Waterloo researcher aims to make TPO-clay nanocomposites easier to process

Finding a way around the ages-old battle to get oil and water to mix is the key to Dr. Leonardo C. Simon’s research with nanocomposites.

Simon, assistant professor, in the Department of Chemical Engineering at the University of Waterloo in Waterloo, Ont. is trying to make a clay-thermoplastic polyolefin (TPO) nanocomposite that is cheaper and easier to process.

It’s easy to understand by thinking of the TPO as the oil and the clay as the water.

“For example, if you fill up a pot of water and you put oil in it, the oil will separate because it is hydrophobic (does not dissolve in or mix with water),” he said. “TPOs are hydrophobic and they behave like oil [whereas] inorganics filler are hydrophilic.”

Clay fillers are treated with organic compounds to make them more compatible with polymers.

Also, clay nano-fillers are shaped like a deck of cards, in layers. To get the clay nano-filler evenly dispersed throughout the polymer, the layers needed to be torn apart, through exfoliation. Otherwise, they clay will agglomerate, Simon explained.

Right now, most TPO nanocomposites are made by a process called melt-mixing. This is simply taking a polymer and a nano-filler, and mixing them in an extruder to compound them. However, with this process, the clay nano-fillers tend to agglomerate.

Simon, on the other hand, is setting his sights on another process called Incito Polymerization, which can get rid of agglomeration. Melt-mixing simply isn’t sufficient.

“If you want to separate a deck of cards in an extruder (by melt-mixing) you need a lot of shear,” Simon explained.

In Incito Polymerization, the clay nano-filler is added to the monomer used to produce the polymer. Then a catalyst is added to polymerize the monomer with the nano-filler already mixed in.

“Incito polymerization is easy to do with nylon because the monomers are hydrophilic, but the technology has not yet been developed for TPOs,” he said.

Simon is working to develop this very process. “We get clay, we add catalysts to the clay, and then we make the TPO with the clay inside the polymerization reactor.”

This results in a clay nano-filler that is well dispersed throughout the polymer.

Because propylene molecules are very small, they fit between the layers of clay. When polymerization occurs, the layers of clay are pulled apart, or exfoliated, resulting in a well-dispersed nano-filler. Further dispersion is achieved afterwards, when the TPO-clay nanocomposite is melt-mixed.

“We still have to process the polymer (through melt -mixing),” Simon noted. “But we want to make it easier, more efficient and cheaper.”

If successful, instead of using high-shear (during melt-mixing) to process the polymer, less energy could be used during, he said.

“(Also), during Incito polymerization, we can make the polymer chains bond to the surface of the inorganic filler,” Simon noted. “This will stabilize the inorganic nano-particles and prevent them from bunching together again during the processing.”

Simon’s goal is to create a clay-TPO nanocomposite masterbatch.

“Right now the plastics industry buys clay treated with organic chemicals, and they do the melt mixing. We would like to create a masterbatch of polymer-clay nanocomposites coming out of the polymerization nano-batches,” he said.

Unfortunately, for this technology to go commercial, the chemical companies like Basell, will have to create the technology themselves and sell the masterbatches.

But the benefits to plastics processors could be huge.

“You could say the commercial value for nanocomposites arises because of the low cost associated with improved strength, fire resistance or impermeability to gases or liquids, or optical properties,” he said.

These include mechanical properties like impact resistance and toughness, as well as optical properties like appearance.

For example, for a greenhouse film, you can’t add traditional filler because the filler’s molecules are too big, Simon explained. As a result, the film would be hazy. But if the filler was very small (nano-sized), then it would be virtually invisible to the naked eye.

“Furthermore, nano-particles with special functionalities can be added, changing the overall properties of the polymer material, including having better semi-conducting, photonic and magnetic properties.” he said.

GM was able to reduce the weight of the 2004 Chevrolet Impala by seven per cent from using a TPO-clay nanocomposite from Basell on the body side molding of the car.

The Chevrolet Impala is assembled at GM’s plant in Oshawa, Ont.