Research On Migration Regularity And Mechanisms Of Residual Toluene From Food Plastic Laminated Films

As food plastic laminated films are prepared from two or more monolayer films that are bonded together by adhesives,they have the excellent properties of each monolayer film.Hence,laminated films are currently the best materials for soft package in the market.With unique moisture-proof and heat-seal properties,low density polyethylene(LDPE)and casting polypropylene(CPP)are often used as inner membrane substrate to directly contact with food.However,the residual printing ink,adhesives and diluters between two layers of films may penetrate through the films and migrate into foods in case of high content or insufficient volatilization.The residual solvents are often mixtures of several organic solvents which mainly include toluene and ethyl acetate etc.,of which toluene,a recognized carcinogenic substance,is prone to being residual due to its high adsorbability.Therefore,this paper systematically studied the migration laws of toluene in plastic laminated films into food,and predicted the migration tendencies by building a mathematical model,so as to profoundly explore the structures of plastic laminated films as well as the migration mechanisms of toluene,thus providing theoretical basis for guaranteeing food safety and promulgating relevant laws and regulations.The main research results are as follows:(1)The higher the temperature was,the larger the migration rate of toluene into simulants would be.Moreover,the longer the migration time was,the larger the migration rate of toluene would be,and the migration rate would finally reach a stable state.Also,simulants had a significant influence on the migration rate of toluene.The sequence of migration rates of toluene in common plastic laminated films into different simulants was as follows:isooctane>50%alcohol>3%acetic acid>10%alcohol.The sequence of migration rates of toluene in boiling-resistant plastic laminated films into different food simulants and seasoning simulants was as follows:olive oil>3%acetic acid>ultrapure water;3 g/100mL sodium chloride>0.1 g/100 mL sodium glutamate>5 g/l00mL cane sugar.The thicker the inner membrane was,the lower the migration rate of toluene into simulants would be.In common plastic laminated films,the sequence of migration rates of toluene penetrating different inner membranes and migrating into different simulants was as follows:LDPE30>LDPE50>CPP30>CPP50.In addition,different microwave heating conditions had certain influence on the migration rates of toluene in boiling-resistant plastic laminated films.The larger the microwave power was,and the longer the heating time was,the larger the migration rates of toluene would be.When the simulants were heated to approximate 80℃.the migration rates of toluene were not greatly different whichever microwave power for microwave heating was chosen.(2)The best condition for extracting toluene from pork was confirmed.Isooctane was taken as the extracting solvent,and oscillated to extract for 40min.Under such condition,the recovery rate of toluene was 80.3%～88.7%,and RSD was 3.2%～6.1%.The higher the boiling temperature was,and the longer the heating time was,the larger the migration rate of toluene would be.However,under the temperatures of 121℃ and 135℃,the migration rates of toluene didn’t change so significantly after boiling for 20min.Furthermore,the larger fat content of pork was,the larger the migration rate of toluene would be.The ratio between superficial area of the plastic contacting with food and the volume of the pork(superficial area:volume)had little influence on migration of toluene.High temperature might weaken the barrier property of the films.The longer the boiling time was,the weaker the bairier property of the films would be.With the rising of the boiling temperature and the extension of the boiling time,the breaking strength and elongation at break would reduce,in particular the elongation at break which would change more obviously.(3)The empirical value(Dexp)of migration and diffusion coefficient of toluene in plastic laminated films and value of Fick’s law(DFick)were calculated by using formulas derived from Brandsch classic model and Fick’s law.The results showed the follows:the empirical value(Dexp)of diffusion coefficient of toluene and value of Fick’s law(DFick)increased with the rising of temperature.Under most conditions,the empirical values(Dexp)of diffusion coefficient of toluene in the three samples were all larger than values of Fick’s law(DFick)(Dexp﹥DFick).CPP30 sample was the only one whose Dexp<DFick when toluene migrated into isooctane under the migration temperature of 4℃～20℃.Whichever simulant was chosen,the empirical values(Dexp)of diffusion coefficients of toluene under the same temperature were identical.The partition coefficient(KP,F)of toluene in plastic laminated films amid migration was calculated by using the definition of partition coefficient.The smaller KP,F was,the more toluene would migrate into simulants.The larger the temperature was,the smaller the KP,F value of toluene migrating into the same simulant would be.The sequence of KP,F values of toluene in common plastic laminated films into different simulants was:3%acetic acid>10%alcohol>50%alcohol>isooctane.The sequence of KP,F values of toluene in boiling-resistant plastic laminated films into different simulants was:ultrapure water>3%acetic acid>olive oil.A single-layer mathematical model was built and simplified,in which Dexp and KP,F were taken as important parameters.Comparison was carried out on the values of migration amount of toluene calculated by the model and obtained from experiments.The results showed the follows:the model could predict the change tendency of migration amount of toluene satisfactorily.In addition to CPP30 sample(the value of migration amount of toluene into isooctane calculated by the model was slightly smaller than that obtained from the experiment),the values of migration amount of toluene calculated by the model were all larger than or equivalent to that obtained from the experiment in LDPE30,CPP30 and RCPP70 samples.(4)The migration conditions of common plastic laminated films(LDPE and CPP)and boiling-resistant plastic laminated films(RCPP)were disposed.In infrared spectroscopy,some absorption peaks of the said three samples all moved towards lower wave numbers,which indicated that the intermolecular forces in the films reduced.Scanning electron microscope showed that the microstructure of disposed samples had wrinkles and distortions on the fracture surface,of which the microstructure change of CPP film was slightly smaller than that of LDPE film,and isooctane and olive oil had significantly influence on the microstructure of common film and boiling-resistant film respectively.DSC analysis showed that the melting points and enthalpy values of the disposed samples all decreased,which indicated that the heat stability of the films were weakened,and the degree of crystallization reduced,of which the change range of CPP film was less than that of LDPE film.For RCPP sample which didn’t contact with the simulants,the degree of crystallization of film reduced,but the heat stability changed slightly.TG curve showed that thermal decomposition temperatures and heat stabilities of disposed LDPE and CPP samples both reduced;the heat stability of RCPP sample which was boiled changed slightly.