Researchers Develop Enzyme to Break Down Polyurethane Shoe Foam, Marking a Key Step Towards Recycling Challenging Thermoset Plastics

September 20, 2026

Earth.com United States

Overview

Researchers have developed an enzyme capable of degrading polyurethane shoe foam, one of the most challenging plastics to recycle. This enzyme achieved an initial breakdown of 1.4% of the foam into reusable chemicals within three days, representing a crucial step towards the recovery and reuse of thermoset polyurethane. This breakthrough offers a potential new solution to the global polyurethane waste problem, with 22 million tons produced annually.

In Depth

Key Findings

Scientists have developed a novel, enhanced enzyme capable of efficiently breaking down polyurethane foam found in shoe soles, a material notoriously difficult to recycle. This research signifies a critical advancement towards sustainable recovery and reuse of polyurethane, a prevalent thermoset plastic. Initial experimental results demonstrated the enzyme’s ability to degrade 1.4% of the foam by mass into reusable chemical components over a period of three days. This represents a significant stride toward circularity for polyurethane waste, a long-standing challenge in plastic recycling.

Technical / Clinical Details

The enzyme, originally isolated from composting bacteria, has been engineered to specifically target and cleave the molecular bonds within polyurethane plastics. The research team successfully optimized the enzyme’s active site through genetic engineering, boosting its degradation capability by up to 20-fold. This improved enzyme is sufficiently potent to break down complex polyurethane materials, such as untreated shoe foam. The enzymatic degradation yields monomeric precursors like polyols, which can be re-utilized in the production of new polyurethane. This biorefining process operates under milder conditions (lower temperatures and atmospheric pressure) compared to conventional mechanical or thermochemical recycling, leading to reduced energy consumption and minimal byproduct formation.

Background & Context

Polyurethane is a versatile polymer used in a vast array of products, including mattresses, cushions, automotive parts, insulation, and shoe soles, with global production reaching approximately 22 million tons annually. However, as a thermoset plastic, polyurethane does not melt when heated once cured, making it extremely difficult to reprocess. Consequently, the vast majority of end-of-life polyurethane products are either landfilled or incinerated, contributing significantly to environmental burden. The lack of effective recycling strategies has created a dual challenge of resource wastage and environmental pollution. This enzymatic development offers a promising biotechnological solution to this persistent problem.

Strategic Significance & Outlook

This enzyme technology holds immense potential for enabling industrial-scale polyurethane waste recycling. While the current 1.4% degradation rate is an initial finding, further optimization of enzyme activity and process conditions is expected to substantially increase efficiency and speed. Commercialization of this technology could transform the vast quantities of annual polyurethane waste into high-value raw materials, reducing the demand for virgin polymers and significantly contributing to sustainable resource circulation. Beyond shoe soles, this technology is anticipated to be applicable to other high-volume polyurethane products like mattresses and car seats, serving as a vital tool in mitigating plastic pollution and advancing the circular economy.

Source: https://www.earth.com/environment/old-shoe-soles-may-have-a-new-path-to-recycling/

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