Over the past few years, the European Chemicals Agency (ECHA) has identified several cyclic siloxanes – and, most recently, further linear siloxanes – as substances of high concern. BYK deploys its regulatory expertise to ensure full compliance with regulatory provisions, and it supports customers in every phase of this transition. The aim is to offer safe product alternatives that correspond to the needs of the market.
Silicone-based products can contain cyclic and linear siloxane oligomers which may have an impact on the classification and labelling of the products. Since June 2018, ECHA has identified the following cyclic siloxanes as substances of very high concern (SVHC): D4 (octamethylcyclotetrasiloxane, CAS 556-67-2), D5 (decamethylcyclopentasiloxane, CAS 541-02-6), and D6 (dodecamethylcyclohexasiloxane, CAS 540-97-6).
Cyclic siloxanes
At BYK, the Research and Development department and the Regulatory department tackled these new challenges at a very early stage, developing purified alternative silicone products with a residual D4, D5, and D6 content of less than 0.1% respectively to ensure their safe use in all formulations. What is meant by “purified”? By adding a further step to the process of producing silicones, the cyclic D4, D5, and D6 siloxane content is reduced to less than 0.1% respectively. BYK is thus able to offer alternative additives with a cyclic siloxane content of less than 0.1%.
Linear siloxanes
ECHA recently carried out new SVHC classification for linear siloxanes. L3 (octamethyltrisiloxane, CAS 107-51-7) was added to the EU-REACH list of SVHC candidates on January 21, 2025. L4 (decamethyltetrasiloxane, CAS 141-62-8) followed on June 25, 2025. The classification of these linear siloxanes is based on their very persistent and very bioaccumulative (vPvB) properties.
BYK is monitoring regulatory developments very closely and has initiated comprehensive analytical testing for the entire portfolio of silicone-based products. In anticipation of the possible future classification of L5 (dodecamethylpentasiloxane, CAS 141-63-9) and L6 (tetradecamethylhexasiloxane, CAS 107-52-8) as SVHC, these substances have also been included in the scope of the testing.
As a consequence of its findings, BYK has updated the EU safety data sheets for BYK-345, BYK-348, BYK-349, BYK-3455, BYK-3456, BYK-L 9520, and further LP products. The first such forward-looking new development recently launched on the market was BYK-3459 (a purified version of BYK-349), and it is available as an alternative with reduced linear siloxane content.
Based on the assumption that ECHA will consider L5 and L6 for forthcoming SVHC classification, BYK continues to analyze its product portfolio proactively, including linear siloxanes such as L5 and L6, in order to meet any future requirements.
News | September 17, 2025
