Making novel bio-based materials mainstream

Queen’s University chemical engineer Michael Cunningham modifies natural products to safely and effectively replace polluting chemicals.

Queen's University chemical engineer Michael Cunningham (right) in his lab with fellow cellulose nanocrystals researchers Omar Garcia-Valdez and Rachel Champagne-Hartley.

Queen’s University chemical engineer Michael Cunningham (right) in his lab with fellow cellulose nanocrystals researchers Omar Garcia-Valdez and Rachel Champagne-Hartley.

A plant-based substance called cellulose nanocrystals (CNC) may be the most promising biomaterial most people have never heard of, says Queen’s University chemical engineer Michael Cunningham.

Stronger than Kevlar, CNC is the crystalline form of cellulose, which is the chief ingredient in the cell wall of trees and other plants. While only recently available commercially (and only from Canadian company, CelluForce), it could eventually be used to make reinforced plastics that replace steel in cars, boats and even airplanes. The resulting lighter weight would mean transportation that uses less fuel and emits less greenhouse gas.

Reinforced plastic made with CNC could also replace hard plastics currently made from polluting and non-renewable petroleum. These plastics are used in everything from computer cases to golf clubs.

“CNC could also provide our forestry industry with a needed boost as a high-value-added specialty material,” says Cunningham, who spent part of his recent five-year tenure as an Ontario Research Chair in Green Chemistry and Engineering making CNC a more suitable ingredient for reinforced plastics.

The challenge is that while CNC is incredibly strong, it tends to clump together. To be truly effective, it must be evenly distributed. Cunningham and his colleagues at Queen’s are developing a process for doing just that.

It involves working at the microscopic level with polymers, which are substances made from long chains of repeating groups of atoms. Natural polymers include cellulose, chitosan, which comes from shellfish, and alginate, which comes from algae. Synthetic polymers include nylon, polyvinyl chloride (better known as PVC) and plastics, many of which are derived from petroleum.

In the case of CNC, Cunningham is forcing it to evenly disperse by chemically attaching, or grafting, synthetic petroleum-based polymers onto cellulose polymers. While the resulting plastic still contains some petroleum, a substantial portion is replaced by CNC.

But mixing cellulose and synthetic petroleum-based polymers is easier said than done. That’s because petroleum repels water, while cellulose attracts it.

“So they don’t mix well — like oil and water,” says Cunningham. However, he and his colleagues, especially Queen’s bio-resource engineer Pascale Champagne, have figured out how to chemically modify the surface of cellulose and other natural polymers so that they will readily mix with petroleum-based polymers.

“It’s what we call a platform technology, which means once the technique is developed, it can be used for other products and materials,” says Cunningham.

The write stuff

Cunningham is currently working with a Canadian company to use the technique to replace some of the petroleum-based polymers found in paper coatings. Paper is made of cellulose, but if you try to write on it without a coating, your ink will soak in and bleed through, making your words illegible. Petroleum-based coatings ensure your ink stays put.

Plant-based starch, which is cheaper, could replace close to half of the petroleum used in these coatings. But it has a tendency to mix unevenly and separate out. As with CNC, the trick to getting starch to evenly disperse is to graft synthetic petroleum-based polymers onto starch polymers. And again, as with CNS, that involves modifying the starch polymers’ surface so they readily mix with petroleum-based polymers.

Whether it’s paper coatings or reinforced plastics, the technique does not totally eliminate the need for petroleum-based polymers but it does reduce it. “Substituting even 20, 30 or 50 per cent of petroleum-based polymers with natural polymers would be a significant advance,” says Cunningham.

Pulling the trigger

During his time as an Ontario Research Chair, Cunningham also worked with Queen’s inorganic chemist, Philip Jessop, on a concept Jessop pioneered — something called carbon dioxide (CO2) switchable polymers. These polymers change the way they act when CO2 is added or removed. In other words, CO2 is a trigger for the polymers’ transformation.

Using CO2 to trigger changes in petroleum-based polymers in latex paints and coatings is an area where the Queen’s researchers have made great strides. In the presence of CO2, these latex polymers are evenly and stably dispersed throughout the paint, making it ready for use.

Remove the CO2 and the polymers clump together.  When latex polymers are clumped, manufacturers can remove the water in the paint, and ship it in concentrated form, which is lighter and takes less space. This in turn reduces emissions from shipping.

When the paint reaches its destination, it can be reconstituted with water in the presence of CO2, which is the trigger that gets the polymers in the latex to evenly disperse again.

“The principle is similar to frozen concentrated orange juice,” says Cunningham.

While there are similar switchable polymers on the market already, most use toxic materials to trigger changes. CO2 is a nontoxic trigger and because Cunningham and his team are using existing CO2, it does not contribute to climate change.

While the processes he has helped to develop have yet to be commercialized, he is at pains to point out that the research is not “esoteric.”

“There is a misconception that anytime you try to do anything green, it will cost jobs and hurt the economy” says Cunningham. “To be blunt, that’s crap. Anybody developing these products is doing it because it makes economic sense. This is good for job creation, in addition to being green.”

 

*Enhancing our prosperity and well-being: Three Ontario Research Chairs, funded by the Ontario Ministry of the Environment and Climate Change, bring forward key findings in the areas of renewable energy technologies and health, and green chemistry and engineering.

Tagged: Environment & Sustainability, Health & Wellbeing, Natural Resources, Technology

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