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.
Acid Scavengers
Meaning
Functional chemical additives neutralize acidic residues left by polymerization catalysts or generated during processing to protect both the polymer matrix and the moulding equipment. These compound choices, often categorized as acid scavengers, prevent the degradation of halogenated polymers and shield steel moulds from corrosive attack. The additive acts by chemical reaction with hydrogen chloride or other acidic byproducts.
Chemical Neutralization
Metal oxides and fatty acid salts react directly with halogen acids to form stable, non-corrosive salts. In linear low-density polyethylene, residues from Ziegler-Natta catalysts can generate hydrochloric acid during high-temperature extrusion, which then initiates chain degradation. The use of hydrotalcite or calcium stearate in the resin formulation halts this destructive chemistry by binding the chlorine ions within a crystalline lattice.
This binding prevents the acid from accelerating further polymer breakdown.
Equipment Protection
Corrosive wear on highly polished mould cavities and extruder screws increases maintenance costs and degrades part surface finish. When acid scavengers are omitted from the compounding recipe, acidic vapours pit metal surfaces during the cooling phase of injection moulding. This pitting forces frequent tool refurbishing and spoils the optical clarity of the produced parts.
Resin Specification
Datasheet values for additive concentrations are set to survive the primary compounding step, but subsequent regrind passes consume the protective reserve. Recycled materials thus demand higher dosages of these additives to maintain process stability. Secondary stabilizers must be adjusted to account for the depletion of the original neutralizing agents.