Study On Migration Law And Thermodynamic Model Prediction Of Four Plasticizers In Polyvinyl Chloride

Food packaging is indispensable in processing,storage and transportation.Plastics are widely used in food packaging for their excellent performance and low price.However,plastic is not a single material,and chemical additives such as plasticizer will be added in its processing to enhance the fluidity and plasticity of the material.These materials can migrate out of the material,contaminate food,and eventually produce toxic effects on the human body.Therefore,studying the migration law of additives in plastic packaging can effectively reduce the risk of packaging contamination of food and guide the better production and use of plastic packaging.In this experiment,polyvinyl chloride（PVC）plastics with four plasticizers（DBP,DCHP,DNOP,DIDP）were added to study the specific surface area and temperature of plastics in anhydrous ethanol and n-hexane.（15°C,25°C,35°C,45°C）and the effect of plasticizer molecular weight on the migration law.The curve relationship between migration concentration and time was established,and the initial migration velocity,equilibrium distribution coefficient and diffusion coefficient were calculated by using the experimental data,and the experimental results were analyzed.At the same time,the Scatcthard-Hildebrand thermodynamic model was used to predict the partition coefficients of different simulated liquids at different specific surface areas and different temperatures,and compared with the experimental values,the accuracy and applicability of the model were further measured.The main results of the experiment are as follows:（1）When the four plasticizers in PVC material migrate to different simulated liquids,the relationship between migration concentration and time is in accordance with the equation Ct=At/（B+t）,and the correlation coefficient R²is greater than 0.98.（2）The larger the specific surface area of the plastic,the larger the equilibrium concentration of migration and the faster the migration speed.The relationship between the initial migration velocity（mg/h）and the reciprocal of the specific surface area（cm²/g）is in accordance with the equation ln V₀=Y₀+Ae ^R/S.The relationship between the equilibrium partition coefficient and the inverse of the specific surface area is in accordance with the equation y=A+B*S+C*S².（3）The temperature rises,the shorter the time to reach equilibrium,the greater the migration amount in the simulated liquid,and the migration rate and migration of the plasticizer in n-hexane.The equilibrium concentration is higher than that in absolute ethanol,but the temperature is less severe than that of absolute ethanol.（4）The migration law is also affected by the solubility parameters of plastics,migrations and simulated liquids.The solubility parameter of the migration is slightly different from that of the plastic.When the solubility parameters of the migration substance are more different from those of the simulated liquid,the amount transferred to the simulated liquid will be smaller and vice versa.（5）Comparing the experimental values of the distribution coefficient with the predicted values of the Scatcthard-Hildebrand thermodynamic model,and finding that the larger the surface area is,the closer the experimental value is to the model value,because the model prediction value does not consider the resistance problem,and the migration is larger when the specific surface area is larger.The smaller the resistance and the infinite surface area,the resistance is considered to be no resistance.At this time,it is the closest to the model value,and the same phenomenon occurs in the temperature experiment.