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.

Influence of N,N′‐ethylene bis oleamide on the flowability of the acrylonitrile‐butadiene‐styrene resin and lubrication mechanism

“…24,25 It can accurately simulate the free volume of the polymer system and the migration ability of the polymer chains. 8,26,27 The simulation results are highly consistent with the experimental values. 28 In this article, we found that EBO was an effective lubricant to strengthen the flowability of the ABS resin.…”

Influence of N, N'-ethylene bis oleamide (EBO) on the flowability of the Acrylonitrile-butadiene-styrene (ABS) resin and lubrication mechanism

“…Due to the rapid advancement of computer simulation, molecular dynamics simulation (MD) has an extensive range of applications in guiding the design of high-performance composites [19,20]. It can accurately simulate the free volume of the polymer system and the migration ability of the polymer chains [21]. The simulation results are highly consistent with the experimental values.…”

Molecular-level investigation of plasticization of polyethylene terephthalate (PET) in supercritical carbon dioxide via molecular dynamics simulation

“…In this work, all the molecular simulation processes were completed by Accelrys Material Studio (MS) 2017 [ 17 ]. The PET chain consisting of 100 repeat units [ 18 ] and CO 2 molecules were built by materials visualizer modules [ 19 ]. The cubic cells with two PET chains were constructed using an amorphous cell module, which is shown in figure 1 , and were subsequently equilibrated using the Forcite module.…”