Recycling biobased polyurethane foams: Efficient dual recovery of polyols and diamines via hydrothermal liquefaction

With a growing emphasis on sustainability and reducing petroleum reliance in polyurethane production, lignin is emerging as a promising petrochemical substitute. However, recycling strategies that are readily adaptable for recovering products of petrochemical and biobased origin remain unexplored. This study for the first time explores hydrothermal liquefaction (HTL) as a means of recovering polyol blends consisting of petroleum as well as lignin-based components along with diamines from polyurethane foams (PUF). The initial optimisation was carried out using petroleum-based PUFs, which resulted in a recovery of 90 wt% of the polyol and 79 wt% of the diamine at optimised conditions (250 °C, 7.5 min, 0.02 M NaOH). Identical physical properties were achieved for PUFs reformulated from the recovered petroleum-based polyols. The elimination of downstream waste treatment was demonstrated through the reuse of the aqueous phase, which did not compromise the product recovery or its chemical characteristics. HTL of lignin-based PUF, consisting of petroleum-based and lignin-based polyols, resulted in a polyol recovery of 93 wt% and a diamine recovery of 74 wt%. The petroleum fraction was unaltered; however, minor modifications in the lignin monomer composition were observed. The reformulated biobased PUF indicated comparable properties to the virgin material, apart from compression behaviour. The underlined work improves the understanding of the recycling process of lignin-based PUFs, paving the way for more sustainable recycling processes. • Optimised polyurethane depolymerisation at 250 °C, 7.5 mins and 0.02 M NaOH • Recovered 90–93 % polyol and 74–79 % diamines for bio and petro PUs • Demonstrated the reuse of the diamine-rich aqueous phase • Reformulated petro-PUs showed physical properties matching the virgin material • Reformulated bio-PUs showed minor changes vs virgin material at full substitution