Crystallinity effect on the gas transport in semicrystalline coextruded films based on linear low density polyethylene

Abstract

This article describes the diffusion and permeability of oxygen, carbon dioxide, methane, ethane, ethylene, propane, and propylene in 1‐octene based polyethylene of densities 0.94, 0.92, 0.904, and 0.87. The isotherms obtained in the time‐lag experimental device display a diffusion coefficient and permeability behavior similar to that of glassy polymers. We apply the dual model to semicrystalline polymers assuming that Henry's sites are related to the amorphous phase, which decreases when the crystallinity percentage increases. Whereas the interphase of the polymeric matrix and the crystalline phase prevails and acts as Langmuir sites. Their effect is to increase both, the tortuosity of diffusion trajectories and the chain immobilization. We now explain this effect using thermodynamic considerations. In fact, the tortuosity is related to the change in activation entropy, and the chain immobilization to the cohesive energy of the polymeric matrix. In those terms, the diffusion coefficient does not follow the same crystalline percentage dependence than the solubility. According to the previous findings, the solubility changes in proportion to amorphous percentages. Instead, diffusion coefficient has exponential dependence. Furthermore, we show that the permeability changes as a consequence of the modification of diffusion and solubility, according to the product of both quantities. Comparison with previous publication has been included. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 634–642, 2010

Formation–structure–performance correlation of thin film composite membranes prepared by interfacial polymerization for gas separation

“…Second, an inverse relationship between crystallinity and gas permeance was clearly presented in the literature [23][24][25]. Crystalline region in polymer acts as impermeable barriers to gas molecules, forcing the penetrants to travel a tortuous path through the polymer, thus decreasing the diffusion coefficient [25]. Finally, increasing the crosslinking extent could decrease the gas permeability [51][52][53] due to the decrease of the gas diffusivity inside the crosslinked network [23,54].…”

“…First, thinner skin layer thicknesses could lead to higher gas permeance [15]. Second, an inverse relationship between crystallinity and gas permeance was clearly presented in the literature [23][24][25]. Crystalline region in polymer acts as impermeable barriers to gas molecules, forcing the penetrants to travel a tortuous path through the polymer, thus decreasing the diffusion coefficient [25].…”

“…On one hand, an inverse relationship between skin layer thickness and gas permeance was clearly presented in the literature [15], which is distinct from the relationship between skin layer thickness and water flux (or salt rejection) for RO membranes as mentioned above. On the other hand, apart from skin layer thickness and crosslinking, crystallinity is also an important structural parameter that influences the gas transport properties [23][24][25]. Nevertheless, the relationship between crystallinity and separation performance has never been investigated in the field of interfacially polymerized TFC RO membranes, although it has been reported in the field of non interfaciallly polymerized membranes that decreasing crystallinity could enhance the water permeability [26][27][28].…”

The Crystallinity Behavior of Polyethylene/Clay Nanocomposites Under the Influence of Water-Assisted Melt Blending

“…Interpretation of ultimate properties of polymer blends and composites in terms of their crystalline structures have widely been addressed in the literature [23,27,[33][34][35] . In case of nanocomposites, however, a few works have been performed until now.…”

Polyoxymethylene Additives

“…It is well known that gas is not soluble in it. Compañ [118] reported for example that if: -D*(T) is the diffusion coefficient in a 100 % amorphous polymer, -D(x am ,T) is the diffusion coefficient in a semi-crystalline polymer (of crystallinity x C ) One has: …”