Recycled Polyolefin Oligomer Identification for Food Contact Clearance
Clearing recycled polyolefins for food contact demands HPLC-GC-FID and GCxGC-MS identification of oligomeric fractions evaluated against TTC thresholds.
Cramer Class Assignment
Meaning
Polymer rheology classification defines the flow behavior of a resin batch against standardized shear rates to predict tool filling performance. A cramer class assignment groups raw materials by their melt mass-flow rate and molecular weight distribution to ensure consistent behavior during injection cycles. This sorting dictates whether a specific resin grade matches the viscosity curves required for precision multi-cavity tooling.
Processing Baseline
Cavity pressure sensors detect shifts in viscosity that arise when a material deviates from its designated group. Each cramer class assignment establishes the target window for fill velocity and pack timing during trial runs. When a resin falls outside its assigned category, the machinery fails to maintain uniform shot weights across consecutive production cycles.
Excess flash or short shots occur when the machine operator ignores these documented flow differences.
Material Economics
Regrind percentage thresholds change based on the assigned category of the original virgin feedstock. A cramer class assignment allows compounders to calculate the maximum permissible contamination levels before the physical properties of the plastic fail to meet mechanical requirements. Using regrind instead of virgin resin often narrows the processing window because the lower molecular weight fractions shift the melt behavior.
Technical Specification
Datasheet values provide a general range, but the molding process requires the narrow bandwidth defined by this categorization method. While manufacturers list a wide melt flow index on product information sheets, the cramer class assignment acts as a precise filter for industrial production. A resin grade with a tighter class window reduces the need for frequent tooling adjustments during high volume runs.