Migration of lactic acid, lactide and oligomers from polylactide food-contact materials

Polylactide (PLA) is used for manufacturing lunch boxes and for packaging fresh food in Japan. PLA can be hydrolysed relatively easily to produce lactic acid, lactide and oligomers. Different types of PLA sheet were subjected to migration tests under various conditions and the lactic acid, lactide and oligomers contents of the migration solutions were determined using liquid chromatography/mass spectrometry (LC/MS). Furthermore, the change in molecular weight was determined by a migration test. PLA was stable at 40°C for 180 days; the total of lactic acid, lactide and oligomers migration levels were 0.28–15.00 µg cm−2. PLA decomposed clearly at 60°C for only 10 days, the total migration levels were increased to 0.73–2840 µg cm−2. PLA sheets with a high D-lactic acid content decomposed particularly rapidly. The amounts of alkali decomposition products, based on the conversion of lactide and oligomers to lactic acid by alkali hydrolysis, corresponded with the total migration levels.