Plastics -- Determination of water content
ISO 15512:2008 specifies methods for the determination of the water content of plastics in the form of granules and finished articles. These methods do not test for water absorption (kinetics and equilibrium) of plastics as measured by ISO 62. The methods are suitable for the determination of water content as low as the following levels:
- Method A 0,1 % or better;
- Method B 0,01 % or better;
- Method C 0,01 % or better.
Three alternative methods are specified:
- Method A is an extraction method using anhydrous methanol followed by a Karl Fischer titration of the extracted water. It can be used for all plastics and is applicable to granules having a maximum size of 4 mm x 4 mm x 3 mm.
- Method B is a vaporization method using heated, dry air or nitrogen gas to evaporate the water, followed by a Karl Fischer titration of the collected water. It can be used for all plastics and is applicable to granules smaller than 4 mm x 4 mm x 3 mm.
- Method C is a manometric method. The water content is determined from the increase in pressure which results when the water is evaporated under a vacuum. This method is not applicable to plastic samples containing volatile compounds, other than water, in amounts contributing significantly to the vapour pressure at room temperature. Checks for the presence of large amounts of volatile compounds should be carried out periodically, for example by gas chromatography. Such checks are particularly required for new types or grades of material.