The effect of the molecular size on the rate of diffusion of these
additives was also reported by Miltz and co-workers (1988) in
HDPE. The mechanism that governs the release of the additives in all cases is anomalous according to Ritger and Peppas (1987)
with values of n between 0.5 and 1. When the additive was BHT
the value of the exponent n was not modified by their concentration.
Furthermore, in films loaded with a-tocopherol, the value of
n depends on the concentration. In these films the release mechanism
has a diffusive contribution and dependent relaxation of the
chains. Diffusive contribution becomes more important when the molecules are more likely to pass through the film as in a-Toc
5 wt.% while, in a-Toc 2 wt.%, and even more in a-Toc 1 wt.%, the release process requires polymer chain relaxation.