Recycled Polyethylene Terephthalate Moisture Testing Methods
Accurate moisture testing below 50 ppm via Karl Fischer oven titration prevents hydrolytic intrinsic viscosity degradation in recycled PET during melt processing.
Dew Point Control
Meaning
Regulation of the temperature at which water vapor in a process gas condenses ensures that the dry air supplied to a polymer drying hopper maintains a consistent, very low moisture content. Maintaining dew point control prevents desiccant degradation and polymer processing problems. This control is critical for hygroscopic materials such as nylon and polycarbonate that degrade when processed with residual moisture.
Drying Efficiency
Moisture removal from the polymer resin depends on the vapor pressure differential between the plastic pellets and the surrounding air. When the dew point is kept at minus forty degrees Celsius, the extremely dry air rapidly extracts moisture from the pellets.
Air Regeneration
Desiccant beds must be periodically regenerated to restore their moisture-absorbing capacity. Heated air is passed through the saturated desiccant to drive off the accumulated water, and the dry air is then cooled before being routed back to the polymer hopper.
Process Automation
Automation systems monitor the humidity levels in the return air stream to adjust the desiccant wheel rotation speed or the switching interval of the drying towers. By dynamically adjusting these cycles based on the moisture load rather than using a fixed timer, the system minimizes energy consumption, which reduces the operating cost of the compounding line.