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theses

Resins in inks, coatings, and adhesives in food packaging are increasingly cured by UV radiation of photo-initiators (PI’s) with minimal energy requirements and without environmentally unfriendly solvents. When exposed to UV light, PI’s produce free radicals that catalyze polymerization of reactive monomers and pre-polymers into resins. PI’s and their photolytic decomposition products do not polymerize during curing but remain as residuals that can migrate into foods stored therein, becoming unintentional food additives. As interest in additive toxicity has increased, food safety organizations worldwide have developed regulations to monitor migration of these substances from food packaging. While intact PI's have been investigated, research on formation and migration of PI photolytic decomposition products is sparse.
This research characterized and quantified decomposition products of twenty-four PI's commonly used in food packaging. UV-photoinitiators were applied as films onto aluminum foil disks, UV-irradiated using an energy level representing the upper limit typically used in commercial production (125-150 millijoules), and extracted from the foil. Structure and contents of migrating compounds were determined by gas chromatography-mass spectrometry (GC-MS) and direct mass spectrometry, and tentative mechanisms of formation were proposed. Non-irradiated photoinitiator standards were analyzed as controls.
In total, 107 photolytic decomposition products were identified, 93 of which have not been previously reported as photolytic decomposition products of UV-photoinitiators. This compilation of PI decomposition products will aid industry in the tracing of the sources of compounds identified in migration testing of food packaging materials.
To assess the frequency and extent of migration of PI’s and photolytic decomposition products in actual products, migration data from 258 UV-cure food packaging samples analyzed in previous studies were re-examined. Migration of PI’s or their photolytic decomposition products was detected in all samples tested. Most commonly observed PI’s: Darocur 1173 (139/258 samples, max 1557 ng/cm2) and benzophenone (88/258 samples, max 948 ng/cm2). Most commonly observed decomposition products: 2,4,6-trimethylbenzaldehyde from (2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) (130/258 samples, max 1938 ng/cm2) and 1-phenyl-2-butanone from Irgacure 369 (83/258 samples, max 441 ng/cm2).
These results show the importance of tracking PI photodecomposition products migrating from food packaging and provide a base for developing analytical libraries to identify them.

ETD_9558

M.S.

Includes bibliographical references

doi:10.7282/t3-380j-r669

ETD graduate

The author owns the copyright to this work.