Migration of titanium dioxide from PET/TiO 2 composite film for polymer-laminated steel.

PET/TiO2 composite film is the most widely used film for polymer-laminated steel, and the migration of TiO2 is very important for the safety evaluation of its packaged food. Microwave digestion, wet digestion and dry ashing were used for pretreatment of composite film to determine the content of TiO2 in composite film. Migration tests were carried out at 40°C, 60°C and 80°C 4% using acetic acid and 50% ethanol as the acid and ester food simulants. The migration amount of TiO2 was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). With increasing temperature and time, the migration of TiO2 increased. In 4% acetic acid, the migration amount of TiO2 at 40°C for 10 days was 1.88 mg kg-1 and the migration amount at 80°C for 8 h was 3.32 mg kg-1 , indicating that the effect of temperature on migration was more obvious. Under the same conditions, the migration amount of TiO2 in 4% acetic acid was greater than in 50% ethanol. X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC) were used to analyse the crystal structure, morphology, chemical groups and thermal properties of the film before and after the migration tests. The results showed that filmTiO2 had a stable rutile type crystal structure and it was almost uniformly distributed. PET and TiO2 were combined with strong chemical bonds. After TiO2 migration, the crystallinity and the glass transition temperature (Tg) of the film decreased, but the change of melting temperature (Tm) was not obvious.