| Ultraviolet (UV) inks are widely used in food-packaging printing due to their excellent properties. They generally do not contain any traditional organic solvents. However, photoinitiators (PIs) are known to give taints, odors, potential migration problems or are suspected to give rise to toxicological problems, which would be a health hazards to consumers.In this paper, detection techniques of additives and PIs, migration experiment and mathematical modeling of migration of PIs from paper-plastic coating materials into food were discussed. The contents are as followings.1. Research on the detection methods of GC-FID (gas chromatography-flame ionization detection)The GC-FID detection method for the standard of UV ink PIs1-hydroxycyclohexyl-1-phenyl ketone (184) and Benzyldimethyl ketal (651) was built. The GC-FID detection method for the analysed 184, 651 and additives from paper-plastic coating materials was built, the detection conditions were as followings: a HP-5 capillary column. Temperature programme set at 100℃initially, then increased by 5℃/min up to 200℃, with a holding time of 2min, then increased by 35℃/min up to 300℃, with a holding time of 5min. Injection volume was 1μL and carrier gas was nitrogen at 2.5mL/min. The injector and detector temperature were 250℃, respectively. The injection was made in a splitless mode.2. Study on the stability of UV ink PIsStability of 184 and 651 in 10%, 95% ethanol and isooctane at 20℃, 40℃and 60℃was studied under no light exposure. At the same time, the effect of stabilizing agent hydroquinone monomethyl ester (HQMME) on stability was discussed. The results showed that the effect of protection of HQMME was not obvious under all heat-exposure conditions tested and in all food simulants used under no light exposure conditions. Photoinitiator 184 was shown to be quite stable under all heat-exposure conditions tested and in all food simulants used whether adding HQMME or not. Photoinitiator 651 was stable almost in all heat-exposure conditions tested and in all food simulants used except in food simulant 10% ethanol at 60℃. The mass spectrum of decomposed product of 651 was detected by GC-MS.3. Study on migration of PIs from paper-plastic coating materialsMigration of 184 and 651 from paper-plastic coating materials 4015 and 6515 into 10%, 95% ethanol and isooctane, from 4025 into 10% ethanol and isooctane, from 3312 into 95% ethanol and isooctane at 20℃, 40℃and 60℃were studied. The results showed that the effect of temperature on migration of the same contaminant into the same food stimulant was obvious. The diffusion rate of high molecular weight 651 was much lower than that of low molecular weight 184. Migration rate of the same contaminant into isooctane was the fastest. However, migration rate into 10% ethanol was the lowest at the same test conditions. The migration amount decreased with the increase of LDPE thickness. The barrier property of PP was better than that of LDPE. At the same test conditions, migration rate of contaminant was relatively slow from high tightness paper. It was also showed that migration amount increased with the increase of initial concentration of contaminant. In addition, the effect factors on migration were also analyzed from a microcosmic viewpoint. The factors included temperature, molecular structure of contaminant, swelling of food simulants, thickness of plastic coating, type of plastic coating and property of paper.4. Migration modelingMigration mathematical modeling of unlimited paper thickness and limited paper thickness were built. In the two modelings, the thickness of paper was considered as unlimited thickness (as far as the thickness of plastic coating was considered) and as limited thickness, respectively. Packaging-food system was studied as limited packaging-unlimited food. New parameter of partition coefficient at the interface of paper and plastic coating was introduced, different diffusion coefficients DP and DC of contaminant in paper and plastic coating were considered. In addition, diffusion equations, initial conditions and boundary conditions were given. A series of analytical solutions were obtained through Laplace transformation and inversion theorem. The effect of kCP, DP, DC and initial concentration CP0, et al on migration behavior was discussed.5. Applicability of mathematical modeling of limited paper thickness and contrastive analysis with experiment valuesThe applicability of mathematical modeling of limited paper thickness as bi-layer polymer packaging and mono-layer polymer packaging was studied. The expression of simplified bi-layer polymer was accordant with the famous Laoubi-Vergnaud modeling, and the expression of simplified mono-layer polymer was the famous Crank diffusion modeling.According to experimental values of partition coefficient kCP at paper-plastic interface and combining other parameters, migration experiment values of PIs 184 and 651 from different paper-plastic materials into different food simulants and calculated values from limited paper thickness modeling were compared. It showed the results that this mathematical modeling with the"worst-case"Dc could ensure the using safety of packaging. In addition, migration mathematical modeling of unlimited paper thickness was not appropriate to predict the migration of contaminants into food or food simulants from paper-plastic materials with thiner paper thickness.
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