Polyolefin Degradation Mechanics in Post-Consumer Resin Recyclate Streams
Polyolefin recyclate degradation occurs via PP chain scission and PE crosslinking; verification requires dual-weight MFR sweeps and 30-minute OIT testing.
Fenton Type Metal Catalyzed Oxidation
Meaning
Catalytic reaction where transition metal impurities accelerate the oxidative degradation of polymers by generating highly reactive hydroxyl radicals. This Fenton type metal catalyzed oxidation occurs when trace iron or copper contaminants in the resin react with hydroperoxides during high-temperature processing. The reaction leads to severe loss of mechanical properties and yellowing.
Radical Generation
Transition metals cycle between oxidation states to continuously decompose polymer peroxides. This Fenton type metal catalyzed oxidation generates a cascade of free radicals that rapidly break down the polymer chains. Adding metal deactivators is necessary to interrupt this process.
Processing Consequence
Recycled plastics often contain higher levels of metal contaminants from sorting residues, which promotes degradative reactions during reprocessing. This Fenton type metal catalyzed oxidation reduces the melt strength of recycled resin during blow molding or film extrusion, causing parison sag or bubble instability. Stabilizing recycled feedstocks requires higher doses of phenolic antioxidants.
Part Degradation
Long-term exposure to moisture and trace metals can cause early part failure in automotive under-hood applications. This Fenton type metal catalyzed oxidation causes surface micro-cracking and loss of impact strength in nylon and polyolefin parts exposed to engine fluids or cooling systems, meaning that moulders must select specially stabilized grades that contain chelating agents to bind metal ions before they can trigger the degradative reaction cascade.