Discussions by organizations promoting a circular, cradle-to-cradle, sustainable plastics economy often address packaging and single-use materials, not engineering plastics and polymers. That's because these constitute by far the highest volumes, especially of plastics polluting the environment. Plastic pollution continues to grow faster than waste management and recycling efforts, says the Paris-based Organisation for Economic Co-operation and Development (OECD). Overall plastics recycling has remained under 10% for many years.
The OECD forecasts global plastic waste will almost triple by 2060 from 2019 levels, with half going to landfills. Both leakage to the environment and greenhouse gas emissions from plastics will more than double during that time. Recycling rates will increase and recycled plastics will grow faster than virgin materials, but by 2060 they will still constitute only 12% of total plastics use.
Meanwhile, suppliers of engineering plastics are establishing sustainability programs to satisfy the demands of their OEM customers, as regulations have come into play and sustainable design becomes increasingly important. These efforts involve several related steps, primarily making raw materials—base chemicals and feedstocks—more sustainable, such as using recycled and bio-based materials, and making the process of manufacturing plastics more sustainable, such as using renewable energy. The last steps in circularity are using mechanical or chemical processes to recycle plastic waste back into new raw materials, and capturing a company's own materials from end-products for recycling.
The cradle-to-cradle ideal of a circular economy depends on the cooperation of multiple private and public enterprises. That means developing an ecosystem, which can take a long time, and requires some kind of standards, in addition to collaboration and partnerships.
More Sustainable Engineering Plastics
For some time now, the mechanical performance of both recycled and bio-based sustainable engineering plastics has been comparable with traditional petrochemical-based versions.
"All the mechanical properties are exactly the same, for both consumer and engineering plastics," said Jeroen Verhoeven, vice president of value chain development for Neste Renewable Polymers & Chemicals. The company is the world's largest producer of renewable fuels, also used to make plastics feedstocks.
While OEM users do want sustainable materials, they don't want the hassle of re-specifying or re-qualifying them: they just want the same properties of materials they're currently using, said Verhoeven. So Neste's renewable and recycled streams will continue to be completely drop-in, and usable in large cracker installations. No changes to any other processes are needed in consecutive downstream steps.
Mechanical characteristics like strength, stiffness, and impact have been the traditional drivers for engineering thermoplastics, said Matthew Marks, SABIC's circular economy leader for the Americas. Until recently, the industry didn't see the value in feedstreams from mechanical recycling and considered them a lower-cost option. "But as customers make commitments and regulations are adopted, there is a changing need to re-evaluate this view and an increase in the value of recycling feedstocks," he said. SABIC's TRUCIRCLE portfolio of products and solutions addresses both carbon emissions reduction and the waste challenge, including producing certified renewable products with bio-based content and certified circular polymers.
SABIC was one of the first polymer producers to receive ISCC PLUS certification for its renewable portfolio, said Marks. Other standards and guidelines include the Roundtable on Sustainable Biomaterials' sustainability framework and ISO lifecycle assessment standards.
DuPont believes the carbon footprint and emissions of polymer products will become key decision factors in materials selection, so the company is innovating products to improve its carbon footprint and developing sustainable solutions. "Designers and engineers selecting polymers will start choosing them based on some sustainability factor and will design a part based on its performance, defining performance as not only mechanical performance, for example, but also taking sustainability into account," said Brian Ammons, global business senior director for Delrin.
Covestro is meeting its circularity goals by using alternative raw materials for engineering plastics, including bio-circular and recycled content, said Lauren Zetts, global head of marketing for healthcare. While sustainable materials are new to the healthcare industry, they've been used in electronics for a long time.
The mechanically recycled products Covestro is developing have near-virgin performance, since they're created to fulfill application requirements. There are some drawbacks. For example, getting optical performance in a recycled polycarbonate (PC) can be challenging, said Zetts. But the company's RE series products, sourced from bio-circular content, deliver identical performance—such as physical, mechanical, optical, and weathering—to that of traditional materials and products.
For its part, LG Chem has commercialized sustainable plastics such as post-consumer recycled (PCR) ABS and PCR engineering plastics that are mainly PC-based. The company's focus is on "stably procuring high-quality raw materials from used electronics and/or home appliances to make these recycled plastics even more sustainable," according to an LG Chem spokesperson.
Renewable or Recycled Feedstocks?
The biggest challenges of using lower-carbon or alternate feedstocks today are lack of availability and price volatility, said DuPont's Ammons. "Price volatility is due to lots of different factors—partly supply issues, since demand is increasing for lower-carbon feedstocks."
