Hydrolysis and how to prevent it from affecting your plastic product

A phenomenon called hydrolysis degrades certain plastic materials and affects their mechanical properties.
This does not apply to all plastics. The polymer structure of the material must have an -OH group in it. Quite many do. Hydrolysis must be considered with (at least) the following plastics:

  • Polyesters PBT, PET, copolyester, PLA
  • Polycarbonate PC
  • Polyurethane PU, TPE-U
  • Polyamides like PA6, PA66, PA12 (Please notice that the common tendency of polyamides to absorb moisture is another thing)
  • Polyacetal POM

As you can see, the majority of the common engineering materials are included. Should you be worried? Not really, as long as you take hydrolysis into account.
The phenomenon itself is not very aggressive. The key nominators (in addition to the required OH-group) are:

  • Time. In short term use hydrolysis is hardly a problem.
  • Temperature. The water must be hot; close to boiling or steam. Rain or splashes of cold water are not harmful.

Kitchen spatulas are typically made of PA66 and constantly sank in boiling water. At least mine are still in use after several years of use.

The scissor handles I wash on almost daily bases are made of PBT. No problems, although the water temperature in a consumer use dishwasher is typically not higher than 50°C.

How to avoid problems with design?

  1. Understand the service environment of the product. Will it be in prolonged contact with hot water or steam? Are you designing a rice cooker or a coffee machine?
  2. To play safe, prefer materials without the OH group.
  3. Try to find a reference case where the corresponding grade has been used successfully under similar conditions. Your material supplier can probably help with this.