Polyolefin Degradation Mechanics in Post-Consumer Resin Recyclate Streams
Polyolefin recyclate degradation occurs via PP chain scission and PE crosslinking; verification requires dual-weight MFR sweeps and 30-minute OIT testing.
Polydispersity Index Crossover Point
Meaning
Rheological frequency value where the storage modulus and loss modulus of a molten polymer intersect during dynamic shear testing. Identifying the polydispersity index crossover point helps determine the molecular weight distribution of a polymer resin without running gel permeation chromatography. It acts as a predictor of resin processability during high-speed extrusion or injection molding.
Viscoelastic Indicator
High frequencies are needed to reach the modulus intersection in narrow molecular weight resins. This polydispersity index crossover point moves to lower frequencies as the molecular weight distribution broadens. Moulders use this value to detect batch-to-batch polymer variation.
Molding Application
Consistent melt elasticity is required to prevent parison sag in blow molding and melt fracture in film extrusion. Monitoring the polydispersity index crossover point ensures that incoming raw materials have the correct balance of flowability and melt strength. This measurement is performed on a rotational rheometer.
Process Stability
Shifted crossover values reveal when recycled polymer or regrind has degraded due to multiple heat histories. This polydispersity index crossover point tracking shows if chain scission or cross-linking has occurred during recycling, which allows technicians to adjust the regrind blending ratio before the modified resin enters the production line and causes unacceptable variations in part dimensions or surface finish.