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Vapour pressure

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Description of key information

Vapour pressure at 20 °C and 25 °C:

VP at 20 °C > 5.087 × 10-5 Pa

VP at 25 °C > 7.476 × 10-5 Pa.

The highest vapour pressure value is likely that of propylene glycol, but the test method used (Knudsen effusion method) does not allow to measure it in presence of other components.

Key value for chemical safety assessment

Additional information

OECD guideline 104 - Knudsen effusion method.

The vapour pressure is calculated by the software of the Vapor Pressure Analyzer applying the Hertz-Knudsen relation with correction factors that depend on parameters of the apparatus.

Due to the nature of test substance, i.e. composed by 3 components with different volatility, 3 tests were run in different temperature ranges.

Test 1: temperature range 50 - 140 °C (VP determined based on component with the highest MW of 494.77 g/mol):

VP at 20 °C > 5.087 × 10-5Pa

VP at 25 °C > 7.476 × 10-5Pa.

Test 2: temperature range 30 - 60 °C; propylene glycol evaporates in the first stage (90 minutes); no significant evaporation for the other 2 components.

Test 3: temperature range 30 - 48 °C; propylene glycol evaporates in the first stage (120 minutes); no significant evaporation for the other 2 components.

A temperature below 30 °C could not be used, due to limitations of the test method. Test 2 and 3 did not allow to identify a value for VP, as propylene glycol evaporated in the first stage and the other 2 components did not significantly evaporate during all the stages. Test 1 allowed to identify the lowest value for vapour pressure.

The highest vapour pressure value is likely due to propylene glycol, but the test method used (Knudsen effusion method) did not allow to measure it correctly in presence of the other components.

The experimental value of vapour pressure of pure propylene glycol is available in the experimental database of EPISuite v.4.11: VP at 25 °C is 0.129 mmHg, equivalent to 17.2 Pa.

In conclusion, at 25 °C, the vapour pressure is likely due to propylene glycol only, while the contribution of the other 2 components may be considered as negligible.