FITNESS

MIGRATION FROM MULTILAYER MATERIALS

MIGRATION FROM MULTILAYER MATERIALSFunctional barriers3D descriptionTrue Multilayer materialsOverviewMigration kinetics are more complex than in monolayer casesEquilibrium concentrationsConservative assumptions for risk assessmentRemoving reservoir layersChanging chemical potentialsExamples: trilayer AbCRefined scenarios: trilayer AbC

Functional barriers

Text from EU regulation 10/2011/EC

(27) In recent years plastic food contact materials are being developed that do not only consist of one plastic but combine up to 15 different plastic layers to attain optimum functionality and protection of the food, while reducing packaging waste. In such a plastic multi-layer material or article, layers may be separated from the food by a functional barrier. This barrier is a layer within food contact materials or articles preventing the migration of substances from behind that barrier into the food.
Behind a functional barrier, non-authorised substances may be used, provided they fulfil certain criteria and their migration remains below a given detection limit. Taking into account foods for infants and other particularly susceptible persons, as well as the large analytical tolerance of the migration analysis, a maximum level of 0,01 mg/kg in food should be established for the migration of a non-authorised substance through a functional barrier. Substances that are mutagenic, carcinogenic or toxic to reproduction should not be used in food contact materials or articles without previous authorisation and should therefore not be covered by the functional barrier concept. New technologies that engineer substances in particle size that exhibit chemical and physical properties that significantly differ from those at a larger scale, for example, nanoparticles, should be assessed on a case-by-case basis as regards their risk until more information is known about such new technology. Therefore, they should not be covered by the functional barrier concept.

Comparatively to monolayer materials, Kinetics are not necessarily homothetic but they can be sill compared for a same Fourier time if a reference layer.

Property description SI units
$t$ contact time $s$
$D_{i,ref}$ diffusion coefficient (in the reference layer) $m^2\cdot s^{-1}$
$l_{ref}$ of the reference layer $fb$ $fb$ ) $m$

Property	description	SI units
$t$	contact time	$s$
$D_{i,ref}$	diffusion coefficient (in the reference layer)	$m^2\cdot s^{-1}$
$l_{ref}$	of the reference layer $fb$ $fb$ )	$m$

Fo = \frac{D_{i,ref}\cdot t}{l_{ref}^2}=\int^t_0\frac{D_{i,ref} \left(T(t)\right) }{l_{ref}^2}dt

3D description

$fb$ $ref$ $fb$

True Multilayer materials

$j=1\dots m$ $j=0$ $k=1$ the layer in contact with food.
$i$ $j$ $i$ $j$ $i$ $j$
$C_{i,j}$ $k_{i,j}=K_{i,F/j}$ $k_0=1$ $D_{i,j}$
$i$ $j$ $p_{i,j}$ $C_{i,j}$ as:
$p_{i,j}=k_{i,j}C_{i,j}$
$j_1$ $j_2$ $k_{i,j}$ $p_{i,j_1}^{eq}=p_{i,j_2}^{eq}$ ):
$K_{i,\frac{j_1}{j_2}}=\frac{C_{i,j_1}^{eq}}{C_{i,j_2}^{eq}}==\frac{k_{i,j_2}}{k_{i,j_1}}$
$k_0$ $K_{i,\frac{F}{j}}=k_{i,j}$ .

$i$ $j$	$i$ $j$	$i$ $j$
$C_{i,j}$	$k_{i,j}=K_{i,F/j}$ $k_0=1$	$D_{i,j}$

Overview

Migration kinetics are more complex than in monolayer cases

delayed kinetics
slowed kinetic
non-monotonic behavior

Concentration profiles

Migration kinetics

delayed kinetics
slowed kinetics
non-monotonic behavior

delayed kinetics
slowed kinetics
non-monotonic behavior

Equilibrium concentrations

C_{F}^{eq}=C_{0}^{t\to \infty }=\frac{\sum\limits_{j=0}^{m}{\frac{{{l}_{j}}}{{{l}_{0}}}C_{j}^{t=0}}}{1+\sum\limits_{j=1}^{m}{\frac{{{k}_{0}}}{{{k}_{J}}}\frac{{{l}_{j}}}{{{l}_{0}}}}}

Conservative assumptions for risk assessment

General principles
Since all equations are linear with concentrations, $m$ $m$ solutions where only one layer is initially formulated at a time. The sum can be constructed in a way that a conservative solution is calculated with less unknowns.
$m\geq r>j$ $reservoir$ $j$ i.e. $k_r\rightarrow\infty$ ).
$1\leq fb<j$ $functional\;barrier$ $j$ i.e. $k_{fb}\leq k_j$ )
Sequential simulation (for different initial solutions) or the construction of a conservative initial solution enables to construct first tier scenarios even in presence of strong uncertainty on partition coefficients.

Removing reservoir layers

reality	conservative	even more conservative

Changing chemical potentials

reality	conservative	even more conservative