Migration studies and chemical characterization of low molecular weight cyclic polyester oligomers from food packaging lamination adhesives

Abstract

Laminate structures are widely used for food packaging applications. Polyester urethane‐based adhesives are very common materials for bonding the layers of such laminates together. Unintended by‐products of polyester synthesis include low molecular weight cyclic polyester oligomers (cyclic oligoesters) that lack the required hydroxyl functionality to react with isocyanates to form the intended high molecular weight polyurethane polymer and remain as impurities with high migration potential. Our investigation conducted migration studies of 537 commercial and/or developmental food packaging laminate structures by using food simulants with gas chromatography‐mass spectrometry analyses of the extracts. A subset of the extracts were also analysed by high‐performance liquid chromatography‐mass spectrometry and gas chromatography‐mass spectrometry with chemical ionization. Migration of cyclic oligoesters of diverse chemical structure was observed in nearly all of the samples analysed. Aside from migrants originating directly from polyolefin sealant films on the food‐contact side of the laminates, cyclic oligoesters were the migrants detected at next highest concentration. This report presents electron ionization mass spectra and molecular structures of 106 cyclic oligoesters including a series of novel as well as previously identified species. Fifty‐six cyclic oligoesters migrated from the 537 laminate samples analysed were evaluated for frequency of occurrence and migration concentration range. The most commonly observed cyclic oligoester migrants were those derived from combinations of the polyhydric alcohols, diethylene glycol, and neopentyl glycol and the dibasic acids, adipic, and phthalic/isophthalic.