Meaning
Chemical breakdown of polymer backbones driven by simultaneous exposure to elevated temperatures and atmospheric oxygen alters mechanical and optical properties during thermoplastic processing. Controlling thermal oxidative degradation is essential for Chinese polymer compounding plants to preserve melt strength and color stability. Governed by national material standards and factory processing guidelines, the chemical reaction generates hydroperoxides and radical species that sever polymer chains.
The degradation mechanism governs high-temperature processing limits, stopping at ambient temperatures where photo-oxidation becomes the primary failure mode.
Reaction Mechanism
Elevated processing temperatures generate free alkyl radicals on polymer chains that combine rapidly with dissolved oxygen. Peroxyl radicals abstract hydrogen from adjacent polymer segments, forming hydroperoxide groups that decompose into secondary radicals. Radical propagation accelerates molecular weight reduction through chain scission or causes unwanted viscosity increases through crosslinking.
Processing equipment equipped with vacuum degassing removes entrapped oxygen to slow oxidative degradation inside extruder barrels. Adding primary hindered phenolic antioxidants suppresses radical formation during melt processing.
Factory Verification
Factory quality assurance teams monitor melt flow index changes between raw resin and finished parts. Chinese national standards specify maximum permissible melt index shifts for export-grade molded goods. Non-compliant melt index shifts indicate thermal damage during manufacturing.
Process Limitation
Antioxidant additives undergo thermal depletion when processing residence times exceed recommended equipment limits. Restricting melt residence time remains necessary to prevent degradation inside hot runner molding systems.
