Contractual Risk Allocation Mechanisms for Recycled Resin Verification
Contractual risk allocation for reprocessed resin requires rigid specification bounds, quarantine controls, and clear price deduction mechanics.
Gel Count
Meaning
Numerical measurements of unmelted or cross-linked polymer particles found in a film or sheet sample determine the optical and structural purity of the resin. A high gel count indicates that the polymer contains localized regions of high molecular weight or contaminated material that did not homogenize during extrusion. This evaluation is typically performed using automated optical sorting systems or manual inspection under polarized light.
The test applies directly to high-clarity packaging films and blow-moulded bottles where visual perfection is required.
Quality Evaluation
Visual inspections on extruded film tapes provide a continuous measurement of polymer purity during raw material production. When calculating the gel count, technicians record the number of defects per square meter of film. These defects are categorized by size, typically ranging from sub-millimeter particles to larger globs that disrupt the film surface.
Consistently low counts are required for medical-grade resins and optical films.
Process Origin
Thermal degradation in the extruder barrel is a primary cause of cross-linked gels in polymer melts. If the resin remains in dead spots of the screw or die for too long, it begins to degrade and form hard, unmelted spots that raise the gel count. Inadequate screw design or incorrect temperature profiles can also fail to melt high molecular weight fractions of the resin.
Regular purging and the use of specialized screw coatings can reduce gel formation.
Part Failure
Mechanical weaknesses in thin-walled molded or extruded parts often originate at the site of an unmelted gel. When the gel count is high, the risk of pinholes in blown films or premature failure in high-pressure pipes increases. These defects act as stress concentrators, causing the polymer to crack or tear under low mechanical loads.
In addition, gels can clog melt filters during processing, which increases backpressure and leads to frequent downtime for filter changes. Processors must reject resins that exceed the maximum permissible gel count to protect their production efficiency and part performance.