Degradation Mechanism
Chemical process involving the breaking of molecular bonds through the addition of water. Occurrences of hydrolytic cleavage result in the permanent breakdown of polymer chains, which leads to a loss of mechanical strength and elasticity. This phenomenon is particularly prevalent in elastomers containing ester or amide groups.
It represents a common failure mode for seals operating in humid or aqueous environments.
Reaction Pathway
High temperatures accelerate the rate at which water molecules attack the susceptible links in the polymer backbone. As the bonds snap, the molecular weight of the material decreases and the component may become soft or gummy. This degradation is irreversible and often proceeds until the material can no longer sustain a seal.
Polymer Sensitivity
Polyurethane and certain polyester based elastomers are highly prone to this type of damage when exposed to steam or hot water. Even trace amounts of moisture trapped during the manufacturing process can trigger the reaction over time. Testing for water absorption provides an initial indicator of how a material might behave under these conditions.
Prevention Strategy
Selecting polymers with ether based backbones or fully fluorinated structures provides a barrier against moisture attack. Hydrophobic additives can also be incorporated into a compound to repel water and delay the onset of bond breaking. Regular monitoring of fluid acidity is helpful since acid or base catalysts can speed up the cleavage process.
The environmental conditions must be thoroughly understood before a material is specified for long term service.
