Migration Of Copper From LDPE-LLDPE-nano CuO Composite Films And Sheets

Copper oxide nanoparticle?Cu O-NP?has low production cost,broad spectrum antibacterial properties,and is used as a filler to enhance the mechanical properties of polymer nanocomposites.Polyethylene?PE?was widely used for various food,material,medicine and agricultural film,packaging material.Low density polyethylene?LDPE?and Linear low density polyethylene?LLDPE?have their respective advantages and disadvantages,the combination of these two can improve the mechanical properties of LDPE and LLDPE processing performance.In this study,LDPE/LDPE-LLDPE-nano copper oxide double-layer composite films and LDPE-LLDPE-nano copper oxide composite sheets were prepared,and their related properties were determined:mechanical properties,optical properties,thermal properties,etc.,the migration assays were conducted,the influences of different sterilization methods on the performance of composite film and copper migration were researched,besides,the dissolution behavior of Cu O-NPs were studied.The main research contents of this paper are as follows:The properties of LDPE/LDPE-LLDPE-nano copper oxide double-layer composite films and LDPE-LLDPE-nano copper oxide composite sheets were tested.The existence of Cu O-NPs improved the degree of crystallinity?X_c?of polyethylene films and sheets,and new melting peaks appeared in the region of 100-110?,which indicates new crystal forms.The FTIR spectrum showed that no new chemical bonds were formed in the nanocomposite films and sheets,that is,Cu O-NPs was physically dispersed in the polyethylene matrix.The uv-visible barrier of LDPE/LDPE-LLDPE-nano copper oxide double-layer composite films were improved by 10%?15%compared with that of the blank LDPE film.The addition of Cu O-NPs significantly enhanced the transverse tensile strength of the nanocomposite films?p<0.05?,but the amount of addition had no significant effect on the tensile strength?p>0.05?.Inductively Coupled Plasma Optical Spectrometry?ICP-OES?was used to detect the effects of concentration of Cu O-NPs,temperature,UV irradiation?254 nm?and repeat usage on copper migration,and 5 g/L citric acid as a food simulant.It's shown that the higher the temperature,the greater the amount of copper released.UV irradiation caused the photodegradation of the material,which reduced the X_c and T_m of the material and significantly increased migration amount of Copper?p<0.05?.The migration amount of copper to 5 g/L citric acid from nanocomposite films is 5.92-33.83?g/dm²,and the migration amount of copper to 5 g/L citric acid from nanocomposite sheets is 0.03-0.16 mg/dm².Based on the experimental results,it can be concluded that the migration of Cu O-NPs mainly comes from surface dissolution and desorption.Secondly,the pores and defects on the surface of materials and the free volume inside the polymer can also provide channels for food simulant to penetrate into the polymer,thus affecting the release of nanoparticles.In addition,matrix degradation can also accelerate the release of nanoparticles.The migration amount of copper increased in the“40?,10 d”migration experiment of the nanocomposite films treated by different sterilization methods?ultra-high pressure,ultraviolet irradiation,gamma irradiation?,but there was no significant difference?p>0.05?between them.In the contact angle test,the contact angles between the nanocomposite films and citric acid was found to be decreased,that is,the compatibility between them were improved.The longitudinal tensile strengths of the nanocomposite films were reduced.After three sterilization treatments,no new characteristic peaks appeared in nanocomposite films,but the peak strength of C-O bond,C=C bond and O-H bond increased,which indicates that the sterilization treatment did not produce new chemical bonds in nanocomposite films,but promoted the thermal oxygen aging of the nanocomposite films and made more citric acid solution penetrate into the film.In the thermogravimetric test,it was found that the thermal stability of the nanocomposite films treated by three sterilization methods were improved.Inductively coupled plasma mass spectrometer?ICP-MS?was used to research the effects of food simulants,temperature and incubation time on the dissolution behavior and size distribution of Cu O-NPs.It's been found that Cu O-NPs dissolved in the acids quickly,the dissolution rate constant k of Cu O-NPs in 5 g/L citric acid at 70?and 40?were 1.2544 h^-1and 0.3616 h^-1,respectively.And Cu O-NPs dissolved slowly in ultrapure water and 20%ethanol,there was a small amount of Cu O-NPs left after“70?24 hours”incubation.Considering the changes of Cu O NPs in the process of incubation:during the migration,at the first stage,food simulant would gradually dissolve nanoparticles on the surface of the nanocomposite material,hence big nanoparticles will gradually dissolve into small particles and drop off into the food simulant,but it's difficult to capture the small nanoparticles,especially in unsaturated acidic food simulant by instrument,since they dissolve quickly.