Post Consumer Polyolefin Recycling Property Degradation Fundamentals
Polyolefin property degradation stems from chain scission, oxidation, and contamination; managing property drift requires strict OIT, melt index, and blend controls.
Olefin Block Copolymers
Meaning
Thermoplastic elastomers featuring alternating hard and soft segments arranged in a linear polymer chain provide exceptional elasticity without requiring traditional vulcanisation steps. Manufacturers utilise olefin block copolymers to control melt flow rates during injection moulding and extrusion processes. Thermal shrinkage creates dimensional instability in finished parts when processing temperatures drift outside narrow operational windows.
Production lines running virgin material achieve predictable shrinkage rates, whereas processing high ratios of regrind introduces melt viscosity shifts that alter final part dimensions. Datasheet values represent optimal laboratory conditions that standard shop floor equipment rarely matches across high volume production runs.
Thermal Window
Optimising tool temperatures prevents surface blemishes during high speed cavity filling stages. Crystallisation kinetics dictate the cooling duration required before part ejection occurs without distortion. Cooling lines operating with mineral scale deposits restrict heat transfer rates and extend cycle times.
Barrel zone profiles govern the melting behaviour of rigid crystalline domains before material enters the injection nozzle. Shear heating generated by high screw rotation speeds degrades soft segments inside the polymer structure.
Melt Viscosity
Molecular weight distribution governs how smoothly molten polymer flows through complex runner systems. Shear thinning behaviour allows high molecular weight grades to fill thin walled geometries at elevated injection pressures. Inconsistent pellet feed rates cause shot weight variations that lead to sink marks on thick structural ribs.
Viscosity measurements obtained from capillary rheometers guide toolmakers during gate dimension calculations. Pressure drops across nozzle tips indicate whether polymer degradation occurs inside heated barrels.
Filler Loading
Inorganic additives modify tensile modulus values to meet specific stiffness requirements in structural automotive components. Compounding virgin resin with talc or calcium carbonate increases flexural modulus while reducing overall material costs. Poor dispersion of mineral fillers creates localized weak points that fail standard drop impact tests.
Shear forces developed by twin screw extruders break down agglomerates to achieve uniform particle distribution. Scrap rates climb rapidly when regrind batches contain excessive moisture levels that generate surface bubbles during plasticisation.