Hygroscopy and hydrolysis – what’s the difference?

Hygroscopy and hydrolysis – what’s the difference?

Do you know the distinction between hygroscopy and hydrolysis? Read on for a reminder of the difference between these two key chemical terms and how they can affect belts.


Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. The material is physically changed, resulting in increased volume and changes to other physical characteristics. These effects are undesirable in belting technology.

With belts, it is mainly polyamide (PA) whose hygroscopic behavior needs to be considered.

Various Habasit products contain construction elements made of polyamide, and these react to humidity with different dimensional changes:

  • Injection-molded polyamide and acetal for plastic modular belts (modules and rods)
  • Stretched polyamide tapes used as a traction layer for power transmission belts
  • Polyamide fabrics used as traction members for conveyor and processing belts, and machine tapes, etc.


Hydrolysis refers to the degradation of a material’s molecular structure at high temperatures and high humidity.

Hydrolysis is a chemical process during which a certain molecule is split into two parts by the addition of a molecule of water (H2O). One fragment of the parent molecule gains a hydrogen ion (H) from the additional water molecule; the other part collects the remaining hydroxyl group (OH). This is the type of reaction that decomposes certain polymers, especially those made by polymerization, such as thermoplastic polyurethane (TPU), polyamide (PA), and polyesters like polyester (PET) and polybutylene terephtalat (PBT). Hydrolysis results in a decrease in mechanical strength.

Not sure how your application environment may affect your belting? We’re here to help. And if you have any questions about other chemical terms involved with belting, contact us for information.

2019 September 23  |  Posted by

Marco Hollander

Marco Hollander joined the Habasit Netherlands team in September 2000 and works as a Technical Manager. He specializes in modular belts, chains and profiles in the food and material handling industries. He is also well-versed in general conveying and spiral applications. Hollander is always ready to answer questions from customers or Key Account Managers with any technical issues. He speaks Dutch, English and German and enjoys the challenge and variety of his work.

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