As with any other polyamide, Stanyl absorbs moisture reversibly due to the
presence of the amide groups in the molecular chain. Moisture absorption is
dependant on the temperature, the relative humidity of the environment, and
the wall thickness of the specific part. In general moisture absorption
results in a decrease of the glass transition temperature (see graph below),
which may lead to an increase in toughness and reduction in stiffness and
strength at room temperature.
This drop in stiffness for Stanyl is small compared to the drop for other
polyamides due to Stanyl’s high level of crystallinity. The performance above
the glass transition temperature (75°C) is not affected by moisture uptake. As
Stanyl is typically used at higher operating temperatures, the effect of
moisture will not be noticed.
Competitive materials such as
semi-aromatic polyamides have a higher Tg, often in the operating temperature
range. A shift in Tg due to moisture uptake will in this case lead to a change
in properties at the critical operating temperatures.
In
addition, due to this higher Tg, higher mold temperatures are required,
resulting in the need for oil or electrically heated molds, with higher safety
risks, higher mold and maintenance costs, and more difficult processing.
For prolonged exposure above 100ºC, Stanyl dries out, especially rapidly at
higher temperatures, and properties will approach those given by the "dry"
curve. This leads to a consistent property profile over a wide temperature
range, especially once the effects of annealing are taken into account.
Shear modulus of glass fiber reinforced thermoplastics.
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