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EC number: 218-485-4
CAS number: 2162-73-4
Information from a variety of sources has
been collected and summarized to facilitate an overview of the
atmospheric fate and potential environmental effects of emissions of
methylenediphenyl diisocyanate (MDI) or the read across approach to
toluene diisocyanate (TDI) to the atmosphere (Tury et.al., 2004).
Atmospheric emissions of both MDI and TDI are low, both in terms of
concentration and mass, because of their low volatility and the need for
careful control over all aspects of their lifecycle from manufacture
through disposal. Typical emission losses for TDI are 25 g/t of TDI used
in slabstock foam production. MDI emission losses are lower, often less
than 1 g/t of MDI used. Dispersion modeling predicts that concentrations
at the fenceline or beyond are very low for typical releases. Laboratory
studies show that TDI (and by analogy MDI) does not react with water in
the gas phase at a significant rate. The primary degradation reaction of
these aromatic diisocyanates in the atmosphere is expected to be
oxidation by OH radicals with an estimated half-life of one day.
Laboratory studies also show that this reaction is not expected to
result in increased ground-level ozone accumulation.
Experiments were carried out with a variety
of TDI concentrations at 27 °C and relative humidity 7–70% in a 17-m³,
Teflon-lined environmental chamber. Atmospheres were monitored for TDI
(by several methods), TDA, TDA-urea, organic carbon, and total bound
nitrogen, and for presence of aerosols. A significant TDI loss rate was
observed, which was matched by an equal loss of organic carbon and
nitrogen, indicative of physical removal from the gas phase by
deposition onto the chamber’s walls rather than chemical conversion. No
evidence for a gas-phase reaction with water vapor was found, and no TDA
or ureas were detected.
Overall, the study clearly indicated
degradation by photolytically generated radicals, rather than by direct
photolysis, and the absence of any hydrolysis in the vapor phase.
A substantial loss rate of TDI caused by
adsorption onto the walls was again observed.
Irradiation substantially increased the loss
rate. The incremental loss caused by irradiation was not affected by the
presence of common urban pollutants: hydrocarbon mixtures, NH3, and
ammonium sulfate aerosol. It was enhanced by the presence of relatively
high concentrations of diazabicyclooctane (DABCO, a PU catalyst) but was
suppressed by nitric oxide, a free radical scavenger. No TDA was
detected in any experiment, corresponding to less than 0.05% conversion
of TDI. Overall, the study clearly indicated degradation by
photolytically generated radicals, rather than by direct photolysis, and
the absence of any hydrolysis in the vapor phase.
The degradation of most trace organic gases
in the atmosphere is initiated by reaction with OH radicals, themselves
generated photochemically. This was confirmed as the dominant process
for TDI by a study of the degradation rate of 80/20 TDI in a large
photoreactor, at ambient temperature and pressure, in the presence of
photolytically generated OH radicals. The reaction rate of TDI with OH
radicals, measured relative to that of toluene, was estimated as≥7.4
x 10E12 cm³/molecule/ sec.
Both isomers of TDI were found to inhibit
ozone formation and radical levels in all experiments. An 18-hr
irradiation showed that the ozone inhibition effects extended over at
least two days. The prediction is made, that TDI is unlikely to have a
positive effect on ozone formation under any atmospheric conditions in
the United States, and it should not be considered an ozone precursor.
This atmospheric degradation of MDI and TDI
by OH radicals raises concerns that the process might lead to ozone or
smog formation. Smog chamber studies have shown that this is not the
case. TDI, in particular, should not be considered an ozone precursor.
Overall, it can be concluded that no
significant long-term or wide-ranging environmental effects would be
expected from current emissions of MDI or TDI to air.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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