Meaning
Volumetric or coulometric analysis measures the trace water content of hygroscopic polymers before melt processing. When performing Karl Fischer analysis, a creeping endpoint titration occurs if the moisture is released too slowly or if side reactions continuously generate water. The phenomenon interferes with the precise quantification of moisture levels in engineering plastics like polyamide or polycarbonate.
Reaction Kinetics
Slow diffusion of bound water from the polymer matrix into the solvent prevents a sharp, stable endpoint. In a creeping endpoint titration, the reagent is consumed continuously at a low rate, mimicking a persistent wet state. Inadequate sample dissolution or low operating temperatures cause this slow extraction rate.
Accuracy Verification
Distinguishing between actual moisture and side reactions is necessary for correct resin prep. Running blank determinations or using specialized extraction solvents minimizes the drifting endpoint. Standardized titration methods define a drift limit to terminate the run once the consumption rate stabilizes.
Process Optimization
Moulders must know the dry weight of their resin to prevent hydrolytic degradation during injection moulding. By fine-tuning the temperature of the titration cell, the extraction speed is accelerated to yield a distinct endpoint. Thermal optimization prevents over-drying of the polymer, which can degrade physical properties, while ensuring that the resin is dry enough to prevent surface splay or bubbles in the moulded part.
