Three siloxanes to be restricted in Europe

On January 11, 2018, ECHA, as requested by the European Commission, included dodecamethylcyclohexasiloxane (D6) in a previous restriction intent of octamethylcyclotetrasiloxane (D4) and Decamethylcyclopentasiloxane (D5) submitted on 13 April 2017.

Octamethylcyclotetrasiloxane (D4)

Decamethylcyclopentasiloxane (D5)

Dodecamethylcyclohexasiloxane (D6)

The scope of the restriction is that leave-on personal care products and other consumer/professional products (e.g. dry cleaning, waxes and polishes, washing and cleaning products) containing D4/D5/D6 in concentrations > 0.1% shall not be placed on the market. In addition, wash off and rinse off cosmetic products containing D6 in concentrations > 0.1% shall not be placed on the market.

The last part will complement the previous Commission Regulation (EU) 2018/35 of 10 January 2018 amending Annex XVII to Regulation (EC) No 1907/2006 of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) as regards octamethylcyclotetrasiloxane (‘D4’) and decamethylcyclopentasiloxane (‘D5’) shall not be placed on the market after 31 January 2020 in wash-off cosmetic products in a concentration equal to or greater than 0.1 % by weight of either substance.

Restricted because of their hazardous properties as a PBT and a vPvB substance in the case of D4 and as a vPvB substance in the case of D5 in accordance with Annex XIII of the REACH Regulation. Annex XVII is the REACH Restriction List. Background document for restriction of D4 and D5.

The chemical and physical properties differ between the three siloxanes (see table).

Properties D4 D5 D6
EC No. 209-136-7 208-764-9 208-762-8
CAS No. 556-67-2 541-02-6 540-97-6
Molecular formula C8H24O4Si4 C10H30O5Si5 C12H36O6Si6
Molecular mass 296.62 370.77 444,92
Melting/freezing point (oC) 17.7 -38 -3
Boiling point                     (oC at 1 atm) 175 210 245
Relative density             (20-25 oC, water = 1) 0.95 0.96 0.98
Vapor pressure               (Pa, 25 oC) 132 33.2 4.7
Partition coefficient       (24 oC, log Pow) 6.49 8.02 8.87
Water solubility               (23 oC,  pH 7, ppb, µg/L) 56 17 5.13


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