Barrier properties sorption

The equilibrium sorption and diffusion coefficient were determined for toluene and tetrahydrofuran in oriented linear polyethylene pipe produced by hydrostatic extrusion The results, which are summarised in Table 4, show that the sorption is about a factor of ten less than that for isotropic material, and the diffusion coefficients are a factor of a hundred less. It is clear from these results, taken in conjunction with those for gases discussed above, that the improvements in barrier properties increase with molecular size. This can be attributed to the increased difficulty of penetrating the structure as the molecular size increases. 

Before edible films can be applied to foods or pharmaceutical products, it is necessary top obtain knowledge of water sorption, permeability, as well as mechanical properties of edible films. Films with good water vapor barrier properties (low or no water permeation and diffusion through film) should not change or change very little with relative humidity (Lawton, 1996). Films should last under mechanical strain and stress to such an extent that they do not break easily under a reasonable mechanical force. Film-forming techniques and composition of films affect such properties of biomaterial... 

No change of the sorption properties of the amorphous phase is observed by thermal treatment. A low gas permeability measured at the biaxially stretched films is related to both a change of the free volume sizes distribution and a tortuosity effect. The barrier properties of biaxially stretched films are kept even after annealing the film at 250°C. 

The engineered barriers of a repository (waste form, container, clay buffer and backfill material and repository stmcmre) which will degrade with time due to various physico-chemical processes, strongly affect the geochemistry of fluids and rocks of the near field environment (redox properties, sorption properties, solubility limits, equilibrium chemistry, etc.) and determine the speciation and the subsequent migration behaviour of the radionuclides into the far field. Extensive... 

The objective of this section is to describe the barrier properties of PH A polymers compared to common polymers and some conunercially available polyesters. To achieve this objective, the transport properties of the polymer films have been performed with diffusing molecules either at liquid state for sorption measmements or at gas and liquid state for permeation measurements. 

Slavutsky and Bertuzzi (2014) recently showed ceUulose nanociystals (C-NC) obtained from sugarcane bagasse. They formulated starch/C-NC composites and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/C-NC films have a lower affinity to water molecules than starch films. The same effect was observed in studies by Savadekar and Mhaske (2012). They studied the effect of C-NC incorporation on TPS matrix and found that the nanofillers addition improved their barrier and mechanical properties. 

Zeppa C, Gouanve Espuche E (2009) Effect of a plasticizer on the structure of biodegradable starch/clay nanocomposites thermal, water-sorption, and oxygen-barrier properties. J App Polym Sci 112 2044-2056... 

Barrier properties of materials indicate their resistance to diffusion and sorption of molecules. A good barrier polymer has low values of both diffusion (D) and solubUity (S) coefficients. Since the permeabUity coefficient P is a derived function of D and S, a high-barrier polymer has low values of P. The diffusion coefficient is a measure of how fast a penetrant will move within the polymer in a particular direction, while the solubility coefficient gives the amount of the penetrant taken (or sorbed) per unit mass of polymer from a contacting phase per unit of sorbate concentration. Both diffusion and solubility can be applied to the reverse process of sorption, that is, the migration of compounds from the polymer to a surrounding media. Several factors influence the effective value of diffusion and solubility coefficients in polymers. 

The barrier properties of the PCL-based composites were investigated. The transport properties, sorption and diffusion, were measured by a microgravimetric method . The studied model permeants were methylene chloride and water vapour for which the zero concentration diffusion coefficient Dq was determined. The presence of clay (hydrophilic platelets) in the composite gives rise to specific sites on which water molecules can be entrapped and immobilized, thus the water sorption increases on increasing the clay content, particularly for microcomposites containing Cloisite Na It was found out that the microcomposites as well as the intercalated nanocomposites have diffusion parameters for water vapour very near to those of pure PCL. 

---