title: Molecular dynamics simulation of three plastic additives' diffusion in polyethylene terephthalate.
abstract: Accurate diffusion coefficient data of additives in a polymer are of paramount importance for estimating the migration of the additives over time. This paper shows how this diffusion coefficient can be estimated for three plastic additives [2-(2'-hydroxy-5'-methylphenyl) (UV-P), 2,6-di-tert-butyl-4-methylphenol (BHT) and di-(2-ethylhexyl) phthalate (DEHP)] in polyethylene terephthalate (PET) using the molecular dynamics (MD) simulation method. MD simulations were performed at temperatures of 293-433 K. The diffusion coefficient was calculated through the Einstein relationship connecting the data of mean-square displacement at different times. Comparison of the diffusion coefficients simulated by the MD simulation technique, predicted by the Piringer model and experiments, showed that, except for a few samples, the MD-simulated values were in agreement with the experimental values within one order of magnitude. Furthermore, the diffusion process for additives is discussed in detail, and four factors - the interaction energy between additive molecules and PET, fractional free volume, molecular shape and size, and self-diffusion of the polymer - are proposed to illustrate the microscopic diffusion mechanism. The movement trajectories of additives in PET cell models suggested that the additive molecules oscillate slowly rather than hopping for a long time. Occasionally, when a sufficiently large hole was created adjacently, the molecule could undergo spatial motion by jumping into the free-volume hole and consequently start a continuous oscillation and hop. The results indicate that MD simulation is a useful approach for predicting the microstructure and diffusion coefficient of plastic additives, and help to estimate the migration level of additives from PET packaging.
authors.affiliation: a Packaging Engineering Institute , Jinan University , Zhuhai , China.|b Key Laboratory of Product Packaging and Logistics of Guangdong Higher Education Institutes , Jinan University , Zhuhai , China.|c Zhuhai Key Laboratory of Product Packaging and Logistics , Jinan University , Zhuhai , China.
authors.forename: Bo
authors.initials: B
authors.lastname: Li
authors.affiliation: a Packaging Engineering Institute , Jinan University , Zhuhai , China.|b Key Laboratory of Product Packaging and Logistics of Guangdong Higher Education Institutes , Jinan University , Zhuhai , China.|c Zhuhai Key Laboratory of Product Packaging and Logistics , Jinan University , Zhuhai , China.
authors.forename: Zhi-Wei
authors.identifier: http://orcid.org/0000-0002-3638-8663
authors.initials: ZW
authors.lastname: Wang
authors.affiliation: a Packaging Engineering Institute , Jinan University , Zhuhai , China.|b Key Laboratory of Product Packaging and Logistics of Guangdong Higher Education Institutes , Jinan University , Zhuhai , China.|c Zhuhai Key Laboratory of Product Packaging and Logistics , Jinan University , Zhuhai , China.
authors.forename: Qin-Bao
authors.initials: QB
authors.lastname: Lin
authors.affiliation: b Key Laboratory of Product Packaging and Logistics of Guangdong Higher Education Institutes , Jinan University , Zhuhai , China.|c Zhuhai Key Laboratory of Product Packaging and Logistics , Jinan University , Zhuhai , China.|d Department of Food Science and Engineering , Jinan University , Guangzhou , China.
authors.forename: Chang-Ying
authors.initials: CY
authors.lastname: Hu
mesh_terms: D004058:Diffusion; D018857:Food Packaging; D056004:Molecular Dynamics Simulation; D010969:Plastics / Q000032:analysis*; D011093:Polyethylene Terephthalates / Q000737:chemistry*
chemical_list: D010969:Plastics; D011093:Polyethylene Terephthalates
keywords: Molecular dynamics simulation; additives; diffusion coefficient; micro-mechanism; polyethylene terephthalate