CHEMICAL RECYCLING OF VISCOELASTIC POLYURETHANE FOAMS VIA AVIDOLYSIS

The purpose of this work is to recycle a waste flexible viscoelastic polyurethane foam through acidolysis, an innovative way of chemical recycling. The foam undergoes a high temperature dissolution in the same polyol used for its production, then the obtained mixture reacts with a dicarboxylic acid which breaks the polymeric chains and converts urethane, urea, amine, and isocyanate functional groups to amides. The resulting product is a polyol-like liquid with a low hydroxyl value, that can replace, at an appropriate percentage, the virgin polyol mixture in the production of a new viscoelastic foam. In a first step, many acidolysis screening tests were performed varying temperature, foam to polyol ratio and foam to acid ratio, while keeping constant the reaction time, aiming on finding the suitable operative conditions which ensure reasonable physico-chemical properties of the product. Six different dicarboxylic acids were evaluated on the performance level: oxalic, fumaric, terephthalic, adipic, tartaric and succinic acid. Once proved that succinic acid was the best performing one, the range of the operative variables was selected and the Design of Experiments (DoE) approach was successfully applied to find the best operative point for the process, which should provide satisfying product properties while maintaining a high waste to raw materials ratio. The choice of the abovementioned operative point is constrained to the restricted value of free aromatic amines content in the acidolysis product. In particular, the concentration of 4,4’-methylenedianiline (MDA), a harmful by-product formed in the process and deriving from the use of 4,4’-methylene diphenyl diisocyanate (MDI), must be below the legal limit of 1000 ppm. Finally, new foams were produced using an increasing amount of recycled polyol, and their structural and mechanical properties were evaluated, leading to the result that mechanical properties benefit from the use of maximum 25% of recycled polyol by weight.