Survey of formaldehyde, acetaldehyde and oligomers in polyethylene terephthalate food-packaging materials

Polyethylene terephthalate (PET) is frequently used as a packaging material for beverage bottles, fruit and vegetable trays, and egg crates in Japan. Levels of formaldehyde (FA), acetaldehyde (AA) and PET oligomers in various PET food packaging were determined. PET samples were initially dissolved in trifluoroacetic acid with 2,4-dinitrophenylhydrazine to derivatize formaldehyde and acetaldehyde to their dinitrophenylhydrazones. The stable derivatives along with the oligomers were analysed using HPLC with ultraviolet light detection at 360 and 254 nm, respectively. The PET pellets contained 3.5-12.4 microg g-1 AA and 4.0-7.2 mg g-1 oligomers, while FA was below the determination limit. FA, AA and oligomer levels in Japanese bottles were 0.6-3.0 microg g-1, 8.4-25.7 microg g-1 and 5.0-8.7 mg g-1, ND-1.6 microg g-1, 5.0-13.1 microg g-1 and 4.9-8.2 mg g-1 in French and Italian bottles, and ND-1.2 microg g-1, 9.1-18.7 microg g-1 and 5.6-8.0 mg g-1 in US and Canadian bottles, respectively. Compared with European bottles, Japanese bottles contain higher FA and AA levels. In sheet-moulding products, their contents were determined as ND-1.1 microg g-1, 11.5-43.1 microg g-1 and 4.6-9.2 mg g-1, respectively. The results show that sheet-moulding products contain lower FA and higher AA in comparison with bottles. FA and AA are considered to be generated from PET during the heating process for moulding the pellets to bottles or sheet-moulding articles and de-aeration during the sheet-moulding process is effective in removing FA. In contrast, the level of the oligomers remains unchanged during the moulding process from pellets to bottles or sheet products.