Meaning
Re-granulated thermoplastic blends combine granulated post-industrial runners, sprues, or discarded edge trim with virgin base resin and stabilizing additives to lower raw material expenditure in conversion facilities. Utilising regrind compound recovers valuable polymer volume inside moulding operations, cutting virgin material procurement requirements across injection, extrusion, and blow moulding lines. Material properties depend on granulator screen size, thermal history count, dust extraction efficiency, and virgin blending ratios.
The operational limit is reached when cumulative polymer degradation, thermal additive depletion, or particulate contamination causes mechanical properties to drop below finished part qualification standards.
Thermal History
Multiple thermal cycles through plasticising screws and hot runner channels sever polymer chains and reduce average molecular weight. Producing a regrind compound requires tracking the thermal generation count to prevent uncontrolled melt flow index spikes across successive production batches. Heat-sensitive polymers like polyamide and polycarbonate experience rapid hydrolytic and thermal oxidation, showing pronounced yellowing and lower tensile elongation.
Stabilising packages containing secondary phosphite antioxidants must be introduced during re-compounding to neutralise free radicals formed during earlier moulding steps.
Pelletizing Extrusion
Direct feeding of coarse granulate into standard moulding machines induces inconsistent feeding, erratic recovery times, and melt temperature variations. Processing through a compounding extruder converts raw regrind compound into dense, uniform pellets with bulk density matching virgin polymer feeds. Continuous melt filtration screens eliminate unmelted fragments, degraded carbon flecks, and metal traces before they reach sensitive mould gates.
Vacuum degassing removes entrapped air, moisture, and lingering volatile degradation products during extrusion.
Mechanical Degradation
Impact resistance drops faster than tensile strength when regrind fractions rise inside technical mouldings. An unmonitored regrind compound introduces short chains and particulate inclusions that act as internal stress concentrators, promoting brittle fracture under impact loading. Automotive interior moulders enforce maximum regrind blending limits of twenty percent to protect against catastrophic part shattering in crash conditions.
Regrind lots must undergo melt flow indexing, ash content testing, and moisture verification before release to automated material conveying systems. Flake size uniformity ensures steady screw torque and prevents cushion variation during part packing.
