Phenolic Antioxidants

Stabilization Mechanism

Thermal shear during extrusion generates free radicals along the aliphatic carbon backbone of polyolefin chains. Active phenolic antioxidants donate hydrogen atoms to reactive peroxyl radicals, converting them into stable hydroperoxides and halting autocatalytic polymer degradation. The resulting phenoxyl radical remains unreactive due to steric hindrance provided by bulky tert-butyl groups on the aromatic ring.

This radical scavenging mechanism prevents polymer chain scission and severe melt flow index shifts during melt processing.

Processing Protection

Multi-pass extrusion studies demonstrate that adding hindered phenols preserves melt viscosity and mechanical impact strength across multiple processing cycles. Injection moulders processing polypropylenes rely on phenolic antioxidants to prevent yellowing and surface embrittlement inside hot runner systems. Inadequate stabilizer loading leads to rapid polymer degradation, resulting in part brittleness and cosmetic surface defects.

Additive Depletion

High processing temperatures and long residence times consume active antioxidant molecules within the polymer melt. Once total additive depletion occurs, rapid resin oxidation leads to loss of physical properties and premature part failure.