Metrology for moisture in materials

Moisture content affects performance, lifespan, processing speed, weight and the price of almost all manufactured products, including paper, food, fuels, pharmaceuticals, glues and coatings. The quality of many industrial products relies on controlling or removing moisture at the end of the production process.

During the production process moisture analysers are used to determine how much water is present in a material or product. These analysers are calibrated through comparison with the ‘loss on drying’ technique, which measures how much of the sample’s water volume is evaporated at a controlled temperature. This technique lacks traceability due to the uncertainty around how well moisture is extracted by the evaporation process and how much is from other extracted volatile materials. Increased accuracy and improved links to the SI units will provide industry with the robust measurements required for the quality control of moisture content.

This project developed new techniques and reference materials to improve traceability to SI units and the transferral of this to industrial moisture measurements nearer to the production process.

The Project:

• Developed four highly accurate reference methods, one using chemical analysis (titration) and three based on measuring water vapour removal from a sample by drying and validating them through comparison exercises
• Developed well-defined reference materials, with confirmed homogeneity, stability and lifespan, in order to transfer traceability from NMIs to calibration laboratories
• Developed a model for predicting how water is absorbed and transported through materials, which could be used to improve product performance, particularly for glues and coatings
• Developed a novel calibration system, using DRIFT spectrometry, in order to transfer traceability to surface moisture measurement probes. This system measures moisture content based on the changing reflectance of infra-red light.

This collaborative project brought together a diverse range of moisture and temperature experts to tackle a lack of traceability and fragmented knowledge in this area across the EU, raising understanding and capabilities across the board. The improved processes developed by the project are now available as two best practice guides on making reliable calibrations, one on titration uncertainty and one on sample handling and transportation uncertainty.

Research into moisture in different materials is also having a direct benefit in various industrial sectors. Biofuels companies can now better determine the water content of wood pellets enabling greater combustion efficiency, coupled with reduced CO2 emissions. Agricultural production requires knowledge of soil moisture based on reliable measurements to optimise irrigation for increased crop yields. A follow-on project will link the project’s primary measurement techniques to soil measurement instruments.