'Cyclic' TP composite technology investigated for automotive uses.

A joint four-year R&D program of Ford Motor Co. and General Electric Co. will examine the feasibility of processing structural thermoplastic composite automotive parts by utilizing GE's proprietary cyclic oligomer ring polymerization technology.

The research program, which was launched in August, hopes to document prototype fabrication of composite underbody structural parts. Components would be processed by the liquid composite molding methods of structural RIM (SRIM) and resin transfer molding (RTM), injecting the thermoplastic cyclic resin into a mold containing a glass preform.

The research effort is believed to be the first full-scale investigation of possible commercial applications for the cyclic oligomer technology, which was first unveiled by GE three years ago (see PT, March '89, p. 14; Oct. '89, p. 131). GE has remained guarded about developments in its cyclic technology since that preview.

The $10.8 million program is receiving half its funding from the U.S. Department of Commerce, with the two partners splitting the balance. GE will supply the polymer research for the program, while Ford is contributing its expertise in processing and part design.

GE and Ford hope to successfully demonstrate the capability for molding prototype components at the conclusion of the research program. At that time the two partners will decide on whether to pursue an expanded commercialization of the technology or possible licensing options. Results of the program will be reported to and documented by the Automotive Composite Consortium, Troy, Mich., the research group founded by the Big Three auto builders of Detroit to promote development of composite technology.

NOVEL CHEMISTRY

As previously reported by GE researchers, the technology involves ring-shaped, low-molecular-weight oligomers, which are short-chain precursors of standard engineering thermoplastics. Under the influence of heat and special catalysts, the oligomer rings open and the units rapidly join together into linear, high-molecular-weight polymer chains.

The cyclic oligomers are powders at room temperature and typically melt at around 390 F. They have pourable melt viscosities around 100 cp, similar to light machine oil.

Carl Johnson, engineering product consultant with Ford, and Kevin McAlea, manager of the Polymer Physics Program for GE Corporate Research & Development in Schenectady, N.Y., say the low viscosity of the molten oligomers permits impregnating and wetting out a glass preform, which is difficult to accomplish when starting with a fully polymerized thermoplastic.

After conversion of the oligomer into a high-viscosity resin, the glass charge would be deeply embedded in the polymer matrix, with greater strength at the molecular interface of fiber and resin. That interface typically is the "weak link" in thermoplastic composites, as high-viscosity engineering resins are unable to fully wet out the preform due to high interfacial tension.

The two executives decline to fully identify the polymer they are working with, but GE's cyclic technology is known to be applicable to polycarbonate, polyarylate, TP polyesters, polyetherimide (GE's Ultem), polyethersulfones, polyetherketones, and others.

Once cured, the composite part would be a true thermoplastic, offering potential advantages such as recyclability, better impact properties, damage tolerance, and energy management options compared with thermoset parts, according to Johnson and McAlea. They also hope to prove that the cyclic processing technology will offer composite parts with more consistent end-use performance properties. Their assumption is based on the relative simplicity and reduced time/temperature history of the cyclic technology, which requires no exothermic reaction or net change in the chemistry of the resin matrix in contrast with a thermoset system.

The processing temperature of cyclic composite parts would be about 390 F, higher than typical SRIM or RTM systems but comparable to temperatures used in SMC molding. Cycle-time range for processing cyclic composite parts has yet to be verified, but the two researchers believe the technology will be able to support low-volume production of niche-vehicle components, projected at an annual demand of 20,000 to 50,000 units. Given this range, they expect the cyclic processing technology to maintain the advantage in lower tooling costs enjoyed by liquid composite molding compared with steel.