Tackling Plastics Pollution with Chemical Recycling: An Interview with Katrina Knauer
This year's Earth Day centers on reducing plastic pollution for the sake of both humanity and planetary health. We spoke with polymer scientist Dr. Katrina Knauer about innovative recycling technologies and the development of new plastics that could make a significant contribution to achieving this mission.
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We may want to improve the quality of our environment, but our options are limited when only a fraction of the population has access to curbside recycling collection, when current mechanical recycling fails to keep plastics out of landfills, and when municipal recycling programs continue to face economic constraints. According to Katrina Knauer, PhD, polymer chemistry could offer a solution.
Katrina, a polymer scientist at the National Renewable Energy Laboratory (NERL) and author of “Circular Plastics Technologies,” spoke to De Gruyter about why plastics are important. More specifically, she covered the obstacles to recycling plastics, how new chemical recycling technologies can combat these challenges, and what each and every individual can do to mitigate the impacts of plastics pollution.
Our interview with her comes to us ahead of Earth Day, whose theme this year is “Planet vs. Plastics.” It was conducted by Alexandra Hinz from De Gruyter.
Alexandra Hinz: What is polymer chemistry and how did you get into it?
Katrina Knauer: Polymers, the ubiquitous macromolecules, have revolutionized consumer products and every facet of our daily lives. They’ve enabled automotive and aviation industries to reduce emissions by replacing heavy metals with lightweight organic materials, facilitated sterile packaging to combat hospital-acquired infections, minimized food waste, and provided access to fresh produce in food deserts. Polymers have even enhanced outdoor experiences through high-performance camping and hiking gear. In essence, polymers are omnipresent.
“With great performance comes great responsibility.”
Yet, with great performance comes great responsibility. While polymers, or plastics, have undoubtedly improved our quality of life, our misuse of them has led to an energy and environmental crisis. This realization fueled my pursuit of polymer science in my PhD studies. With a PhD in polymer science, I hoped to wield enough influence to demonstrate that these materials can be part of a circular economy and contribute to a more sustainable future.
AH: It is estimated that only 9% of all plastic waste is recycled. Why is that?
KK: The low recycling rates aren’t due to recycling “not working” as alarmist headlines suggest. Rather, a major factor is the limited access consumers have to curbside recycling collection. Only 30% of the U.S. population has this service, leaving over 200 million Americans without convenient options for recycling pickup. This challenge isn’t unique to the U.S.; many countries heavily reliant on plastics lack adequate recycling infrastructure altogether. Despite PET bottles being highly recyclable, only 3 out of 10 bottles are recycled due to these limitations. Establishing comprehensive, nationwide recycling systems is costly, and the lack of collection infrastructure remains a significant bottleneck.
Moreover, recycling is inherently complex as it involves managing waste. Post-consumer plastic bales are heavily contaminated with food residues, colorants, metals, dirt, hazardous organic compounds (HOCs), and non-recyclable materials. Dealing with these challenges is both financially demanding and physically taxing, prompting global efforts to find sustainable solutions.
AH: How could chemical recycling solve these problems?
KK: Chemical recycling isn’t flawless, and there’s significant room for improvement and optimization in the emerging technologies within this realm. However, envisioning a future devoid of chemical recycling also means envisioning a future without plastics.
Mechanical recycling, our current state-of-the-art method, falls short in effectively diverting plastics from landfills and establishing a circular carbon economy. This process entails separating plastics into highly pure streams based on chemical composition and then blending them together through melt processing. While simple and low-energy, mechanical recycling is hindered by contamination and material degradation.
“Chemical recycling enables the transformation of materials back into highly pure compounds, ensuring safe reuse in plastic manufacturing.”
Chemical recycling offers a promising alternative by breaking down carbon-rich materials into processable intermediate building blocks. These “blocks” can be purified using chemical engineering processes akin to those used in their original production from fossil fuels or biomass. Rather than merely blending waste and hoping for adequate performance, chemical recycling enables the transformation of materials back into highly pure compounds, ensuring safe reuse in plastic manufacturing.
AH: Do you find any of these technologies particularly exciting or promising?
KK: Absolutely! The discourse around chemical recycling often fixates on methods like pyrolysis or gasification, overshadowing a vast array of innovative technologies. Solvolysis, including glycolysis, hydrolysis, methanolysis, and enzymatic processes, shows immense promise in breaking down polyesters, even in textiles. Oxidation chemistry offers a low-energy pathway for polyolefin degradation, yielding valuable building blocks for new plastics like polyurethanes and nylons.
