Proposal of a set of model polymer additives designed for confocal FRAP diffusion experiments.

The migration of additives from food packaging to food stuffs is kinetically governed by the diffusion coefficient (D) of the additive within the polymer. Food safety authorities have recently allowed the use of mathematical models to predict D, with the additive molecular weight as a single entry parameter. Such models require experimental values to feed the databases, but these values are often scattered. To deal with this issue, a fluorescent chemically homologous series of model additives was synthesized with molecular weights (MW) ranging from 236 g.mol (-1) to 1120 g.mol (-1). This set was then used to collect diffusion coefficients D through confocal fluorescence recovery after photobleaching (FRAP). This microscopic technique allows in situ packaging micro migration tests. The FRAP method was tested against results from the literature before being applied to two different model polystyrenes in a preliminary study to investigate the relationship D = f(MW). Our intermediate objective was to compare various experimental D = f(MW) from our method with predictions from other mathematical or semiempirical models.