Low-Viscosity Reactive PBT Tackles Composites.

Cyclics Corp. in Rensselaer, N.Y., has developed a new one-component version of a low-molecular-weight, reactive PBT oligomer that can be polymerized in a mold to form a normal, high-MW engineering thermoplastic. In its unreacted form, the material has very low viscosity, which allows it to easily impregnate fiber reinforcements for production of thermoplastic composites. Another possibility is production of highly filled thermoplastic parts, such as polymer-bonded magnets that contain up to 80% by weight magnetic powder.

The new one-component version is easier to handle and process than the two-component systems developed several years ago by General Electric Co., which subsequently sold the technology to Cyclics Corp. The one-component system includes a catalyst that is non-reactive at up to 302 F, so at ambient temperatures it offers a virtually infinite shelf-life, Cyclics says. Since the one-component system needs no metering and mixing, two sources of end-product quality variation are removed.

The one-component system reportedly retains all benefits of the two-component cyclic PET, such as ability to demold parts without cooling and absence of volatile organic emissions. One-part materials can be processed directly into finished parts via injection, compression and rotational molding, and by thermoset composite processes such as pultrusion, RTM, SMO, and BMC. Thermoplastic prepregs or GMT sheet can be wetted out efficiently with cyclic oligomer, which is then cured, allowing the composite material to be stored without refrigeration until final processing.

"With this material there is no boundary between thermoset and thermoplastic processing," says Arse Nielson, Cyclics' director of marketing. Material is now available from a pilot plant, but "significant capacity" for the one-part system is due to be operating late this year.

An emerging application area for Cyclics' one-component system is large wind-turbine blades and rotors, which until now have been made of thermoset composites. Cyclics CEO John Ciovacco says higher production rates of thick-section parts are realized due to faster curing times (under 1 hr) and absence of exotherm during cure.