These breakthroughs represent just the tip of the iceberg in plastics upcycling. Despite current imperfections, ongoing technological advancements over the past five years signal a bright future for chemical recycling. While plastics remain ubiquitous and mechanical recycling struggles, chemical recycling offers a compelling solution. With further refinement and optimization, these technologies hold significant potential to revolutionize waste management and promote a more sustainable future.
AH: What are the challenges that need to be overcome to implement chemical recycling of plastic waste on a large scale?
KK: Foremost, the crucial issue lies in feedstock availability. Municipal collection programs fail to provide sufficient plastics for large-scale chemical recycling operations, hampering their economic viability. To compete with fossil fuels, these plants must operate at scale, producing commodity chemicals. Upgrading global collection infrastructures is imperative to ensure an adequate supply of feedstock for burgeoning chemical recycling facilities.
Secondly, energy consumption and emissions pose significant challenges. Breaking plastic bonds demands considerable energy, sometimes surpassing emissions from virgin plastic production. Optimization efforts, including process refinement, catalyst utilization, and integration of renewable energy grids, are essential to mitigate these environmental impacts.
Thirdly, akin to mechanical recycling, the abundance of additives in plastic formulations complicates chemical recycling. Heightened awareness may spur regulations to minimize additives, simplifying material recycling.
Overcoming these hurdles demands concerted efforts in technology, infrastructure, and regulatory frameworks to realize the full potential of chemical recycling in fostering a sustainable future.
AH: Are there any real-world applications or success stories that you find particularly compelling?
KK: The chemical recycling landscape boasts numerous success stories! Novoloop, for instance, introduced the first thermoplastic polyurethane (TPU) for shoe soles, incorporating waste monomers from oxidized polyethylene film. On’s new CloudPrime running shoe features Novoloop’s TPU, showcasing the practical application of these innovations. Carbios is scaling their enzymatic recycling facility in France to tackle polyester packaging and textile waste with enzymes. Eastman has revamped their methanolysis plants to recycle various polyester materials, including carpets. These examples highlight the industry’s strides, and I anticipate further momentum as we address feedstock collection challenges in tandem.
AH: Your work at NREL focuses not only on recycling plastics, but also on developing new plastics. Can you tell us a little bit more about that?
KK: Yes! This topic is equally as important as recycling. Enter the era of “recyclable-by-design” polymers. Our aim is to revolutionize plastics by harnessing biogenic carbon and prioritizing end-of-life recyclability. Current plastics were never intended to revert to their original components; they were engineered for durability, not degradability. We’re pioneering a paradigm shift, designing polymers from biomass with built-in mechanisms to easily return to their monomeric form under significantly lower energy conditions, facilitating more efficient and eco-friendly chemical recycling.
“Our vision hinges on effectively utilizing biomass feedstocks and achieving high recycling rates to propel us toward a net-zero emissions plastics economy.”
Simultaneously, we’re incorporating a “back-up plan” by developing materials capable of biodegradation into harmless molecules. While biodegradation isn’t the primary recycling method, it serves as a safeguard against environmental contamination if plastics are improperly disposed of. Our vision hinges on effectively utilizing biomass feedstocks and achieving high recycling rates to propel us toward a net-zero emissions plastics economy.
AH: Besides recycling household plastic waste, is there anything that individuals can do to contribute to the creation of a circular plastics economy?
KK: There is so much you can do in your everyday life to help! Get involved in your local community to conduct waste collection/cleanup efforts and spearhead education initiatives on proper recycling and household waste management! Many people assume they’re recycling correctly, but each municipality has its own rules and regulations. Empowering individuals with this knowledge can yield significant improvements. It all begins at home.
Moreover, be mindful of your purchasing habits and the associated plastic waste. Reduction should always take precedence. When comparing products, consider the packaging’s environmental impact and opt for items with minimal plastic. Embrace sustainable practices like using a refillable water bottle, bringing reusable utensils and containers while traveling, and utilizing reusable shopping bags. Additionally, address the issue of textile waste by avoiding fast fashion brands that promote disposable clothing.
These small changes can collectively contribute to a more sustainable future. All the power is in your hands!
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[Title image by Christopher Vega via Unsplash]