Several years ago, the University of Minnesota (UMN) was issued a US patent for its High Strength Lignin-Based Plastics (20140254, Dr. Simo Sarkanen), a new generation of lignin plastics that feature “very high lignin content and exhibit comparable — or even superior — properties compared to conventional PMMA (polymethylmethacrylate) and polystyrene (PS). These innovative polymeric materials contain at least 80% lignin and are predominantly comprised of methylated or non-methylated lignin sulfonate,” said UMN.

At that time, lignin-based plastics lacked satisfactory mechanical properties and previous processes had limited the amount of lignin that could be incorporated, as they exhibited significant degradation with more than 35 to 40% of lignin content. The high-lignin plastics and polymeric materials showed promising tensile strength with formulations using 85 to 100% lignin content.

Not only were those plastics stronger than current lignin-based polymers at that time, but they added value to the bio-refining and pulp industries that produce lignin as a byproduct and most often burned it for its fuel value. UMN stated that this technology “offers a route to realizing significant commercial value from lignin in the form or a new renewable plastic.”

Unlocking lignin's potential as renewable bioplastic

In 2018, the Natural Resources Research Institute (NRRI) of UMN announced a $3 million grant from the US Department of Agriculture to NRRI’s Wood Products and Bioeconomy Initiative to unlock lignin’s potential as a high-value, renewable bioplastic. The aim was to develop a patented process that separates a tree’s cell wall compounds — cellulose, hemicellulose, and lignin — to make a plastic that can replace the popular acrylonitrile-butadiene-styrene (ABS). The lignin would be converted into ABL (acrylonitrile-butadiene-lignin) resin, worth about $1.20 per pound, and would compete directly with ABS.

NRRI claimed that the institute would begin developing composite siding products from Minnesota’s fast-growing hybrid poplar tree species. Within three years, plans were to have sufficient quantities of the lignin-based resin to demonstrate its properties. Then it planned to branch out into the automotive market and more.

Making plastics from wood is now trending, pushed by the desire to create biodegradable plastic with the mechanical strength of fossil-based plastics. Every week I get more press releases about companies turning to wood-based and plant-based alternatives to plastic. Last week, a news item from Forest.fi, a news organization promoting the forest sector in Finland, about a project to replace Styrofoam and bubble wrap with wood-based products. “The project is based on biomimetics — a field that emulates natural phenomena,” said Professor Mikko Alava, in a news release from Aalto University. “We use AI to develop a foam with properties similar to wood such as strength, flexibility, and resistance to heat.”

The researchers strive to optimize the properties of the foam — a mixture of lignin, wood fiber, and laponite (nanoclay) — that can be processed into shock- and heat-resistant foam and used instead of plastic. Lignin, the news item explained, is the “compound that binds wood fibers together. As a dried foam, it is hard and water resistant and even conducts electricity.”

This same method, according to the researchers, “can be used to make foam out of powdered carrots, cowberries, cranberries or beetroot, and that can be further processed in crisps that resemble potato crisps,” said researcher Juha Kivisto.

PulPac, PA Consulting, and Seismic Solutions recently announced these companies have joined forces to replace single-use plastics with a novel “sustainable, affordable, Dry Molded Fiber technology.” PulPac has “pioneered the technology of cellulose (wood pulp) molding, enabling customers to replace single-use plastics with a sustainable and cost-competitive alternative globally.”

Recently, Ren Com AB changed its name to Lignin Industries AB. The Sweden-based company produces Renol, a lignin additive based on wood pulp that acts as a bio-additive to virgin thermoplastics including ABS, PE, PP and others. According to Lignin Industries’ website, 80 million tones of lignin, a byproduct of the pulping industry, is processed globally, “making it the largest natural byproduct on earth. Today, 99% of the lignin produced is burned for its energy value.”

March 18 was Global Recycling Day, and I received a press release from the Plant Based Products Council (PBPC) that promotes plant-based products made from renewable materials, such as agricultural crops and food waste. These plant-based products are also easy to dispose of through composting and recycling, said the information. PBPC’s members include PepsiCo, Sweetgreen Georgia-Pacific, and many other small and large companies.

The use of wood to make paper-based products such as many single-use items required for food takeout and packaging for shipping products, in addition to the use of wood pellets to burn as fuel to heat homes, means that we’ll need a lot of trees and other plants to fulfill the need for millions of products.

