A03049: An investigation of functional barriers currently used by the food industry and an assessment of their efficacy

Study Duration: June 2004 to April 2006

Contractor: Central Science Laboratory

A functional barrier may be considered to be a barrier consisting of one or more layers which either reduces the migration of authorised substances below their specific migration limit (SML) or reduces the migration of non-authorised substances into foods or food simulants to a �not detectable� level.

The concept of a functional barrier has been proposed for inclusion in regulations on plastic food contact materials and articles. Although functional barriers are mainly associated with the use of recycled plastics for food packaging the concept has general relevance and may, in principle, be applied to any type of multi-layer structure.

Any barrier layer will need to prevent/reduce chemical migration from one or more of the following sources:

• an adhesive used in a laminate.
• a non-food contact plastic layer
• non-food contact paper/board layer
• a printing ink or coating applied to the non food contact surface of a packaging material.

There are many chemical substances present in these sources. This project will establish the ability of selected systems to act as functional barriers to migration.

Information on the use of barriers in food contact applications was obtained from a study of packaging systems currently available in UK supermarkets. Forty packaging materials were purchased, their compositions determined and thickness measured. To establish the performance of the materials as barriers, an EU recognised migration model is applied. Following this theoretical approach, the ability of selected food contact materials to act as functional barriers under their defined conditions of use is investigated experimentally.

The analysis of 40 packaging samples confirmed that a variety of plastics was employed, including polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, nylon, ethylene vinyl acetate and polyvinyl stearate.The thickness of these barrier materials was typically 20-50 µm for thin films, 50-100 µm for thicker films and 300-1000 µm for articles such as bottles and trays. Typically printing inks, other materials where the plastic was laminated with adhesives, labels, other plastics, paper or aluminium foil, were on the outside (non-food contact surface) of these plastics.

The modelling exercise considered the worst case, i.e. the full contamination of the food contact layer at the time that the food storage began (zero lag time) and the assumption that the migrant was completely soluble in the foodstuff. This is an overestimation of the true migration as it is very unlikely that all of the migrants present will have fully contaminated the barrier layer at time zero. For example, a substance present in the printing ink would be more likely to remain in the ink where it acts as a stabiliser or plasticiser rather than diffuse through the food contact plastic. In addition, the migration model itself is intended to overpredict migration levels into food simulants which are in turn intended to be more severe than foodstuffs.

Of the systems studied only one (a polyethylene terephthalate (PET) tray to which a sticky label was applied, used to package cold meat) was considered to be a functional barrier for all considered situations.

Twelve packaging materials were also tested experimentally for their barrier properties against the migration of some model migrants – benzophenone, diphenylbutadiene, Chimassorb 81 (a UV stabiliser), bisphenol A diglycidyl ether hydrolysis product, Irganox 1076 antioxidant and PET-trimer. All of the packaging materials investigated acted as a functional barrier to a certain extent, dependant on the nature and concentration of the external substance, the nature of the food type, and the time and temperature storage conditions.

This work underlines the importance of considering the use and efficiency of plastic materials as functional barriers on a case-by-case basis.
Unlike solid layers of glass or metal, for plastics it is not possible to state categorically that any type or thickness of plastic will act as a functional barrier under all circumstances. Rather, the conditions should be fully described to substantiate any claim that is made.

The final report is available from the Agency's 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 For more information please click here