Tar, wood

Surface tension

Description of key information

The surface tension of an aqueous solution of Tar wood was determined as
60.24 ± 0.15 mN/m at 19.9 °C.
One measurement was performed for verification (after 67 minutes). No significant changes
and thus no significant dependence on time were observed.
As the mean of all measured values was higher than 60 mN/m Tar wood was classified as not surface active.
The surface tension of the negative control lay within the accepted range.
The concentration was determined with 510.78 mg test item/L (based on analysis of dissolved
organic carbon in the test solution).

Key value for chemical safety assessment

Surface tension:

60.24

in mN/m at 20°C and concentration in mg/L:

510.78

Additional information

The study was performed in order to determine the surface tension of an aqueous solution

of Tar wood. The method was based on the measurement of the force which was necessary

to exert vertically on plate, with an edge in contact with the surface, in order to draw

up the film that has formed. Surface tension of water may be influenced by substances

which form micelles, such as tensides (= surfactants), or alcohols.

During the specified period of time, no relevant changes in the surface tension were detected.

Values between 59.84 and 60.38 mN/m were recorded showing no relevant variations.

As the mean determined surface tension of all measured values of Tar wood was

higher than 60 mN/m, the test item can be classified as not surface active.

Literature value for the surface tension of H2O at 19.5 °C: 72.83 mN/m (taken from Vargaftik

et al., “International Tables of the Surface Tension of Water”, J. Phys. Chem. Ref.

Data 12, 817, 1983).

The surface tension of the negative control was determined with 72.86 mN/m at 19.3 °C,

therefore showing a difference of 0.04 % from the stated literature value. The difference

lies within the accepted range of 1 % deviation from literature value.

The values of the single determinations of the aqueous solution of the test item show no

relevant difference (0.42 %). All measured values scattered around the threshold for surface

tension (60 mN/m) which is stated in the guidelines. From the 20 individual measurements,

a mean value of 60.12 mN/m was calculated. The corresponding standard deviation

0.18 mN/m corresponds to a relative standard variation of 0.30 %. The mean lies a

little above the threshold which is given in the guidelines.

Therefore, the result of the test is considered valid and the test item Tar wood is classified

as “not surface active” in a concentration of 510.78 mg/L

The surface tension of the negative control was determined with a difference of 0.04 %

from the stated literature value.