Barrier performance

Gas-Barrier Properties. The oxygen-barrier properties of PVA at low humidity ate the best of any synthetic resin. However, barrier performance deteriorates above 60% th (Fig. 9). No additives or chemical modifiers are known that can effectively reduce moisture sensitivity. The gas-barrier performance is affected by the degree of hydrolysis and rapidly diminishes as the hydrolysis is decreased below 98%. 

Triton Systems and the U.S. Army [202] have conducted further work on barrier performance in a joint investigation. The requirement here is for a nonrefrigerated packaging system capable of maintaining food freshness for 3 years. Nanoclay polymer composites are currently showing considerable promise for this application. 

A somewhat more esoteric possibility arises from enhanced barrier performance of blown films recently suggested for artihcial intestines. 

Crowse, J.L., Dejonge, J.O., and Calogero, F. (1990) Pesticide barrier performance of selected nonwoven fabrics in laboratory capillary and pressure penetration testing, Textile Research., 60 137-142. 

H. R. Moghimi, B. W. Barry, and A. C. Williams. Stratum corneum and barrier performance A model lamellar structural approach. In R. L. Bronaugh and H. Maibach (eds.), Percutaneous Absorption—Drugs, Cosmetics, Mechanisms, Methodology, Marcel Dekker, New York, Basel, Hong Kong, 1999, pp. 515-553. 

Limited information exists on contaminant effects on barrier performance. 

The oxygen-barrier properties of PVA at low humidity are the best of any synthetic resin. However, barrier performance deteriorates above 60% rh,... 

The solution of Eq. 1 requires specification of boundary conditions (BCs) and additional equation(s) that describe the sorption reaction. The assumptions reflected in these choices strongly influence the process of extrapolating barrier performance from laboratory column data. Furthermore, as discussed below, there are significant differences in the treatment of these choices between low- and high-permeability systems. 

Because laboratory columns are often operated using flow rates higher than those associated with natural groundwater movement, the choice between an equilibrium and kinetic formulation is probably more significant for interpreting experimental data than for predicting barrier performance in the field. For example, we have observed kinetic effects in short-term (2 to 6 weeks) column experiments in which advection plays a significant (but not... 

Khandelwal, A., and Rabideau, A. J. (1998). Enhancement of soil/bentonite barrier performance by the addition of natural humus, Proceedings of the 4th International Symposium on Environmental Geotechnology, Boston, MA, 9-12 August, 1998. 

Mott, H. V. and Weber, W. J., Jr. (1992). Sorption of low molecular weight organic contaminants by fly ash considerations for the enhancement of cutoff barrier performance, Environmental Science Technology, 26, 1234-1241. 

The pilot test results demonstrate that contaminant retardation by an SMZ permeable barrier can be well predicted from laboratory characterization of the SMZ. Furthermore, the engineered water control, sampling, and containment system developed for this project serves as a general model for testing permeable barrier performance. 

The research described in this chapter is part of an effort to develop and test a zeolite-based permeable barrier system for containing and remediating contaminated groundwater. The specific goals of this work were to scale up the production of SMZ, install the SMZ in a pilot-scale permeable barrier, and compare barrier performance to predictions based on laboratory characterization of the SMZ. 

Although the plume deflection during this phase of the experiment was a setback and a disappointment, it illustrated the value of an intensive sampling array in assessing barrier performance. With less spatial resolution of the contaminant plume, we may have reached the erroneous conclusion that contaminants were passing through, rather than around, the barrier. 

Using the above equation we calculated retardation factors of 44 for chromate and 39 for PCE. These pilot-test retardation factors are very close to the estimates of 42 and 29 calculated in section 3.1 for chromate and PCE based upon their laboratory sorption isotherms. The pilot test results thus confirm that the field barrier performance of SMZ may be predicted reasonably well from laboratory characterization of contaminant interactions. 

Stabilization of the thickness pore size heat and gas barrier performance of the protecting surface layer, hindrance of the dipping of the melt phase... 

Other important properties are the barrier performance, which is defined as the resistance to the transport of permeant molecules and thus is the inverse of permeability, and the selectivity of a polymer between two types of molecules, which is the ratio of its permeabilities to those molecules, e.g. Po2/Pn2 is the selectivity between oxygen and nitrogen. 

Barrier Plastics. When plastics replace metals and glass in packaging, their permeability is often a limiting property. Barrier performance generally increases with density and crystallinity. The most promising barrier plastics include ethylene/vinyl alcohol, polyvinylidene chloride, polyacrylonitrile, and polyethylene naphthoate. These are used most efficiently by laminating them to commodity plastics such as polyethylene and polyethylene terephthalate. 

FKuR also introduced Biograde 200C in 2005, an unfilled cellulose blend with high stiffness and transparency for cast film and injection moulding. The material can also be blow moulded into bottles and thermoformed into cups and trays. Injection moulded Biograde 200C exhibits properties comparable to polystyrene, but with the addition of barrier performance comparable to PLA. It consists of 100% renewable resources, but does not contain starch. 

NatureFlex is available in an uncoated form and in three different coated versions providing moisture and gas barrier performance, and is certified to EU and US standards for industrial and home composting. 

Yamada-Takamura, Y. et al.. Hydrogen permeation barrier performance characterization of vapor deposited amorphous aluminum oxide films using coloration of tungsten oxide. Surface and Coatings Technology, 153, 114 (2002). 

In addition to the blood-brain barrier, two other barrier layers limit and regulate molecular exchange at the interface between the blood and the neural tissue and its fiuid spaces the choroid plexus epithelium between blood and ventricular CSF and the arachnoid epithelium between blood and subarachnoid CSF. These CNS barriers perform a number of functions such as the ionic homeostasis, the restriction of small molecule permeation, the specific transport of small molecules required to enter or leave the brain, the restriction and regulation of large molecule traffic by reducing the fluid-phase endocytosis via pinocytotic vesicles, the separation of peripheral and central neurotransmitter pools, and the immune privilege [16]. 

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