Meaning
Equilibrium moisture content absorbed by hygroscopic polymers from ambient air directly governs resin hydrolytic stability during melt processing. Engineering resins like polyamide and polyethylene terephthalate absorb water molecules into their amorphous regions through hydrogen bonding. Moisture sorption establishes the water content threshold above which molecular weight degradation and visual surface defects occur in moulded parts.
Processing resin without drying below critical limits results in brittle components and compromised mechanical performance.
Equilibrium Diffusion
Environmental relative humidity drives water molecule absorption into polar polymer chains until saturation equilibrium occurs. Understanding moisture sorption kinetics allows material handlers to predict how quickly open resin gaylords absorb atmospheric moisture in humid processing environments. Diffusion rates increase significantly at higher ambient temperatures.
Processing Degradation
Water present during polymer melting undergoes a high-temperature chemical reaction that breaks ester or amide linkages. High moisture sorption leads to rapid molecular weight reduction during extrusion, causing splay marks and severe impact strength loss in finished components. Controlling water levels prevents hydrolytic chain cleavage.
Drying Kinetics
Dehumidifying desiccant dryers remove absorbed water by surrounding resin pellets with dry air at elevated temperatures. Measuring post-drying moisture sorption ensures processing water levels fall below the threshold required for processing stability. Proper drying restores mechanical integrity before moulding.
