Meaning
Chemical contaminants present in organic pigment batches represent a risk for color masterbatches used in food-contact plastics. During the synthesis of pigment colorants, diarylide yellow impurities such as unreacted dichlorobenzidine or monoazo intermediates can remain within the crystalline pigment structure. These chemical residues pose migration risks if the polymer is exposed to fatty foodstuffs.
Thermal Stability
Processing colorants at temperatures exceeding two hundred degrees Celsius causes thermal degradation of these organic pigment contaminants. Heated diarylide yellow impurities release primary aromatic amines which are restricted substances under global food safety standards. This thermal breakdown limits the use of diarylide pigments to low-temperature resins like polyethylene or plasticized polyvinyl chloride, where melt temperatures remain well below the degradation threshold of the pigment molecule.
If processed in polymers like polyamide, the high processing heat breaks the diarylide linkage to generate hazardous amines that migrate to the surface of the molded article.
Detection Method
High performance liquid chromatography coupled with mass spectrometry provides a reliable way to quantify these chemical leftovers in raw pigments. Analytical testing of diarylide yellow impurities requires extraction of the pigment matrix with organic solvents to separate the target analytes. Testing laboratories run these protocols to verify compliance before compounding the pigments into masterbatches.
Regulatory Threshold
Limit values for primary aromatic amines in final molded products determine the acceptable concentration of pigment-borne contaminants. Exceeding these levels during extraction tests leads to batch rejection. Moulders must balance the color strength of these pigments against the potential liabilities of chemical migration.
