Fuel Cells Spur Development of Conductive Molding Compounds.

NPE 2000 last month in Chicago saw the introduction of two new conductive thermoset molding compounds designed for fuel cells. These cells generate "clean" electric power and heat without combustion. They electrochemically convert hydrogen, natural gas, or other fuels into water. They are starting to power homes, offices, and experimental vehicles from all major automakers. Stacks of up to 200 bipolar plastic plates can consume 50 to 150 lb per residential fuel cell or 100 to 200 lb per vehicle. Some sources foresee a 2-billion-lb market in 2003.

At NPE, Premix Inc., North Kingsville, Ohio, introduced its Pemtex material for injection molded fuel-cell plates. Bulk Molding Compounds, Inc. (BMCI); West Chicago, Ill., announced its BMC 940 material for compression molding. [Circle 141]

The materials now cost several dollars per pound, though the eventual goal for high-volume production is $2/lb or less. Both compounds are of vinyl ester, because the plates require some corrosion resistance. They also need conductivity of about 100 S/cm on the surface and 20-30 S/cm through the plane. That is achieved with 70-80% carbon-based fillers. Compound consistency is likened to wet concrete or wet beach sand. The materials do not flow easily and are a challenge to mold with the necessary flatness and intricate surface channels.

To overcome this challenge, Premix subsidiary Quantum Composites, Midland, Mich., worked with thermoset equipment supplier Apex Plastic Technologies, South Elgin, Ill., and Ferromatik Milacron, Batavia, Ohio. They refined the stuffer, screw, barrel, tooling, and control software. Premix applied for a patent on a special molding technique for Pemtex. Premix plans to mold fuel-cell plates and to sell the compound.

Premix and BMCI sources agree that injection molding offers faster cycles, more precise shot weight, and easier automation than compression molding. However, BMCI trials show that compression molding achieves better through plane conductivity than either injection or injection-compression.