Karl Fischer Moisture Testing of Recycled Polyethylene Terephthalate
Coulometric Karl Fischer testing with oven desorption at 170 °C isolates true water content in rPET below 50 ppm, preventing costly IV degradation during melt processing.
Argon Purging Protocol
Meaning
Oxygen displacement procedure that introduces dry inert gas into hopper dryers and feed throats during hydroscopic resin processing prevents thermal degradation and moisture absorption. Establishing a continuous inert blanket inside processing equipment stops polymer chains from hydrolyzing when moisture contacts molten material at elevated temperatures. Polycarbonate and polyethylene terephthalate production lines rely on this specific inerting technique to maintain intrinsic viscosity values within strict limits.
Moisture Control
Controlling dew point levels inside the drying hopper protects moisture sensitive polymers from premature chain scission during melting. Introducing inert gas at a regulated volumetric flow rate forces ambient air out of the material bed before heating begins. Virgin pellet drying operations depend on maintaining low moisture levels to ensure the final moulded part achieves its specified mechanical strength.
Regrind material introduces unpredictable moisture variations that overwhelm standard drying loops unless continuous inert gas injection compensates for the additional volatiles.
Resin Degradation
Thermal oxidation occurs rapidly when oxygen interacts with polymer melts inside the barrel of an injection moulding machine. Supplying inert gas through the feed throat displaces reactive oxygen species and halts molecular weight reduction during the plastication phase. Datasheet values for melt flow rate remain stable across long production runs only when oxygen contact stays below strict concentration thresholds.
High processing temperatures accelerate degradation if the inert gas blanket fails, which yields brittle mouldings with compromised impact resistance.
Surface Defect
Preventing moisture streaks and splay marks on optical components requires absolute control over ambient humidity during the moulding cycle. Surface blemishes ruin transparent parts and force operators to reject entire production batches due to aesthetic noncompliance. Component specifications dictate strict visual standards that tolerate no microvoids caused by trapped moisture vapor expanding against the mould wall.
Tooling geometry determines how efficiently displaced gases vent from the cavity before final compaction seals the polymer front.