Evaluating Thermal and Oxidative Polyolefin Flake Degradation
Thermal and oxidative degradation alters polyolefin flake viscosity and residual stability, demanding MFR, OIT, and Carbonyl Index verification before processing.
Volatile Moisture Content
Meaning
Unbound water molecules and low-boiling compounds trapped within polymer pellets can cause severe hydrolytic degradation and surface defects during high-temperature melt processing. For hygroscopic engineering resins like polyamides and polycarbonates, volatile moisture content must be kept below strict threshold limits prior to extrusion or injection molding. Failure to dry the resin properly allows the water to react chemically with the polymer chain at high temperatures, reducing molecular weight and mechanical toughness.
Processing Defect
High levels of trapped moisture vaporize within the injection barrel, creating pressurized steam bubbles that exit the nozzle and deform the plastic melt. This expansion shows up as silver splay marks or cosmetic streaks on the surface of the molded part.
Drying Efficiency
Desiccant dryers apply hot, dry air to the resin hopper to drive off the moisture before the material enters the feed zone. Because the diffusion rate of water out of the polymer depends on temperature, drying times must be calculated based on the starting volatile moisture content of the lot. Processing regrind often demands longer drying cycles than virgin resin due to its irregular flake size and higher surface area.
Measurement Method
Precise coulometric Karl Fischer titration or loss-on-drying balances verify that the moisture levels have fallen below the maximum allowed processing limit.