Tough, stiff, lightweight, and environmentally friendly. These are the promises of fiber-reinforced composites made with Fulcrum, a new high-performance resin/processing technology from Dow Chemical Co. Designed for pultrusion fabrication (where strands of reinforcing fiber are wet with a resin and pulled through a die of almost any shape), the resin is based on new thermoplastic polymer technology that, for the first time, allows the composites to exploit the toughness, damage resistance, and formability these polymers possess. Even at typical plastics-processing temperatures, other thermoplastic resins are too high in viscosity to flow among and moisten the fibers used in creating a composite, which typically is 70% glass (or other) fibers. The Dow Isoplast thermoplastic urethane resins used in the Fulcrum technology, however, actually "depolymerize at processing temperatures, dropping to a viscosity below the melt viscosity of any existing thermoplastic polymer, allowing flow and wet-out of the fibers to occur," says Chris Edwards, market development engineer and project leader. As the material cools, it polymerizes or rebuilds again to a high-molecular-weight polymer, binding the fiber reinforcement in a composite. Because the resin is a thermoplastic, the resulting composites can be thermoformed, and scrap materials can be recycled and molded into other products. In fact, most reinforced composite materials today are made from thermosetting resins such as epoxies and polyesters, but these materials cannot be postformed. In addition, polyesters release volatile materials into the atmosphere when processed. While the strength and stiffness properties of composites of Fulcrum technology and thermosets are basically equivalent, the former exhibits greater than two times the damage tolerance in impact tests. Suggested applications include medical equipment, structural profiles, window frames, sporting equipment, and steel-rebar replacement. John Teresko, John Sheridan, Tim Stevens, Doug Bartholomew, Patricia Panchak, Tonya Vinas, Samuel Greengard, Kristin Ohlson, and Barbara Schmitz contributed to this article.
