A03008: Investigations into how glass reinforced plastic (GRP) vats can be repaired to minimise migration of styrene into food
Wednesday 18 June 2003
This research project aims to minimise the amount of styrene in food which is produced and stored in glass-fibre reinforced plastic vats.
Background
Glass-fibre reinforced plastic (GRP) vats are used in the UK in the production and storage of some food or drink, including wine, vinegar, milk, grain and grape juice, and for potable water. The unsaturated polyester resins used to make the plastic vats are cross-linked with styrene. Any styrene monomer that has not reacted completely during the curing of the resin, might migrate into a foodstuff that is subsequently stored in the vat. This report describes some systematic studies of manufacturing parameters as they affect the amount of residual styrene and its subsequent migration.
Discussions with GRP repairers had suggested that field operatives often do not or cannot follow the recommended curing procedures laid down by the polyester resin suppliers. Repairs to food contact surfaces do not lend themselves to the normal approach of taking representative samples of industrial production and sending them to a test lab. A repairer (be it of GRP vats, conveyer belts, processing equipment or food preparation surfaces) cannot test each and every repair 'in-situ' nor can they remove it to a lab for analysis. Consequently, users require recommendations along good manufacturing practice (GMP) guidelines. For these reasons, the time and temperature characteristics of GRP vat repairing need to be fully evaluated as they affect the potential for styrene migration.
The purpose of the project was therefore, to fully characterise procedures used for the repair of GRP vats resulting in data that could be used to recommend GMP guidelines.
Research Approach
Specimens for testing were made both in laboratory and industrial settings. The parameters investigated were the effect of curing temperature (50o, 80o and 100oC studied), the effect of curing duration (0, 3 and 6 hours studied) and the effect of washing with detergent solution at 60oC (0, 2 and 4 hours studied). More limited work investigated the effect of catalyst level used. Specimens were tested for residual styrene content and for styrene migration into the appropriate EU food simulants; distilled water, 3 percent acetic acid and 15 percent ethanol. Single-sided migration cells were used with test conditions of 10 days at 40oC.
Results and findings
The tests showed the importance of using correct manufacturing conditions to keep the potential for styrene migration low. The dominant factor in reducing residual and migration levels of styrene is temperature. The resin self-heats as it cures, typically up to 50oC, and so any further lowering of styrene content requires a higher temperature than this. At low cure temperatures the heating effect of washing at 60°C was more important than the washing effect of the detergent. Thus, curing at 65°C prior to washing gave just a modest lowering in styrene levels whereas a 3 hour cure at 80oC reduced both the residual content and the migration levels by about a factor of one-hundred. A three hour cure at 100°C reduced the residual content and the migration levels even more, by about 300 to 500 –fold.
When less than the recommended level of curing catalyst was used (2 per cent was recommended, 1.0 per cent and 0.5 per cent were also tested) then residual styrene levels rose dramatically, by 5-fold and by 20-fold respectively. There was a linear relationship between residual content (mass fraction) and styrene migration (mass per unit area) and the slope of the correlations demonstrated that migration was lowest into distilled water, was intermediate into acetic acid and was highest into the ethanol simulant.
This link between composition and migration that was established in this work, could be used to set Good Manufacturing Practice (GMP) parameters for ensuring the quality of GRP vat repairs using resins with styrene as a starting substance. For example, GMP guidelines could be drawn-up to specify minimum time and temperature curing conditions required to achieve a migration potential below any SML value that was set. The link between composition and migration may also provide a quick and simple system of experimentally monitoring the repairs as a periodic check that the GMP guidelines were effective.
Dissemination information
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 (020 7276 8181/8182 or at library&info@foodstandards.gsi.gov.uk).
See Also