Comparison of different solvolysis processes for the chemical recycling of rigid polyurethane foams

The aim of this work is to apply different solvolysis techniques (glycolysis and aminolysis) to chemically recycle rigid polyurethane foams. The purpose is to find the best method in order to obtain polyol with good characteristics to use for the production of new rigid expanded polyurethane foams. Those qualities are explored through a characterization of the final product, investigating its viscosity, hydroxyl number, FT-IR spectrum and content of 4,4’-methylenedianiline (MDA). MDA is a carcinogenic aromatic amine and a harmful by-product formed in the process and deriving from the use of 4,4’-methylene diphenyl diisocyanate (MDI), and must be below the legal limit of 1000 ppm. In the first part are presented the glycolysis tests, and then the aminolysis tests performed usually with a glycol as solvent. Then, there is the optimization part and the comparison with pure glycolysis. The addition of polyethylene terephthalate can reduce the amine content and the viscosity of the final product, so there is a comparison between the glycolysis with both wastes together and a new pathway in which a fast glycolysis of polyethylene terephthalate is followed by an aminolysis of polyurethane conducted at lower temperature. Finally, with the optimized product from those different chemical recycling methods, the new foams produced using an increasing amount of recycled polyol are presented with the evaluation of their structural, mechanical and insulating properties. The result is that these properties benefit from different percentages of recycled polyol depending on the method used: 50% with aminolysis, 75% with the addition of polyethylene terephthalate with both pure glycolysis and 2-steps glycolysis and aminolysis.