Meaning
Quantitative measurement of contaminant removal expressed as a percentage or logarithmic reduction determines the cleaning performance of plastic recycling processes applied to post-consumer polymer streams. In post-consumer polyolefin and polyethylene terephthalate recycling, decontamination efficacy dictates whether recycled flake satisfies food-contact compliance requirements established by regulatory authorities. The metric evaluates the extraction of volatile organic compounds, industrial chemicals, flavour compounds and deep-seated migrant substances out of the polymer matrix.
Physical verification ends at the limits of analytical detection for designated surrogate challenge chemicals.
Challenge Testing
Evaluation protocols run deliberate challenge tests using surrogate contaminants of varying molecular weights and polarities to benchmark recycling machinery. Contaminants such as toluene, chlorobenzene, phenylcyclohexane and benzophenone are compounded into polymer batches at concentrations reaching thousands of parts per million. The contaminated material runs through washing, drying, solid-state polymerization, and vacuum degassing extruders to measure cleaning power.
Comparing contaminant levels before and after processing yields the logarithmic reduction factor. Regulators require a minimum four-to-five log reduction for hazardous surrogates before authorizing food-contact flakes for bottle-to-bottle processing.
Extrusion Stripping
Decontamination operations rely heavily on deep vacuum stripping, heat exposure and high residence times within continuous processing vessels. Multi-vented twin-screw extruders peel away surface contaminants while drawing vacuum levels below five millibar to pull volatile molecules out of the low-viscosity polymer melt. Diffusion rates within solid-state polymerization reactors rise when temperatures reach twenty degrees below the resin melting point under an inert nitrogen blanket.
Highly crystalline recycled polyethylene terephthalate resists contaminant infusion, whereas polyolefins possess high chain mobility that allows deep chemical absorption. Moulders running recycled materials must match resin source history to the stripping efficiency of their upstream suppliers.
Production Economics
Reaching elevated cleansing targets consumes substantial energy, expanding production costs per ton of recycled polymer. High vacuum pumps, extended residence towers and heated washing systems with caustic soda add capital expense to regrind preparation lines. When decontamination falls short of food-grade criteria, recyclers downgrade resin sales to non-food packaging, horticultural containers or drainage pipe extrusion.
Regrind sold into food-grade streams commands price premiums of thirty to sixty percent over non-cleansed utility recyclates. Virgin pellets maintain consistent baseline purity without the processing overhead of surrogate verification and gas chromatography screening. Virgin-to-regrind blending ratios are governed by the certified decontamination efficacy of the recycled batch.
