Verifying Inorganic Filler Concentrations in Foreign Masterbatches Crossing Trade Borders
Verify masterbatch ash content via ISO 3451 calcination at 600°C to protect duty lines, catch mineral substitution, and prevent process failures.
Moisture Adsorption
Meaning
Accumulation of water molecules onto the surface of plastic pellets happens when hygroscopic resins are exposed to ambient humidity during storage or transport. Unlike absorption, which involves water migrating into the polymer bulk, moisture adsorption concentrates water on the exterior surface of the granulate. This surface moisture must be removed prior to molding to avoid steam generation and hydrolytic degradation in the melt.
Processing Defect
Surface moisture on incoming resin pellets vaporizes immediately when exposed to the high temperatures inside the injection molding barrel. This rapid boiling causes moisture adsorption to result in cosmetic defects such as splay, silver streaks, and foaming at the nozzle. In polycondensate resins like PET and nylon, the presence of surface water also triggers chain scission, which severely reduces mechanical properties.
Dryer Performance
Dessicant dryers must be calibrated to remove surface moisture and lower the resin’s water content below specified limits. Monitoring the dew point of the drying air ensures that the pellets remain below critical moisture thresholds.
Material Selection
Resins exhibit different sensitivities to water based on their chemical structure and surface energy. While polar polymers are highly susceptible to moisture adsorption, non-polar polymers like polypropylene are less affected. Polymer specifiers must account for this behavior when designing the packaging and handling protocols for raw materials.
For instance, storing moisture-sensitive materials in metal-lined bags prevents the ingress of atmospheric humidity during long-term warehouse storage.