Biodegradability of crude glycerol-based polyurethane foams during composting, anaerobic digestion and soil incubation
Abstract In this study, the biodegradability of polyurethane (PU) foams made from crude glycerol- and petroleum-based polyols was compared during composting, anaerobic digestion (AD), and soil incubation. Chemical changes in the PU foams before and after composting were further analyzed using Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Evolved Gas Analysis–Mass Spectrometry (EGA–MS), and Fourier Transform Infrared Spectroscopy (FT-IR). The results showed that during composting, AD, and soil incubation conditions, none of the PU foams were mineralized more than 10%. PU foams made from 100% crude glycerol-based polyols were mineralized during 320 days of soil incubation at rates faster than those observed for the petroleum-based analogs. However, no significant differences in soil mineralization rates were observed between PU foams made from blend polyols, which contained 50% crude glycerol-based polyols and 100% petroleum-based polyols. SEM analysis showed that some surface deterioration occurred in the PU samples made from bio-based and blend polyols during composting. Minor differences were observed in the TGA curves of the PU foams made from petroleum-based polyols before and after composting and pronounced differences occurred in PU foams made from both crude glycerol-based and blend polyols in the thermal regions of urethane and ester segments. In terms of EGA–MS analyses, the major degradation of PU foams made from crude glycerol-based and blend polyols was attributed to the decomposition of FAMEs and fatty acid chains in the polyol side of the polymer. FT-IR analysis showed that little degradation of urethane and ester segments of the polymer occurred during composting of petroleum-based PU foam. FT-IR analysis of PU foams made from 100% crude glycerol-based polyols revealed that the ester segments (–COO–) of the material were the preferred sites of microbial attack. The PU foams made from blend polyols showed some structural changes in urethane linkages (–NHCOO–) but degradation was more noticeable in the ester segments (–COO–) of the polymer, similar to that observed for 100% bio-based polyols.