Study On The Migration Law Of Nano-silver In Polylactic Acid-based Ultra-high Pressure Food Packaging Film

In this work,new biodegradable films of polylactic acid/nano-silver were prepared using polylactic acid and nano-silver as raw materials.The film materials were subjected to ultrahigh pressure treatment,and their migration behaviors in acidcontaining,alcohol-containing,and oily food packaging were studied.The effects of ultrahigh pressure on the migration of nano-silver and the polylactic acid-based nano-silver composite film used in food packaging containing acid were investigated.The applicability and safety of PLA/nano-silver films for ultrahigh pressure food packaging were revealed.(1)PLA/nano-silver composite packaging films were prepared by blending PLA with nano-silver and sent to ultrahigh pressure treatment.Using 4 %(v/v)acetic acid solution,50 %(v/v)ethanol solution,and isooctane solution as food simulation solution,the migration content of nano-silver in PLA-based films was determined by atomic absorption spectrometry.The measured migration content was fitted by Fick's second law curves,and the migration rules of nano-silver in the PLA-based films post ultrahigh pressure treatment were studied and migration models were established.The results showed that nano-silver had the largest migration amount and diffusion coefficient in 4 %(v/v)acetic acid solution,followed by 50 %(v/v)ethanol solution and the lowest in isooctane solution.It was possible that water activity in food simulants affected the molecular binding force between PLA and nano-silver in the films.Silver atoms or ions had stronger coordination ability with oxygen atoms on the carbonyl group of acetic acid,and the solubility of nano-silver in acetic acid solution was higher.The correlation coefficient(R)of the fitted trend line of migration model was between 0.957 and 0.997.Considering the balance between the preparation of nano-antibacterial active packaging with good performance and the migration of nano-silver from packaging materials to food,adding a small amount of nano-silver in the composites was the most effective method for limiting nano-silver migration and achieving good performances.(2)Polylactic acid-based films containing 5 wt% nano-silver were treated at 0,100,200,300,and 400 MPa for 10 minutes and immersed in 4 %(v/v)acetic acid solution.The effects of different pressure treatments on the migration behavior and migration law of nano-silver were studied.For films treated with 200 MPa,nano-silver migration was minimal at the end of storage.Proper high pressure(200 MPa)might restrict the movement of polymer chains,induce dense film structures,and inhibit the adsorption of acetic acid mimetics.In addition,appropriate high pressure(200 MPa)caused an increase in the tortuosity of the diffusion path,which led to decrease in the diffusivity of the nanoparticles.However,high-pressure treatment above 400 MPa would cause the diffusion rate of nano-silver to increase.Considering the amount of nano-silver migration,200 MPa was the most effective method to control nano-particle migration in our study.(3)Polylactic acid-based films containing 5 wt% nano-silver were treated with 0,200,and 400 MPa and immersed in a 4 %(v/v)acetic acid solution.SEM,DSC,XRD,FTIR were used to test the microstructure,thermal properties,chemical interactions and physical bonding of the composite films during migration.The effects of ultrahigh pressure treatment on the properties of PLA/ nano silver films during migration were evaluated,and the applicability of the films for ultrahigh pressure food packaging was investigated.As the storage time in the acetic acid solution increased,at the end of the storage time,suitable high-pressure food processing(200 MPa)resulted in denser structures and higher crystallinity of the films.However,high pressure of 400 MPa could destroy hydrogen bonds between PLA molecules and nanoparticles.High pressure treatment had no effect on the characteristic peaks of the film immersed in the food simulant,and PLA had maintained amorphous structures during storage.However,during the later storage period,the migration of nano-silver to acetic acid mimic resulted in decrease in the intensity of specific characteristic peaks of the films.The migration of nanoparticles would directly promote the interaction between molecular chains.Therefore,proper ultrahigh pressure treatment of food(200 MPa)has the least impact on the performance of the composite film during the migration process.