How do you reformulate silicones for D4, D5 and D6 restrictions?

These steps apply to industrial silicone antifoams, sealants, adhesives and casting compounds placed on the EU or EEA market under REACH Annex XVII entry 70. Under the same entry, D4 and D5 in wash-off cosmetics have been restricted since 31 January 2020, other cosmetics follow after 6 June 2027, and medical devices and medicinal products after 6 June 2031 (EU Regulation 2024/1328, 2024). Other jurisdictions apply their own rules. Whether a derogation fits a product is for your regulatory team.

What do you need before reformulating silicones for the D4, D5 and D6 limits?

Before reformulating a silicone antifoam or sealant for the D4, D5 and D6 limits, you need four things: a list of every silicone raw material with its share by weight, a residual cyclics figure for each raw material, the entry 70 limit that applies to the product's use, and baseline performance data on the current grade.

The raw material list comes from the formula sheet. Include silicone fluids, gums, resins, silicone-treated silica, crosslinkers and any premixed emulsion or masterbatch, because each can carry D4, D5 or D6 as a residue. Intertek notes that D4, D5 and D6 are used as monomers for a large variety of silicone polymers and "can be present at low concentrations in these substances as an impurity" (Intertek, 2024).

The residual figure has to name D4, D5 and D6 separately in mg/kg or percent by weight, because entry 70 sets its limit per substance, not for total cyclics. Grand Ingredients advises that suppliers "should provide sufficient information to support concentration assessments" when their ingredients may introduce restricted cyclic siloxanes (Grand Ingredients, undated web page).

Baseline data on the current grade matters as much as the regulatory data. Record the antifoam's knockdown and persistence, or the sealant's cure, adhesion, hardness and storage behavior, before anything changes, so the new grade has a fixed target to match.

Which silicone antifoams and sealants fall under the D4, D5 and D6 restriction?

Every silicone antifoam and sealant placed on the EU market as a mixture falls under the D4, D5 and D6 restriction in REACH Annex XVII entry 70, but the limit differs by use. The general limit is below 0.1% by weight of each substance after 6 June 2026, and paragraph 6 of the entry sets higher limits for named uses when the cyclics are residues from silicone polymers (EU Regulation 2024/1328, 2024).

The table below shows which entry 70 limit applies to each silicone product and use.

The key row is the first: an antifoam has no residue derogation of its own, so a silicone antifoam mixture must keep each cyclic below 0.1% by weight (EU Regulation 2024/1328, 2024). A sealant keeps the 1% limit only while the cyclics come from silicone polymers and the use is adhesion, sealing, gluing or casting. Paragraph 4(a) separately exempts D4, D5 and D6 placed on the market for listed industrial uses, such as polymer production and the formulation of mixtures; whether a given supply qualifies is a legal question.

Where do D4, D5 and D6 residues in silicone antifoams and sealants come from?

D4, D5 and D6 residues in silicone antifoams and sealants come mainly from the silicone polymers themselves, because the catalysts that build siloxane chains also form short cyclic rings. A Dow Corning patent explains that equilibration catalysts "catalyse both the scission and formation of siloxane bonds and as such cause the formation of short chain cyclic siloxanes" (Dow Corning, 2014).

How much remains depends on the process and on any stripping step after polymerization. The same patent reports that less than 0.5% by weight of its final product is volatile cyclic siloxane impurities such as D4 and D5 (Dow Corning, 2014). A figure like that, given for total cyclics, does not show that each substance is below 0.1%.

Finished silicone products vary widely. FDA scientists found D4, D5 and D6 at 0.5 to 269 µg/g in silicone nipples and D6 at up to 7,030 µg/g in silicone bakeware, which is about 0.7% by weight (Zhang et al., 2012).

In a mixture, the polymer's residue is diluted by everything else in the formula, but dilution may not settle the question for an antifoam. Paragraph 5 lifts the constituent limit only for a silicone polymer on its own or in a mixture derogated under paragraph 6 (EU Regulation 2024/1328, 2024). An antifoam has no paragraph 6 use, so the cautious reading keeps each silicone polymer in it, as well as the finished emulsion, below 0.1% per substance. Confirm that reading with your regulatory team.

How do you reformulate a silicone antifoam or sealant for the D4, D5 and D6 limits, step by step?

The four steps in the answer expand into six actions, from the raw material list to a measured finished product.

1. Calculate the worst case per substance: each raw material's highest declared D4, D5 and D6 times its share by weight, summed.

