Chemical migration contact materials

As for all food contact materials, chemical migration from materials and articles which come into contact with snack and take-away foods occurs as a result of diffusion processes that are subject to both kinetic and thermodynamic... 

While it is inherently probable that product formation will be most readily initiated at sites of effective contact between reactants (A IB), it is improbable that this process alone is capable of permitting continued product formation at low temperature for two related reasons. Firstly (as discussed in detail in Sect. 2.1.1) the area available for chemical contact in a mixture of particles is a very small fraction of the total surface (and, indeed, this total surface constitutes only a small proportion of the reactant present). Secondly, bulk diffusion across a barrier layer is usually an activated process, so that interposition of product between the points of initial contact reduces the ease, and therefore the rate, of interaction. On completion of the first step in the reaction, the restricted zones of direct contact have undergone chemical modification and the continuation of reaction necessitates a transport process to maintain the migration of material from one solid to a reactive surface of the other. On increasing the temperature, surface migration usually becomes appreciable at temperatures significantly below those required for the onset of bulk diffusion within a product phase. It is to be expected that components of the less refractory constituent will migrate onto the surfaces of the other solid present. These ions are chemisorbed as the first step in product formation and, in a subsequent process, penetrate the outer layers of the... 

Why does the amount of acid in paper make such a difference Acids are corrosive chemicals. Corrosive chemicals can destroy material or living tissue on contact. Paper does not contain enough acid to burn skin, but over time the paper becomes stiff and brittle and eventually falls apart. As a result, precious personal memories or important historical documents that were written on acidic paper can be lost. Acid-containing paper can also transfer the acid to other objects in a process called acid migration. The acid can weaken or destroy the fibers in fabrics. It can also ruin photographs. Therefore, to preserve those irreplaceable memories, be sure to use paper that is acid-free. 

Research on chemical migration from other types or components of packaging material - e.g. glass, wood, cork, coatings, adhesives - has been carried out sporadically. There is now a concerted UK programme to study chemical migration from these so that problems can be identified and dealt with in a consistent way (Working Party on Chemical Contaminants from Food Contact Materials and Articles, 1999). 

Aurela, B., and Soderhjelm, L. (2007). Food packaging inks and varnishes and chemical migration into food. Ch. 13. In "Chemical Migration and Food Contact Materials" (K. A. Barnes, C. R. Sinclair, and D. H. Watson, eds.), pp. 302-319. Woodhead, Cambridge, England. 

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