Valorization of undervalued recycled polyethylene terephthalate (rPET) by supercritical CO2-assisted extrusion foaming CO2-assisted extrusion

Project Information

R-PETFOAM

Grant agreement ID: 101148945

DOI

10.3030/101148945

Project closed

EC signature date 24 April 2024

Start date 2 September 2024

End date 1 March 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 135 864,72

Coordinated by

FUNDACION CIDAUT
Spain

Periodic Reporting for period 1 - R-PETFOAM (Valorization of undervalued recycled polyethylene terephthalate (rPET) by supercritical CO2-assistedextrusion foaming CO2-assisted extrusion)

Reporting period: 2024-09-02 to 2026-03-01

Summary of the context and overall objectives of the project

Plastics have fundamentally improved modern living, yet their short life cycle and the sheer volume of resulting waste have triggered a global environmental crisis. Polyethylene terephthalate (PET) is the most widely used plastic for beverage packaging. While clear PET bottles are successfully mechanically recycled back into new bottles, the same cannot be said for mixed-color, or opaque PET streams. Because these colored plastics have high compositional variation and lower aesthetic appeal, they suffer from low industrial demand. Consequently, this "orphan" waste stream is frequently downcycled into fibers, sent to landfills, or incinerated, breaking the loop of the circular economy.

The R-PETFOAM project was born to solve this exact problem. The overall objective was to upcycle these undervalued, mixed-color PET waste streams into high-performance, high-value structural foams. Polymeric foams are lightweight, rigid materials filled with tiny gas bubbles, widely used as the structural core in wind turbine blades, aerospace components, as well as construction and automotive panels. Because foams are inherently opaque, the variable color of the plastic waste become completely irrelevant.

The project's pathway to impact relies on replacing toxic, highly polluting, or expensive virgin core materials (like PVC or virgin PET foams) with a 100% recycled alternative, processed using an eco-friendly blowing agent: supercritical carbon dioxide (scCO2). By demonstrating that mixed-color waste can be transformed into a premium engineering material, R-PETFOAM aims to create a lucrative market pull. Valorizing just a fraction of Europe’s undervalued colored PET waste could generate millions in revenue while drastically reducing the carbon footprint of both the waste management and composite manufacturing sectors.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To turn degraded, mixed-color plastic waste into a robust foam, a major technical hurdle had to be overcome: recycled PET loses its "melt strength" during its life cycle. When melted, it flows like water, making it impossible to trap expanding gas bubbles without them collapsing.
1. Restoring the Plastic’s Architecture:
The project team conducted an exhaustive screening of chemical additives known as "chain extenders" (molecules that act like bridges to reconnect broken plastic chains). The main achievement in this phase was the discovery of a "topological synergy." By combining two different types of extenders (one that linearly lengthens the chains, and another that creates hyper-branched, web-like connections), the researchers successfully restored the required melt strength without causing the plastic to harden or clog the machinery.
2. Developing the Green Foaming Process:
The team successfully retrofitted a pilot-scale, continuous twin-screw extruder machine to handle this complex recycled material. They integrated a high-pressure pumping system to inject supercritical CO2 directly into the molten plastic. As the plastic exits the machine, the CO2 expands, creating a foam structure with a high number of trapped bubbles.
3. Turning "Contamination" into a Feature:
The most remarkable achievement occurred when foaming the 100% mixed-color waste. The researchers discovered that the residual solid contaminants inherent to colored waste (such as microscopic aluminum particles and pigments) actually aided the process. These tiny particles acted as "seeds" (nucleating agents) around which the gas bubbles could easily form and the plastic could rapidly crystallize. Instead of ruining the product, the contaminants actively reinforced the cell walls of the foam.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The R-PETFOAM project pushed the boundaries of mechanical recycling by achieving the first successful continuous scCO2 foaming of 100% highly contaminated, mixed-color rPET.
The resulting engineered foams achieved metrics successfully rivalling established products and commercial standards of the PET foam industry. The project proved that we can achieve excellent structural performance using the lowest-grade plastic waste.

Extrusion Foaming Final Setup

Extrusion Foaminog progress