2. Fix the limit in the formulation brief as a measurable condition: each of D4, D5 and D6 below 1,000 mg/kg in the finished mixture, or below 10,000 mg/kg where paragraph 6(a) applies (EU Regulation 2024/1328, 2024), with a margin you set, such as half the limit (illustrative). For an antifoam, add the same 1,000 mg/kg limit for each silicone raw material.

3. Rank the raw materials by their contribution and replace the largest contributors first with lower-cyclic grades of the same viscosity and function. The general method for substituting a raw material in an existing formulation applies here.

4. Change nothing else in the first trial, so performance changes trace to the new raw material.

5. Measure D4, D5 and D6 in the trial batch by gas chromatography.

6. Run the performance retests against the baseline.

Lubinpla fixes the regulatory limit as a measurable condition in the formulation brief and, from your own data sheets and certificates, sets the substitute raw material candidates and the scope to recheck.

Handle silicone fluids and extraction solvents with the protection in section 8 of each safety data sheet, and dispose of trial batches under section 13 and local waste rules.

How do you measure residual D4, D5 and D6 in a silicone raw material?

Residual D4, D5 and D6 in a silicone raw material are measured by solvent extraction followed by gas chromatography, with each substance quantified separately against its own calibration standard. Two detector choices appear in published work: flame ionization detection, which a Dow Corning patent used on a 30 m DB-1 column (Dow Corning, 2014), and mass spectrometry in selected ion monitoring mode.

The mass spectrometry route is more sensitive. FDA scientists extracted silicone products by pressurised solvent extraction and analysed them by GC-MS in selected ion monitoring mode; their methods reported limits of quantification from 6 ng/g for L3 to 15 ng/g for D6 (Zhang et al., 2012). Either detector can reach a 1,000 mg/kg limit; the choice depends on the matrix and the laboratory.

Ask the laboratory for three things. First, report D4, D5 and D6 as separate values in mg/kg, since the limit is per substance. Second, test the product in the form it is placed on the market, such as the emulsion or the uncured sealant in its cartridge, because entry 70 restricts the mixture as placed on the market. Third, keep samples sealed until analysis, because D4, D5 and D6 are volatile and can evaporate from an open container.

What performance should you retest after a low-cyclic silicone switch?

After a low-cyclic silicone switch, retest the properties the silicone delivers: knockdown and persistence for an antifoam, and cure, adhesion, hardness and storage stability for a sealant, each against the current grade. A lower-cyclic grade can differ from the old one in polymer distribution even at the same viscosity, so equal viscosity on the certificate is not proof of equal performance.

The table below decides whether a reformulated batch can replace the current grade.

The key row is the first: the batch fails unless each cyclic is measured below its limit in the finished mixture. For antifoams, ASTM E2407, a defoamer test for agricultural spray mixtures, was withdrawn in 2024 with no replacement (ASTM, 2024), so a side-by-side test in the plant's own foaming liquid is the practical reference. For sealants, ASTM C920-18(2024) specifies adhesion and cohesion after cyclic movement, adhesion-in-peel, hardness and weight loss, and ASTM C794-18(2022) is the adhesion-in-peel method.

Which mistakes keep reformulated silicones above the D4, D5 and D6 limits?

Six mistakes keep reformulated silicone antifoams and sealants above the D4, D5 and D6 limits; most come from reading a figure that does not match the per-substance limit.

1. Treating a total cyclics figure, such as less than 0.5% by weight of volatile cyclic siloxanes (Dow Corning, 2014), as proof that each substance is below 0.1%.

2. Checking only the silicone polymer instead of the mixture. Paragraph 5 of entry 70 exempts D4, D5 and D6 as a constituent of a silicone polymer on its own, but the antifoam or sealant made from it is a mixture with its own limit (EU Regulation 2024/1328, 2024).

3. Assuming the 1% sealing derogation covers every silicone product. Paragraph 6(a) names adhesion, sealing, gluing and casting only, and applies only to residues from silicone polymers.

4. Relying on one declaration for all lots. Residual cyclics differed widely between silicone products in the FDA study (Zhang et al., 2012), so ask for values per lot and spot-check them.

5. Releasing the low-cyclic grade without a performance retest.

6. Missing the timing. The restriction covers placing on the market after 6 June 2026 (EU Regulation 2024/1328, 2024), so stock made before that date but placed on the market after it must also meet the limit.