When you board a plane, the flight attendant prepares you for the worst with these words:
“Take a moment to locate the closest exit to you. It might be behind you”.
The principle of circular design works much the same way: you identify your exit as you enter. When selecting a polymeric material—plastics, rubbers, bioplastics, or other biopolymers—its end-of-life and transition into the next use cycle are planned from the very beginning. The exit might be behind you, to your side, down beneath your feet, or even above you in the air. Here’s how those exits can look like for polymers:
▶️ Reuse as a Product
For polymers, as with most materials, the ideal exit is straight ahead: passing the entire product forward for reuse, with repairs or refurbishments as needed.
- To enable this route, products must be designed for durability and repairability.
◀️ Mechanical Recycling
When direct reuse isn’t feasible—due to obsolescence or safety concerns etc.—many polymers can exit via a step back, through mechanical recycling. This involves melting and granulating the material so it can be remoulded into new products. Thermoplastics are best suited for this because they have been solidified through cooling without forming covalent bonds, allowing them to be re-melted and reshaped.
Designing for this route requires maintaining material purity: minimize the mixing of different plastics, additives, or contaminants. To optimise mechanical recycling [Ref]:
- Choose easily recyclable plastics like ABS, PC, PC/ABS, PP, HIPS, or PA
- Avoid combining plastics with fillers, fibres, or other plastics
- If mixing is unavoidable, use plastics with different densities to facilitate separation
⏪ Chemical Recycling
When materials are too contaminated or require high safety standards (e.g., for food contact or medical applications), an exit further back may become necessary via chemical recycling. This process breaks polymers down into their monomers or even further into petrochemical precursors through depolymerization, pyrolysis, gasification, or hydrothermal treatment.
Although more complex and resource-intensive than mechanical recycling, chemical recycling is an evolving field striving for economic viability.
- To enable this route, select polymers with established chemical recycling pathways.
⏩ Reuse as Material/Component
Thermoset polymers pose a recycling challenge due to their covalently crosslinked structures, essentially forming one large molecule that’s hard to remould or break down. While recyclable thermosets are in development, creative solutions are needed for existing materials—such as repurposing old wind turbine parts into playground equipment, like in the case of Wikado.
However, such niche applications can’t absorb all thermoset waste. Scalable solutions and reduced reliance on unrecyclable thermosets are critical.
To support this route:
- Design component shapes with potential future uses in mind
- Avoid thermosets and elastomers when possible
- If used, ensure they differ in density from recyclable plastics to facilitate separation
🔽 Composting
Since 1950, humanity has produced 8 billion tons of petrochemical plastics, while the plant kingdom generates annually much larger volumes of biopolymers, like 8 billion tons of lignin, 60 billion tons of hemicelluloses, and 2000 billion tons of cellulose every year [ref]. These biopolymers naturally exit down into the soil via degradation after serving their biological roles, illustrating a built-in circularity.
When biopolymers are cultivated and sourced in a way that supports ecosystem services like biodiversity and carbon sequestration, they become sustainable raw materials for circular products. Even when their properties fall short compared to petrochemical plastics, biobased polymers can be enhanced through modifications, or even by building the polymers biotechnically from monomer up.
Emerging technologies are also making petrochemical-based polymers more digestible for microbes, helping reduce microplastic pollution and thus biodegradable [ref]. Even though material cycles should primarily be closed by reusing the synthetic material for the same purpose, these technologies complement this approach by decreasing the release of microplastics during the product’s use cycles.
To enable this route:
- Select regeneratively sourced biopolymers
- Maintain biodegradability through any modification or processing
- Avoid mixing with non-degradable materials that would become contaminants when composting
🔼 Incineration and Carbon Capture
Incineration is generally not a circular process, as it releases carbon back into the atmosphere. However, when combined with carbon capture and utilisation to produce new plastics, it can essentially close the cycle [ref].
- Any safely incinerable polymer can follow this route, though it’s far less efficient than direct material reuse.
🔄 Conclusion
Multiple pathways exist towards polymer circularity, each at varying levels of technical maturity. These serve as tools to design an exit for your polymers from one use cycle and entry into the next one. Crucially, closing material loops in practice requires more than recyclability: it demands systems and business models that create greater value through reduced material consumption.
At Ethica, we approach circular economy holistically—from the molecular to the systemic level. We’re here to help you find circular solutions tailored to your applications.
Author:
Meri Lundahl, D.Sc. (Tech.)
Senior Consultant, Circular Economy
