Stanyl® absorbs moisture reversibly because of the amide groups in its molecular chain. In general, moisture absorption results in a decrease of the glass transition temperature, which may lead to an increase in toughness and reduction in stiffness and strength at room temperature.
Competitive materials like semi-aromatic polyamides have a higher Tg, often in the operating temperature range. A shift in Tg due to moisture uptake will often lead to a change in properties at the critical operating temperatures.
What’s more, due to this higher Tg, higher mold temperatures are needed, 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 100°C, Stanyl dries out especially quickly at higher temperatures, and its properties reach those outlined 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
Moisture uptake leads to dimensional changes. However, because highly filled compounds are used in many applications this dimensional change is limited. Due to glass fiber orientation, dimensional changes mainly take place in the direction perpendicular to the flow direction (thickness of the part, see tables below).
Dimensional change as a function of moisture uptake of non-flame retardant grades
|Dimensional Change (%) in Flow/Per. to Flow||Stanyl||Stanyl
|50%RH - oriented part||0.7/0.7||0.15/0.6-0.9||0.1/0.4||0.1/0.3-0.4||0.1/0.5-0.8|
|50%RH - non oriented part||0.8/0.8||0.3/0.6-0.9||0.15/0.4||0.15/0.3-0.4||0.3/0.3-0.6|
|90%RH - oriented part||1.8/1.9||0.35/1.4||0.2/1.0||0.2/0.5||0.2/1.2|
|90%RH - non oriented part||2.2/2.2||0.5/1.5||0.4/0.9||0.2/0.3||0.8/0.8|
orientated part: thickness 2 mm
not-orientated part: thickness 3-4 mm
Dimensional change as a function of moisture uptake for flame retardant grades
|Dimensional Change (%) in Flow/Per. to Flow||PPA
|50%RH - oriented part||0.1-0.15/0.3||0.1-0.2/0.5||0.1-0.15/0.4||0.05-0.1/0.4|
|50%RH - non oriented part||0.2-0.3/0.5||0.15-0.25/0.5||0.15-0.25/0.5|
|90%RH - oriented part||0.15-0.2/0.5||0.2-0.3/1.1||0.15-0.2/1.0||0.15-0.2/0.9|
|90%RH - non oriented part||0.4-0.6/1.1||0.4-0.5/1.0||0.4-0.5/0.9|
This is the direction that in terms of dimensions is often the least critical. The effect of moisture on dimensions is small compared to the dimensional change due to temperature changes (Coefficient of Linear Thermal Expansion - see table below). Stanyl has excellent performance in many applications where dimensions are very critical, including many small connectors or SMT components. For E&E applications where dimensional stability is very critical, we developed special flame retardant, reinforced grades: 46HF5050 and 46HF5041LW.
Typical CLTE values for Stanyl grades
Moisture absorption usually happens at room temperaturum is reached. When using the application at operating temperatures - which for Stanyl parts is often above 100°C (210°F) - drying is extremely fast. This means that full saturation is very often not seen in many applications (see figure below) and effects of moisture uptake are often limited.
Water absorption at 23°C/50%RH followed by desorption at 180°C of Stanyl (3.2 mm thickness sample)
Annealing significantly reduces moisture uptake
Moisture absorption is significantly reduced following the annealing of Stanyl. Annealing results in the densification of the amorphous part of Stanyl when exposed to high temperatures (> 100°C). This phenomenon is unique to Stanyl and is irreversible.
Annealing happens during operation at elevated temperatures in for instance automotive applications. Annealing may result in a moisture uptake reduction by a factor of three. Annealing can also be used as a separate step to improve the dimensional stability of Stanyl parts (preferably using a nitrogen atmosphere). Moisture uptake reduction depends on the annealing time and temperature – which is why we have developed a model to quantify this.
Properties like stiffness, strength, fatigue, creep and abrasion resistance are generally improved upon annealing while toughness might be slightly reduced although at a level that still outperforms competitive materials. This leads to a strongly improved property profile for applications like gears.
Moisture uptake at extreme humidity can lead to blistering during soldering at very high peak temperatures close to a material’s HDT. This is a phenomenon not unique to Stanyl but is also common in other polyamides and even for LCPs. Blistering can be prevented by protection from moisture, and optimized processing.
Reduction of water uptake of Stanyl GF and competitive materials at anneal conditions
Blistering is also very dependent on the thickness of the application. Our research has proven that below a certain thickness (typically in the range of 0.4mm), Stanyl doesn’t blister. A blister model is in place to accurately predict, based on the humidity and temperature, the optimum thicknesses and application designs for non-blistering Stanyl.
And when designs are blister sensitive, we now offer a a totally new material: Stanyl ForTii.