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- Practical Guide -
Page 69 of 153
Two principal procedures can be followed with the model:
(i)
Based on knowledge of the existing initial concentration of a migrant of known
molecular weight in a polymer its specific time and temperature dependent migration
into a given food simulant or food can be calculated from Eq. (2).
(ii)
Reversely, based on a given migration limit or SML value, the maximum initial
concentration (MIC) of a migrant of known molecular weight in a polymer that can be
used in a food contact can be estimated from Eq (3).
As a general rule: In cases where the migration estimation scheme outlined above leads to
results which are above the legal limits (SML), an experimental test of compliance is
compulsory. In case of doubt or that the polymer specific A'
P
value is not known or
applicable from the tables given in paragraph 3, a kinetic study should be carried out as
described in the procedure given in Annex B to establish the Q versus SM relationship /10/.
4.1
Compliance testing of substances with specific migration limits (SML)
One major objective of this report is to give guidance for compliance testing. Consequently,
one major field of application is concerned with the control of substances found in the
positive lists of the Directive 2002/72/EC. From the many compounds listed, all the
substances were extracted which can be considered to fulfil the assumptions in the foregoing
paragraphs /13/. That means for example, only organic compounds, soluble in the polymeric
matrix are considered and all the external applicable additives, as antistatics, lubricants, etc.
are excluded for modelling. In addition, all the electrolytes, salts, oxides, metals, are
excluded, and only compounds with well defined molecular weight or mixtures with well
defined ranges of molecular weights are considered. But even with this selection criteria, a
considerable number of compounds remains.
It must be emphasised that at the present stage of knowledge the migration model is suitable
for polymers in paragraph 3. The Annex A lists the compounds considered for migration
modelling extracted from the Directive 2002/72/EC and its amendments. Therefore this list is
a useful reference for those users, who need or desire to perform estimations without any
uncertainty in the right selection of the appropriate parameters. In fact, under these
conditions the problem of swelling is not relevant because it is inherently included in the
model. It must be underlined that the model cannot be used for migration predictions in iso-
octane or other test media with a high swelling power. In such cases it is recommended to
consider reference /9/. Moreover, the problem of blooming is not relevant because
substances, which are accumulated at the surface of the plastic article are not listed in Annex
A.
Finally it should be noted that by using Eq.(3) a value for the maximum initial concentration
(MIC) of a migrant in P can be estimated for which a specific migration limit (SML) for an
additive cannot be exceeded.