See-through and tough too

Pittsfield, MA-Plenty of thermoplastics offer strong chemical resistance. The same goes for ductility. Ditto for transparency. But try finding one material with all three properties, and the field narrows considerably. This month, GE Plastics introduced a family of thermoplastic blends that targets this formerly improbable trio of properties.

These new Xylex blends combine polycarbonate with a patented, fully-miscible polyester that GE researchers came up with two years ago. According to Dan Oberle, manager of the company's crystalline resin business, the polyester sets Xylex apart from other clear materials-including its closest benchmark, ordinary polycarbonate.

With a light transmission up to 88%, Xylex approaches the transparency of a standard, non-optical polycarbonate whose light transmission would typically reach about 91%. Notched izod impacts in the 15-to-21 ft-lb range mean that the blends can also rival polycarbonate in ductility. But Xylex really pulls ahead when it comes to confronting chemicals. "Polycarbonate's limitation has always been chemical resistance," Oberle says, before rattling off a long list of substances that have "little or no effect" on Xylex. These include gasoline, grease, cleaning fluids, toothpaste, body oils, and suntan lotion.

From a design-freedom standpoint, Xylex also enables the use of special visual effects on transparent parts. "Special effects have traditionally had a tendency to take away ductility," Oberle explains. Xylex, however, works with GE's range of special-effect colorings without the ductility sacrifice that often topped 40% with earlier materials. "Parts that once had to be opaque can now be clear," he adds.

The addition of polyester to polycarbonate improves other important properties, too. For one, polyester improves UV resistance, Oberle says. For another, Xylex flows well. Oberle notes that Xylex offers as much as a 50% improvement in flow lengths over ordinary polycarbonate.

Today, the Xylex family consists of five grades aimed at applications in telecommunications, consumer electronics, eyewear, and consumer housewares. These materials cover an HDT range from 167 to 206F (@264 psi) and a flex modulus range of 232 to 285 kpsi. Oberle adds that the amount of polyester in Xylex grades can run "anywhere from 10 to 90%." In general, greater amounts of polyester improve chemical resistance and flow lengths at the expense of HDT and flex modulus.

For more information about Xylex from GE Plastics: Enter 540