Thermoplastic Polymer Moisture Absorption Mechanics during Storage
Polymer moisture absorption follows Fickian kinetics, requiring hermetic packaging, Karl Fischer verification, and desiccant drying to prevent hydrolytic cleavage.
Relative Humidity
Meaning
Environmental measurements of moisture saturation represent the ratio of the partial pressure of water vapor to the saturated vapor pressure at a given temperature. Under relative humidity, the moisture content of the air influences how quickly hygroscopic materials absorb water. This parameter represents a critical factor in plastics storage.
Thermal Equilibrium
Amount of water vapor that air can hold increases as the temperature rises. When the air temperature in a warehouse drops, the percentage of moisture saturation increases, which can lead to condensation on the surface of stored polymer packaging. This condensation represents a major hazard because it can saturate the material as soon as the package is opened.
Moisture Absorption
Hygroscopic polymers like nylon or polyester absorb water until they reach an equilibrium moisture content that corresponds to the moisture level of the surrounding air. High ambient moisture levels drive the absorption process faster because of the increased vapor pressure differential. This moisture uptake alters the electrical, mechanical and dimensional properties of the polymer.
Processing Vulnerability
Molders must monitor the moisture level of the factory air to adjust their material handling and drying procedures. High moisture levels in the processing hall can lead to rapid re-absorption of water by pre-dried polymer as it sits in the machine hopper. Controlling the environment or using sealed hoppers prevents this moisture pickup and ensures consistent molding quality, which reduces the rate of rejects during high-humidity seasons.