General Assist Technical Information

Why Old Plastic Turns Yellow

Understanding discolouration of older ABS plastic components
Why wall controllers and other plastic components can become yellow or brown over time
Older ABS plastic components can gradually develop a yellow or brown appearance over time. This is associated with the chemistry of flame-retardant additives used in some older plastics and their exposure to ultraviolet light.

1. What Causes Plastic to Turn Yellow?

The yellowing seen on some older plastic components is associated with a flame retardant called bromine that was used in older ABS plastics.

When exposed to ultraviolet (UV) light, the bromine molecules can destabilise and move towards the surface of the plastic. Over time, this can cause the plastic to change from its original colour to:

  • Yellow
  • Dark yellow
  • Brown in more advanced cases
Modern plastics: Improvements in plastic chemistry mean that newer materials are generally less susceptible to this particular type of discolouration.

2. Why Can Two Identical Products Look Different?

Plastic components do not necessarily yellow at the same rate, even when they are from the same product range.

For example, one wall controller may become noticeably yellower than another controller installed elsewhere in the same home.

This can occur because different components may have been produced from different batches of plastic, with variations in their composition.

It is possible to see:
  • Two controllers of the same model with different levels of yellowing.
  • Different plastic sections of the same product ageing at different rates.
  • One piece of plastic remaining relatively white while another becomes yellow.

These differences can be caused by variations in the composition of the plastic used for each component.

3. Can the Yellowing Be Prevented or Reversed?

Unfortunately, there is no recommended method to completely prevent this ageing process once the plastic begins to discolour.

There is also no approved process that we can recommend to reliably return the plastic to its original colour.

Important: Products or chemicals promoted online for whitening old plastics are not recommended unless specifically approved for the product. These treatments may damage the surface finish, markings or plastic itself.

4. Quick Reference

QuestionAnswer
Why has the plastic turned yellow?Ageing of older ABS plastic associated with UV exposure and flame-retardant additives.
Why is one controller yellower than another?Different batches or compositions of plastic can age at different rates.
Can different parts of the same unit be different colours?Yes. Different plastic components may have different material compositions.
Can the original colour be restored?There is no restoration process that we can recommend.