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.

Measurement of styrene oxide in polystyrenes, estimation of migration to foods, and reaction kinetics and products in food simulants.

The concentration of styrene-7,8-oxide has been measured in nine base resins and 16 samples of polystyrene articles intended for food contact. The epoxide was not detected in the resins (limit of detection 0.5 mg/kg) but was found in 11 of the 16 packaging samples at up to 2.9 mg/kg. Assuming that the propensity of styrene oxide to migrate is the same as styrene monomer, and using existing survey data for styrene monomer in packaging and foods, the migration levels expected for styrene oxide were calculated. Estimates were from 0.002 to 0.15 microgram/kg styrene oxide in foods. The stability of styrene oxide in the four standard EU food simulants was studied at 40, 100, 150 and 175 degrees C, to establish the transformation products to be expected following migration testing. The half-life at 40 degrees C in distilled water, 15% aqueous ethanol, 3% aqueous acetic acid and olive oil was 15, 23, < 1, > 2000 hr, respectively. The principal product was the diol from hydrolysis of the epoxide group. Ring opening in aqueous ethanol simulant gave the diol and also the glycol monoethyl ether. It is concluded that this instability of styrene oxide will reduce concentrations in foods, from an already low migration level to even lower levels with the formation of hydrolysis products that are less toxic than the parent epoxide.

Element residues in food contact plastics and their migration into food simulants, measured by inductively-coupled plasma-mass spectrometry.

Polymers intended for food contact use have been analysed for inorganic residues which can be attributed to a range of substances employed as polymerization aids (e.g. catalysts), or to additives incorporated into the polymer to fulfil a specific task (e.g. lubricants). The migration of these residues into food simulants was studied. Residues were determined by using the multi-element capability of Inductively-Coupled Plasma-Mass Spectrometry (ICP-MS). Semi-quantitative analysis was carried out on acid digests of polymer materials, obtained by microwave heating in sealed Teflon containers. Limits of detection in the polymer were generally less than 1 mg/kg. Migration experiments were carried out with three food simulants and under two sets of conditions. Analysis for element residues was performed directly or, in the case of olive oil, on an emulsion of the simulant. Migration of certain elements into aqueous simulants was observed: Zr from polystyrene (650 micrograms/kg), Sb from polyethylene terephthalate (4 micrograms/kg) and Mg from acrylonitrile/butadiene/styrene copolymer (50 micrograms/kg). In all cases, where limits of detection permit, the levels which migrated from polymer to stimulant were less than proposed limits on migration.