Plastics that leave no space unfilled.

Plastics that leave no space unfilled

Many cars, planes, tennis racquets and other modern accoutrements come off assembly lines at least partly built with composite materials composed of a plastic reinforced with, say, carbon or glass fibers. These composites often are tougher, lighter, more impact resistant and more easily formable than the metal, glass, wood and other materials they replace.

A team of chemists, engineers and materials scientists at the General Electric Co. in Schenectady, N.Y., has come up with a process for making high-strength, recyclable composites that can be shaped after they are made. "These are fundamentally new materials," claims John W. Verbicky, manager of GE's Chemical Synthesis Laboratory.

The newness lies in the composites' plastic component. Typically, the interwoven molecular architectures underlying plastics form from smaller precursor molecules that link into huge, stringy polymer molecules. But the linearity of these molecules makes them tangle up and leads to melts of the polymeric material that resist flowing into the smaller spaces within a composite's reinforcing fibers. The GE scientists devised a way of forming the polymer network from circular, rather than linear, precursor molecules, which readily flow into and infiltrate the reinforcing fibers. Once the molecules are in place in and around the fibers, a catalyst opens their rings and latches them into polymer networks.

The process uses thermoplastics such as polycarbonate and polyetherimides, which engineers can reshape with heat treatments even after the initial polymerization reaction. Most existing composites involve thermosetting polymer resins that take on an unalterable shape once polymerized. The processing advantages of the new composites could help manufacturers reach previously inaccessible market niches in the automotive, aerospace and construction industries.