPa and 376.8S·cm-1.The material also had a good gas barrier and corrosion resistance, and could be used in long-term PEMFC environment. To further verify the milled carbon fiber reinforced resin/graphite composite could be applied to the material of bipolar plate. Basing on the selection of a typical bipolar plate flow field layout, we designed and manufactured a corresponding mold, and then focused on the key issues of stripping effect in molding. After studying a variety of release effect of internal and external mold release agents, when in the direct using of zinc stearate as external mold release agent, the suppression of clear channel flow bipolar plate flow was succeeded.Using the theory of fiber reinforced composite, and considering the direction coefficient, bond coefficient and the effective length coefficient of the fiber, we got the strength prediction formula of composite reinforced by three-dimensional orientation of short carbon fiber. According to the experiment data, the estimated formula was verified. With the increase of carbon fiber content, the error between the estimated values and the measured ones increased. With the prediction formula to improve the reinforcement effect of carbon fiber, we made several suggestions:1. use carbon fiber of length close to the critical length of fiber 2. appropriate amount of carbon fiber 3. enhance the bond strength between carbon fiber and resin. |
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