FPL Researchers Pioneering Steps into a Sustainable Plastics Future

As the public focuses more on climate change and sustainability solutions, the numbers and facts can be staggering, nearly crippling to think about. The Great Pacific Garbage Patch is growing, an estimated 8 million metric tons of plastic enter the ocean each year, and our fish seem to be drowning in plastic instead of thriving under the sea. A June 2020, National Geographic article that projected 600 million metric tons of plastic waste in the ocean by 2040 if global plastic habits don’t change.

Hearing these projections and statistics can be discouraging and scary.

Ronald Sabo
Engineered Composites Science
Research Materials Engineer

But fear not, people like Forest Products Laboratory’s (FPL) Ron Sabo and his team of researchers are looking up the mountain, seeing the goal of a sustainable-eco-plastic future at the top and taking on the challenge with the diligent steps needed to make that future a reality.

The team reported their findings in a recent paper, “Novel Method of Compounding Cellulose Nanocrystal Suspensions into Poly(Lactic Acid) and Poly(Vinyl Acetate) Blends.”

Single-use plastics, the kind found in food packaging for example, are one of the biggest contributors to plastic waste globally. Sustainable biobased and biodegradable polymers (a polymer is any chemical, natural or synthetic, that is made of a long chain of repeating molecules) have been one proposed solution. “Poly(lactic acid) (PLA) is one of the most commonly used bioderived and biodegradable thermoplastics.”

Yes! Who wouldn’t love to be free of the guilt from accidentally leaving behind a plastic water bottle or utensil on a hike, knowing that it’ll just biodegrade back into the earth?

Except, with anything worth striving for, major challenges must be overcome. Current biopolymers and PLA have some disadvantages—they can be too brittle or have a water vapor and oxygen barrier that doesn’t perform as well as mainstream plastics.

But trees can make a difference—at the nanoscale.

Eucalyptus trees that were converted into cellulose nanocrystals (CNCs) and mixed into PLA have been shown to increase the performance of PLA in both strength and water vapor/ oxygen transmission.

But again, there’s another hurdle to clear. The most common methods to produce thermoplastic cellulose nanocomposites, spray drying and freeze drying, cause the nanocrystals to agglomerate, or clump. This clumping reduces not only the aesthetic of the product but also the mechanical function.

Imagine plastic film that crackles when unrolled or has lumpy bits in it. Not pleasing or useful.

Sabo explains further, “One of the major challenges is that nanocellulose loves water, and if you casually dry it, the nanocellulose fibers/particles will bond to themselves and agglomerate into large particles. Freeze-drying and spray-drying have become popular with researchers, but these methods are slow and costly, which is a detriment to commercializing cellulose nanocomposites. Therefore, a major portion of our research on cellulose nanocomposites is how to combine nanocellulose with polymers without losing the nanoscale structure of the cellulose.”

And yet another challenge: how to make two incompatibles, biopolymers such as PLA and water, work together. Water is problematic because it can speed up the degradation of biopolymer.

“This whole challenge of putting materials together that are not naturally compatible has been a tough nut to crack. There are probably hundreds of groups around the world trying to find ways to produce cellulose nanocomposites, but it is quite difficult to combine nanoscale particles/fibers that love water with hydrophobic polymers,” said Sabo.

Enter the thermokinetic mixer.

Thermokinetic mixer at FPL
Visiting scholar loading the kinetic mixer with an aqueous slurry of cellulose nanomaterials and polymer powder
Steam discharge from the thermokinetic mixer as the water evaporates during compounding

With speeds between 5,000 and 6,000 rpm, the thermokinetic mixer can dry and blend the nanocellulose with biopolymers in a single rapid step.  

“As the blades of the kinetic mixer rotate at high speed, it results in friction between the polymer particles and the chamber wall, which generates enough heat to volatilize the water and melt the polymer,” described Sabo.

This single-step process, called wet-compounding, produced a PLA-cellulose nanocomposite with higher strength and more even nanocellulose distribution. That means producing a sustainable product much closer to traditional plastic.

A PLA-CNC thermoformed
cup produced at Michigan State University

By tweaks and careful adjustments of mixer speeds, cycle times, chemical formulations, and discharge temperatures, a whole new world for cellulose nanocomposites has begun.  

Sabo and his team are pragmatic and realistic about their approach to reaching a future with sustainable plastics. But the possibilities are tantalizing now that they’ve worked through some major challenges.

“The potential of cellulose nanomaterials to be used as fillers or reinforcements for plastics has been touted for decades, but commercialization has been elusive in large part to the challenge of drying. We hope that our research can help overcome these challenges and will result in cellulose nanocomposites being a commercially available option. Currently, one can order polymers with glass fibers or carbon particles, and they will be commercially compounded. We hope that cellulose nanocomposites can also be widely available as a sustainable material to replace some of the unsustainable options being used today” explained Sabo.

This is not a mountain that can be conquered in a single bound. It’s a painstaking step-by-step process. But small changes and tweaks cumulatively produce significant long-term results.

When asked whether he had any predictions for the future of cellulose nanocomposites in mainstream production and fabrication, Sabo said, “I don’t feel bold enough to make any predictions, but I hope that one day all our plastics are made from sustainable materials that do not have negative environmental impact. I think that wood can play a role in engineering sustainable, degradable materials with the desired performance, but we are a long way from realizing this.”   

We’re not quite there yet but we are one mighty step closer.

To find out more about the amazing advancements our scientists are making, visit the Forest Products Laboratory at https://www.fpl.fs.fed.us/