Meaning
Gravimetric moisture determination methods measure total mass reduction of resin samples against initial wet mass under controlled heating conditions. A loss on drying balance combines an infrared or halogen heating element with a precision weighing cell to measure water content in polymer pellets. Heating evaporates volatile components while internal scales track real-time mass loss until sample mass stabilizes.
Thermal decomposition of the polymer matrix defines the upper boundary where gravimetric measurements become invalid due to material degradation. Moulders rely on these instruments for rapid verification prior to processing moisture-sensitive engineering plastics.
Moisture Evaporation
Thermal energy drives absorbed water molecules out of plastic pellets placed on the sample pan. Operating a loss on drying balance requires selecting heating temperatures that evaporate surface and internal moisture without degrading the polymer resin. Non-aqueous volatile additives or processing aids can evaporate simultaneously, introducing positive error into moisture calculations.
Precise temperature control ensures that mass loss reflects actual water content rather than additive volatilization.
Thermal Exposure
Resin samples subjected to excessive temperatures undergo thermal oxidation or chain scission during testing. Using a loss on drying balance above polymer degradation thresholds causes ongoing mass reduction from off-gassing resin, preventing mass stabilization. Unstable mass readings lengthen test times and distort moisture percentage metrics.
Calibration protocols establish optimal drying profiles for specific polymer families to prevent thermal breakdown.
Mass Precision
Analytical resolution determines the ability of weighing systems to detect minute weight changes in light samples. High performance balances measure mass down to fractions of a milligram to verify dryness in hydroscopic polymers like nylon or polycarbonate. Small sample sizes reduce test duration but increase sensitivity to draft currents and mechanical vibrations.
Enclosing the measurement chamber stabilizes readings during heating cycles.
