Airborne thermal degradation products of polyurethane coatings in car repair shops

A methodology for workplace air monitoring of aromatic and aliphatic, mono- and polyisocyanates by derivatisation with di-n-butylamine (DBA) is presen ted. Air sampling was performed using midget impinger flasks containing 10 ml of 0.01 mol l(-1) DBA in toluene and a glass-fibre filter in series afte r the impinger flask, thereby providing the possibility of collecting and d erivatising isocyanates in both the gas and particle phases. Quantification was made by LC-MS, monitoring the molecular ions [MH](+). Air samples take n with this method in car repair shops showed that many different isocyanat es are formed during thermal decomposition of polyurethane (PUR) coatings. In addition to isocyanates such as hexamethylene (HDI), isophorone (IPDI), toluene (TDI) and methylenediphenyl diisocyanate (MDI), monoisocyanates suc h as methyl (MIC), ethyl (EIC), propyl (PIC), butyl (BIC) and phenyl isocya nate (PhI) were found. In many air samples the aliphatic monoisocyanates do minated. During cutting and welding operations, the highest levels of isocy anates were observed. In a single air sample from a welding operation in a car repair shop, the highest concentrations found were: MIC, 290; EIC, 60; PIC, 20; BIC, 9; PhI, 27; HDI, 105; IPDI, 39; MDI, 4; and 2,4-TDI and 2,6-T DI 140 mu g m(-3). Monitoring the particle size distribution and concentrat ion during grinding, welding and cutting operations showed that ultrafine p articles (< 0.1 mu m) were formed at high concentrations. Isocyanates with low volatility were mainly found in the particle phase, but isocyanates wit h a relatively high volatility such as TDI, were found in both the particle and gas phases.