Analysis for organic residues from aids to polymerization used to make plastics intended for food contact

Polymers intended for food contact use have been analysed for organic residues which could be attributed to a range of substances employed as polymerization aids (e.g. initiators and catalysts). A wide range of polymers was extracted with solvents and the extracts analysed by gas chromatography mass spectrometry (GC-MS). The overwhelming majority of substances identified were not derived from aids to polymerization but were oligomers, additives and adventitious contaminants. However, a small number of substances were identified as initiator residues. These included tetramethylsuccinonitrile (TMSN) which was observed in two polymers and it derived from recombination of two azobisisobutyronitrile (AIBN) initiator radicals. Methyl benzoate, benzoic acid, biphenyl and phenyl benzoate were detected in one poly(methyl methacrylate) sample and in two polyvinylchlorides and they are thought to be derived from benzoyl peroxide initiator. TMSN was subsequently targeted for analysis of poly-(methyl methacrylate) plastics using proton nuclear magnetic resonance spectrometry (1H-NMR) and GC-MS. NMR detected the presence of cyanoisopropyl radical residues in the plastic at 470-3400 mg/kg whereas GC-MS detected TMSN at only 65-540 mg/kg in the samples. It is concluded that the bulk of cyanoisopropyl residues detected by NMR were either polymer-bound or were the products of side-reactions of the initiator radical. The migration of TMSN itself into the food simulants 3% aqueous acetic acid, 15% aqueous ethanol, and olive oil, at 40 degrees C for 10 days, was measured using GC-MS. Migration was very low with < 1 microg/kg released from a finished article (a drinking straw) and < 5 microg/kg from resin pellets. The overall conclusions from this work are that organic residues from aids to polymerization are generally found at reassuringly low levels in plastics intended for food contact and their potential for migration to foods is correspondingly low.