A03046: Chemical migration from silicones used in connection with food contact materials and articles

Study Duration: April 2003 to January 2005

Contractor: Rapra Technology Ltd.

Silicones are used in a variety of different food contact situations and conditions. The silicone class of polymers is very versatile and the physical form of the silicone product can vary from relatively low molecular weight lubricants and oils, through high molecular weight rubbery polymers to extensively cross-linked hard resins. At present there is no specific EU harmonised legislation for food contact silicone materials. However, they are covered by Regulation (EC) No 1935/2004, which in Article 3 provides that substances should not migrate into food in quantities that would harm human health or affect the quality and characteristics of the food. Annex 1 of this Regulation includes silicones within a list of materials and articles that will be covered by specific measures. There is also a Council of Europe resolution on Silicones (Resolution AP 2004) but this is intended for guidance use by the industry and is not legally binding.

This project was carried out to provide detailed information on the types and composition of silicone based products that are used in contact with food and identify the extent to which migration of specific constituents into food could occur. The project builds on information previously obtained on elastomeric silicone food contact materials such as seals and tubing.

Information on the types of silicone products that come into contact with food and available migration data was reviewed. Additionally, possible migrants, including reaction/breakdown substances, were predicted from available manufacturing, compositional and curing data. To check these literature-based findings, representative commercial food contact silicone products (four silicone rubbers, three silicone fluids and three silicone resins) were obtained. A range of analytical techniques (eg Gas Chromatography – Mass Spectrometry and Liquid Chromatography – Mass Spectrometry) was used to identify substances that were present with a potential to migrate. Overall and specific migration experiments were carried out on each of the silicone products using distilled water, 3% acetic acid, 10% ethanol and 95% ethanol (solvents that simulate different food types) to assess substances that did migrate. The test conditions for migration experiments reflected in-service contact conditions for the products. Substances with potential migratory behaviour were targeted and, where found, quantified. Specific migration tests on the silicone products were also carried out with foods (carbonated water, orange juice, white wine and olive oil). In addition migration testing was undertaken on examples of bakeware items coated with a heat resistant, non-stick silicone resin coating.

Main types and uses of silicones in contact with food

From the research, the main types and uses of silicone products in food processing and cooking have been identified as:

• Silicone rubbers - used in a range of applications including baking tray coatings, baby soothers and feeding teats, tubing, stoppers, seals/gaskets, valves, moulds and milk liners.
• Silicone fluids - used as processing aids in the manufacture of food and as flow promoters in the processing of other polymer products.
• Silicone resins - used for a variety of non-stick applications as an alternative to teflon type coatings eg. loaf pans, swiss roll tins, trays, and as linings for ovens.

Differences in chemical composition and rubber cure type were identified and water based, solvent based and low solvent content resin types are used. In addition to non-stick properties, silicone materials have the advantage of high heat stability and so can be used in applications where heat resistance is important. For example, in drink dispensing machines - where both silicone seals and tubing are used, and in food manufacturing (eg food dispensing valves). The materials can also be used at, or near ambient temperatures, e.g. as stoppers for wine barrels and bottles and as milk liners. Silicone products are used in contact with both aqueous foodstuffs (eg orange juice and boiled sweets), alcoholic drinks (eg wine and beer), and fatty foods (eg meats, cheese and cream).

Compositional analysis

Silicone oligomers (ie low molecular weight polymer molecules) were shown to have the greatest migration potential. Oligomers in the range trimer (ie 3 monomer units) to those containing greater than 20 units were detected. In some product types, the cyclic hexamer was most abundant, although in general the abundance of the individual oligomers in the product increased with their molecular weight. Cure related species (eg platinum catalysts and peroxide breakdown products) where detected were at very low (parts per million) levels. Silicone rubbers and resins are subject to high temperatures during manufacture and in service and this has the potential to generate oxidation products (eg formaldehyde). Some evidence for these types of chemical species was found but, as with the cure related species, they were at very low levels.

Migration to simulants and food

As expected from the compositional analyses, the only substances found to migrate were silicone oligomers. For rubbers and resins in contact with the aqueous food simulants, and the resins in contact with the fatty food simulant (95% ethanol), overall migration tests showed that the total amount of siloxane material was below the Council of Europe Resolution guideline value (10 grammes per square decimetre).

Higher levels of migration were found where the rubbers were in contact with fatty food simulant, but this is a severe test and analysis showed that a significant proportion of the migrant was above the molecular weight upper limit (1000 Daltons) for significance in terms of absorption in the gastro-intestinal (GI) tract. Rubbers showed a higher level of migration into foodstuffs than resins, particularly into fatty type foods. Lower values were found into aqueous type foods (eg orange juice). Only one, very low positive result was obtained for the migration of oligomers from commercial resin coated bakeware. This was obtained using olive oil.

Silicone fluids behaved differently to the rubbers and resins because of their physical form. Experimental methods were developed to investigate migration. Test conditions, particularly the ratio of fluid to simulant, had to match in-service usage as this ratio affected the amount of fluid that migrated. Higher levels of migration were found than from the rubber and resin products. Silicone oligomers were detected as migrants in both simulants and foodstuffs, with the amount migrating increasing as the viscosity (ie average molecular weight) of the fluid decreased. Again the amount of oligomeric material that migrated was found to be higher with fatty food simulants than aqueous simulants. Food constituents interfered with the data in the migration tests carried out into food. However, where data could be generated it showed reasonable agreement with that obtained using simulants.

The final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency (tel: 020 7276 8181/8182) or email: library&info@foodstandards.gsi.gov.uk).

Contact: For any enquiries concerning this research project, please contact the relevant Programme contact or email science@foodstandards.gsi.gov.uk