Evaluating Degradation Mechanisms in Post-Consumer Polyolefin Flake
Polyolefin degradation evaluation requires coupling multi-load melt flow testing and OIT analysis to quantify chain scission and restabilize flake lots.
Karl Fischer Moisture Titration
Meaning
Analytical chemistry procedures offer a highly specific method for measuring trace water content in solid samples. The process of karl fischer moisture titration relies on the chemical reaction of water with iodine in an anhydrous medium to quantify moisture down to a few parts per million. This technique is standard for assessing the dryness of engineering resins before injection moulding.
Reagent Chemistry
The method uses a dedicated titration cell where the sample is dissolved or heated to release its moisture into a solvent. Iodine is generated coulometrically or added volumetrically to react with the water present in the solvent. This chemical reaction proceeds with high selectivity, ensuring that other volatile substances do not interfere with the measurement.
Sample Preparation
Polymer samples often require heating in a specialized oven to vaporize the moisture, which is then carried by a dry gas into the titration cell. This vaporization step is necessary because many engineering plastics do not dissolve easily in the standard titration solvents. Inadequate heating can lead to incomplete extraction, resulting in an underestimation of the water content.
Conversely, too high a temperature can cause thermal degradation of the polymer itself, releasing chemically bound water and inflating the titration results.
Resin Dryness
Excess moisture during melt processing causes hydrolytic degradation in polymers such as polyesters and polycarbonates. Conducting a karl fischer moisture titration prior to start-up ensures that the resin moisture level is below the critical threshold. When the material is processed with too much water, the physical properties of the moulded part are compromised.