Meaning
Reclaimed scrap materials generated during moulding and extrusion undergo mechanical granulation to re-enter primary conversion processes. Consisting of sprues and rejected parts, polyolefin regrind is blended with virgin polyethylene or polypropylene to reduce raw material costs. Granulated flake size and thermal history define material performance boundaries in subsequent moulding runs.
Excessive re-processing degrades polymer molecular weight, restricting the allowable blend percentage in structural components.
Material Degradation
Repeated thermal cycles reduce polymer chain length through thermal-mechanical shear inside the extruder barrel. Incorporating high fractions of polyolefin regrind lowers melt viscosity and reduces environmental stress crack resistance in finished parts.
Economic Utility
Blending granulated scrap directly into virgin resin streams lowers net material cost per part. A twenty percent blend of polyolefin regrind maintains acceptable tensile properties while reducing reliance on prime virgin resin. Moulders manage flake size uniformity through screen pack selection in granulators to prevent hopper bridging.
Blending accuracy prevents melt flow variations that cause flash or sink marks during injection moulding.
Quality Limits
Contamination from foreign polymers or degraded fines introduces weak points in moulded part geometry. Higher proportions of polyolefin regrind shift resin melt flow index, altering cavity filling times and part shrinkage. Moulders enforce maximum regrind addition limits, often capping usage at fifteen to twenty percent for technical components.
Regular melt flow index testing ensures that scrap blend lots meet quality specifications before production starts.
