Metal cans are often protected from corrosion by vinylic organosol coatings, made from PVC and
epoxyphenolic (EP) resins. Using electron spin resonance, BADGE, a monomer of EP, was shown
to plasticize PVC. Optimization of extraction allowed extraction of 4 mg of BADGE/dm2, so vinylic
organosols appear to be worst-case coatings. Comparison of behavior between BADGE and a
paramagnetic probe revealed that these compounds were trapped to a large extent in the cross-linked EP network and could not migrate at 40 °C. Contact with triglycerides, which plasticize the
coating, induced high migration of BADGE. Neither isooctane nor ethanol could mimic fats, in
contrast to isooctane/tert-butyl acetate mixtures. In aqueous foodstuffs, BADGE hydrolyzed into a
monoepoxide and then into a bisdiol. The total amount of toxicologically relevant epoxides over
shelf life was shown to reach a maximum value within 3 weeks at 40 °C, at very low levels, whatever
the aqueous food simulant. After sterilization at 120 °C (20 min), the level of BADGE in the migrate
is very low, whereas up to 2 mg of hydrolysis products is found in the liquid/dm2. During further
storage at 40 °C, the amount of epoxides rapidly decreases.
SYNOPSISRelated to the study of interactions between food and aluminum cans, structural features of a vinylic organosol coating were studied by electron spin resonance (ESR). Paramagnetic probes were incorporated separately in the normal formulation of a widely used varnish, which was then cured a t high temperature for different times. The behavior of aminoxyl probes, differing by their volatility and their functional groups, was studied. When 4-amino-2,2,6,6-tetramethylpiperidinoxy (3) was used as probe, it grafted onto the polymeric chains during curing. Two transitions could then be observed, corresponding to N O in two environments, which were assigned to the PVC (Tfs, 132-142OC) and to the epoxyphenolic (EP) (T50G, 142-152°C) phases of the varnish. This was confirmed by a separate study of the PVC and EP constituents. Both transition temperatures depended on the extent of curing, suggesting that the PVC phase was plasticized by reactive constituents of the coating. The transition temperatures were also influenced by the extent of penetration of the PVC in the E P phase. Probes which could not graft on the polymer were lost by volatilization during curing.
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