REACH - Applications for authorisation AFA053-01 - NPEO

Closed 2 May 2024

Opened 7 Mar 2024


Public consultation on alternatives

Reference: AFA053-01

Applicant: Chemetall Limited

Application type: Review Report

Substance name: 4-Nonylphenol, branched and linear, ethoxylated (NPE)

Proposed use: Mixing, by Aerospace Companies and their associated supply chains, including the Applicant, of base polysulfide sealant components with NPE-containing hardener, resulting in mixtures containing < 0.1% w/w of NPE for Aerospace uses that are exempt from authorisation under REACH Art. 56(6)(a).

Broad information on use applied for (conditions of use and function):

Polysulfide sealants in the scope of this AfA comprise a base and a hardener component.  Only the hardener component contains very low concentrations (0.6%) of NPE. This use covers the mixing of the base and the hardener components.  Mixing is carried out in a highly controlled manner using manual or mechanical methods.  Once mixed, the concentration of NPE in the sealant is always less than 0.1% w/w, so the mixed sealant is exempt from authorisation.

These polysulfide sealants are used to deliver specific safety functions in production, maintenance and repair within the aerospace industry in accordance with the requirements of airworthiness regulations or applicable aerospace requirements, uses include, but are not limited to, sealing structures/components to:

  • keep moisture or other fluids out (to prevent corrosion or attack of structures/components),
  • keep fluids in (e.g. fuel, hydraulic fluids, etc.)
  • prevent airflow to maintain cabin pressure
  • Isolating components to separate dissimilar substrates/metals to prevent corrosion or provide thermal/ electrical insulation
  • Filling gaps to create an aerodynamic surface (aero smoothing) and eliminate moisture accumulation or traps
  • Provide adhesion in engines and nacelles, when flexibility and compatibility with mating gap filler is required; bonding structures requiring flexibility; and bonding/sealing of wires
  • Electrical potting in connectors, PC boards, circuit boards

They are used in a range of applications including fuel tanks (to prevent leakage), window sealing (ensuring air tightness and pressurisation of passenger cabins), actuators, electronic controller connections, gyros, wiper blade systems, propeller blades, ball screws for actuators, flight control rudder pedals, joint sealing of general aircraft structures during assembly process, to assemble structures, etc.

The properties of the sealants include, but are not limited to:

• Resistance to degradation by fuel and other chemicals

• Flexibility over a wide range of temperatures, most uniquely extreme cold

• Adhesion to a wide range of substances

• Ability to stress-relax, thereby maintaining adhesion to expanding and contracting substrates

List of descriptors:

  • Sector of end use (SU): 0: other: Aerospace
  • Environmental release category (ERC): 6b
  • Process category (PROC): NA
  • Product category (PC): 1 [Adhesives, sealants]
  • Article category related to subsequent service life (AC): N/A
  • Technical Function: Surfactant

Annual tonnage used: <1 tonne/year

Review period requested: 6 years

How to submit comments

Provide some basic information on possible alternative(s) in the online survey below but more detailed information should be provided in document(s) prepared using the commenting templates in the related section below. A “public version” should always be completed and will be published after the consultation has closed. If you want to include confidential information in your submission, please additionally complete a “confidential version” and submit both versions as attachments.

The consultation lasts for 8 weeks (unless otherwise specified) and closes at 23:59 London time (BST).


  • Applications for authorisation


  • Registration, Evaluation, Authorisation & restriction of CHemicals (REACH)