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Abstract
Abstract In this study internal and seam covering coatings as used in food cans were investigated on their potential to release nanomaterials (pigments, fillers) when food is stored and processed (sterilised) within coated cans. Two interior lacquers based on epoxy- and polyester- (with and without bisphenol A) resins and two seam covering coatings were used as lacquer matrices covering typical lacquer formulations. Eight different nanomaterials (four pigments and four fillers) were investigated that are typically used for adjusting colour and enhancing thermal and mechanical stability of the coatings. Aqueous sodium dodecylsulfate surfactant solution showed best suitability to disperse the nanomaterials with sufficient stability. A stable multi-nanomaterial dispersion, containing all eight nanomaterials at the same concentration each, was successfully used to develop an analytical method based on asymmetric flow filed-flow fractionation (AF4) coupled with multi angle laser light scattering (MALLS) detection and inductively coupled plasma mass spectrometry (ICP-MS) that allowed screening for possibly migrating nanomaterials at a limit of detection of 0.5 mg/dm2. Coated metal plates were brought in contact with the aqueous surfactant solution as alternative food simulant for 2 h at 130 °C (sterilisation) followed by for 10 days at 60 °C (long-term storage). Via AF4/MALLS measurements the release of small oligomeric components from internal coating formulations was detected. However, the particle- and element-specific detection system demonstrated the none-migration of nanomaterials (fillers or pigments) from all test samples.
Highlights
Metal based packaging finds application as e.g. closures, lids, tubes, beverage and food cans
Via the morphology obtained by Transmission electron microscopy (TEM) and the elemental composition as determined by nano-spot-energy dispersive X-ray spectroscopy (EDX) analyses a clear allocation of different nanomaterials was possible
The analytical method based on AF4/multi angle laser light scattering (MALLS) was capable to characterize and detect the eight nanomaterials in an aqueous surfactant solution used as alternative food simulant
Summary
Metal based packaging finds application as e.g. closures, lids, tubes, beverage and food cans. To prevent interactions between the metal and packed food (especially in case of e.g. acidic food) cans need to be lacquered or coated on the inside food contact side. The metal sheets are coated by a liquid lacquer and heat cured before cutting and forming the cylinder or the end parts. After forming the base cylinder, there is a free metal edge at the seam which still needs to be protected. In the lacquer formulation, additives are used to adjust properties of the coating like flexibility, mechanical/thermal stability, barrier effect or colour (Dubbert, Schwirn, Völker, & Aper, 2014; Koleske, Springate, & Brezinski, 2013, Oldring & Nehring, 2007)
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