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Top1. Introduction
Polymer recycling processes attract significant attention as a direct result of the enforcement of environmental legislation. Massive enforcement of the environmental laws has provoked an extensive re-examination of various approaches to utilize end-of-life plastic waste as an alternative to landfill disposal. Creative and profitable recycling methods for polymers have been proposed to reduce their environmental impact by removing them from the waste stream and recovering the valuable material due to the increasing cost of raw material and regulations on its disposal (Simón, D. (2014a). Polyurethane is one of the most versatile and adaptable polymer materials widely used in different applications, which makes its recycling an urgent task. A broad spectrum of polyurethane specialties, linear or reticulated, can be produced to meet each specific application's need depending on the polyol and the isocyanate employed in the reaction and the extension of the reactions involved (Engels, H. W., Pirkl, H.-G., Albers, R., Albach, R. W., Krause, J., Hoffmann, A., Casselmann, H., & Dormish, J. (2013)). The reaction's mechanism is a nucleophilic addition of oxygen of an alcohol group to the carbon of the isocyanate group while its active hydrogen is added to the negatively charged nitrogen. The reaction takes place through a six-centered ring transition state (Sonnenschein, M. F. (2021). Creative and profitable recycling methods for polyurethane foam have been proposed as a result of the disposal regulations. Polyurethane waste originates from various applications, including end-of-life vehicles (ELVs) and waste from electrical and electronic equipment (WEEE) (Hennebert, P. (2020). The majority of polyurethane foam waste is usually incinerated or dumped in landfills but recycling the most effective and economical alternative disposal method. Polyurethane recycling routes be divided into mechanical, chemical and energy recovery. In mechanical recycling, polyurethane waste is ground into powders to be reprocessed in different ways without chemical treatment. The mechanical recycling route is convenient and straightforward, with low cost, but the recovered product's performance is poor, limiting its applications (Kemona, A., & Piotrowska, M. (2020). Energy recovery refers to the incineration of polyurethane foam waste' combustion to harness energy. The energy recovery method is only limited to scrap with polyurethane laminates and commingled materials. However, polyurethane foams contain flame-retardants making this method flawless. Furthermore, polyurethane foams can release toxic compounds like hydrogen cyanide, carbon monoxide and nitrogen oxides and during thermal degradation under aerobic conditions.