Moisture Content and Regain Testing
topic
Moisture regain (MR%) = (wet mass − dry mass)/dry mass × 100. Dry mass: 105°C oven to constant mass. Conditioned mass: ISO 139 standard atmosphere (20±2°C, 65±4% RH, 24 h conditioning). Karl Fischer titration: reagent-based coulometric method, measures actual H₂O content (ppm) — used for PET chip moisture before spinning (target <50 ppm). NIR spectroscopy (1940 nm O-H overtone) for online moisture measurement in drying hopper. Moisture sorption isotherm (DVS, Dynamic Vapour Sorption): mass vs. RH at constant temperature — characterises hysteresis and sorption kinetics.
Role
Moisture characterisation of polyester spans the range from ppm-level pre-spinning chip moisture (process critical) to equilibrium moisture regain (comfort critical), requiring different analytical techniques with different sensitivity ranges — an important methodological distinction.
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