Recycled Polyolefin Oligomer Identification and Toxicological Screening Basics
Verify recycled polyolefin food contact clearance by combining LC-GC-FID quantification of C10-C50 oligomers with toxicological screening under Cramer Class thresholds.
Secondary Extrusion
Meaning
Additional compounding or shaping step where pre-molded or compounded plastic materials are melted and extruded a second time. This secondary extrusion is commonly utilized to blend regrind with virgin polymer or to apply protective coatings to molded products. It can degrade polymer chains if thermal stabilizers have been depleted during the first heat cycle.
Material Degradation
Multiple heat cycles reduce the molecular weight of the resin through thermal-oxidative degradation. This secondary extrusion requires the addition of fresh process stabilizers to prevent loss of impact strength. Measuring melt flow rate identifies this degradation.
Economic Benefit
Incorporating post-industrial scrap back into the production stream reduces raw material costs for molders. This secondary extrusion must be carefully monitored to keep the ratio of degraded polymer within acceptable limits. This step requires specialized screw designs to handle regrind flakes.
Process Optimization
Temperature profiles and shear rates must be kept low during this second processing run to protect the polymer. This secondary extrusion causes a decrease in melt viscosity that can lead to flashing or dimensional instability in the molded parts, which requires the extrusion operator to use cooling technologies and precise melt-pump controls to maintain a stable output across the entire manufacturing run.