Some think the ideal would be making materials out of CO2 taken directly from the air, in various carbon capture schemes. For example, in 2015, SABIC opened what it says it the world's largest carbon capture and utilization plant at United, an affiliate in Saudi Arabia. It has 500 Ktons capturing capacity for converting CO2 into valuable chemicals, said Marks.
Neste is also working on carbon capture technologies. While plastics based on them may become an industrial-scale reality in the future, in the meantime, "We should stop making any plastics out of fossil materials ASAP," said Verhoeven. "We as a company feel that any drop of fossil fuel or fossil feedstock we can replace with something more sustainable is a win for the environment. But at this moment, there's not sufficient recycled content available, so an additional source is needed."
That source, say many, is bio-based, especially bio-circular, materials.
"With bio-based materials, we've sequestered carbon in the product from the get-go," said Verhoeven. "Lifecycle analysis shows that carbon emissions are up to 85% better when our renewable products based on Neste's NEXBTL process replace fossil feedstock." This process transforms a wide variety of renewable fats and oils into high-quality renewable fuels and feedstock for polymers and chemicals production.
For its part, DuPont has launched its Delrin Renewable Attributed (RA) product as part of the company's renewable platform. The base polymer's feedstock is 100% bio-based, said Ammons.
SABIC's bio-based and renewable materials utilize several different sources of feedstocks. "We focus on second-generation bio-based materials that are not in direct competition with the human food chain, such as pulp from the forestry industry or used cooking oil," said Marks. Life-cycle analysis has shown that its certified renewable PC's carbon footprint is reduced by 61%, and its fossil depletion potential by up to 35%.
Chemical Versus Mechanical Recycling Methods
Because they address the possibility of re-utilizing plastic waste and therefore reducing pollution, a lot of time and effort is going into developing more-effective recycling methods.
Most manufacturers use traditional mechanical recycling methods. LG Chem, for example, successfully produced the world's first eco-friendly, commercial PCR white ABS in 2019. "Earlier ABS became weak and lost color when recycled and could only be produced in black or gray," said the company spokesperson. The company even improved recycled ABS properties to virgin level and now supplies high-quality, high-content, eco-friendly plastics that contain 60% PCR PC. It plans to increase the PCR PC content to 85% and expand the product portfolio to polyolefin and polyvinyl chloride.
In many cases, though, the quality and performance of mechanical recycling's results degrade over time, so these processes end up making downcycled products. In addition, mixed waste streams can be difficult to use—they require sorting at the front end.
Some suppliers are evaluating advanced recycling processes, such as chemical recycling, and others are already investing in these methods.
"Chemical recycling breaks waste plastic back into the basic building blocks, so you can rebuild from them," said SABIC's Marks. "You can therefore get virgin materials and build what you need—high-value specification materials targeting specific applications."
SABIC is working with Plastic Energy and its advanced plastics recycling technology on a facility targeted for completion in the first quarter of 2023.
"It will be the world's first commercial–scale unit to upscale the production of SABIC’s certified circular polymers—made from the upcycling of post-consumer recycled mixed and used plastic—for our TRUCIRCLE portfolio as a drop-in solution," said Marks. "Previously, pyrolysis technology has been only feasible at lab-scale."
The facility's feedstock will use pyrolysis to convert mixed plastic waste into an oil that can be fed back into petrochemical processes. This process applies heat and pressure to waste plastic in an oxygen-free operation, meaning it does not burn. "The demand for that asset, in every region of the world, is out the door and we're not even complete yet," he said.
Neste is working with Alterra Energy to develop a chemical recycling technology, based on Alterra's thermochemical process for liquefaction of hard-to-recycle plastics. The company has also purchased the European rights to Alterra's technology.
LG Chem is collaborating with UK-based Mura Technology on hydrothermal plastic recycling, a proprietary chemical recycling technology using supercritical water, said the company spokesperson. It plans to build the first plastic recycling facility in South Korea using this process, slated for completion by the first quarter of 2024, with an annual capacity of 20,000 tons.
Debates about the claimed environmental advantages of pyrolysis and depolymerization/chemical recycling processes are ongoing, said Richard Collins, research director for IDTechEx. The research firm recently published a report on chemical recycling methods focusing on both processes.
Pyrolysis's challenges include the inability to use all waste, so sorting is required at the front end. "At the back end there are additional steps before the pyrolysis oil can re-enter the supply chain alongside virgin material," said Collins. "And for each process, the yield, efficiency, and molecular weight distribution of each product made with that process has to be considered."
