(119v) Rheology of Bulk Molding Compounds

Most bipolar plates for fuel cells are currently made from bulk molding compounds consisting mainly of graphite powder, thermoset resins, and various additives. The rheological (flow) properties of bulk molding compounds (BMCs) are not well understood, hindering efficient design. This study used a variation of the squeeze flow method, where samples are squeezed between a stationary and a moving flat plate. The degree of slip at the surface of the plates affects the interpretation of squeeze flow data. Experiments were designed to determine the effects of force, temperature, and amount of material on the degree of slip for BMC 940-13905 from BMC, Inc. (West Chicago, IL), one of the BMCs used to make bipolar plates. Teflon particles were placed as markers on pucks made by compressing a given amount of the BMC in a cylindrical mold using a small manual press. The pucks were then compressed at room (69°F) or elevated (284°F) at various forces in a larger press. Slip was observed for all conditions. Slip for tracer at the outermost edge of pucks ranged from about 1.5 to 2.25 of its original position. The force used to compress the pucks had little effect on the amount of slip observed.