Heavy PETing - polyethylene terephthalate car bodies

Automotive Industries, Sept, 1998 by Gerry Kobe

Chryler's CCV proved it was possible. Now the idea of injection-molded body panels has the industry passionate for PET.

What began as a "think outside the box" challenge to Chrysler engineers, has now taken on industry-changing proportions. Chrysler's CCV program (see Nov. `97, AI p. 58) pioneered the idea of injection molding car bodies out of polyethylene terephthalate (PET) for Third World consumers. But in the process, Chrysler and other automakers quickly discovered that the potential for PET as a engineering composite is only beginning to be realized.

Although many different resins were considered and actively evaluated for CCV, PET was chosen because it best met the four critical elements for developing-country consideration. Specifically, PET -- commonly used to make soft drink bottles -- was affordable, recyclable, had an existing infrastructure and most importantly, had a substantial global supply.

"If you are going to start building automobiles in quantity out of a new material, you'd better have an infrastructure and capacity already in place," opines Steve Leyrer, program director for CCV's resin supplier Ticona. In the case of PET, the base material is not only plentiful in virgin form, it can also be reclaimed from soda pop bottles, old carpeting and even polyester clothing.

Having met the criteria for availability, the fact remained that PET was not the ideal material for large, structural automotive parts. Working closely with Chrysler, Ticona modified the base resin for UV stability, added pigment for mold-in-color capability and added glass fiber and chemical modifiers for structural integrity and improved flow. At the same time it proved the material could be highly impact-resistant as well. The end result inspired a new product line from Ticona called Impet Hi, that has many of the properties of Chrysler's proprietary resin.

Subsequent to CCV, Chrysler has signaled its intentions to go forward with PET-molded vehicles. First, it pushed plans for a plastics-dedicated R&D center ahead by two years. In July 1999, the Novi, Mich. facility it will share with CCV molder Husky Injection Molding Systems should be fully operational. Second, the company continues to introduce production-feasible plastic concepts like its Dodge ESX2 hybrid-electric vehicle, with a body that is designed to be molded from PET in just six pieces. Also, the Plymouth Pronto Spyder sports car, with molded-in satin finish and projected manufacturing costs that are 80% less than a comparable steel-bodied car.

Advance engineers at Ford tell AI that Chrysler's pioneering efforts have not gone unnoticed. "We have renewed our research into plastic pickup-truck boxes using that material," says a source familiar with the program. Ticona's Leyrer could not comment, but confirmed that a pickup box was possible. Ford sources intimated that unlike the one-piece box it developed in the past, the PET box would have an inner and outer layer bonded together that would fit over frame-mounted uprights at the corners and then bond to the flame.

GM, too, is rumored to be looking at PET on its trucks, but in this case for cab floors. Our source says it eliminates the concern for class-A finish, solves corrosion issues and offers a quantum leap in NVH suppression. The configuration is said to be two layers with a mastic material between them.

For Ticona's part, it continues to work on a resin that will mold in color with a repeatable class-A finish. However, any resin with glass content will degrade the highly polished surface of a mold over time, malting it too costly to maintain. The supplier also looks to educate designers on the lessons it learned from CCV, on how to design in PET as a steel substitute.

"Designing-in box structures adds tremendous rigidity and possibilities," Leyrer says. "So only the creativity of the designer sets the outer limits of this material."