3+1 tips on residual moisture when processing engineering thermoplastics in the injection molding process

The processing of technical thermoplastics in the injection molding process requires maximum precision in order to produce high-quality moulded parts. A decisive factor that is often neglected and has a significant influence on quality is the residual moisture of the plastic granulate used. Residual moisture can cause a variety of problems – from mechanical weaknesses to surface defects. In this article, we will give you 3+1 important tips on how to effectively manage residual moisture in the processing of engineering thermoplastics in order to produce high-quality molded parts.

3 + 1 tips on residual moisture when processing engineering thermoplastics in the injection molding process

1. Understanding the problem

Many plastics are hygroscopic, which means that they can absorb water. This moisture can be present both within the granules and on the surface. The quality of the injection-molded parts depends largely on the moisture in the pellets. The residual moisture in the plastic granulate can affect many aspects of the processing and quality of the molded parts. It influences the hydrolytic degradation of the molding compound, mechanical properties, flow behavior of the molding compound, injection pressures, surface quality, burr formation as well as the formation of mold deposits and clogging of the mold vent. A deeper understanding of these relationships is crucial in order to determine the optimum residual moisture for your specific processing method.

2. Understanding the wording

It is important to know the difference between moisture content and residual moisture. Moisture content refers to the water content in the material, while residual moisture describes the mass fraction at a defined temperature. Depending on the measuring method, other volatile substances can also be detected, which can lead to inaccurate results.

3. selection of the correct measurement method

The exact determination of residual moisture is crucial. There are various measuring methods for this, such as the infrared balance, the vapor pressure method by reacting the water with calcium hydride and Karl Fischer titration. Each method has its advantages and disadvantages. The choice depends on the requirements and available resources:

(a) The infrared balance is a common method for measuring residual moisture. It measures the weight loss of the sample due to the evaporation of water. Note, however, that this method is not specific to water, as other volatile substances can also evaporate and thus falsify the result. When using infrared balances, it is also important to ensure that the result is not influenced by external factors such as draughts or vibrations.

b) The vapor pressure method by reaction with calcium hydride is a reliable method for measuring residual moisture. It allows a specific detection of water and minimizes the influence of other volatile substances. This method provides accurate results, but requires careful handling and periodic replacement of the calcium hydride reagent as well as regular maintenance runs to dry the system.

c) The Karl Fischer titration method is a precise measurement method for determining residual moisture. Water is detected using a reaction with iodine and sulphur dioxide.The sample is heated to release the water, which is then added to the titration solution.The amount of water is measured using the iodine solution consumed.The method is extremely accurate, but also comparatively complex to handle. Each measurement produces chemical waste, which is expensive to dispose of.

Our recommendation as an additional tip:

As a renowned supplier of engineering plastics, BARLOG Plastics recommends the vapor pressure method using calcium hydride for measuring residual moisture. This method offers sufficient accuracy and minimizes additional influences (draughts/additives) on the measurement result. We use state-of-the-art measuring equipment to ensure optimum processing moisture. When using moisture-sensitive materials, choosing the right measurement method is crucial to ensure the maximum performance of the plastics. Overall, the control of residual moisture is crucial when processing engineering thermoplastics in the injection molding process. Using the right measurement method, handling the equipment accurately and following the recommendations of our experts will help you improve the quality of your injection-moulded parts and minimize downtime.