Microwave-Assisted Depolymerization of Polyurethane and Polyisocyanurate Foams with Diethylene Glycol and Epoxidized Tall Oil-Based Polyol

Polyurethane (PU) foams have been widely used for decades for various applications, and this high demand for PU products, naturally, increases the amount of waste; therefore, effective recycling methods must be explored. Depolymerization via glycolysis has already been performed on an industrial scale with different glycols. Meanwhile, our research focuses on the incorporation of epoxidized tall oil-based (ETOFA) polyol into the depolymerization process. Even though glycolysis does not require harsh conditions, novel depolymerization methods should still be investigated, focusing on shortening reaction time, for example, microwave (MW)-assisted reaction. In our research, four PU and polyisocyanurate (PIR) foams from bio-based and petrochemical polyols with different isocyanate indexes (110 and 400) were depolymerized with diethylene glycol (DEG) and epoxidized tall oil fatty acids/diethanolamine (ETOFA/DEOA) polyol. MW-assisted depolymerization was achieved within 5–10 min under the tested conditions, while conventional depolymerization required up to 5.5 h. Recycled polyols obtained with DEG showed OH values of 542–619 mg KOH/g, while partial substitution of DEG with ETOFA/DEOA resulted in lower OH values of 320–450 mg KOH/g, reflecting the lower OH value of the ETOFA/DEOA polyol. Incorporation of ETOFA/DEOA increased the viscosity of the recycled polyols, which should be considered for further processing.