Humidity measurement

Plastics absorb moisture or water at different rates and in different amounts. Moisture measurement is carried out before processing hygroscopic materials such as polyamides and polyesters, but it is also an important quality assurance measure for conditioning polyamide components. Moisture measurements before and after the conditioning process provide an accurate indication of the moisture absorption of the components.

For many materials, the residual moisture content before processing is decisive for the processing and quality of a component. It therefore also plays an essential role in determining the material and component properties. The use of material with an excessively high moisture content leads to processing problems and quality impairments in the component during injection molding. These can manifest themselves in surface defects or losses in mechanical properties. This moisture content must therefore be below the maximum residual moisture content specific to a material in order to prevent damage to the material.

Conditioning of polyamide components is required to varying degrees depending on the application. Moisture measurement can be used to determine the moisture content in different areas of the component, since the uptake depends not only on the conditioning process but also to a large extent on the wall thickness.

In the BARLOG Plastics test laboratory, moisture meters are used that work according to the vapor pressure method, as these measure the moisture content specifically and the result cannot be falsified by other volatile components in the material. During measurement, the water vapor released by heating reacts with calcium hydride. The resulting hydrogen increases the pressure in the measuring system, which is converted into the moisture content.