25 YEARS ANNIVERSARY 13 PETplanet Insider Vol. 25 No. 05/24 www.petpla.net aldehyde migration. Also acetaldehyde reducing additives are applied in the preform manufacturing process. Acetaldehyde reducing additives Traces of acetaldehyde can migrate from the PET bottle wall into natural mineral water. The main goal in preform and bottle manufacturing is to reduce the acetaldehyde concentration in PET. From migration theory, the bottle wall concentration of acetaldehyde is directly proportional to the migration under the same storage conditions. This means that the reduction by a factor of two results in half of the migrated amount of acetaldehyde into bottled water. 2-Aminobenzamide, also known as anthranilamide, is the most popular acetaldehyde reduction additive and called an acetaldehyde scavenger used in PET preform manufacturing. This additive reacts chemically with acetaldehyde to form a non-odorous and higher molecular weight substance. As any other additive, 2-aminobenzamide must be approved for the application in PET bottles and the specific migration limit of 2-aminobenzamide of 0.05mg/kg food (Table 1) has to be controlled in routine tests by the mineral water filling company. Monomers (ethylene glycol and terephthalic acid) In general terms, the migration of monomers from plastics can never be totally prevented. PET, however, is highly inert compared to other plastics. Thus, only extremely small quantities of monomers may migrate into bottled water. For example, a study has shown that the level of migration of the monomers ethylene glycol and terephthalic acid from PET bottles is far below statutory limits. Nonetheless, water bottling companies constantly monitor levels of monomer migration from PET bottles. Antimony Antimony trioxide is the major catalyst used to polymerise PET. In principle, the catalyst will remain in the PET after polymerisation. Typically, concentrations of antimony in PET bottles are below of 300mg/kg PET. Alternative catalysts for the polymerisation of PET have also been developed, mostly based on titanium, aluminium or germanium. However, to date the alternatives developed have not succeeded in making a major commercial breakthrough and antimony trioxide remains by far the dominant catalyst employed by resin suppliers. As with all the substances employed in the manufacture of PET, antimony is subject to strict statutory regulations in Europe. The maximum permitted level of antimony migration from a PET bottle into the finished product is 0.04mg/l (Table 1). Under normal storage conditions, the level of antimony migration from PET bottles is extremely low. The limit value for antimony migration from PET packaging may not be exceeded during the shelf life of the beverage, even when bottles are stored in warm climates for many months. The limit value for antimony in water is considerably lower than the limit value for migration from PET packaging. In Europe, for example, a maximum of 0.005mg of antimony may be present in one litre of natural mineral, spring or drinking water at the time of packaging. Even if, from a legal point of view, the migration limit of 0.04mg/l is valid for bottled . Bio-PET Traditionally, the monomers of PET are manufactured from fossil-based resources. However, a synthetic route for ethylene glycol, one of the two monomers, was developed from biomass as early as in the late 1980’s. Sugar-cane is transformed to bio-ethanol. In the second step, bio-ethanol is oxidised to the monomer ethylene glycol, which is subsequently used for the polymerisation of PET. A mass fraction of about 30% by weight is realised when using bio-ethylene glycol as monomer for PET. The second monomer of PET, terephthalic acid, is not commercially available using biobased resources. However, synthetic routes from biomass to terephthalic acid are available in laboratory/pilot scale. From a chemical point of view, bio-PET is indistinguishable from fossil-based PET. Therefore, the same manufacturing facilities for PET pellets, preforms and bottles can be used. Also, bio-PET is fully recyclable along with fossil-based PET. Such bio-based equivalents to fossilbased polymer are called “drop-in” biopolymers. * Neumann, E H. Thermoplastic polyesters in Encyclopaedia of Packaging Technology, ed Bakker M. John Wiley, New York 1986. https://www.petcore-europe.org/images/news/pdf/ factsheet_the_facts_about_pet_dr_frank_welle_2018.pdf Substance Specific migration limit in mg per kg food Acetaldehyde 6 Terephthalic acid 7.5 Isophthalic acid 5 Mono- and diethylene glycol 30 Antimony 0.04 2-Aminobenzamide 0.05 Table 1: Requirements according to European Packaging Legislation (EU 2011)
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