Meaning
High molecular weight breakdown species, crosslinked gel networks and heavy oxidized residues remain within polymer matrices following high temperature thermal processing. Resin streams retain non volatile degradation contaminants because these substances possess boiling points exceeding standard devolatilization temperatures in vented extruders. The residual compounds impair mechanical performance, lower optical clarity, increase haze and seed premature fatigue failures in molded polyolefin parts.
Technical data sheets report initial polymer purity, but thermal stress during compounding and moulding generates these permanent chemical impurities within the polymer matrix.
Degradation Mechanism
Thermo-oxidative cleavage generates free radicals that recombine to build high molecular weight crosslinked structures during polymer processing. Accumulation of non volatile degradation contaminants occurs when resin experiences extended residence time in dead zones inside barrels or hot runner channels. Antioxidants retard radical formation, yet severe thermal spikes deplete primary stabilizers and accelerate gel formation.
Reusing regrind multiples thermal exposure, compounding gel concentrations in subsequent molding cycles.
Surface Defects
Melt fracture, pinholes, micro-voids and surface haze appear on extruded films and injection molded surfaces containing degraded polymer fractions. Solidified non volatile degradation contaminants create un-melted nodes that disrupt orientation during film stretching operations, causing web breaks. Injected parts exhibit splay, flow lines, reduced impact strength and localized discoloration where degraded species aggregate.
Surface appearance degrades rapidly when processing temperature limits are exceeded to lower melt viscosity.
Filtration Limits
Fine mesh screen packs remove rigid particles but fail to capture soft crosslinked gels under high extrusion pressure. Deformable non volatile degradation contaminants squeeze through fine mesh openings, requiring ultra-fine continuous extrusion separation systems to purify high-grade resins. Degassing ports vent low molecular weight volatiles while leaving heavy oxidized residues within the melt stream.
