A03038: An investigation of the breakdown products of curatives and antidegradants used to produce food contact elastomers

Study Duration: April 2002 to December 2004

Contractor: Rapra Technology Ltd.

Elastomeric rubber products are used in a variety of food contact situations under different conditions. An inventory list of substances added to food contact elastomers during their production has been compiled by the Council of Europe (CoE). The list does not take into account the fact that two of the major classes of substances, curatives and antidegradants, will undergo reactions during the processing and service life of the rubber products.

Curatives may undergo several reactions during vulcanisation (i.e. curing), using up the majority of the original curative. Antidegradants, which protect the rubber from degradation, will undergo reactions depending on the service conditions. Therefore, it will not just be the original compounds that have the potential to migrate into food, but also the breakdown products of these reactions. The majority of these reaction/breakdown products will have relatively low molecular weights so their migration potential may be high.

The primary objective of this project was to provide as comprehensive a list as possible of the breakdown/reaction products that may originate from the curative and antidegradant compounds given in the CoE Rubber Resolution. Some work was also carried out using food simulants and food products to assess the potential of these breakdown/reaction products to migrate into food.

A literature search provided information on known breakdown products of the curatives and antidegradants listed in the CoE Rubber Resolution. This included information on the curative blends used in commercial food contact rubbers. This information was supplemented with theoretical predictions of reaction/breakdown products.

In order to assess the accuracy of these predictions, 19 food contact rubber �compounds� were manufactured. Test sheets were cured from these �compounds� and some of these sheets were aged under industry standard conditions to ensure that the antidegradants had broken down. The breakdown products present in these aged and unaged test sheets were then identified using both headspace and solvent extraction gas chromatography-mass spectrometry (GC-MS).

Migration studies were performed on 10 of the test sheets using worst case time and temperature contact conditions. Ethanol was used as a fatty food simulant and the migrants identified and semi-quantified using GC-MS. Aqueous simulants (3% acetic acid, 15% ethanol and water) were analysed by liquid chromatography-mass spectroscopy (LC-MS). Migration work was also undertaken using some food products (whisky, white wine, beer and olive oil), again using worst case contact conditions and GC-MS.

Over 900 potential breakdown/reaction products were predicted from the 161 curatives and antidegradants present on the CoE list. This project has shown that a complex situation exists, with the breakdown products formed from the curatives and antidegradants in a given rubber 'compound' being dependent on a number of factors, for example:

• the type of rubber (e.g. styrene-butadiene rubber (SBR), natural rubber, or nitrile rubber) - due to the specific reaction chemistry and interaction with residual monomers etc
• the other ingredients present - due to interactions occuring between them and the breakdown products
• the concentration (i.e. amount) of each ingredient in the compound - due to solubility effects
• the heat history of the compound, e.g. curing and ageing temperatures

Therefore, not all the breakdown products that can be predicted for a particular 'compound' are present in all circumstances. As a guide, from the analysis of the test sheet extracts carried out during this project, between 25% and 50% of the predicted breakdown products were present in a rubber 'compound' at detectable levels. In general, good agreement was found between the predicted breakdown products and those detected and identified by this analytical work.

Migration experiments into food simulants using worst case conditions were conducted on 10 of the test sheets. Semi-quantitative data was obtained and where possible any substances detected above approximately 50 microgram/kg were identified. Between 20 and 100 migrants were detected for the more complicated formulations. Limited data was obtained from the food samples.

This work has demonstrated the importance of considering reaction/breakdown products especially in complex materials such as food contact elastomers. It is clear that starting substances alone should not be considered as the only potential migrants when evaluating a food contact material. This is being taken forward in Brussels, for example with respect to plastics.

The final report is available from the FSA Information Centre. To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@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