Determining Karl Fischer Titration Parameters for Engineering Plastics
Headspace Karl Fischer titration requires temperature optimization between desorption and polymer decomposition to measure true moisture without pyrolytic errors.
Dew Point Calibration
Meaning
Systematic verification of moisture sensor accuracy ensures that resin drying systems operate at the correct dry-air parameters. Performing a regular dew point calibration involves comparing the readings of the sensor against a certified reference standard under controlled conditions. This procedure ensures that the dryer achieves the low moisture levels needed to process hygroscopic polymers without causing hydrolysis.
The calibration must be performed annually or after exposure to contamination to maintain process control.
Verification Method
Technicians insert the moisture probe into a calibration chamber that receives a gas stream of known moisture content. During the dew point calibration, the output of the sensor is adjusted to match the reference value at multiple points. This multi-point adjustment corrects for sensor drift caused by high temperatures or chemical exposure.
The reference instrument must be traceable to national standards to ensure accuracy. If the sensor cannot be adjusted, it must be replaced to prevent incorrect readings. Most calibration systems use chilled mirror hygrometers as the reference.
Process Integrity
Sensors that have drifted can report a low dew point when the air is actually wet, leading to incomplete resin drying. This drift can cause hydrolysis during melt processing, which degrades the polymer and reduces its mechanical properties. By ensuring accurate sensor readings, calibration maintains the drying process within the specified window.
This control is critical for medical or aerospace moulding, where process parameters must be documented. Consistent calibration records provide traceability for quality audits.
Economic Impact
Accurate drying parameters reduce scrap rate by preventing moisture-related defects like splay and brittleness. Energy costs are also reduced because the dryer does not run regeneration cycles more often than necessary. Implementing a calibration schedule extends the life of the sensors and ensures reliable production runs.
This prevention of unexpected defects improves the overall efficiency of the moulding facility.
Desiccant Dryer Dew Point Calibration and Karl Fischer Titration Verification
Dew point monitoring alone fails to guarantee dry resin; coulometric Karl Fischer titration per ISO 15512 Method B is mandatory to prevent hydrolytic scission.