# Recycling of Polyurethane Waste: Facile Hydrothermal Conversion Using Acidic and Basic Additives

## TL;DR

This study shows how polyurethane waste can be efficiently recycled into monomers using hydrothermal treatment with organic amine catalysts under mild conditions.

## Contribution

The use of organic amines, particularly ethylenediamine, is shown to significantly improve polyurethane depolymerization efficiency compared to inorganic catalysts.

## Key findings

- Ethylenediamine achieved a TDA yield of 13.6 wt% and 28.2% PU conversion at 180°C.
- Organic amines outperformed inorganic acids and bases due to zwitterion interactions and phase distribution.
- Hydrothermal treatment with organic catalysts enables selective PU depolymerization under mild conditions.

## Abstract

Polyurethane (PU) is a widely utilised plastic material due to its versatile properties. The chemical recycling, especially by hydrothermal treatment, is an effective way to achieve the circular use of PU. This article reports the results of hydrothermal treatment of PU with and without the use of acidic and basic catalysts. Both non‐catalytic and catalytic approaches showed that PU could be depolymerised to the monomers using hydrothermal treatment. The use of a catalyst improved PU conversion and 2,4‐toluenediamine (TDA) yield. An organic amine showed better catalytic activity than inorganic base NaOH, inorganic acid H2SO4, and organic acid acetic acid. Among the catalysts tested, the organic amine ethylenediamine exhibited the highest activity, achieving a TDA yield of 13.6 wt% and a PU conversion of 28.2% at 180°C. Organic bases outperformed inorganic acids and bases, such as H2SO4, acetic acid, and NaOH, which is attributed to their ability to form ionic interactions with PU‐derived zwitterions and their uniform distribution across vapour and liquid phases under vapour–liquid equilibrium.

Ethylenediamine efficiently catalyses the hydrothermal recycling of polyurethane (PU) into monomers. The N—H functional groups promote carbamic acid decomposition via zwitterion interactions, outperforming inorganic acids and bases, and enabling selective depolymerisation of PU under mild conditions for circular chemical utilisation.© 2025 WILEY‐VCH GmbH