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<p>Polyurethane (PU) is widely used across various industrial sectors. Its strong chemical resistance renders conventional recycling methods inefficient. Developing greener and more energy-efficient depolymerization strategies is therefore essential. Previous methods for DES-based depolymerization of PU usually require high temperatures and long reaction times. This study proposes a two-stage microwave-thermal treatment process to accelerate PU degradation under milder operating conditions. This study investigates deep eutectic solvents (DES) as sustainable media for PU degradation to identify an efficient treatment system that lowers processing temperature and reaction time while improving product recovery. Choline chloride (ChCl)-based DES formulated with urea, glycerol, and levulinic acid was synthesized and characterized for density, viscosity, and thermal stability. PU depolymerization was evaluated under heat treatment (160 ℃ to 180 ℃, 120 to 480&#xa0;min), microwave irradiation (360&#xa0;W to 700&#xa0;W, 3 to 7&#xa0;min), and a two-stage microwave-thermal treatment process approach. Structural analysis and degradation kinetics of the products were conducted using <sup>1</sup>H NMR. Incorporating microwave irradiation at 360&#xa0;W for 3&#xa0;min before heating resulted in 100% PU conversion at only 160 ℃ within 90&#xa0;min, reducing the reaction time by up to threefold and lowering the required temperature by 20 ℃ compared with conventional heating. The observed improvements suggest reduced energy consumption and offer a more sustainable alternative to traditional PU recycling methods. This combined method also enhanced <i>o</i>-toluidine recovery, reaching 3.63&#xa0;g ± 0.18 recovered from 5&#xa0;g of PU. Spectroscopic analysis suggests that the degradation of PU in a ChCl-urea system may proceed through a synergistic pathway in which urea-mediated hydrogen bonding polarizes urethane carbonyls, facilitating nucleophilic attack by choline moieties, leading to cleavage of C-O bonds and the recovery of constituent monomers. This work establishes ChCl-urea DES, coupled with microwave-thermal processing, as an efficient, low-temperature pathway for PU degradation, contributing toward greener recycling strategies.</p>

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Two-Stage Microwave-Thermal Treatment Process for Depolymerization of Polyurethane in Deep Eutectic Solvents

  • 期刊论文

  • 发表日期：

    2026年7月23日

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  • Amirah Nasuha Mohd Razib,
  • Mohd Sharizan Md Sarip,
  • Nik Muhammad Azhar Nik Daud,
  • Mohd Asraf Mohd Zainudin,
  • Amirul Ridzuan Abu Bakar,
  • Ahmad Hazim Abdul Aziz,
  • Zuhaili Idham,
  • Abul K. Azad,
  • Ken-Ichiro Sotowa

摘要

Polyurethane (PU) is widely used across various industrial sectors. Its strong chemical resistance renders conventional recycling methods inefficient. Developing greener and more energy-efficient depolymerization strategies is therefore essential. Previous methods for DES-based depolymerization of PU usually require high temperatures and long reaction times. This study proposes a two-stage microwave-thermal treatment process to accelerate PU degradation under milder operating conditions. This study investigates deep eutectic solvents (DES) as sustainable media for PU degradation to identify an efficient treatment system that lowers processing temperature and reaction time while improving product recovery. Choline chloride (ChCl)-based DES formulated with urea, glycerol, and levulinic acid was synthesized and characterized for density, viscosity, and thermal stability. PU depolymerization was evaluated under heat treatment (160 ℃ to 180 ℃, 120 to 480 min), microwave irradiation (360 W to 700 W, 3 to 7 min), and a two-stage microwave-thermal treatment process approach. Structural analysis and degradation kinetics of the products were conducted using 1H NMR. Incorporating microwave irradiation at 360 W for 3 min before heating resulted in 100% PU conversion at only 160 ℃ within 90 min, reducing the reaction time by up to threefold and lowering the required temperature by 20 ℃ compared with conventional heating. The observed improvements suggest reduced energy consumption and offer a more sustainable alternative to traditional PU recycling methods. This combined method also enhanced o-toluidine recovery, reaching 3.63 g ± 0.18 recovered from 5 g of PU. Spectroscopic analysis suggests that the degradation of PU in a ChCl-urea system may proceed through a synergistic pathway in which urea-mediated hydrogen bonding polarizes urethane carbonyls, facilitating nucleophilic attack by choline moieties, leading to cleavage of C-O bonds and the recovery of constituent monomers. This work establishes ChCl-urea DES, coupled with microwave-thermal processing, as an efficient, low-temperature pathway for PU degradation, contributing toward greener recycling strategies.