Substance transfer from the packaging material into foodstuff is known as migration, and polyurethane adhesives may contribute to this substance transfer. The lower the molecular weight of the substance, the more likely it is to migrate into the food, either in direct contact by diffusion or indirect via the gas phase. Typically, compounds below 1000 dalton show migration potential, where pure polymers of several thousand dalton and above do not need to be considered.
Several measures can be taken to reduce the risk of migration. On the one hand, reducing low molecular weight compounds of less than 1000 dalton within the solvent-based adhesive formulation may help to reduce the general substance transfer. On the other hand, packaging design can be an appropriate tool: installation of barrier layers prevents migratable packaging constituents from being transferred into the food, such layers reduce or even inhibit migration under defined conditions of use, or may even act as an absolute barrier.
Although analysis of real foodstuff flexible packaging gives the most realistic information about migration in these food contact scenarios, it is time consuming, complex and its results are only valid for the investigated application. To simply it there are three different approaches to estimate migration have been established:
- calculation: some constituents can be ruled out by taking their maximum concentration in the formulation and assuming a total substance transfer in the real application.
- migration modelling: as migration follows the law of diffusion, computer models have been established to predict the expected migration of defined compounds under defined conditions.
- Migration testing.( it is appropriate and accepted way to estimate substance transfer from a packaging material into foodstuff.
