Melt Shear History and Contaminant Catalyzed Scission in Post Consumer Polyolefin Silo Blends
Deactivate metal catalysts and neutralize acid traces with targeted additives to stabilize viscosity drift and optimize landed cost per good recycled part.
Sterically Hindered Phenols
Meaning
Primary organic antioxidants protect polymers from thermal and oxidative degradation by donating hydrogen atoms to free radicals. These chemical additives, known as sterically hindered phenols, interrupt the propagation phase of the oxidation cycle by forming stable, unreactive phenoxy radicals. They are added during resin manufacturing and compounding to ensure long-term thermal stability of the plastic parts.
Chemical Architecture
The molecular structure contains a phenolic ring with bulky alkyl substituents, typically tert-butyl groups, located adjacent to the hydroxyl group. This steric hindrance prevents the resulting phenoxy radical from attacking the polymer backbone or participating in chain transfer reactions. The bulky groups ensure that the radical remains stable and unable to propagate degradation.
This molecular configuration makes these additives effective primary antioxidants for a wide variety of thermoplastic resins, particularly polyolefins subjected to continuous thermal stress.
Stabilization Performance
During long-term exposure to heat and oxygen, these additives scavenge propagating peroxy radicals to prevent chain scission and cross-linking. This protection preserves the mechanical properties, such as tensile strength and elongation at break, of the moulded components over their service life. Without these stabilizers, polyolefins would become brittle and fail within a short period of environmental exposure.
Industrial Sourcing
High-molecular-weight phenol additives are selected for applications demanding low volatility and resistance to extraction by water or solvents. In recycled resin streams, compounding operations must measure the remaining antioxidant level and replenish these additives to restore long-term stability. This restabilization process enables the reuse of post-consumer resins in demanding consumer and automotive applications.
Evaluating Degradation Mechanisms in Post-Consumer Polyolefin Flake
Polyolefin degradation evaluation requires coupling multi-load melt flow testing and OIT analysis to quantify chain scission and restabilize flake lots.