Step On It!

General Motors Corp. is going to have a “step up” on the competition in the '02 model year.

The automaker, with the help of several suppliers, says it will debut an advanced thermoplastic olefin (TPO) nanocomposite step-assist part on its GMC Safari/Chevy Astro minivans. The announcement is important because TPO nanocomposites might provide plastics with the key upgrades the materials needs to win big vehicle applications, such as body panels, from steel and aluminum.

Nanocomposites make plastic parts firmer and more dimensionally stable and improve surface quality, GM claims. Weight is reduced, costs are cut and low-impact performance is improved as well, says the automaker. Like other thermoplastics, TPO nanocomposites are made by introducing a solid material into a plastic resin.

What's different is that the particles being added are extremely small compared with conventional fillers that are 1,000 times thicker. For noncomposites, smectite clay is used to replace traditional fillers such as talc or glass-fiber.

“In the case of these materials, the additive is tiny flakes of a clay that are only a nanometer (one millionth of a millimeter) thick,” says Alan I. Taub, executive director of science for GM Research and Development. “They have huge surface areas relative to the other additives we use, like talc, and the result is exceptional improvements in the properties of the plastics with only a fraction of the inorganic filler.”

The clay flakes are so flat and thin that only 5 grams (0.18 oz.) could cover the surface area of a football field, says an official at supplier Southern Clay Products, Inc. The use of clay avoids some of the negative characteristics associated with talc, mica or glass-fiber, which make surface finishes bumpy and cause parts to crack more easily in cold temperatures.

A TPO with as little as 2.5% inorganic nano filler is as stiff and much lighter than parts with 10 times the amount of conventional talc filler, GM says. That can result in parts that are as much as 20% lighter. The cold-temperature impact performance of nanocomposite TPOs also is far superior to conventional TPOs. Because there is less overall filler material, the parts are easier to recycle, too, GM says.

Despite the impressive performance characteristics of nanocomposites, GM is easing the new technology into production. “When you use new materials, you often get surprises. Walk before you run,” reasons Mr. Taub.

Volume for the step-assist is low; about 8,000 Astro/Safaris are made with this option annually. Moreover, the minivans are scheduled to go out of production in 2003. “We chose to go with a low-volume product and scale up,” says Mr. Taub. “While it may not be a product that's going to be here in five years, we do have commitment from the cycle plan to learn what we need to learn from this field test.”

Other new exterior and interior TPO applications are expected to start trickling out over the next several years at GM, including rocker panels, semi-structural parts, cladding and body panels. Work also is being done on the “Holy Grail” of plastics applications: non-painted, molded-in color exterior body parts. “Obviously we're not at that stage yet,” says Bill Windscheif, vice president of advanced polyolefins at Basell Polyolefins, a supplier that helped GM develop the step-assist nanocomposite part. “I don't want to deceive anyone. But that is the direction the technology is going. If you think about it, if you're able to reduce the filler content and keep the equivalent stiffness or increase the stiffness, that opens the door for all kinds of things you can do with nano-composite TPOs.”

The new plastic also represents a breakthrough in the way GM works with suppliers.

When the automaker first announced it was developing the nanocomposite material in December 1998, it marked one of the first times the automaker happily shared the spotlight in public with the suppliers it is collaborating with: Basell, Southern Clay Products and Blackhawk Automotive Plastics.

Since then, the relationship has continued to evolve. GM, Basell and Southern Clay now have an agreement that grants mutual confidentiality, which GM says is unprecedented in its relationships with outside suppliers. Basell also has an exclusive license on GM's process to manufacture the material, and GM will be the only automaker using the material for now. Mr. Taub will not reveal further details of the exclusivity agreements or their length, but says a second-generation nanocomposite likely will debut on GM products by the time the current material becomes available to other automakers.