Study on Effects of Molded Conditions on the Fiber Orientation and Electrical Conductivity of Injection Molded Bipolar Plate for Fuel Cell

Fuel cells constitute one of the most promising sources of clean energy for the 21 century and bipolar plate is an important component of a PEM fuel cell. Polymers filled with conducting fibers have been chosen as a candidate material for bipolar plates which needs to fulfill the surface conductivity requirement. In the present paper, effect of processing parameters including melt temperature, mold temperature, injection velocity, and packing pressure on the surface conductivity in the conventional injection PPS polymer composites filled with 50 wt % carbon fiber was investigated. How flow channel design affects the conductivity distribution was also studied as well. Correlation of fiber orientation and distribution resulting from molding conditions with surface conductivity performance was also examined. It was found that molding conditions play a significant role in influencing part conductivity performance. Higher melt temperature, mold temperature, and packing pressure would increase surface conductivity due to a random orientation or closely tangled the carbon fiber. However, higher injection velocity leading to highly-orientated of fiber reduces surface conductivity. Injection-compression molded parts have superior overall conductivity performance than conventional injection molded parts. As far as the performance of bulk conductivity in the different regions of part is in a sequence of far-gate regions>near-gate regions>center regions. This can be attributed to the combined effects of fountain flow, frozen layer thickness and gapwise melt front velocity. Bipolar plate with channel design provides an advantage of approximately 50-60% higher values than those of the plate without channel design due to the existing of channel leading to more random fiber orientation. Meanwhile, 3D-CAE simulations were also conducted to verify fiber dispersion and orientation under different molding parameters and show reasonable consistency.