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- Practical Guide -
Page 90 of 153
Validated standard test procedures for determination of phenolic antioxidants such as Irganox
1010 and 1076 and erucamide slip additives in polyethylenes are given in ASTM standards D
5524-94 and D 5815-95.
Further useful guidance to extraction of polymers can be found in Paragraph 8 of the Final
Report of EU Project AIR-94-1025 `Safety and quality control of plastics materials for food
contact' dated April 1999 and literature given therein. Moreover, this document provides
further instructions on analytical techniques to obtain analytical fingerprints of unknown
plastics constituents and how to step forward to identification and quantification of these
potential migrants in the test material expressed as initial concentration, c
P,0
, or quantity in
the plastic, Q.
It must be noted here that according to item 2 of the `General requirements' (Annex I, B.) it
is required that the test migrant is homogeneously distributed in the plastic. Blooming
effects, i.e. the inhomogeneous deposition of a migrant on or in the plastics surface, lead to
non-applicability of the migration model and need to be recognised and eliminated. One way
to check blooming effects is to shortly (approx. 30 seconds) immerse the plastic with gentle
movement into a solvent like 95 % ethanol and/or iso-octane followed by analysis of the
rinsing solvent. Significant amounts of migrant found in that way indicate a blooming effect.
Further indication can be obtained from an anormal kinetic migration curve measured under
5.2.
Based on the obtained results one ore more suitable test migrants need to be selected for step
ii (5.2).
5.2
Kinetic migration measurements (step ii)
Depending on the thickness and structure of the polymeric test sample the migration
experiment can be done either by total immersion or using a migration cell in the single sided
mode. As a general rule and for guidance, high diffusivity polymers comparable to the
behaviour of polyolefines should be thicker than 500 m for being applied to the total
immersion test; low diffusivity polymers comparable to the behaviour of PET can be totally
immersed at a thickness higher than 100 m. If the sample is not homogeneous and socalled
edge effects may occur, then the one sided test is obligatory. As a general remark, the one
sided test should always be the preferred one and carried out where possible.
Migration experiments are conducted at two different temperatures such that the full kinetic
migration curve can be established by taking sufficient and suitably positioned time points. If
necessary, a pre-experiment needs to be carried out. Ideally, the shape of the migration curve
is expected to originate at time zero with zero migration and sloping linearly with square root
of time until approximately 60% of maximum migration has occurred. Finally, the curve
approaches asymptotically at equilibrium the maximum concentration. Blooming effect of a
migrant can be recognised from the curve where significant migration is already observed at
time zero. The tests should be carried out as follows:
Migration at temperature T1 at regular practical test conditions:
In general, migration may be measured after 1, 2, 4 and 10 days at 40 C (obligatoric kinetic
experiment). In case of very high diffusion and/or very thin materials the curve may be
necessary to be established already within a few hours and may reach equilibrium very early.