Toward chemical recycling of PU foams: study of the main purification options.

The recovery of the polyol component, after glycolysis of polyurethane (PU) foams coming from automotive waste, was investigated. Several separation methods such as simple sedimentation, centrifugation and liquid-liquid extraction, eventually preceded by an acid washing step, were tested. The obtained fractions were characterized by infrared spectroscopy and CHN elemental analysis. Furthermore, multivariate data analysis was carried out on the infrared spectra by principal component analysis to classify the fractions based on purity. IR spectroscopy coupled with principal component analysis was able to estimate the success of the separation and eventual culprits such as contaminations, which were then quantified by CHN elemental analysis. This approach addresses some critical limitations associated with classical analytical techniques such as NMR, TGA, GPC, MALDI-TOF that often require an extremely accurate separation of the depolymerized product fractions. Moreover, IR spectroscopy and CHN elemental analysis techniques are cheap and widespread in standard materials science laboratories. At last, based on the results of the analysis of the regenerated polyol fractions, and on the foaming tests, considerations were made to guide the choice of the purification method according to the application specifications and greenness.