Chemical recycling of polyurethane adhesives through acidolysis process

The purpose of this work is to chemically recycle two different polyurethane adhesives (namely Duditerm PU 115 and Duditerm PU 127/5) via acidolysis, using succinic acid as cleavage agent. As the first step of this study, determinations of the optimal reaction time and temperature, as well as suitable ranges of polyurethane to acid and polyurethane to polyol ratios, were performed. These analyses were then followed by a Design of Experiment, which was carried out to determine the best operative conditions to be used to recover a recycled product with satisfying properties, while using a content of polyurethane scraps as high as possible. The variables considered during the Design of Experiment procedure were: operating temperature, polyurethane to acid ratio and polyurethane to polyol ratio. The polyurethane wastes are first dissolved at high temperature with a stabiliser in a suitable polyol, subsequently this mixture reacts with the dicarboxylic acid, which reacts with the urethane bonds producing a polyol blend. The acidolysis products were also analysed to determine their aromatic amines content, since, due to their harmfulness, a legal limit must be respected. Specifically, the 4,4’- methylenedianiline content must be lower than 1000 ppm. Finally, new adhesives were produced using an increasing content of recycled polyol. The properties and performances of the recycled polyurethanes were then evaluated and compared with the virgin ones. These tests showed that the Duditerm PU 127/5 produced using up to 16.5%w of recycled polyol has comparable mechanical properties to the virgin material, while the Duditerm PU 115 benefits from the use of the acidolysis products up to 27.5%w, even displaying a higher stability of the adhesive in the gluing phase when compared to the virgin PU.