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. 2024 Oct 16;9(43):43438-43446.
doi: 10.1021/acsomega.4c04671. eCollection 2024 Oct 29.

Polyurethane Waste Recycling: Thermolysis of the Carbamate Fraction

Marthe Nees  1 , Muhammad Adeel  1 , Lukasz Pazdur  1 , Matthew Porters  1   2 , Christophe M L Vande Velde  1 , Pieter Billen  1
Affiliations

Polyurethane Waste Recycling: Thermolysis of the Carbamate Fraction

Marthe Nees et al. ACS Omega. .

Abstract

The alcoholysis of polyurethane waste is currently being industrialized, making it one of the most advanced chemical recycling processes for polyurethanes. However, the recycling potential of the dicarbamate phase, which accounts for 10-40% of the polyurethane mass, is often disregarded, as mainly the polyol components are (partially) retrieved in many alcoholysis processes. In this study, we present a two-step recycling method in which the valuable carbamate fraction obtained in the initial alcoholysis step is transformed into an isocyanate-rich mixture through an additional thermolysis step. For this purpose, different carbamates were synthesized and thermolyzed, which showed that thermolysis with isopropyl-carbamate was the most favorable, obtaining a yield of 35%. As a result, the isocyanates obtained through thermolysis and the polyols obtained through alcoholysis can be reused as starting materials in polyurethane synthesis.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Schematic overview of different chemical recycling techniques of PU foam.
Figure 2
Figure 2
Schematic overview of the proposed alcoholysis–thermolysis recycling method.
Figure 3
Figure 3
Chemical structures of the dicarbamate used in this study.
Figure 4
Figure 4
TGA curves of octyl-carbamate, butyl-carbamate, methyl-carbamate, and isopropyl-carbamate and their FTIR spectrum after a thermolysis reaction at 250 °C for 5 min.
Figure 5
Figure 5
General blocking reaction of the isocyanate groups and HPLC chromatograms of thermolysis mixtures of isopropyl-carbamate.
Figure 6
Figure 6
(A) Two reaction steps of the thermolysis reaction and (B) possible side reactions of MDI during the thermolysis reaction.
Figure 7
Figure 7
Recycling of flexible PU mattress foam with the alcoholysis–thermolysis process analyzed via HPLC with (a1) the reaction products after the alcoholysis reaction, (a2) the HPLC chromatogram of the reaction mixture after the alcoholysis reaction, (b1) the reaction products after the thermolysis and blocking reaction with MeOH, and (b2) the HPLC chromatogram of the reaction mixture after the thermolysis and blocking reaction with MeOH.
See this image and copyright information in PMC

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