Probing the combustion and pyrolysis behaviors of polyurethane foam from waste refrigerators

Polyurethane foam (PUR) from waste refrigerators has long been recognized as a difficult-to-treat electronic waste, due to its bulkiness, low weight and chlorofluorocarbon content. In this work, the combustion and pyrolysis behaviors of PUR were investigated using a versatile thermogravimetric-Fourier infrared spectrum-mass spectrum (TG/FT-IR/MS) technique. The decomposition mechanisms in both thermal processes were determined, and the fate of halogens was probed well. TG analysis indicated that the PUR combustion could be divided into three main stages with peak temperatures of 328, 557 and 970 degrees C, respectively. As a comparison, its pyrolysis could be divided into two steps with peak temperatures of 332 and 970 degrees C. FT-IR results indicated that the PUR combusted vigorously at 400-600 degrees C, whereas it decomposed drastically at the lower temperature of 200-400 degrees C in pyrolysis. MS analysis revealed that the urethane bonds in the PUR molecules broke into isocyanates and polyols at 200-400 degrees C in combustion, which further decomposed at 400-650 degrees C and reacted with halogens. However, the ester bonds ruptured into aromatic nitro compounds and ethers at 200 degrees C below in pyrolysis. At higher temperature range of 200-500 degrees C, more halogenated derivatives were detected with lower intensity. In addition to the halogenated products such as chlorofluorocarbons, chlorobenzene, dichlorobenzene, o-chloroaniline, and trifluoroacetone, small molecules of hydrogen cyanide, ammonia, carbon dioxide, carbon monoxide were all detected.