4. Conclusion
The experimental work of this study showed that TiN
nanoparticles do not migrate at detectable levels out of a
LDPE matrix when in contact with food simulants. Since our
sensitive ICP-MS measurements showed that even under the
applied severe test conditions no Ti was released from the
polymer films, migration of TiN in its nanoparticulate form
appears not to take place. Since this conclusion is limited by
the underlying analytical sensitivity further efforts were
undertaken to establish a migration model for nanoparticles.
This model is based on an existing migration model for
conventional plastics additives and presents an extension to
nanoparticles in general by a worse-case design to solid
spherical nanoparticles with calculated quasi-molecular
weights as determinants of their diffusion coefficients and,
lastly, their migration. The results of modeling demonstrate a
correlation between particle size and migration rates and
support the experimental findings. The modeling results
suggest that only particles up to a size of approximately
3.5 nm in diameter may cause measurable migration, if they
are present in high concentrations in the polymer. Larger
particles have an exponential decrease in mobility in the
polymer and therefore no potential to migrate out of the
polymer.