Food-contact epoxy resin: co-variation between migration and degree of cross-linking

In order to predict the behaviour towards foodstuffs of an epoxy resin composed of bisphenol A diglycidyl ether (BADGE), 4,4'-methylenedianiline (MDA) and additives (plasticizers: dibutylphthalate (DBP), dioctylphthalate (DOP); accelerator: salicylic acid; inorganic fillers), a co-variation was established between the parameters evaluating the degree of cross-linking of the three-dimensional network and the migration of constituent molecules into various food simulants (distilled water, distilled water/ethanol/acetic acid, distilled water/ethanol). Varied degrees of cross-linking were obtained by subjecting the resin to different curing temperatures: respectively, 5 degrees C, 20 degrees C, 50 degrees C and 90 degrees C for 7 days. Irrespective of the food stimulant tested, specific migrations (DBP, DOP, salicylic acid, primary aromatic amines) diminished greatly as the curing temperature increased. At the same time, the degree of cross-linking increased with curing temperature, as indicated by the increase in glass transition temperature, the decrease in residual reaction exotherms and increased stability of the rubber storage modulus E'rub (increase in cross-link nodes), the fall in relaxation enthalpies (reduction in physical ageing) and the decreased amplitude of the loss-factor, tan delta (reduction in chain mobility). Maximum cross-linking was obtained in the resin cured at 90 degrees C (temperature above Tg infinity). In contrast to the degree of cross-linking, evaporation contributed little to the reduction of migration due to the elevation of curing temperature.