How to analyse moisture in plastics?
Plastics resins which are affected by moisture, can be classified as two types:
- Non-Hygroscopic Resins collect moisture only on the surface of the pellet. This surface moisture can be dried by exposing the resin to a continual blow of the hot air.
- Hygroscopic Resins collect moisture inside the core of the pallet and can be best dried by dehumidifying dryers. Hygroscopic resins like PA, ABS, PET, PC, PS etc., which have a high affinity for moisture, need to be dried thoroughly and properly to ensure quality and finish of the final product. Improper and inadequate drying can result in loss of structural, impact strength and tensile strength, cosmetic defects and many other moisture related defects and deficiencies.
With hygroscopic materials, you must force low dew point heated air over the material to make the molecules of moisture disengage from the polymer chains to the surface of the pellets where that all important airflow carries the moisture away. Dew Point is the temperature at which moisture in the air begins to condense. The low vapour pressure (dew point) of the dry air surrounding the pellets causes the freed moisture molecules to migrate to the surface of the pellet. Most plastic processors measure dewpoint on their material dryer and then dry the material according to the material drying guidelines set down by the supplier. This is obviously good practice but, the amount of drying time is very much dependent upon the amount of moisture within the material and the efficiency of the dryer itself. The best way to of checking exactly how dry the material really is and to ensure batch-to-batch consistency is to use a moisture analyzer. The results of this can be incorporated into your quality procedure and give real traceability.
How Does it Work? The moisture analyzer comprises of a balance and an integrated heater. The analyzer will first weigh the material sample in a foil tray at the start of the process; it will then heat the sample up, removing the moisture, and continue heating sample until it stops losing weight. This data is then used to calculate the moisture content based on the moisture loss rate, known as a drying curve.
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- fast response time
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- Built-in memories for storing products and settings (for future reference)
- USB port host for memory card and USB I/O interface