| Nanocopper has attracted lot of attention in food packaging area in recent years due to its broad spectrum antimicrobial activity and low cost.In this paper,nanocopper/LDPE composite films were prepared,methods were developed for the determination of copper,and the migration behaviors of nanocopper were studied,the characterization and properties of the composite films were tested.Besides,the diffusion coefficient of copper was calculated.Detailed studies are as follows:(1)Nanocopper and nanocopper modified by(3-aminopropyl)triethoxysilane(KH550)was mechanically mixed with LDPE granules respectively,new granules containing nanocopper and modified nanocopper were reproduced and then the composite films were manufactured by a film-blowing machine.The films were exposured to 3%(w/v)acetic acid and 10%(v/v)ethanol at 40℃ for 10 days,the migration of copper in 3%(w/v)acetic acid and 10%(v/v)ethanol were determined by inductively coupled plasma optical spectrometry(ICP-OES)and graphite furnace atomic absorption spectroscopy(GFAAS)respectively.For both food simulants,the results showed the calibration curves of copper were linear in the range of 0.02~0.50 μg/mL and2.50~25.00 μg/L with correlation coefficients not less than 0.999.The spiked recoveries at different spiked levels were in the range of 81.42%~100.22% and81.71%~96.05% with relative standard deviation(RSD)of 1.02%~8.87% and1.66%~8.24%,respectively.The limit of detection were 0.90 μg/L and 0.20 μg/L and the limit of quantitation were 3.10 μg/L and 0.68 μg/L,respectively.The results indicated that both methods were precise,highly sensitive and accurate.(2)3%(w/v)acetic acid and 10%(v/v)ethanol were selected as food simulants,migration of nanocopper from the composite films were carried out with different time and temperatures.The results indicated that copper migration increased with time and temperature in both food simulants,and copper migration increased dramatically in the first few days of the experiment,thereafter,it decreased and then reached steady state.The maximum migration of CF-0.05,CF-0.25 and CF-0.25#films for 3%(w/v)acetic acid were 24.94%,28.61% and 41.22% at 70℃,and 6.81%,8.02% and 11.81% at 40℃,while at 20℃,equilibrium was reached after a long period exposure of 22 days and the maximum migration of CF-0.25 and CF-0.25#films were 4.21% and 6.37%.As for 10%(v/v)ethanol,the maximum migration ratios of CF-0.25 and CF-0.25# films were 5.74‰ and 8.68 ‰ at 70℃ respectively,while at 40℃,equilibrium was not reached even after exposure of 20 days and few migration amount of copper were detected.The migration of copper from CF-0.25#films was higher(P<0.05)than that from CF-0.25 films in all tested conditions.It could be concluded that the addition of KH550 was favorable for the migration of copper.(3)Food samples including rice vinegar(RV),Chinese liquor(CL),lemon soft drink(LM),olive oil(OL)and bottled water(BW)were selected to investigate the copper release at 40℃ for 10 days and at 70℃ for 2 hours.RV samples demonstrated higher(P<0.05)migration levels than the other food samples under the same conditions,and represented the highest migration level with a value of 540.00 μg/L.The migration of copper from CF-0.25 into RV and OL was lower than that from CF-0.25#,while into LM,BW and CL it was higher than that from CF-0.25#,which was inconsistent with the migration behavior in food simulants.Thus,there are gaps when replacing real food with food simulants.(4)Field emission scanning electron microscopy(FE-SEM)and atomic force microscopy(AFM)were used to confirm the original morphology of copper nanoparticles or their morphology and presence in nanocopper/LDPE composite films before and after their exposure to food simulants,and physical,mechanical properties were also tested by material testing machine.The results showed that the shape of the copper nanoparticles was spherical in nature and formed aggregates with variety of sizes.With the addition of nanocopper increased,the dark-gray color of the film became severer,and the surface roughness increased,however,CF-0.25# films showed a little lower average roughness(Ra)and root mean square roughness(RMS)than CF-0.25,due to KH550 being in favour of copper nanoparticles getting well dispersed in LDPE,hence reducing the surface roughness.The color of the films changed from dark-gray to blue-green after exposure in 3%(w/v)acetic acid at 40℃for 10 days,however,the color sense was not strong(△E < 6).The addition of nanocopper resulted in the decrease of tensile strength and the increase of elongation at break,whilst the decrease of light transmittance.However,the light transmittance kept the same after the migration experiment.(5)With reasonable assumptions,the migration model of copper was established.As one of the most important parameter in the migration model,the diffusion coefficient(DP)was fitted by the software Matlab.Correlation coefficients were in the range of0.872~0.988,which illustrated good fitting effect of Matlab and reflected copper migration accurately.With the temperature increased,the DP of copper increased.The DP of copper in 3%(w/v)acetic acid was higher than it in 10%(v/v)ethanol at 70℃,therefore higher diffusion rate and equilibrium was reached after a shorter period. |
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