Depolymerization doesn't work well with every polymer, he said. Although it's mostly championed for polyethylene teraphthalate, used in containers and textiles, and polystyrene, it can also be used for engineering plastics like polyurethane, PC, and polyamide, as well as polymethyl methacrylate, and some engineering-oriented acrylics.
Even with these new technologies coming online, the race is on to stay ahead of plastic waste production. IDTechEx forecasts over 20 million metric tons per year of plastic waste will be recycled worldwide by 2033 using pyrolysis and depolymerization. "In terms of chemical recycling, that's a huge change from approximately 150,000 to 200,000 metric tons per year now in recycling capacity worldwide for each process type," said Collins. "But 20 million metric tons is still a small number in the total plastic universe. The OECD estimated that the global annual plastic waste exceeds 350 million metric tons in 2019, which will continue to escalate in the decades ahead."
Sustainable Manufacturing Processes
Most suppliers want to use some kind of renewable energy in their manufacturing operations, to reduce their products' carbon footprint even further. Some are still in the planning stages, while others have major projects underway.
DuPont, for example, manufactures the base polymer for its renewable Delrin RA product with 100% renewable electricity and heat recovered from incinerating municipal waste. "Compared to standard fossil-based Delrin, we've been able to reduce our carbon emissions by as much as 75%, down to less than 1 kg CO2e/kg," said Ammons.
SABIC has specific roadmaps to achieve carbon neutrality for each plant site. In addition to renewable feedstocks, these include transitioning to renewable energy, improving energy efficiency, electrifying assets, and carbon capture. "For example, we have committed to a strategy of facilitating 4 gigawatts of renewable energy by 2025 and 12 GW installed capacity by 2030," said Marks.
The company also is collaborating with BASF and Linde to electrify one of its steam crackers. Construction of what will be the world's first large-scale electrically heated steam cracker furnace began in January of this year.
DuPont's Ammons points out that the main challenge in decarbonizing operations is complexity. "We're trying to change highly efficient and integrated production facilities with multiple pieces of highly optimized equipment," he said. "So, to minimize waste and emissions, we must tackle each piece of equipment methodically, and this takes time."
Circularity: Capturing End-Products Back at EOL
Perhaps the toughest nut to crack in circularity is recovering a company's own plastics materials for recycling from end-products. The supply chain is not yet set up to accomplish this last step in the cycle.
This step is also important because, from a lifecycle perspective, "Most greenhouse gas emissions occur at the product's end of life, when it's incinerated, ends up in landfill, or worse, in the environment," said Neste's Verhoeven.
Getting back engineering materials is even harder than many consumer materials, since they must last a long time and perform a specific function in a product or device, said DuPont's Ammons. "It's not like a polypropylene container or a PET bottle, where the package is the product." So the challenge is collecting all the parts and extracting the materials.
For example, services that recycle elements of an automobile begin with the large parts, such as the motor and tires. "The rest of the car, those smaller parts that we want to get back, go elsewhere," he said. "[But] we don't have to change the entire process—we just need to insert a step in recycling that vehicle to get to those smaller parts back."
Covestro is working with different partners to meet the challenges of recovering EOL materials, said Kennedy. This includes an automotive recycling program with Oak Ridge National Laboratories through the American Chemical Council.
For its part, SABIC is working on multiple closed-loop initiatives with the entire value chain to collect and recycle waste materials, said Marks.
It Takes an Ecosystem
These collaborations to help close the last link in the loop between grave and cradle are examples of the joint solutions and cooperation needed to build an ecosystem for a sustainable, circular plastics economy.
Covestro, for example, considers joint solutions an essential part of its sustainability program. "Since we can't become circular by ourselves, we're looking at partnerships or other kinds of collaboration with either our own customers and value chain or outside of those," said Zetts. "We're also looking at how our customers can be more circular, such as more ease of assembly or using fewer varieties of materials to make recycling easier, for application-specific or part-specific items."
Designing for sustainability so each part has a recycling option will be one of DuPont's major focuses, said Ammons.
LG Chem is collaborating with several recycling partners worldwide as well as increasing its R&D to increase the recycled content of its PCR products and strengthen their properties, said the company spokesperson.
Collaborating with partners up and down the value chain, instead of the historical focus on in-house development, will be key, said SABIC's Marks. "For example, our partners bring expertise in chemical recycling technologies, feedstocks, conversion technologies, and OEM and brand commitments. The entire value chain needs to be engaged for success."