The Detection And Migration Of Small Molecule Compounds In Polyethylene Terephthalate(PET)

Polyethylene terephthalate(PET) production has developed rapidly in recent years. However, because of the complexity of the PET raw material and the industrial production process, PET material may contain a few small molecule compounds, which may migrate into the food when PET material contacted with food. Thus, there is a potential hazard to human health. The wide application of recycled PET materials brings more challenges to food safety. This article selected six small molecule compounds potentially added in PET as research object, including Toluene, Chlorobenzene, Benzaldehyde, Butylated hydroxytoluene, Di-2-ethylhexylphthalat and Dibutyl phthalate, established the corresponding detecting methods, and conducted the migration research under different temperature and initial concentration.The detection method developed for determination of six small molecule compounds in PET by Gas chromatography Mass spectrometry detector(GC-MS) was synchronous and rapid. Six compounds showed peaks in 14.2min. The LOD, LOQ, recoveries, RSD of intra-day, RSD of inter-day of the method can meet the requirements of detection. Methylene chloride ultrasonic assisted extraction was optimized, and the optimum was solid to liquid ratio 1:15, 30 min extracted time for once. The method can be used for determining six small molecule compounds in PET.The method was applied in the determination of six small molecule compounds in 25 kinds of food packaging PET on sale and self prepared PET samples. The result obtained by this method showed that Toluene, BHT or DEHP were detected from some PET samples on sale, but had not exceed the added limit stipulated by EU. Six small molecule compounds were detected in self prepared PET samples, so the samples can meet the requirements of migration experiment.The detection method developed for determination of six small molecule compounds in 2,2,4-Trimethylpentane by GC-MS was synchronous and rapid. The detection method were used to study the migration process of six small molecule compounds from PET to 2,2,4-Trimethylpentane. Except Toluene in 2,2,4-Trimethylpentane can not be quantified, the migration rate of other five small molecule compounds were related to temperature, initial concentration, boiling point and other properties of compounds.Based on the migration experimental data, distribution coefficient(KP,F) of five small molecule compounds was calculated when migration got equilibration, Fick’s diffusion model and Brandsch empirical formula were used to calculate diffusion coefficient(DP) of the five small molecule compounds. All of the KP,F of five small molecule compounds were greater than 1000, the value of DP were between 10-11 and 10-18 cm2 / s. KP, F and DP would change depending on temperature, initial concentration and the chemicals. Compared with Fick’s model, Brandsch empirical formula would overestimate the value of DP.