HDI oligomers, isocyanurate

Endpoint summary

Additional information

Overall conclusion on environmental fate:

The only relevant pathway for the substance to enter the environment is water. Volatilisation does not play a significant role due to the low vapour pressure.

In water, the key property of Hexamethylene diisocyanate, oligomerisation product (isocyanurate type) is the rapid hydrolysis within less than 3 h at ambient temperature. Within a half life of 7.7 hours, isocyanate groups are hydrolysed. If released to waste water, the substance is decomposed prior to reaching a STP. Hydrolysis products are non-soluble and inert polymeric and oligomeric ureas. Exposure to soil with the substance is therefore not possible. If sludge from the STP is applied to agricultural soil, it does not contain the substance but only the inert ureas.

Detailed conlusions

Stability (hydrolysis):

In a screening test at 50°C the HDI Trimer was found to hydrolyse by 84 – 89% within less than 1 hour at pH values of 4, 7, and 9 (Bayer Industry Services, 2007). Approximate mean half lives of 3 hours at 25°C were estimated at any pH and environmental relevant temperatures. A theoretical possible hydrolysis product based on the hydrolysis of the 3 Isocyanate groups to the corresponding amine functions has been discussed (BIS, 2007).

Based on the determination of the Isocyanate function, the half-time of HDI Trimer in the the acetonitrile/water solution is approx. 7.7 hour at room temperature (23 °C) (Bayer AG, 1999). Hydrolysis products have not been elucidated. However similar substances containing several isocyanate groups like HDI, MDI are known to react rapidly with water forming insoluble oligomeric and polymeric ureas. The below mentioned corresponding triamine is only a theoretical worst-case assumption in order to have a basis for assessment but which in reality reflects only insignificant traces.

Phototransformation in air:

The atmospheric oxidation rate constant of the main component HDI trimer (Isocyanurat, n=3) of Desmodur N 3300 and Desmodur N 3600 is 37.5 * 10^-12cm³/(molecule *s) and its atmospheric half-life is 10.3 hrs (Currenta, 2014c).

The atmospheric oxidation rate constant of the corresponding triamine of the main component HDI trimer (Isocyanurat, n=3) of Desmodur N 3300 and Desmodur N 3600 is 129.1 * 10^-12cm³/(molecule *s) and its atmospheric half-life is 3.0 hrs (Currenta, 2014d).

Biodegradation (in water, screening test):

Within 28 days, a degradation of 1 % was determined for Desmodur N 3600 in a 'Closed Bottle Test' (Bayer AG, 2001). Both, Desmodur N 3300 and Desmodur N 3600 are regarded as "not readily biodegradable".

Bioaccumulation:

The direct and indirect exposure of the aquatic compartment is unlikely because Desmodur N 3300 hydrolysis completely in water within 8 hours. Therefore the BCF-values were calculated. Bioconcentration factors (BCF) of 141 and 88.7 L/kg wet-wt for the main component HDI Trimer (Isocyanurat, n=3) of Desmodur N 3300 and Desmodur N 3600 and its corresponding triamine were obtained (Currenta, 2014e/2014f).

Even the corresponding triamine of HDI Trimer (Isocyanurat, n=3) with a bioconcentration factor of 88.7 L/kg wet-wt does not have high bioaccumulation potential (Currenta, 202014f). Only minor amounts (ca. 4%) of the hydrolysed substance are soluble in water indicating that bioaccumulation is not expected. 

Adsorption / desorption:

The QSAR determination of the carbon partition coefficient for the main component HDI Trimer (Isocyanurat, n=3) of Desmodur N 3300 and Desmodur N 3600, 1,3,5-Triazine-2,4,6(1H,3H,5H)-trione,1,3,5-tris(6-isocyanatohexyl)- (CAS 3779-63-3) using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v4.11 revealed values of 1.843*10⁰⁶ L/kg (logKow method) and 1.311*10⁰⁷L/kg (MCI method) for the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program (Currenta, 2014g). The organic carbon partition coefficient (Koc) of the corresponding diamine, 1,3,5-Triazine-2,4,6(1H,3H,5H)-trione,1,3,5-tris(6-aminohexyl)- was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v 4.11. The Koc was estimated to be 6891 L/kg (logKow method), and 82300 L/kg (MCI method). The results relate to the unaffected molecule of the substance as any decomposition (e.g. hydrolysis) of the substance is not taken into account by the program (Currenta, 2014h).

Volatilisation

With a vapour pressure of <0.0001 hPa volatilisation of the substance is unlikely.

Distribution modelling

HDI Trimer hydrolyses rapidly in the presence of water yielding a complex mixture of oligomeric and polymeric urea derivatives which are non-soluble in water. Due to the rapid hydrolysis of HDI Trimer, a transport of the substance between environmental compartments is unlikely. Consequently, a calculation of the distribution between the environmental compartments according to the Mackay fugacity model level 1 or 3 is not suitable.