Depolymerisation of polyurethane and polyisocyanurate foams with diethylene glycol and tall oil-based polyols

Polyurethane (PU) foams have been widely used for decades in various applications – thermal insulation, aerospace industry, furniture, automotive industry, and many other both domestic and industrial fields. This high demand for PU products, naturally, increases the waste amount, therefore effective recycling methods must be explored. Depolymerisation of PU foams by glycolysis is already being performed at an industrial level, but novel recycling methods should be investigated since several industrial methods might be limited in the future due to the negative impact of petrochemical reagents on the environment. Addition of polyols based on tall oil fatty acids (TOFA) and epoxidized tall oil fatty acids (ETOFA) can be equally effective in depolymerisation process, also emphasizing renewable product utilization for such actions. In this study we performed depolymerisation of four different PU and polyisocyanurate (PIR) foams which were produced from both bio-based and petrochemical polyols with different isocyanate indexes. Firstly, recycled polyols were obtained through glycolysis with diethylene glycol (DEG), and further achieved to depolymerise foams with addition of TOFA- and ETOFA-based polyols. The results showed that, for example, recycled polyols from foam 110bio (made from bio-based polyols with isocyanate index of 110) with zinc acetate as catalyst had OH value of 607 mgKOH/g and viscosity 2309 mPa·s, but recycled polyol obtained by partially substituting DEG with ETOFA-based polyol had OH value 450 mgKOH/g and viscosity above 35000 mPa·s. Separation into two phases was observed for several recycled polyols depolymerised with TOFA-based polyols. Our results demonstrate that depolymerisation of PU foams could be done by substituting DEG with ETOFA-based polyols, the resulting end-products have higher viscosity, which must be taken into account when using it for further applications.