Measurement Uncertainty Modeling for Trace Migrants in Post-Consumer Resins
Quantifying trace migrant compliance in post-consumer resins requires modeling sampling heterogeneity and analytical variance to establish guardbanded decision rules.
Gy Sampling Theory
Meaning
Mathematical framework that defines the conditions required for representative sampling of particulate materials holds that the total sampling error must be minimized through correct sampling equipment and sample mass. In the plastics industry, gy sampling theory provides the formulas to calculate the correct sample size of resin blends, masterbatches and regrind. It prevents the distortion of quality control tests by ensuring that the collected sample matches the true composition of the bulk material.
Blend Inconsistency
Blending virgin resin with recycled regrind creates a coarse, multi-phase mixture that is prone to segregation in the supply hopper. Applying the principles of gy sampling theory allows the moulder to determine the correct mass of polymer to sample for moisture or additive analysis. This precaution is essential to avoid using incorrect processing temperatures that are based on unrepresentative measurements.
Defect Reduction
Inconsistent dispersion of flame retardants or plasticisers leads to mechanical failure in the moulded component. When the sampling process violates the rules of this theory, the resulting analytical error can lead to the acceptance of a deficient batch. This error can manifest as brittle failure in the field or cosmetic defects like surface splay and color shifting.
Economic Value
Incorrectly rejecting compliant polymer shipments because of poor sampling techniques costs time and money. This mathematical approach protects the processor from the double cost of false rejections and unexpected production shutdowns.