Research On The Performance And Migration Amount Of The Polylactic Acid-based Nano-silver Composite Film Before And After Ultrahigh Pressure Treatment During The Migration Process

Polylactic acid(PLA)is a polymer derived from lactic acid,which is a biodegradable and biocompatible renewable polyester.It can be obtained from the production of renewable materials such as sugar beet,sugar cane and corn fermentation;it consumes a lot of carbon dioxide and consumes greenhouse gases during the production process.Therefore,polylactic acid is an energy-saving and environmentally friendly green material.Because polylactic acid has good antibacterial,biodegradability and biocompatibility,polylactic acid is widely used in various fields such as medicine,food,etc.,such as medical catheter materials,food packaging materials,etc.The following are the main contents of the experiment.:(1)We selected polylactic acid as the matrix,and added different contents of nano-silver1%,5%,10%,15%,20%,and made polylactic acid-based nano-silver composite film PLA/1%Ag by solvent evaporation method.,PLA/5%Ag,PLA/10%Ag,PLA/15%Ag,PLA/20%Ag.At the same time,the composite membrane is treated with ultra-high pressure equipment,and the ultra-high pressure conditions are ultra-high pressures of 100,200,300,and 400 MPa,and the treatment time is 10,20,and 30 minutes.Samples that were not subjected to ultrahigh pressure treatment were used as controls.In the experiment,isooctane was selected as the oil food simulating liquid,and the composite membrane was immersed in the food simulating liquid for 49 days,and the content of nano-silver in the simulated liquid was detected every 7days.Exploring the effect of ultra-high pressure conditions on the migration ability of nano-silver particles in composite membranes.The experiment found that the ultra-high pressure has no significant effect on the migration rate of nano-silver in the composite film.The migration law of the same sample under the same ultra-high pressure condition is consistent with the migration law of nano-silver in the composite film before ultra-high pressure.The migration rate of nano-silver particles has experienced a trend of decreasing first and then increasing.In the later stage of the experiment,when the ultra-high pressure treatment time is constant,the increase of the ultra-high pressure or the increase of the treatment time under the condition of the ultra-high pressure will cause the migration of nano-silver in the composite membrane to increase.Finally,according to Fick’s second law,the diffusion coefficient of the composite membrane before and after the ultrahigh pressure treatment was calculated and compared.The diffusion coefficient D of each sample showed a decreasing,increasing and decreasing trend with the prolongation of storage time.The pressure of the ultrahigh pressure has no significant effect on the diffusion coefficient,but can affect the diffusion coefficient D of the composite membrane to some extent.Compared with the ultra-high pressure,the time of immersion of the composite membrane in the simulated liquid has a more significant effect on the migration of nano-silver in the composite membrane.(2)Scanning electron microscopy was used to observe the microstructure of the composite membrane before ultrahigh pressure treatment.It can be seen from the pictures on the scanning electron microscope that no matter how the amount of nanoparticles is added,each sample shows the same change trend in the simulated liquid,that is,the nanoparticles continuously migrate into the simulated liquid,and the surface of the composite film gradually becomes rough.The tensile strength(TS),elastic modulus(EM),and elongation at break(ε)of the composite film were measured using an electronic universal testing machine.It was found that as the content of nano-silver in the polylactic acid packaging film gradually increased and the storage time in the food simulating liquid gradually prolonged,TS was gradually reduced,while EM andεshowed an upward trend.The thermal properties of the composite membrane were measured using a differential scanning calorimeter(DSC)such as its melting temperature(T_m),glass transition temperature(T_g),cold crystallization temperature(T_c),and crystallinity(X_c).The exothermic peak of each sample was continuously moved to the high temperature direction with the migration time,and the approximate temperature was between 110°C and120°C.Among them,the melting temperature(T_m)of the composite film is not significantly changed by the amount of the nano-silver particles added.The glass transition temperature(T_g)of the composite film showed an increase with the migration time,and all of the samples exhibited this tendency.At the same time,as the migration time and the content of nano-silver increase,the cold crystallization temperature(T_c)and crystallinity(X_c)increase.This may be caused by the heterogeneous nucleation of the nanoparticles in the polylactic acid matrix due to the addition of nanoparticles.With the change of migration time,the barrier property of polylactic acid-based nano-silver composite film to water vapor and carbon dioxide showed a downward trend as a whole.(3)The effect of ultra-high pressure on the nano-silver composite membrane was discussed.The structural properties,mechanical properties,thermal properties,carbon dioxide permeability and water vapor transmission rate of the composite membrane were measured.It was found that the brittle fraction of the composite film after ultra-high pressure treatment was reduced,but the wrinkling phenomenon was more obvious and a large number of depressions and holes gradually appeared.The higher the pressure of the ultrahigh pressure treatment,the more obvious the phenomenon.The ultra-high pressure has little effect on the mechanical properties of the composite membrane,and the change of the mechanical properties of the composite membrane before and after the ultra-high pressure increases with the increase of the nano-silver content.TS and EM have a decreasing trend with the increase of ultra-high pressure,andεhas a tendency to gradually decrease.The permeability of the composite membrane to water vapor and carbon dioxide showed a trend of decreasing first and then increasing as the migration time increased.It was found by DSC that the melting temperature(T_m),glass transition temperature(T_g)and cold crystallization temperature(T_c)of the composite film after 400 MPa treatment were slightly smaller than the value of 200 MPa,and the composite film ratio after 400 MPa treatment.The 200 MPa composite film has a higher degree of crystallinity,but there is no significant change.It shows that the ultra-high pressure treatment does not change the absorption and release of heat of the composite membrane.