Applied Sciences Inc.Cedarville, Ohio

Pyrograf vapor-grown carbon fibers

Stealth fighter planes and state-of-the-art golf clubs and tennis rackets have at least one thing in common: carbon fiber. This high-tech reinforcement lends strength and stiffness at low weight in composites with epoxy resins, for example. Despite its excellent reinforcing value, carbon fiber has not penetrated the highly cost-sensitive automotive industry because of its relatively high price compared with the workhorse reinforcement, glass fiber. But that could change if Applied Sciences Inc. has its say. This small company located near Dayton has just demonstrated the commercial viability of a new vapor-grown carbon fiber that has the potential performance the automotive industry desires at a cost it can live with. "This year we learned scaling factors that have allowed us to improve production rates by a factor of 40 since we licensed the technology from GM," says Applied Sciences President Max Lake. "That demonstrates the commercial viability of being able to produce at $3 per pound. Three to five dollars per pound is considered to be the breaking point for use of carbon fiber in the automotive industry. "We have also made the first-ever composites this year. They show excellent thermal and electrical properties in organic-matrix composites and significantly improve the strength and stiffness over neat resin. This demonstrates their ability as a reinforcement in polymers to yield engineering properties that are viable." Unlike conventional continuous polyacrylonitrile (PAN) and pitch-based carbon fibers, which are created by oxidizing a spun or extruded fiber, Applied Sciences' Pyrograf carbon fibers are grown in a one-step process by heating a hydrocarbon gas in the presence of a catalyst in a reducing atmosphere. The resulting fibers are a nanostructure some 10 microns long, similar to a fullerene tube, which is a more linear form of the geodesic form of carbon called "buckyballs." As a composite reinforcement, these materials have increased the modulus (stiffness) of both polypropylene and epoxy resins three to five times, in an isotropic array (no alignment of the reinforcement), according to Lake. "In theory we should be able to generate reinforced plastics with seven times the modulus of aluminum," says Lake. "The idea is to engineer polymers with a range of properties that are significant and valuable." In the last quarter of 1995, Applied Sciences received a $2.1 million grant from the National Institute of Standards & Technology's Applied Technology Program to further pursue the technology, with additional contributions from General Motors, Goodyear, and Applied Sciences itself for a total of $5.1 million ("We literally sold the farm on this project," says Lake). Goodyear is currently evaluating the vapor-grown fibers in tires to replace carbon-black reinforcement. "The high aspect ratio [the ratio of fiber length to fiber diameter] of the fibers allows lower loadings for equivalent reinforcement as carbon black, but lower loadings reduce rolling resistance increasing vehicle fuel efficiency," says Lake. "GM would like to use the fibers in a number of applications including lithium-ion batteries, fuel cells, and interior and exterior door panels. "I think these fibers have the capability to revolutionize engineering plastics," says Lake. "It is a potential new industry between carbon black and carbon fibers."

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