Calculating Masterbatch Addition Rates for Post Consumer Polyethylene Compounds
Masterbatch let-down rates for post-consumer polyethylene compounds require mass-balance adjustments offsetting baseline additives, ash, and carrier viscosity.
Carrier Resin Compatibility
Meaning
Thermodynamic miscibility and rheological matching between a masterbatch vehicle polymer and a base moulding resin govern whether additives disperse homogeneously without causing phase separation during plastication. In colour and additive delivery systems, carrier resin compatibility establishes the physical boundary conditions for incorporating concentrates into bulk pellets during extrusion or injection moulding. When this molecular affinity fails, unblended interfaces generate localized stress concentrations and optical haze.
The condition terminates where liquid colorant delivery systems replace solid thermoplastic carriers entirely.
Melt Rheology Matching
Viscosity ratios between masterbatch vehicles and base polymers determine the shearing efficiency inside the plasticating screw barrel. Achieving carrier resin compatibility requires a vehicle resin with a melt flow index equal to or slightly higher than the parent moulding resin under equivalent processing temperatures. When carrier viscosities exceed host melt values, masterbatch pellets bypass proper homogenization and form gel defects in final parts.
Conversely, excessive fluid fluidity induces premature phase slip across the screw flights.
Phase Interface Integrity
Co-crystallization behaviour between disparate polymer backbones sets the mechanical cohesion of the moulded wall. If carrier resin compatibility fails at cooling interfaces, non-polar polyolefin carriers form immiscible inclusions within engineering thermoplastics like polycarbonate or polyamide. These microscopic boundaries act as micro-notches under impact loading, dropping tensile impact strength below virgin datasheet baselines.
Reclaim streams compound this breakdown through accumulated foreign resin carriers.
Optical Surface Defect
Surface appearance across decorative components reflects the distribution of additive packages in the skin layer. Incompatible masterbatch carriers cause delamination, pearlescence and splay marks along mould flow fronts as segregated polymer droplets migrate toward low-pressure cavities. Molders increase barrel temperatures to force miscible blending, but prolonged thermal exposure degrades fragile organic pigments and functional stabilizers.
Such thermal degradation accelerates tool fouling and drives scrap rates upward during high-speed production cycles.