Study On The Effect Of Ultra-high Pressure Treatment On The Properties And Migration Of Polylactic Acid Nano-food Packaging Materials

In this paper,polylactic acid,nano-silver and tributyl acetyl citrate were used as raw materials to prepare PLA/AgNPs composite films by solvent evaporation method.Ultra-high pressure technology was used to treat polylactic acid-based nano-silver film-forming solution,and 200 MPa and 400 MPa ultra-high pressure treated composite films were prepared.In this paper,the structure-activity relationship between the barrier properties and the microstructures of PLA films was studied by analyzing the changes of barrier properties and migration of PLA films before and after ultra-high pressure,and the effects of the structural changes of PLA nanocomposites on the diffusion behavior of small molecules were revealed.(1)PLA/AgNPs composite films were prepared by solvent evaporation method,and the cross-sectional morphology,internal structure,thermal properties,barrier properties and mechanical properties of the composite films were characterized.It was observed by scanning electron microscopy(SEM)that the cross section of the composite film was smooth from flat to coarse as the amount of nano silver added was low to high;the addition of nanosilver by XRD pattern analysis did not change the crystal structure of the composite films;The addition of nanoparticles by FTIR analysis did not change the functional groups inside the polylactic acid.The thermodynamic properties of the composite membrane were obtained by differential scanning calorimetry.It was found that only the crystallinity of the composite membrane increased.By means of gravimetric analysis and oxygen permeation instrument,it was found that proper amount of nanoparticles could improve the barrier properties of composite films.The mechanical properties of composite films showed that the composite films had good mechanical properties and poor flexibility.(2)PLA/AgNPs composite films were prepared by solvent evaporation method after the PLA/AgNPs film-forming solution was treated at 200 MPa and 400 MPa respectively by ultra-high pressure technology.The cross-sectional morphology,internal structure,thermal properties,barrier properties and mechanical properties of the composite films were characterized,and the influence of ultra-high pressure treatment on the diffusion of small molecules in the composite films was analyzed.Scanning electron microscopy(SEM)showed that the cross section of the composite film changed from roughness to smoothness with the increase of pressure;XRD analysis showed that high pressure treatment did not change the crystal structure of the composite film;According to the FTIR spectrum analysis,the high pressure treatment does not change the internal chemical bond of the composite membrane;the high pressure treatment by the differential scanning calorimeter only increases the crystallinity of the composite membrane;Through gravimetric analysis and oxygen permeation analyzer analysis,it was found that high pressure treatment can reduce the water vapor permeability and oxygen permeability of the composite film;Through the analysis of mechanical properties,high pressure treatment can improve the elastic modulus and tensile strength of the nanocomposite film,and reduce the elongation at break of the composite film.(3)PLA/AgNPs composite films under ultra-high pressure treatment conditions of 0 MPa,200 MPa and 400 MPa were studied,using 50% alcohol as food simulation solution,the entrapment amount and mobility of three new PLA/AgNPs composite films were determined by atomic absorption spectrometry in 5,10,15,20,30 and 40 days.The results show that the embedding amount of the composite membrane before and after the ultra-high pressure is about 90%;the migration tendency of the nano-silver particles in the composite membrane before and after the ultra-high pressure is sharply increased first and then stabilized;The migration amount of the nano silver particles in the treated composite film was lower than that of the composite film not subjected to the ultrahigh pressure treatment,and the migration amount of the composite film treated by the ultrahigh pressure of 200 MPa was the smallest.