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

Abstract

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.

Selective chemical disassembly of elastane fibres and polyurethane coatings in textiles

“…Our previous endeavours on depolymerisation of PU materials revealed tert -amyl alcohol with catalytic amounts of KOH as an efficient solvolysis medium. 44,45 In those studies, we demonstrated the general value of the depolymerisation process for flexible foam-, rigid foam-, flexible solid- and rigid solid polyurethanes. Herein, we disclose our efforts to disassemble elastane by this process initially starting from virgin elastane, moving to elastane recovered by dissolution and finally directly from textile blends to assess the possibility of recovering the main textile component and isolating monomers suitable for repolymerization of elastane (Scheme 1b, bottom).…”

Polyurethane Foam Chemical Recycling: Fast Acidolysis with Maleic Acid and Full Recovery of Polyol

“…Products isolated from this additional treatment were significantly lighter in color than the original hydrolyzed repolyol. While most literature concerning acidolysis focuses on the recovery of the polyol component of PUF, TDA obtained after hydrolysis could be a valuable coproduct from PUF acidolysis. , Toluene diisocyanate (TDI), a precursor to PUF, is synthesized by reacting TDA with phosgene; if the TDA component of PUF can be isolated, it can be useful in the creation of new PUF materials as well. , In our approach, a total of around 80 wt % of the input PUF can be recovered as repolyol (66–68 wt %) and TDA (12–13 wt %) for use in making new PU materials. Additionally, excess MA from acidolysis was neutralized to MA disodium salt after workup, which allows for the input MA to be recovered and recycled by reacidification.…”

Depolymerization within a Circular Plastics System

“…High yields of toluenediamine (>95%), a diisocyanate precursor, and polyols were recovered . In a further work, they showed that the recycled polyol could 100% substitute virgin polyol in PU synthesis, while maintaining good mechanical performance (e.g., virgin PU tensile strength = 93 kPa, and recycled PU tensile strength = 96 kPa) . Zhao and Semetey investigated the methanolysis of PUs using a range of basic catalysts (DBU, TBD, tert -butoxide) .…”