Polyolefin Recyclate Quality Verification Methods for Packaging Resin Compounds
Polyolefin recyclate quality verification relies on multi-temperature melt flow testing, oxidation induction time, and continuous screen filtration tracking.
Screen Pack Filter
Meaning
Layered wire mesh assemblies mounted against a breaker plate remove solid contaminants and homogenize polymer melt upstream of an extrusion die. A screen pack filter captures un-melted gel particles and foreign debris from the flowing polymer matrix. The assembly also generates backpressure within the extruder barrel, improving thermal mixing and shear uniformity before shape forming.
The governing function terminates at liquid phase separation, as dissolved moisture and volatile organic compounds pass through the mesh unhindered.
Mesh Construction
Arranging woven wire screens with coarse mesh supporting fine mesh prevents screen rupture under high hydraulic pressure. A typical screen pack filter arranges a fine center mesh between coarser protective layers to maximize filtration surface area and structural integrity. Stainless steel wire weaves resist thermal degradation and chemical attack at elevated processing temperatures.
Pressure Differential
Contaminant accumulation on the upstream face of the mesh restricts melt flow and increases pressure drop across the breaker plate. Rising pressure increases melt temperature through viscous dissipation, altering polymer viscosity and extrudate dimensions. Moulders monitor pressure transducers to schedule manual screen changes before melt fracture occurs.
Homogenization Effect
Forcing polymer melt through narrow mesh openings shears agglomerated color pigments and eliminates thermal gradients within the stream. The resulting uniform flow yields consistent extrudate wall thickness and superior surface finish. Clean filter assemblies stabilize output rates during long production runs.