Chemical Recycling of Polyurethane Foams

Polyurethane foams (PUFs) are used in a variety of applications, particularly mattresses, upholstered furniture, electronics and automotive industries, and construction. The global PUF market is expected to increase to 20 million tons by 2025 due to growing end-use industries. As a result, the amount of PUF waste is expected to increase. In line with global efforts to reduce environmental pollution, there is a clear need to recycle PUF waste to sustain the growth projections for PUF production. Mechanical recycling and pyrolysis are unsuitable methods for treating PUF waste due to the cross-linked PUF structure and environmental issues caused by the release of toxic gasses during pyrolysis. Therefore, chemical recycling has recently become an intensively researched topic. Chemical recycling of PUFs can be carried out by various methods, mainly by conventional heating. Few reports deal with microwave (MW)-assisted PUF degradation, which ensures shorter reaction times and thus lower energy consumption and carbon dioxide emissions compared to methods based on conventional heating. Chemical recycling of polyether polyol-based PUFs is based on the cleavage of the urethane bonds in the PUF structure. However, current recycling technologies suffer from incomplete urethane group degradation and/or various side reactions and produce either (i) recycled polyols of lower quality compared to virgin polyols, which are therefore only used as partial substitutes for virgin polyols in PUF formulations, or (ii) highly complex and poorly defined degradation mixtures that are used in less demanding applications. The aim of the project is to develop a degradation process for flexible PUFs that: (i) enables efficient degradation of urethane groups to produce polyether polyols that are close equivalents of virgin polyols in terms of functionality, molecular weight, and purity; (ii) prevent formation of unwanted aromatic diamines during degradation process; (iii) enable easy separation of the liquid polyol phase from the remaining PUF hard segments and allow for simple and efficient polyol purification, and (iv) is energy-efficient. To this end, we propose MW-assisted aminolysis and ammonolysis with previously unreported degradation reagents. We will study the influence of the experimental conditions, i.e., type and amount of degradation reagent, reaction temperature and time, on the functionality of the recovered polyols, their molecular weight characteristics, the presence of side products soluble in the polyols, and the degree of degradation of the remaining PUF hard segments. The recycled polyols will be used for the synthesis of new flexible PUFs, where we intend to replace virgin polyol with the recycled polyol to a higher extent than it is currently possible (20 ut%). The morphology and mechanical properties of the PUFs will be studied to evaluate the influence of the structural properties of the polyols on the quality and performance of the flexible PUFs made from the recycled polyols. Finally, the oligourea residues of the PUF hard segments will be degraded to aromatic diamines, which serve as a raw material for the production of diisocianates, in order to meet the requirements of circular economy. To critically evaluate the robustness and potential scalability of the proposed recycling process, we will degrade PUFs produced from different diisocianates and polyols, and post-industrial and post-consumer PUF waste containing different additives (flame retardants, dyes, fillers). The tendency of the most promising process to down-cycling will be evaluated by subjecting PUFs to the recycling process several times, while its environmental impact will be assessed by life-cycle analysis. Successful implementation of the project could have the potential to reduce the consumption of fossil resources and the landfilling of plastic waste, which could ultimately contribute to the integration of the circular economy into the PU plastics value chain.