There is no universal definition for the term moisture. Commonly, it’s the measuring principle used for moisture measurement that determines its definition. So, it is necessary to distinguish between “moisture” and “water content”.

The moisture of a material includes all those substances that volatilize during heating. In addition to water these are e.g.

-          Evaporating organic solvents

-          Alcohols

-          Greases, oils, aromatic components

-          Plasticizers

-          Decomposition and combustion products

Only systems that measure exclusively the water content of a material can be called as water-specific ones. Here, other evaporating substances, like those mentioned above, do not influence the readings.

In the field of plastic drying and processing especially, where very low water contents must be detected, a water-specific method is highly recommended. It ensures reliable readings of the actual water content of the polymers.

The HydroTracer determines the water content of the sample by a chemical-analytic method, based on calcium hydride. The test sample is heated in the reactor, only evaporated water is converted into hydrogen and the hydrogen content is detected by a hydrogen-sensitive gas sensor. This patented measuring method specifically measures the water content, other volatile ingredients are not detected.

It's not possible to measure liquids. The measuring capability is limited to solids only, in the form of granules, powders or flakes. Foils, fibres or thin-walled injection moulded parts can also be measured.

The HydroTracer is mainly used in the plastics processing industry and in particular the injection moulding and extrusion industries where the water content is checked and monitored at the goods-in stage and throughout the drying process. Our moisture analyser is also used successfully by raw material manufacturers and compounders as well as for research, development and teaching at universities and research institutes.

Yes, for all engineering and high-performance plastics in the field of injection molding or extrusion. There are only 2 exceptions:

-          PVC - here the thermal stability must be considered. During decomposition, side reactions may occur that affect the readings of the HydroTracer

-          Polymers containing blowing agents e.g., thermoplastic or elastomeric foams

A thermogravimetric moisture analyzer consists of a scale with an overhead heating source e.g., infrared, halogen or microwave based. The sample is heated on the scale the weight loss is interpreted as moisture content. This simple method is practical for the determination of high moisture contents, e.g., in food or agricultural industry, when the proportion of water is very high compared to other contained volatiles.

Disadvantages: Only a weight loss is measured, the cause of the weight loss cannot be determined. It could be water or other volatile substances such as plasticizers, paraffin’s, fire inhibitors, etc.

A frequent sales argument for thermogravimetry is the assumption that at a low heating temperature - for example, 110 °C - the proportion of the other volatiles can be ignored. However, at these temperatures in the presence of atmospheric moisture, the water only partially escapes from a hygroscopic test material until a state of equilibrium with the water content of the air is reached.

A further disadvantage is the heating source: Contrary to the statements of the manufacturers, it is not possible to heat a plastic granulate evenly by means of heat radiation. The surface will absorb more heat than the core. This accelerates the thermal degradation of the plastic (and therefore an additional weight loss). In the case of translucent material, this is clearly seen as discoloration.

For decades, the Karl-Fischer Titration it is the reference method for detecting the water content in many substances. It is a chemical-analytical method based on the oxidation of sulfur dioxide in methanolic-basic solution by iodine. As water-specific method it measures the water content down to the single-digit ppm (0.0001%) range.

This method is used in many industries, but mainly in laboratories. Because of its complexity and the peripheral equipment required (aging & toxic reagent, carrier gas supply) and also the test preparation involved (blank value determination, shut-off criterion), users must be trained or need to have a specialized knowledge to perform meaningful tests.

This is where the HydroTracer comes in. When developing the HydroTracer, the focus was always on providing an easy-to-use and cost-effective water content analyzer without sacrificing the analysis quality of an expensive and complex laboratory device. Many comparative measurements with the Karl Fischer titration prove both the absolute measured value achieved and the repeatability of HydroTracer test results.

The measuring range is between 0 mg and 25 mg of water.

The measurement accuracy is 0.14 mg in a range from 0 mg to 5 mg of water, 0.24 mg in a range of 5.1 and 15 mg of water, 0.34 mg in a range of 15.1 and 20 mg of water and 0.64 mg in a range of 20.01 and 25 mg of water.

Here, we must consider the absolute accuracy valid in the respective measuring range. To determine the relative water content of the sample material, the water mass of the sample is divided by the weight of the sample. This will be illustrated using 3 typical use cases:

Example 1: After 4 hours of drying at 80°C a 10 g specimen of Polyamide 6 GF 30 is measured

A water content of 2 mg is determined during a measurement, the sample mass was 10 g. The average error according to the calibration certificate is 0.14 mg. The relative water content is thus: 2 mg / 10.000 mg = 0.0002 = 0.02% = 200 ppm. Neglecting the weighing error, the average error of the relative water content is 0.02% x (± 0.14 mg / 1 mg) = ± 0.0014 % and ± 14 ppm, respectively.

Example 2: Crystallized and dried PET granules for PET-preform production

A water content of 1 mg is determined during a measurement and the sample mass is 30 g. The average error according to the calibration certificate is 0.14 mg. The relative water content is thus: 1 mg / 30000 mg = 0.000033 = 0.0033% = 33 ppm. Neglecting the weighing error, the average error of the relative water content is 0.0033% x (± 0.14 mg / 1 mg) = ± 0.00047% and ± 4.7 ppm, respectively

Example 3: PA6.6 injection moulded part conditioned in a 65°C water bath for 24 hours
A water content of 20 mg is determined during a measurement and the sample mass is 1 g. The average error according to the calibration certificate is 0.34 mg. The relative water content is thus: 20 mg / 1000 mg = 0.02 = 2.00% = 20.000 ppm. Neglecting the weighing error, the average error of the relative water content is 2.00% x (± 0.34 mg / 20 mg) = ± 0.034% and ± 340 ppm, respectively.

These examples illustrate the great importance of the sample quantity to the accuracy of the measurement result.

Calibration is included in the initial supply. The measurement accuracy can be checked by the customer, but we recommend the maintenance and calibration by aboni or an authorized service partner on a regular basis every 1-2 years.

The calibration is based on a method described in DIN EN ISO 15512:2019 PLASTICS - DETERMINATION OF WATER CONTENT.
A defined amount of an analytical salt is heated to 175 °C in the closed reactor, thereby ensuring complete evaporation of the entrapped water. The salt used is sodium molybdate dihydrate of analytical grade, the crystal water content is 14.89 mass%.

The salt is weighed with an analytical balance, the resolution of the scale is 0.01 mg, the accuracy +/- 0.03 mg, so the accuracy of the water weighed is 0.03 mg x 0.1489 = 0.005 mg.

The traceability of this method is based on a tested scale with which the calibration salt is weighed.

The average results must be within a tolerance range and the allowed values are:

• 0.14 mg in a range of from 0 mg to 5 mg of water,
• 0.24 mg in a range of 5.01 to 15 mg of water,
• 0.34 mg in a range of 15.01 to 20 mg of water and
• 0.64 mg in a range of 20.01 to 25 mg