Oxygen permeability, electron spin resonance, differential scanning calorimetry and positron annihilation lifetime spectroscopy studies of uniaxially deformed linear low‐density polyethylene film

Abstract

Linear low‐density polyethylene (PE‐LLD) films were mechanically deformed at room temperature in both parallel and perpendicular directions to their initial orientation obtained during the manufacturing process. The degree of deformation ${\lambda}$, defined as ${\lambda} = l/l_{0}, l$ and l0 being the length of the deformed and relaxed samples, respectively, was varied from 1.0 to 2.0. Oxygen transport was investigated by a manometric method and the results were correlated with differential scanning calorimetry and positron annihilation lifetime spectroscopy measurements in order to investigate the contribution of various factors that influence the permeability of deformed PE‐LLD films. An electron spin resonance spin‐probe method was employed to determine the influence of uniaxial deformation on the chain segmental mobility in the amorphous phase. The results show that the deformation process reduces oxygen permeability and diffusion coefficients. It was found that the reduction is a combined effect of an increased crystallinity and reduced fractional free volume. The decrease of the chain segmental mobility with deformation plays an important role in the gas diffusion mechanism. © 2012 Society of Chemical Industry

Diffusion of low‐molecular‐weight permeants through semi‐crystalline polymers: combining molecular dynamics with semi‐empirical models

“…The values of D obtained from all of the chosen reported results were averaged out over a temperature range of 293–308 K with steps of 5 K to compare with the simulated values obtained over the same temperature range. The difference in the extent of diffusion between the amorphous and crystalline PE can also be appreciated by the differences in the MSD observed for the O 2 molecule at the same temperature.…”

“…The variation of D with temperature for simulated amorphous and crystalline PE is compared with the averaged values of D obtained from the literature in Fig. .…”

“…The D value for the O 2 molecule in the amorphous and crystalline PE systems was estimated as a function of temperature ( T ). The MD approach used to estimate D was as follows: Incorporate the O 2 molecule in either the crystalline or amorphous PE simulation box using the Dreiding force field. Subject the combined system to an energy minimisation step. Longer NVT (2 ns) and NPT (5 ns for the amorphous and 10 ns for the crystalline system) steps were used when estimating D and studying the diffusion of oxygen as compared to when building the amorphous and crystalline simulation boxes. D was estimated from the linear region of the overall MSD plot for the NPT run using Eqn (1). Thirty NPT runs for each system were carried out at each temperature (293, 298, 303 and 308 K) on the gstar HPC system at Swinburne University of Technology The simulated D values were used to predict overall D using the models presented in Table . The predicted values were then compared to the experimental data of the diffusion of oxygen in LLDPE to determine which predictive model is best suited for our system. …”

“…Further, the data obtained from the simulation of oxygen diffusion in the simulated crystalline and amorphous LLDPE systems were input into the various expressions presented in Table and D values were predicted. These were then compared with the averaged reported data obtained from five representative articles published on the transport of oxygen in LLDPE to see which model is the best suited for describing this system. It is ensured that the crystallinities of the samples analysed in the papers are 30 ± 5% estimated using the enthalpy of 100% crystalline PE which is 289.9 J g −1 .…”

Polyolefin/graphene nanocomposites: a review

“…101 A number of methods are available for improving the barrier properties of polymeric materials along with some drawbacks due to high cost, opacity, humidity sensitivity and low mechanical strength. 102 Polymeric materials such as PE, 103 PP, 104 and other matrices 105,106 have been extensively used to coat thin lm layers for low gas permeability. However, their applications are limited because of the high gas permeability, as compared to high demands for the modern packaging application.…”