Chemical recycling of rigid polyurethane foams containing phosphorus and chlorine-based flame retardants

The purpose of this work is to evaluate the effect of flame retardants on the glycolysis parameter during the chemical recycling of rigid polyurethane foams. Particularly phosphate and chlorinated retardants, which are commonly used in the manufacturing processes to increase the flame-resistance properties of the artifacts. At first, three different foams were produced: a reference one without any flame retardant and the two others with triethyl phosphate (TEP) and tris(1-chloro-2-propyl) phosphate (TCPP). Foams were then recycled through glycolysis using the same operating conditions but changing catalyst type and concentration. Potassium acetate turned out to be more effective than titanium butoxide, which resulted in a product with lower polyurethane degradation and higher molecular weight. The glycolysis of the reference foam without flame retardants generated a high quantity of free aromatic amines, namely 4,4’-methylenedianiline (MDA), a carcinogenic by-product obtained during the glycolysis of PU due to the utilization of 4,4’-methylene diphenyl diisocyanate (MDI) during the foam production phase. The TEP-containing one had slightly fewer amines due to a deaminating effect of the flame retardant, however, their concentration was still far higher than the labelling legal limit of 0.1% by weight. The TCPP contained in the third foam had a stronger effect on both amines’ concentration’s reduction and catalyst activity since it can release hydrochloric acid, which neutralized both MDA and KOAc; in fact, its reaction with the catalyst yielded a precipitate, potassium chloride. Therefore, recycling a foam with TCPP resulted in a highly viscous product with a lower amine concentration; thus, a large excess of catalyst was needed to further increase foam degradation and reduce the product’s viscosity. At last, all the glycolyzates required a deamination process to meet the safety standards; however, only the foam with TEP produced a polyol mixture with MDA content below the legal limit. Whereas the other two cases led to products with high viscosity, thus, a complete amine abatement could be performed. Finally, new foams were produced and characterized by increasing the percentage of recycled polyol. Results showed that compression resistance increased with the percentage of recycled polyol, whereas fire resistance was lost due to the consumption of flame retardants during the chemical recycling process.