As with all polyamides, Akulon absorbs moisture reversibly from the
environment until it reaches an equilibrium. PA6 absorbs more water than PA66,
especially under high humidity conditions, however the resulting dimensional
change is the same as PA66. Glass fiber reinforced and glass/mineral filled
materials reduce moisture absorption to a level sufficient for most
applications. Akulon, even reinforced and filled grades, are not recommended
for programs requiring very tight tolerances. Consult with a DSM Engineering
Plastics specialist for guidance on use of Akulon grades for these types of
applications.
Absorbed water acts as a plasticizer reducing strength and stiffness at low
temperatures, but increasing toughness. Although at room temperature moisture
uptake reduces the stiffness and strength of PA6 more than for PA66, the
difference is not significant. This is particularly true in applications that
operate in environments above 100°C (212°F) since any moisture absorbed is
rapidly desorbed under these conditions. For critical designs at elevated
temperatures the influence of water absorption on mechanical properties can be
ignored. Note however that the temperature effects on properties need to be
considered in those cases.
Moisture content vs relative
humidity.
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