Rubber migration tests

A migration test was developed to simulate human exposure patterns. 5 g of rubber material was cut into 1-2 mm stripes and then immersed in 20 ml of standard test solution of artificial saliva (4.2 g NaHC03, 0.2 g K2CO3, 0.5 g NaCl, 0.03 g NaNO, ad 1000 ml with aqua dest.j. After 24 h incubation at 40 C volatile nitrosamines were determined in an aliquot and determined after destination with a standard technique (GC-TEA-method). 

German body which sets legislation on compounding ingredients and migration testing for rubbers which come into contact with food. 

The objective of this chapter is to provide a comprehensive overview of the use of rubber as a food contact material, from an initial description of the types of rubber and rubber products that are used in the industry, through the formulation of products, and the contact regulations and migration testing regimes, to the research that is on-going to improve its safety and the trends for the future. 

All of the rubber compounds tested were found to contain chemical species that have the potential to migrate into food. Whether these migrating species are of concern will depend on the time, temperature, surface area of rubber that is in contact with them, and the fat content of the food (Table 8.1). 

Migration of N-nitrosamines from nipples and pacifiers after incubation in a standard test with artificial saliva for 24 h at 40 C. Concentrations in ug/kg rubber product (- <1 ppb)... 

In most cases the pigments used are also required to be migration-resistant. The suitability test is also carried out with 5 different pigment concentrations. To test the fastness to bleeding, the unvulcanized colorations are brought into defined contact with a white milled sheet of specific composition and vulcanized wet for 20 minutes in open steam at 140°C. During this process, half the coloration is often covered with a wet cotton cloth to determine whether the cloth, the rubber or both are stained by bleeding. 

There have been suggestions that a further method is needed to measure staining caused by the close proximity of the rubber without actual contact. This type of staining can occur, for example, in the boot of a car due to airborne migration of constituents of the spare tyre and tests have been devised by individual motor companies. 

Plasticizer migration from the vinyl part into the adhesive bond line can degrade the strength of the joint. Adhesives must be tested for their ability to resist the plasticizer. PVC can be made with a variety of plasticizers. An adhesive suitable for a certain flexible PVC formulation may not be compatible with a PVC from another supplier. Nitrile rubber adhesives have been found to be very resistant to plasticizers and are often the preferred adhesive for flexible PVC films. However, certain epoxy adhesive formulations have also been found to provide excellent adhesion to flexible PVC substrates. Several such starting formulations are presented in Table 16.7. A comparison of the performance of several classes of adhesive when bonding PVC to itself and to various other materials is given in Table 16.15. 

The finished rubber product will have to meet a specification in which a number of properties (e.g. hardness, tensile strength and elongation) are given target values. A number of other properties can be assessed, and these will depend upon the type of rubber and the application that it is going to be used in. An important example is the overall migration limit test, with the food simulant and test conditions (temperature and time) being dictated by the end use conditions. 

Cells to be tested are grown in a tissue culture dish (not a flask, which would be difficult to scrape) until confluent. Most of the growth medium is removed, and an artificial linear wound is made in the monolayer, by using, e.g. a sterile pipet tip, or a rubber policeman . Care has to be taken to clean all the wounded area from cells, because in case an uneven scraper is used, which leaves behind some attached cells, their presence at the end of the experiment may complicate the interpretation of the results. The plate is then rinsed several times with PBS to remove all the debris, and the test medium (containing dilutions of the supposed migration-... 

Polyvinyl Chloride (PVC) With PVC plasticizer migration to the adhesive bond line can cause difficulties, especially in the softer, highly plasticized materials. Adhesives must be tested for their ability to resist the plasticizer. Nitrile-rubber adhesives are resistant to plasticizers. Polyurethanes and neoprenes are also used. Even rigid PVC contains up to 5% plasticizer. Most vinyl materials are fairly easy to... 

Migration from Food-Contact Rubbers and Some Tests... 

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