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- Practical Guide -
Page 70 of 153
4.2
Optimising compliance control
Migration models can be used to optimise compliance control strategies. In fact there is an
infinite variety of packages to be tested, with different geometry, size, type and thickness of
polymer, food, shelf life of food, temperature etc and the effort to check all these influences
is huge. By using the migration model one can find out relatively easily the worst case
system, (covering all the less severe situations) and then reduce the experimental migration
measurement just to those cases or samples where it is possible to be in non-compliance at
all. In order to find this system, one can use the equations and parameters given above (see
paragraphs 2 and 3).
Having the experimental result from one selected test, all the different conditions and
parameters, as mentioned above, are then modelled without a supplementary experimental
test. In this manner a significant increase of the quality assurance is possible with many
samples controlled during the same time compared to one experiment without the additional
tool of modelling. Of course, the nature of the plastic material must be known as well as the
initial concentration of the concerned migrant (known or disclosed by producer or
experimentally tested). If not, a reasonable upper limit can be used.
Models must be applied properly. That means the results obtained by modelling can be only
as good as the assumptions of the model are fulfilled. If it cannot be assumed that the
concerned sample is a polymer as specified in table 2 or 3, the model is not properly applied.
In this case a quick kinetic study can be recommended as proposed in the procedure
described in Annex B.
Crucial questions for enforcement laboratories in connection with compliance control,
especially on the retail market, are: Which migrateable compounds (additives, rest-
monomers) are present in the objects to control? What substances from the positive list can
be used in practice in PO?
This, however, is not a specific issue of modelling, but represents
an inherent requirement to any control lab. It is not so uncommon that no knowledge about
the manufacture of the material exists from the producer, but is indeed impossible to test all
substances from the positive lists with SML values < 60 mg/kg. Following the traditional
experimental way, several analyses often with different techniques (MS/GC, MS/HPLC,
FTIR) should be performed to try to identify the components in the materials; in this
situation, migration models can help to restrict the number of experimental analyses /11/.
It is well known that for a given polymer only a very limited number of substances from the
positive lists in the Directive 2002/72/EC and their Amendments are used. In the following
tables 4.2.1 (PO) and 4.2.2 (non-PO) some of such substances are extracted from the table in
Annex A. These tables were prepared by consulting the most important producers of plastic
materials and the newest secondary literature referring additives for plastic materials /12/. In
addition to the identification numbers the upper limits of initial concentrations claimed to be
used in materials and articles for food contact are shown. Nevertheless, as fully specified in
reference /13/ this table should be considered only as an example to offer a first guide in
selecting specific additives if no other information is available about the composition of a
sample to be tested