Technology Trends: Additives

Promise of compounds containing nanoclays becoming reality?

Nanocomposites have been the Next Big Thing in the plastics industry for several years now. What has been lacking in all that time is the killer application to prove out the hype.

W hat has appeared instead is a slow trickle of relatively modest applications, mostly in automotive, along with a realization that the best way forward for the technology may be through ''hybrid'' compounds that contain nanofillers—minerals, mostly clay but also talc and others—and conventional fillers.

Because they are so small, nanofillers have a much larger surface/volume ratio than more conventional additives, so any mechanical property enhancements they provide through surface effects can be achieved at much lower addition levels. But it takes a lot of know-how and expertise to disperse and distribute nanofillers in the compound.

This at least partly explains why various players in the development chain are working together more closely than they have in the past. Typical examples are PolyOne''s strategic alliance with Nanocor, which has yielded Nanoblend concentrates and, more recently, Maxxam LST compounds; and collaborative work involving polymer supplier Basell, additive supplier Southern Clay, and end-user General Motors, that has led to the world''s largest applications for nanocomposites. In all cases, the host polymers are polyolefins.

Here is a not-untypical claim by PolyOne (Cleveland, OH) for Maxxam LST: "Compared with many other engineered materials...Maxxam LST compounds require lower processing temperatures, flow easier and cool faster. As a result, with Maxxam LST compounds, customers often use less material, improve cycle times, and lower their energy and equipment costs."

Applications targeted by PolyOne and others include auto interior and exterior trim; small appliance and power tool housings; packaging liners, containers and closures; pipe, conduit, fittings and fascia used in construction; and consumer goods.

Maxxam LST nanoclay compounds are said to offer a combination of light, stiff, and tough attributes and are designed to meet or exceed the capabilities of many engineered thermoplastics, while offering the processing advantages that are inherent to polyolefins.

"We have enhanced the exfoliation process [for separating individual leaflike particles that tend to cling together in stacks], which has enabled us to maximize the performance of the product and make it easy to use," says George Zollos, nanocomposites market development manager.

"This is a significant accomplishment, in that early industry efforts to compound and process nanopolymers failed to achieve significant property improvement and were extremely difficult to process due to improper exfoliation."

GM leading the way

The 2005 version of the Hummer H2 SUT truck is the latest vehicle in General Motors'' lineup to incorporate nanocomposites. Its cargo bed uses more than 3 kg of a Basell compound for its trim, center bridge, sail panel, and box rail protector. H2 program Engineering Manager Bill Knapp says GM designed the vehicle to use the nanocomposite parts for their low weight and dimensional stability.

GM introduced the first commercial automotive exterior application of nanocomposites on the step assist of the 2002 GMC Safari and Chevrolet Astro vans. This January, they debuted on the body side molding for the 2004

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