Meaning
Non-intentionally added substances migration describes the mass transfer of unintended chemical compounds from polymer packaging or moulding equipment into contacting media during thermal processing or final use. Molecular fragments move through the solid matrix via diffusion driven by concentration gradients established between the plastic part and adjacent contents. Barrier layers and crystalline fractions restrict this molecular mobility by lengthening the tortuous path diffusing species must travel.
Regulatory thresholds govern allowable migration limits for specific migrants based on toxicological data derived from migration testing protocols.
Thermal Degradation
Polymer processing temperatures exceeding thermal stability thresholds accelerate chain scission and generate new non-intentionally added substances within the melt. Extruder barrel residence time and localized shear heating determine the extent of polymer breakdown occurring prior to cavity filling. Volatile decomposition products migrate rapidly toward the surface of moulded articles during cooling phases due to high initial concentration gradients.
Recycled polymer streams accumulate higher baseline levels of thermal degradation byproducts through repeated exposure to processing heat cycles.
Regrind Economics
Incorporating post-industrial regrind introduces cumulative non-intentionally added substances that alter the chemical profile of finished mouldings compared to virgin resin formulations. Economic pressures frequently incentivize higher regrind inclusion rates despite the increased risk of contaminant accumulation across successive reprocessing loops. Virgin material blending dilutes migrant concentrations to maintain compliance with regulatory migration limits established for food contact applications.
Analytical screening of regrind batches requires thermal desorption gas chromatography to quantify unknown degradation products before production release.
Part Specification
Finished moulded components demand rigorous migration validation that distinguishes bulk material properties from actual surface release characteristics observed under end-use conditions. Moulder process settings including injection speed and mold temperature influence skin-core morphology and localized crystallinity which directly affect surface diffusion rates. Surface area to volume ratios dictate the apparent migration kinetics of thin-walled packaging items exposed to liquid simulants.
Material certificates of analysis reflect virgin resin purity rather than the actual migration performance of parts shaped under aggressive production conditions.
