Christophe M. L. Vande Velde

This review addresses the fate of isocyanate-derived fractions from PU chemical recycling. It highlights valorization routes beyond polyols, noting promising pathways but also technical, economic, safety and regulatory limits.

One tire, two value streams, zero waste. Putting a brake on tire waste by re-routing a recalcitrant thermoset into biocompatible platform acids and intact carbon black filler through sustainable low temperature oxidative deconstruction.

This study reports the synthesis of urea-functionalized MOFs (UA-1, UA-2, UA-3) where synthesis conditions controlled interpenetration levels, and a detailed analysis of host–guest interactions between the UA-3 framework and various solvents.

Polyurethanes are versatile materials, but their thermoset nature limits mechanical recycling as they do not melt under heating. However, chemical recycling by depolymerization does not yet provide complete circularity, given the highly diverse monomers and additives. Especially for rigid foams, with short and multifunctional polyols, the separation of depolymerization products is challenging. In this paper, we propose a strategy to screen the separation of these products via liquid–liquid extraction by comparing molecular dynamics simulations with experimental results performed on a synthesized model rigid foam depolymerised by hydrolysis. Bifunctional ethyleneoxide polyols with molecular weights of 200, 400, 600 and 1000 are used together with 4,4′-methylene dianiline (MDA). The tested solvent systems are acetonitrile/n-hexane, water/dichloroethane, water/ethyl acetate and water/n-octanol. Coarse-grained (CG) molecular dynamics simulations were used to model the large-scale morphological organization during solution-processing. Our results show a clear separation between the polyols and the depolymerised aromatic components, except for the acetonitrile/n-hexane solvent system, where all solutes dissolve in acetonitrile. Polyols preferentially migrate to the aqueous phase, while aromatic amines such as MDA favour the organic phase. The simulations reveal that larger polyols tend to accumulate at the interface, particularly in the water/dichloroethane and water/ethyl acetate systems. Experimental partition coefficients, consistent with simulation predictions within error margins reported for the Martini 3 forcefield, indicate a strong correlation between polyol molecular weight and phase behaviour. This separation is further influenced by solvent polarity, with water/n-octanol systems exhibiting 2–3 times more MDA aggregation than the other systems, as predicted by the analysis of radial distribution functions and density profiles. The combined approach of molecular dynamics and experimental validation offers a promising strategy for optimizing liquid–liquid extraction in polyurethane depolymerization, guiding future design-for-circularity processes.

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.

This article explores the important, and yet often overlooked, solid-state structures of selected bioaromatic compounds commonly found in lignin hydrogenolysis oil, a renewable bio-oil that holds great promise to substitute fossil-based aromatic molecules in a wide range of chemical and material industrial applications. At first, single-crystal X-ray diffraction (SCXRD) was applied to the lignin model compounds, dihydroconiferyl alcohol, propyl guaiacol, and eugenol dimers, in order to elucidate the fundamental molecular interactions present in such small lignin-derived polyols. Then, considering the potential use of these lignin-derived molecules as building blocks for polymer applications, structural analysis was also performed for two chemically modified model compounds, i.e., the methylene-bridging propyl-guaiacol dimer and propyl guaiacol and eugenol glycidyl ethers, which can be used as precursors in phenolic and epoxy resins, respectively, thus providing additional information on how the molecular packing is altered following chemical modifications. In addition to the expected H-bonding interactions, other interactions such as π–π stacking and C–H∙∙∙π were observed. This resulted in unexpected trends in the tendencies towards the crystallization of lignin compounds. This was further explored with the aid of DSC analysis and CLP intermolecular energy calculations, where the relationship between the major interactions observed in all the SCXRD solid-state structures and their physico-chemical properties were evaluated alongside other non-crystallizable lignin model compounds. Beyond lignin model compounds, our findings could also provide important insights into the solid-state structure and the molecular organization of more complex lignin fragments, paving the way to the more efficient design of lignin-based materials with improved properties for industrial applications or improving downstream processing of lignin oils in biorefining processes, such as in enhancing the separation and isolation of specific bioaromatic compounds).

Metal-organic framework (MOF)-74 is known for its effectiveness in selectively capturing carbon dioxide (CO₂). Especially the Zn and Cu versions of MOF-74 show high efficiency of this material for CO₂. However, the activation of this MOF, which is a crucial step for its utilization, is so far not well understood. Here, we are closing the knowledge gap by examining the activation using, for the first time in the MOF, three-dimensional electron diffraction (3DED) during in situ heating. The use of state-of-the-art direct electron detectors enables rapid acquisition and minimal exposure times, therefore minimizing beam damage to the very electron beam-sensitive MOF material. The activation process of Zn-MOF-74 and Cu-MOF-74 is systematically studied in situ, proving the creation of open metal sites. Differences in thermal stability between Zn-MOF-74 and Cu-MOF-74 are attributed to the strength of the metal-oxygen bonds and Jahn-Teller distortions. In the case of Zn-MOF-74, we observe previously unknown remaining electrostatic potentials inside the MOF pores, which indicate the presence of remaining atoms that might impede gas flow throughout the structure when using the MOF for absorption purposes. We believe our study exemplifies the significance of employing advanced characterization techniques to enhance our material understanding, which is a crucial step for unlocking the full potential of MOFs in various applications.