HomeIndustry InsightsHeat and Mixing Unlock New Path for Recycling Complex Polyester Waste

Heat and Mixing Unlock New Path for Recycling Complex Polyester Waste

2025-07-22

A team of French researchers has unveiled a groundbreaking method to recycle unsortable polyester waste—including automotive non-woven scraps and sportswear textiles—by harnessing heat and leveraging leftover manufacturing catalysts. The study, published in Proceedings of the National Academy of Sciences (PNAS), proposes a novel alternative to traditional recycling that bypasses tedious sorting.

Polyester-based plastics like PET (polyethylene terephthalate), PBT (polybutylene terephthalate), and PTT (polytrimethylene terephthalate) are widely used in packaging, textiles, and engineering materials. While conventional PET bottles are relatively easy to recycle using enzyme-catalyzed depolymerization, mixed polyester waste presents a major challenge due to the presence of dyes, plasticizers, and differing polymer structures. These factors hinder enzymatic breakdown, particularly when polymers crystallize into tightly packed chains.

Smart Blending and Thermal Treatment: A Two-Step Solution

In their study, researchers proposed an innovative two-step recycling strategy. First, various polyester waste streams were intentionally blended in controlled ratios, then heated to 270°C. This process triggered melt transesterification—a chemical reaction that reconfigures polymer bonds—thanks to residual catalysts like antimony trioxide from the original manufacturing process. The result: copolymers with a random, less crystalline structure more amenable to enzymatic attack.

However, in cases where PBT-rich waste still crystallized too quickly, scientists added an epoxy-based cross-linking agent (a vitrimerization technique) to delay solidification. Cooling the melt in an ice bath produced a polymer matrix that enzymes could break down more efficiently.

From Waste to Monomers: Recycling Made Easier

The processed material was ground and treated with standard PET-recycling enzymes. Remarkably, the yield of recoverable monomers soared—rising from 20% for PET and just 1% for PBT when processed individually, to 90% when the two were blended.

This counterintuitive discovery suggests that mixing—rather than separating—polyester waste streams could be a more practical and scalable solution for chemical recycling. It also opens new possibilities for processing complex, post-consumer synthetic textiles that previously ended up in landfills or incinerators.

As global demand grows for circular economy solutions, this method may mark a turning point for the sustainable management of synthetic polymer waste.

Source: Based on an article by Sanjukta Mondal originally published on Phys.org, summarizing findings from the Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.2505611122). Edited and paraphrased for clarity and length.