tert -Amyl Alcohol-Mediated Deconstruction of Polyurethane for Polyol and Aniline Recovery

Self Cite

The production of thermoset materials makes up 12% of global plastic production. With increasing demands for plastics and with emphasis on the legacy burden of thermoset polymers, new solutions are indispensable to shift our society from the current linear make–use–dispose mindset to a scenario where materials are utilized in a more circular fashion. In 2020, the production of polyurethane (PU) reached approx. 24 million tons, making it the sixth most produced polymer. However, the inherent stability of PU renders chemical recycling difficult, often providing a secondary feed with different characteristics and properties from the original polyol and isocyanate. In our previous work, we demonstrated how tert-amyl alcohol could be used as a solvent and reagent for the simple chemical recycling of PU via a solvolysis process. Herein, our efforts are presented for attaining a recycled polyol (recyclate) via chemical recycling of flexible thermoset PU foams using the tert-amyl alcohol-mediated solvolysis process and scaling it to produce new flexible thermoset PU foams. The produced recyclate is similar to virgin polyol, allowing for 100% substitution of virgin polyol for the recyclate while maintaining both mechanical and physical properties of the foams containing up to 64 wt % of recycled materials. Moreover, the foams prepared from the recyclate were also deconstructed to retrieve the recycled polyol, showcasing for the first time the possibility to form closed-loop polyol recycling processes for flexible PU foams. Finally, the recyclate was applied as a substitute for virgin polyols in the formulation of PU resins, where the recycled content amounted to 81 wt % while still attaining mechanical properties comparable to those of materials prepared with virgin polyol.

Section: Resultsmentioning

confidence: 99%

Closed-Loop Recycling of Polyols from Thermoset Polyurethanes by tert-Amyl Alcohol-Mediated Depolymerization of Flexible Foams

Johansen,

Donslund,

Larsen

et al. 2023

Self Cite

“…More recently, Johansen et al studied the chemical recycling of a model flexible PU foam, as well as a variety of postconsumer PU materials, using tert-amyl alcohol as the glycolysis agent. 56 Notably, from a KOH-catalyzed reaction at 225 °C, after 2.25 h, over 95% yield of toluene diamine (TDA) was obtained. TDA is a precursor for making toluene diisocyanate (TDI) for PU synthesis.…”

Section: Glycolysismentioning

confidence: 99%

Opportunities in Closed-Loop Molecular Recycling of End-of-Life Polyurethane

Liu

Westman

Richardson

et al. 2023

Polyurethane (PU) is the sixth most used plastic. Total production reached 24 million metric tons in 2018 and continues to grow at an annual rate of 4%. As production increases, so does the accumulation of PU waste and the need to find a viable recycling method. However, due to the highly cross-linked structure and complex composition of postconsumer PU, mechanical recycling methods produce lower-value products with limited reusability. Chemical treatments that extract reusable components can offer alternative approaches to PU waste valorization. Chemical recycling of PU waste is underdeveloped given the significant potential economic and environmental impacts. Mechanistic studies on chemical recycling pathways, such as hydrolysis, acidolysis, glycolysis, and aminolysis, are incomplete, and few of these methods have been used commercially. This perspective provides an overview of several closed-loop chemical recycling methods that can be used to produce recycled polyol (repolyol) from waste PU, which can be used in place of virgin polyol. We delineate what is known regarding the chemistry and mechanisms, identify knowledge gaps, and compare the utility of the products from each recycling method. We also suggest ways that density functional theory can be used to fill knowledge gaps.

“…Since pyrolysis and mechanical recycling are not the most suitable methods for treating PUF waste due to environmental issues and the cross-linked structure, respectively, chemical recycling has recently become a very interesting research topic. ,− Chemical recycling of PUFs made from polyether polyols is based on the cleavage of the urethane bonds, leaving the ether groups in the polyether polyol intact. Depending on the mechanism of urethane bond degradation, recycling technologies are mainly classified into hydrolysis, , glycolysis, − alcoholysis, acidolysis, ,− aminolysis, − and hydrogenation. , To achieve efficient degradation of urethane groups, the process of PUF recycling must be carried out at high temperatures (200 °C and above) by heating the reaction mixtures by conventional heating or, less commonly, by microwaves (MWs), which allows an equally effective degradation process in a much shorter time. ,,,, …”

Section: Introductionmentioning

confidence: 99%

“…49,50 To achieve efficient degradation of urethane groups, the process of PUF recycling must be carried out at high temperatures (200 °C and above) by heating the reaction mixtures by conventional heating or, less commonly, by microwaves (MWs), which allows an equally effective degradation process in a much shorter time. 7,20,26,40,42 PUFs can be efficiently degraded by hydrolysis, 15,16 alcoholysis with tert-amyl alcohol, 35 or catalytic hydrogenation, 49,50 but these reactions are not selective for the degradation of only the urethane groups, as the urea groups of the hard segments in the PUF structure also completely degrade, resulting in a mixture of recycled polyols and undesired aromatic amines (e.g., toluene diamine, TDA, or methylene diphenyl diamine, MDA). Glycolysis is the most studied chemical recycling method for polyurethane (PU) waste and involves transcarbamoylation of the urethane bonds.…”

Section: ■ Introductionmentioning

confidence: 99%

“…PUFs can be efficiently degraded by hydrolysis, , alcoholysis with tert -amyl alcohol, or catalytic hydrogenation, , but these reactions are not selective for the degradation of only the urethane groups, as the urea groups of the hard segments in the PUF structure also completely degrade, resulting in a mixture of recycled polyols and undesired aromatic amines (e.g., toluene diamine, TDA, or methylene diphenyl diamine, MDA). Glycolysis is the most studied chemical recycling method for polyurethane (PU) waste and involves transcarbamoylation of the urethane bonds.…”

Section: Introductionmentioning

confidence: 99%

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Chemical Recycling of Flexible Polyurethane Foams by Aminolysis to Recover High-Quality Polyols

Grdadolnik

Zdovc

Drinčić

et al. 2023

Polyurethane foams (PUFs) are widely used commodity materials, but most of them end up in landfills at the end of their life, which is not in line with the circular economy approach. Here, we introduce microwave-assisted aminolysis with amine reagents that contain primary and tertiary amino groups in the structure. These reagents enable complete degradation of the urethane groups in the structure of the flexible PUFs with a much lower amount of degradation reagent than is typically required for solvolysis reactions. The purified, recovered polyols are close equivalents to the corresponding virgin polyols in terms of their structural and molar mass characteristics. Therefore, they can be used for the production of high-quality PUFs without having to adapt the synthesis process. The flexible PUFs made from recovered polyols have comparable mechanical properties to those made from virgin polyols.