GM takes first step with new plastic

DETROIT - General Motors is equipping some of its 2002 rear-wheel-drive minivans with a side step that is a breakthrough for the use of plastics with a microscopic filler material.

The step on the GMC Safari and Chevrolet Astro, which will be a dealer-installed option, is made from a thermoplastic olefin plastic resin with a minute filler, known as a nanocomposite. The filler, a clay powder from Southern Clay Inc. in Gonzales, Texas, is added to the plastic before the part is formed to make it stronger.

The part is molded by Blackhawk Automotive Plastics Inc. of Salem, Ohio.

Fewer than 10,000 units are expected to be produced for the first model year.

But the technology could lead to complete exterior panels that are molded in color with a Class A surface finish that eliminates the need for paint.

"This is just the first of several applications," said Alan Taub, executive director of science at GM Research and Development in Warren, Mich.

GM, which has been working on the project since 1998, has tested the material for use on parts such as clad- ding, fenders and rear liftgate doors, with painted and nonpainted surfaces.

The resin is less prone than other plastics to expand and contract in extreme temperatures, which will lead to smaller gaps between panels.

The material also shows promise for interior uses, replacing either metal or existing heavier composites in a variety of parts.

"The growth (pattern) on this is going to take off like a hockey stick," said Bill Windscheif, global business vice president for Basell Polyolefins of Wilmington, Del., which has worked with GM in developing the material.

Unlike a glass- or talc-filled plastic, the nanocomposite uses minute particles of a clay additive, called smectite. The filler is only one-millionth of a millimeter thick. Five grams of smectite would cover a football field, said Robert Briell, senior scientist for Southern Clay.

As a result, the nanocomposite may have as little as 2.5 percent of the fill material vs. 20 percent or more in a conventional composite, Windscheif noted.

In production parts, that adds up to a weight savings of up to 20 percent, which can be used to improve fuel efficiency, Taub said.

Manufacturers, meanwhile, will see improved material flow, which means faster cycle times and fewer defects. The material also works with existing production machines.

Even greater promise is "just around the corner," Windscheif said, as the researchers look to combine the structural properties of the nanocomposite with the growing studies of in-mold coloring.

The auto industry can reduce cost greatly if it can produce parts complete with a Class A surface that do not require painting.

So far it has proved difficult to turn out the metallic colors preferred by automakers at a cost they are willing to pay.

You can reach Rhoda Miel at

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