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Physical & Chemical properties

Surface tension

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Endpoint:
surface tension
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
the study does not need to be conducted because based on structure, surface activity is not expected or cannot be predicted
the study does not need to be conducted because surface activity is not a desired property of the material

Description of key information

Triallyl cyanurate is not expected to form micelles based on its molecular structure. The measured surface tension of the test substance is 52.9 mN/m. This value is above the assessment value of the Federal Environmental Agency, Germany (50mN/m) and above the international trade tariff value for detergents of 45 mN/m. Considering these conventions, physico-chemical effects like forming of emulsions and/or microemulsions and/or micelles, and adsorption at water-solid interfaces in a relevant extent are not expected. Therefore, the definition for surfactant according to the detergents regulation (EU Directive 648/2004), which has been cited in the REACh guidance document R.7a is not met. In conclusion, it can be stated that based on structural properties and experimental data the surface tension is not a relevant physico-chemical property and has not to be considered in further physico-chemical or environmental tests with Triallyl cyanurate. Accordingly, physico-chemical properties like the measurement of the octanol/water partitioning coefficient are considered reliable and determination of the critical micelle concentration would not be appropriate to refine these results.

Key value for chemical safety assessment

Additional information

Triallyl cyanurate does not contain surface active groups like hydrophilic groups (e.g. –SO3‾, -SO4‾, -(OCH2CH2)n, -N+(CH3)3 ) and a hydrophobic tail (e.g. linear or branched alkyl chain). According to EU Directive 648/2004 (Article 2 (6)): Surfactant means any organic substance and/or preparation used in detergents, which has surface active properties and which consists of one or more hydrophilic and one or more hydrophobic groups of such nature and size that it is capable of reducing the surface tension of water, and of forming emulsions and/or microemulsions and/or micelles, and of adsorption at water-solid interfaces.

The REACh guidance document, chapter R.7a ((Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7a: Endpoint specific guidance, version 6.0, July 2017) also cites this definition. A comparable definition of surface active substances can be found in the REACh guidance document chapter R.7c (Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7c: Endpoint specific guidance, version 3.0, June 2017) and Tolls and Sijm, 2000: A substance is surface active when it is enriched at the interface of a solution with adjacent phases. Surfactants consist of an apolar and a polar moiety, which are commonly referred to as the hydrophobic tail and the hydrophilic headgroup, respectively. According to the charge of the headgroup, surfactants can be categorised as anionic, cationic, non-ionic or amphoteric (Tolls and Sijm, 2000) [Tolls J and Sijm (2000) Estimating the properties of surface-active chemicals. In Boethling and Mackay (Eds.) Handbook of property estimation methods for chemicals, Lewis Publisher].

The structure of the test substance Triallyl cyanurate with symmetrical short residues, does not reveal a hydrophilic headgroup and a hydrophobic tail, like it is observed for detergents. The ability to form different zones of hydration is not given by the molecule structure. The formation of the apolar and a polar part in the molecule does not seem to be likely for the completely symmetrical molecule structure of Triallyl cyanurate. Assymetrical side chains would promote the emergence of an apolar and polar moiety in the molecule, but this case is not given for the test substance. Physico-chemical effects like formation of emulsion or micelles in a relevant extent are not expected. Therefore, based on the molecular structure, Triallyl cyanurate is not predicted to be a surfactant and is not expected to form micelles.

A study on the surface tension of Triallyl cyanurate is available according OECD 115 (ring test). In this test the surface tension of Triallyl cyanurate was measured with 52.9 mN/m. Different trigger values for surface tension have been described. In the REACh guidance document, no regulatory numerical value is given for the physico-chemical endpoint surface tension. In the guideline OECD 115 (adopted 1995) no trigger value has been defined as well. The EU Method A.5 (Surface Tension) interprets results < 60 mN/m as having surface-active properties.

In a publication of staff of the Federal Environmental Agency, Germany a surface tension above 50 mN/m at a concentration of 1 g/l should not be considered as surface active substances [Franke et al. (1994) The assessment of bioaccumulation, Chemosphere 29(7)1501 -1514, 1994].

The European commission (2011) rates a value of 45 mN/m as capable for reducing surface tension, which is cited below:

EUROPEAN COMMISSION, ENTERPRISE AND INDUSTRY DIRECTORATE-GENERAL, Question and agreed answers concerning the correct implementation of Regulation (EC) No 648/2004 on detergents (Version September 2015)

4.6 Which value for the surface tension of water is used in the definition of a surfactant?

Article 2(6) defines the term “surfactant” using a number of criteria, one of which is: “capable of reducing the surface tension of water”. However, many detergent ingredients are capable of reducing surface tension by small amounts, leading to uncertainty concerning the scope of the definition. It was therefore decided that the reduction in surface tension should be quantified, and the international trade tariff value for surfactants of 45 mN/m was chosen. Reduction of surface tension is only one part of the definition of surfactants, however, and there must also be an ability to form adsorption monolayers. Consequently, substances which are capable of reducing surface tension below 45 mN/m, but which do not form adsorption monolayers (for example alcohols or acetic acid) are not to be regarded as surfactants with the meaning of the Detergents Regulation.

 

Based on the answer of the European Commission, surfactants have a surface tension <45 mN/m and must have the ability to form adsorption monolayers. Considering that no surface active groups are available in the molecule Triallyl cyanurate, surface activity like forming of micelles cannot be expected only based on the value of surface tension. For example many solvents like ethanol, methanol etc. data of surface tension are far below 60 mN/m (Ethanol: 22.55 mN/m, Acetone: 23.30 mN/m, cited in Wikipedia) nevertheless forming of micelles of these substances cannot be expected due to missing surface active groups in the molecule itself. Therefore, Triallyl cyanurate does not fulfil the definition of surfactants in the detergents regulation EU Directive 648/2004.

Overall, the measured surface tension of Triallyl cyanurate (52.9 mN/m) is above the international trade tariff value for surfactants of 45 mN/m and the assessment value of 50 mN/m of Federal Environmental Agency, Germany. Considering these conventions, physico-chemical effects like forming of emulsions and/or microemulsions and/or micelles, and adsorption at water-solid interfaces in a relevant extent are not expected.

In conclusion, the definition of a surfactant according to the detergents regulation (EU Directive 648/2004), which has been cited in the REACh guidance document, is not fulfilled for Triallyl cyanurate. Therefore, it can be stated that based on structural properties and experimental data the surface tension is not a relevant physico-chemical property which has not to be considered in further physico-chemical or environmental tests with Triallyl cyanurate. Accordingly, physico-chemical properties like the measurement of the octanol/water partitioning coefficient are considered reliable and determination of the critical micelle concentration would not be appropriate to refine these results.