A New Word to Know: Nano-Composites!

An advanced thermoplastic nano-composite part is being used on the just-released 2002 General Motors GMC Safari and Chevrolet Astro mid-size vans. It's the first automotive exterior application of this lightweight, high performance and affordable material.

Nano-composites are stiffer, lighter and less brittle in cold temperatures than conventional plastics. They will also be more recyclable because there is less additive material in the plastic mix.

On a volume basis, parts made of nano-composites cost only about as much as conventional thermoplastic because less material is needed to manufacture them. Also, no new tooling is required to mould these parts. Further, GM expects the price to improve as nano-composites find their way into more parts.

The nano-composite part being used on the GM vans is a side step, a dealer-installed option.

"Although the step is a simple, low-volume part, we see this as a significant and exciting first step that opens the door to increased use of nano-composites in future vehicles," said Alan Taub, executive director of science for GM Research and Development.

Clay Additive

Like other thermoplastic olefins, nano-composites are made by introducing a solid material into a plastic resin to give it added strength and other positive properties. What's significant about these new plastics is that the particles being added are extremely small. In comparison, the filler in conventional thermoplastic olefins is - on average - one thousand times thicker.

The process of adding inorganic fillers to polymers is actually an old idea, like making bricks with straw in them. The fibrous straw additive makes the brick more resistant to forces that would otherwise crack it.

"In the case of these materials, the additive comprises tiny flakes of a clay material which are only a nanometer (one-millionth of a millimetre) thick," Taub explained. "Because of their flat shape 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 being needed."

A thermoplastic with as little as 2.5 percent inorganic nano filler is as stiff and much lighter than parts with 10 times the amount of conventional talc filler. The weight savings can reach 20 percent, depending on the part and the material that is being replaced by the thermoplastic nano-composite.

GM's breakthrough has been to devise a way to peel apart the very thin flakes of the clay, like separating pages in a book. This process of clay separation is termed exfoliation.

"The greater the extent of exfoliation, the thinner the particles are, and a greater surface area is available for interaction with the polymer matrix, resulting in better performance," Taub said.

Nano-Composite Nylon

However, it's not the first time that nano-composite plastics technology has been used in cars. Toyota researchers found nearly a decade ago that by adding just 5 per cent (by weight) of clay particles to nylon, the following improvements were found:

• 40 per cent higher tensile strength
• Heat distortion temperature increased from 65 degrees C to 152 degrees C
• Much greater flexing strength

Other benefits that have been observed include:

• Increased resistance to solvents
• Decreased thermal expansion
• Reduced permeability
• A flame retardant capability

It's important to note that both strength and toughness are increased by the nano clay particle addition; usually, increasing tensile strength produces a more brittle material.

Nano-composite plastics are used to form the timing belt covers in some Toyota vehicles, while Mitsubishi is also using the technology under license to produce timing belt covers for its range of GDI engines.

Technology Breakthrough

But the GM breakthrough is to use nano-composite technology with thermoplastic olefins, opening up a whole new area of commercialisation. Other automotive parts being developed from the material include exterior door and rear quarter panels - items which when made from the new plastic, will spring back into shape after low-speed impacts.

Share this Article: 

Digg this story

Seed Newsvine

Post to Reddit

Save on del.icio.us

Email