Breakthrough produces durable, sustainable bioplastics

Turning trees into plastic is becoming the trendy thing to do at the academic level, as well. Yale and the University of Maryland just announced that a research team, led by Yale School of the Environment (YSE) professor Yuan Yao and Liangbing Hu from the University of Maryland, has created a “high-quality bioplastic from wood byproducts that they hope can solve one of the world’s most pressing environmental issues [plastic waste].” According to the announcement, efforts to “shift from petrochemical plastics to renewable and biodegradable plastics have proven tricky — the production process can require toxic chemicals and is expensive, and the mechanical strength and water stability is often insufficient.” However, these researchers claim to have made a “breakthrough using wood byproducts that shows promise for producing more durable and sustainable bioplastics.”

A study published in Nature Sustainability, co-authored by Yao, outlines the process of deconstructing the porous matrix of natural wood into a slurry. The researchers say the resulting material shows high mechanical strength, stability when holding liquids, and UV-light resistance. It can also be recycled or safely biodegraded in the natural environment, and has a lower life-cycle environmental impact than petroleum-based plastics and other biodegradable plastics.

“There are many people who have tried to develop these kinds of polymers in plastic, but the mechanical strands are not good enough to replace the plastics we currently use, which are made mostly from fossil fuels,” said Yao. “We’ve developed a straightforward and simple manufacturing process that generates biomass-based plastics from wood, but also plastic that delivers good mechanical properties.”

This new plastic can be used to make film for plastic bags and packaging; it can also be molded into different shapes with the “potential for use in automobile manufacturing.” Yao led a comprehensive life-cycle assessment to test the environmental impact of the bioplastic against common plastics. Sheets of the bioplastic that were buried in soil fractured after two weeks and completely degraded after three months. However, Yao did not reveal the thickness of the sheets used. Researchers said the bioplastic can be broken back down into the slurry by mechanical stirring, which also allows for the deep eutectic solvent (DES), a new class of solvents formed by mixing choline chloride (quaternary ammonium salt with choline caiton and chloride anion) with hydrogen bond donors to be recovered and reused. 

Like most new developments the law of unintended consequences is always in play. While the process currently uses wood byproducts such as sawdust from wood-processing facilities, the researchers note that they are “keenly aware that large-scale production could require the usage of massive amounts of wood, which could have far-reaching implications on forests, land management, ecosystems, and climate change, to name a few.” Yao said the research team has already begun working with a forest ecologist to create forest simulation models, linking the growth cycle of forests with the manufacturing process.

At some point all of these companies and universities that are trying to make “plastic” out of anything and everything besides natural gas and oil from nature’s storehouse of ancient biomass will have to decide if using new trees that take decades to grow and serve as carbon sinks is worth it. At least we’re lucky enough to be in an interglacial period in which the climate is warmer and the increase of CO₂ is feeding trees and plants the nutrients needed to speed up growth rates.

That’s good because Eastman, Eastman Foundation, and Georgia Pacific (GP) Cellulose are working together in cooperation with the Longleaf Alliance to provide 60,000 longleaf pine seedlings to Torreya State Park in Northwest Florida. According to the announcement, the conservation collaboration is intended to “help protect forest ecosystems, support delicate wildlife communities, and help repair the planet for future generations.”

Torreya State Park was selected because of the devastation to the area from Hurricane Michael in 2018. According to the Florida Forestry Association, there are 17 million acres of forestland in Florida, covering almost half the state’s total land area. The forest industry contributes $25 billion to the state’s economy, and 10 counties economically depend on the forest industry, according to the announcement. Obviously we’re going to need more forests to meet the requirements of the increased development of plastics from trees and plants.

Wood-plastic composites gain popularity

Wood-plastic composite (WPC) materials are popular today for decking, railing, fencing, and siding. These materials use recycled plastics mixed with wood sawdust, and over the past two decades they have become popular building materials due to their nearly maintenance-free benefits. WPCs have a role to play in eco-friendliness and as a way to use wood waste along with plastic waste.

Thus far, however, I’ve not found any information on whether any of the lignin-based bioplastic materials have been commercialized at scale to make them economically competitive with traditional plastics or conventional wood-plastic composites. I’m guessing that making these lignin-based materials is not as cost effective as traditional polymers. It may be many years before these become a viable alternative to recyclable plastic materials.

In fact, I really have to question the wisdom of using massive amounts of trees and plant matter to make a bioplastic that promises biodegradability with the mechanical strength of fossil-fuel plastic, especially when the actual biodegradation rate of these materials is questionable.

Where are all the “tree-huggers” when you need them?