Characterisation and migration properties of silicone materials during typical long-term commercial and household use applications: a combined case study

Abstract

In consequent continuation of previous described studies, pre-characterised silicone materials were assessed for chemical and physical parameters during long-term usage. In a particular case study silicone moulds were used in a commercial pizza bakery on a daily basis up to 1700 times. Migration behaviour, uptake of fat, the amount of volatiles and extractables, as well as physical properties (elongation, tensile strength) were monitored for the whole period. The main question was whether a significant degradation or even breakdown of the silicone elastomer could take place yielding enhanced migration of dimethyl siloxanes. Oligomeric dimethyl siloxanes are reaction side-products of the polymerisation process and despite their origin as so-called non-intentionally added substances (NIAS) were found to be the by far most dominating constituents of the overall migration. Furthermore, the influence of long-term thermal stress on the functionality of the elastomer was proven. Migration into food was determined by ¹H-NMR and was found to decrease during the experiment from values between 11 and 18 mg kg⁻¹ to levels below the limit of detection (LOD < 1 mg kg⁻¹). No formation of migrating siloxanes beside the initial amount in the new, unused moulds could be observed. The loss of extractable siloxanes of the used compared with the new moulds was compensated by an uptake of fat and other lipophilic food constituents. The release of volatile organic compounds (VOC) decreased from 0.44% for the new moulds to 0.14% for the longest used ones (about 1700 individual uses; the corresponding summarised baking time was approximately 400 h at 180°C). GC-MS analysis of evaporating volatile compounds showed only cyclic oligomers for the new moulds but exclusively incorporated food components for the heavily used moulds. The physical properties of the silicone moulds remained almost constant during the experiment; no limitations in function due to the repeated thermal stress were observed. Similar results were obtained for baby teats under household conditions of use: a 100 times repeated simulated use in contact with milk followed by subsequent microwave sterilisation did not influence the function or mechanical properties. Because milk is only a weak extracting agent no significant changes in the amount of extractable siloxanes between new and used teats could was seen. Again an uptake of fat was seen and the amount of VOC decreased from 0.26% to 0.17%.

Keywords:

• analysis – NMR
• GC
• polydimethylsiloxane
• bakery products
• infant formulae

Acknowledgements

The authors would like to thank the Centre Européen des Silicones (Brussels, Belgium) for financial support of the studies and for helpful advice. The companies MAPA and Lurch as well as the Ditsch bakery (all Germany) were very helpful in providing defined samples for testing. The authors also gratefully acknowledge Dr Margit Gruner and Annett Rudolph (Technical University of Dresden, Institute of Organic Chemistry) for doing numerous NMR measurements.