Migration Of Copper From Nano-copper/polypropylene Composite Films And Its Properties

Giving that low raw material price but with excellent performances,polypropylene?PP?is currently widely used in food packaging.Also,nano-materials as novel solution have been widely studied and developed for food packaging,resulting from its characteristics including its small sizes and large specific surface area.In this project,nano-copper with varied concentration was selected and was mixed with homopolymer polypropylene?PP-H?matrix to prepare composite films.The performance of films were measured,like,the physical properties,the migration behavior of copper,the diffusion coefficient and partition coefficient of copper in the composite films as well as the migration model of copper.Additionally,films biologically safety were evaluated and were applied to fresh pork preservation.The specific studies are as follows:?1?9 kinds of nano-copper/PP-H composite films were prepared by melt blending food grade PP-H master batch with nano-copper powder with different concentrations?or nano-copper powder modified by coupling agent KH550?,respectively.The thickness,transparency,color,thermal stability,mechanical properties and microscopic morphology of the composite films were measured as well as the molecular structure of the films.Results showed that the addition of nano-copper had significantly improved the thermal property of the composite films.CF-0.25,CF-0.5,and CF-1 films began to lose weight at 235.77,240.09,and 228.53?,respectively,which was dramatically higher than the pure PP-H film?130.28??.The absorbance and?E increased with increased nano-copper concentrations?P<0.05?whilst the transparency and L*value decreased?P<0.05?.The thickness and tensile strength of the composite films showed no significant differences,compared with that of pure PP-H film.However,the nominal tensile strain at break increased significantly?P<0.05?,among which CF-0.25 film reached a maximum of 292.60%.The shape of nano-copper particles was approximately spherical and uniformly dispersed in the PP-H matrix at a low concentration.However,with increased concentration,the nano-copper slightly agglomerated in the films and thereby increasing the film roughness.There was no new chemical bonds formed between the nano-copper and the PP-H,inducating that the nano-copper particles were merely physically dispersed in the matrix.The addition of the coupling agent KH550 improved the distribution of nano-copper in the composite films,but had no significant effect on the other properties.?2?The effects of time,temperature,nano-copper content,coupling agent,gamma ray irradiation treatment,repeated use and the concentration of acetic acid simulant on the release of copper from nano-copper/PP-H composite films were studied by using inductively coupled plasma optical emission spectrometer?ICP-OES?.The mechanical properties and morphology of films after migration tests were explored.It was found that the increase of migration time,temperature,nano-copper content and acetic acid food simulants concentration,gamma ray irradiation treatment all accelerated the migration of copper?P<0.05?.The coupling agent KH550 had no significant effect on the migration of copper.When contacted with food simulant,the migration amount of copper in each cycle corresponded with nano-copper content.After migration tests,the mechanical properties of the films were relatively stable while the thickness and transparency increased significantly?P<0.05?.The aggregation state of nano-copper particles and film roughness were affected by migration behavior.?3?Based on Fick's second law and reasonable assumption,the migration model was built.The partition coefficient K_P.F.F of copper migrating into 3%acetic acid food simulant from nano-copper/PP-H composite films,the diffusion coefficient D_p and modelling fitting were performed using Matlab software.The migration of copper from the composite films to the acidic food simulant was simulated by AKTS-SML software,and was compared with experimental values.It was observed that with increased temperature?20,40,50 and 70??,K_P,F,F decreased whilst D_p increased.Furthermore,under the same temperature,the K_P,F,F decreased with the increase of initial content of copper in the films.The correlation coefficient R² of Matlab fitting trend line was between 0.848-0.991,which illustrated that the fitting result was good and the Crank model can be used to predict the migration behavior of nano-copper from composite films into acidic food simulants.The simulated values of copper migration amount acquired by the AKTS-SML software were slightly lower than the experimental values under all experimental temperatures except 70?,2 h.The simulated results of migration amount were considered to be accurate because the deviation between simulated values and experimental values was within 10%and the deviation of migration ratio was within 20%.Therefore,AKTS-SML software was suitable for estimating the amount of migration of nano-copper composite films into acidic simulants under a stable equilibrium system.?4?The safety and antibacterial properties of the nano-copper/PP-H composite films and its application on fresh pork preservation were studied as well.It was observed that the nano-copper/PP-H composite films can effectively inhibit the survival of Escherichia coli,Staphylococcus aureus,Shigella castellani and Bacillus subtilis.And the overall antibacterial effects against Gram-positive bacteria was greater than Gram-negative bacteria?P<0.05?.When the Cu²⁺concentration reached 4.5?g/mL,the L-02 cell viability was 92.22%?P<0.05?of the control group,which began to damage the L-02 cells.When Cu²⁺concentration was greater than10?g/mL,the inhibition of L-02 cell viability was extremely significant?P<0.001?.Therefore,the appropriate amount of nano-copper should be chosen to prepare composite films to prevent excessive copper migration into the food system,which was probably harmful to human health.Moreover,the composite films had a good potential to improve shelf-life and sensory quality of pork.Considering all various indicators,it was most suitable to use CF-1 film for packaging pork.