Analytical approaches to identify potential migrants in polyester-polyurethane can coatings

Area of Science:

• Materials Science
• Polymer Chemistry
• Analytical Chemistry

Background:

• Polyester-polyurethane coatings are used in food packaging.
• Assessing chemical migration is crucial for food safety.
• Understanding migration requires detailed analytical characterization.

Purpose of the Study:

• To evaluate the safety of a specific polyester-polyurethane can coating.
• To identify and quantify potential chemical migrants from the coating.
• To establish parameters for achieving a full cure and low migration.

Main Methods:

• Solvent extraction of cured coating films.
• Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) for migrant identification.
• Quantification of migrants, including polyester oligomers and isocyanates.

Main Results:

• Overall migration primarily consisted of 13 polyester oligomers (cyclic and linear) up to MW 800.
• No detectable residues of blocked or unblocked 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl cyclohexane homopolymer (IPDI) were found (<0.01-0.02 µg/dm²).
• Migration levels were influenced by cure time, temperature, catalyst, additives, and formulation aging.

Conclusions:

• The primary migrants are polyester oligomers, with minimal isocyanate residues.
• Coating cure completeness, indicated by extractable IPDI levels, is critical for low migration.
• Specific parameters can be defined to ensure effective curing and minimize migration in commercial production.