Meaning
Chemical additives mixed into polymer resins prevent oxidative degradation during processing and long-term product exposure. Formulators use antioxidants to protect the molecular weight of the polymer from breaking down under heat and shear forces. These substances function by scavenging free radicals or decomposing hydroperoxides before they can initiate chain scission.
This protection is necessary to maintain mechanical properties like tensile strength and impact resistance in both virgin resin and recycled feedstocks.
Thermal Protection
Primary radical scavengers neutralize the propagation phase of thermal degradation in the melt. These antioxidants react rapidly with alkoxy and alkyl radicals to form stable products, preventing the runaway reaction that leads to polymer crosslinking or chain scission. Secondary stabilizers work in tandem by reducing hydroperoxides to stable alcohols.
This cooperative action is necessary when compounding highly sensitive materials like polypropylene or polyethylene.
Extrusion Retention
Multiple heat passes during extrusion or moulding consume the active additives. If the concentration of antioxidants falls below a critical threshold, the melt flow index of the polymer shifts. This shift results in short shots or flashing.
Recycled resins require booster doses to survive reprocessing.
Depletion Measurement
Oxidation induction time testing evaluates the remaining protective capacity of the additive package in a formulated resin. By heating a small polymer sample under an oxygen atmosphere until an exothermic oxidation reaction occurs, laboratory technicians measure how long the stabilizers can resist degradation. This measurement provides a direct timescale of material stability at a set temperature.
The resulting data allow moulders to predict the storage life and thermal durability of the raw material before committing it to a high-volume production run.
