Research On Characteristic And Safety Assessment Of Nanoparticle Modified LDPE Film For Food Packaging

Due to unique physical and chemical characteristics, nanoparticles have been well-received by researchers recently. Polymer nanocomposites that incorporate nanoparticles increasingly being developed for food package. Nano-package protects food during storage and transportation, and withstands thermal stresses from food processes treatments. Nanoparticles that are incorprated within the package to improve functionality, may interact with food and migrate into it.Nano-TiO2 and nano-ZnO are two kinds of nano metallic oxide which have been extensively researched. Nanoparticle modified materials have revealed their advantages in food preservation these years. In this research, nano-TiO2 modified low density polyethylene (LDPE) film package and nano-ZnO modified LDPE film package were produced through blending LDPE with nano-TiO2 and nano-ZnO, respectively. Experimental and theoretical methods both can be used to assess nanoparticle release from food contact materials by diffusion, dissolution, and desorption. The main results were as follows:1) Preparation of nanocomposite filmsNano-TiO2 and nano-ZnO were treated with titanate coupling agent, and then blended with LDPE, respectively. Transmission electron microscopy indicated that nanoparticles had good dispersion in LDPE and could reach nano-scale. Nano-TiO2 LDPE film and nano-ZnO LDPE film with were produced by single screw extruder and the final nanoparticle dosage were both 1%. TG curves of three kinds of films obtained their thermal degradation (Td) temperature,437.71,434.12 and 435.91℃, decreased by 0.82% and 0.41% compared to normal LDPE film, both nanoparticle modified packaging had a good thermal stability; DSC curves of them showed a slight decrease of fusible temperature (0.7882% and 0.1075%) and crystallization temperature (0.76% and 1.35%), whereas increased the melting enthalpy (1.11% and 1.90%) and crytallinity of nanocomposite and then enhanced the barrier property of them.2) Migration of Ti and Zn into four kinds of food stimulants under 40 and 70℃ for a period of time were investigated.Migration tests were conducted under 40℃ for 1,4 and 7 days, as well as 70℃ for 2 hours. Results showed that among the aqueous food stimulants tested,3% acetic acid solution demonstrated the highest migration levels, while the 95% ethanol was the least effective migration medium. Migration of Ti and Zn increased with time and reached equilibrium. Polarity of stimulants, swelling of materials, pH of stimulants and solubility of metal and metallic oxide accounted for different concentrations of Ti and Zn in four different food stimulants. Concentration of Ti and Zn under 70℃ 2h were similar to the condition of 40℃ Id, which showed that higher temperature fostered the migration process, in accordance with Arrhenius law.3) Applicability test of Piringer model in migration characteristic prediction of nanoparticle modified LDPE film and establishment of migration regression modelPiringer model based on Fick’s theory could not be developed to predict the extent of migration from both nanoparticle modified LDPE film into four food stimulants effectively. We tried to develop a prediction statistical mathematical model, by performing an evaluation of influence of the effect of temperature, time, stimulant polarity and pH through an analysis of multiple correlations between overall migration concentration as the dependent variable. The model could reduce the time and costs of the experimental work associated to the analysis with a prediction capacity, and provide a guidance for the risk assessments.4) Effect of microwave heating and ultraviolet radiation on migration of Ti and ZnMigration tests were conducted under different microwave heating and ultraviolet radiation in advance. Results showed that the higher the power of microwave, the more Ti and Zn migrated from nano-film and microwave facilitate the migration of nanoparticles from the package film. Release of Ti and Zn from nanoparticle modified film into acidic stimulants under the pressure of ultraviolet radiation decreased first and then increased within UV intensity of 864kJ/m2. The treatment didn’t result in more release concentration of Ti and Zn.5) Determination of sanitary characteristics of nanoparticle modified LDPE film and risk assessment of heavy metals migration into acidic food stimulantsThe sanitary characteristics of both Nano-film precede normal LDPE film and conformed to national food sanitary standards. Migration tests of several heavy metals were conducted at 40℃ 4d,40℃ 7d and 70℃ 2h, the concentration of Pb, Cd and Cr were measured by ICP-MS. Results showed that the heavy metal migrants were far below national food contaminants limits. Therefore, incorporation of nano-TiO2 and nano-ZnO into LDPE will not lead to exceeding national standard of toxic metals.