Research On The Properties Of Polylactic Acid-based Nano-titanium Dioxide Composite Film And The Migration Of Nanoparticles In Food Simulants

In this study,the modified nanocomposite films were prepared,which combined with ultra-high pressure technology to evaluate the release of nanoparticles from food packaging materials to food simulation solution.Moreover,we also evaluated the influence of ultra-high pressure treatment on the properties of the new composite material systematically.The main results were as follows:?1?We prepared the PLA/nano-TiO₂ composite film with the Solvent evaporation method,and the composite film were treated with the ultra-high pressure.We compared the basic properties of composite membranes before and after ultra-high pressure treatment.The microstructure of the brittle section was observed by SEM scanning electron microscope?SEM?.It was found that the micro section of the composite film after ultra high pressure treatment became very rough,and the structure was depressed.The thermodynamic properties of the composite films were measured by DSC?differential scanning calorimeter?.It was found that the other thermodynamic properties were not significantly changed in addition to the increase of the crystallinity of the composite film.The structural changes in the internal functional groups of the composite films were analyzed by the FTIR?Fourier infrared spectrometer?.It was found that the ultra-high pressure treatment did not form a new chemical bond between the nanoparticles and the polylactic acid.XRD?X ray diffractometer?analysis showed that the ultrahigh pressure composite films did not change its internal crystal structure.By weight analysis,we found the permeability of composite membrane is increased after ultra-high pressure treatment.?2?We used the 50%ethanol water solution as an alcoholic food simulation solution to stimulate the packaging environment of the composite films.After 0,5,15and 30 days contact migration experiment,the performance changes of the composite film during the contact migration experiment were detected.It is observed by SEM that the roughness of the composite film increases with the increase of the contact time with the food simulant solution.Through DSC detection,it is found that the glass transition temperature of the composite film decreases first and then increases,and there is no significant change in the cold crystallization temperature and melting temperature.it is found by the FTIR that there are no new chemical bonds between the polylactic acid matrix and the nanoparticles,the polylactic acid matrix and the ethanol solution,and the nanoparticles and the ethanol solution during the contact migration experiment with the food simulated liquid.t is found by the vapor transmission experiment that the permeability of composite film increases gradually during the migration experiment.?3?The contact migrates experiment of the films after ultra-high pressure treatment was carried out in the simulated liquid of alcohol food represented by 50%alcohol solution.After 0,5,15 and 30 days contact migration experiment,the performance changes of the composite film during the contact migration experiment were detected.It was found by the SEM that the micro truncation surface of the composite film is becoming more and more coarse,causing severe shrinkage and even holes.Through DSC measurement,it is found that the vitrification point of the composite film in the migration stage of the food simulated liquid increases obviously,the cold crystallization temperature and the melting temperature have no significant change,and the crystallinity decreases with the increase of the migration time.By FTIR,the structure of internal functional groups did not change during the migration stage.By XRD,it is found that the inner crystal structure of the composite film not change during migration time.The water vapor permeability of the composite film after UHP treatment was measured.It was found that the vapor permeability of the composite film increased with the increase of migration time.?4?After the contact time of 0,5,10,15,20,25,30,35 and 45 days,the ICP-AES instrument was used to measure the amounts of nanoparticles in the food simulation solution.The results showed that both kinds of composite films showed the trend of increasing first and then stabilizing,moreover,the migration nanoparticles amount of the composite after UHP treatment was little than the migration amounts of composite films without UHP treatment.Finally,based on the Fick second law,the diffusion coefficient D value of nanoparticles in the composite film without ultra-high pressure treatment is calculated.It is known that the diffusion coefficient of nanoparticles migrate to alcoholic food simulant solution increases with the increase of nanoparticle content and migration time.