Application barrier

Smith, P. M., et al., Chemical Vapor Deposition of Ternary Refractory Nitrides for Difiusion Barrier Applications, Proc. 13th. Int. Conf. on VLSI Multilevel Interconnections, Sandia National Labs., Albuquerque, NM (1996)... 

Many polymers are used in barrier applications, either to keep contents in or contaminants out. Food packaging is an excellent example of such usage. Plastic films and containers of many types are used to package food. Blow moldedbottles often contain numerous layers, each of which provides specific benefits. Polyethylene layers are excellent water barriers, polyvinyl alcohol is a good oxygen barrier, and polyethylene terephthalate impedes the diffusion of carbon dioxide from carbonated drinks. Other barrier applications include toothpaste tubes, diaper backsheets, tarpaulins, and geomembranes, which are used to line containment ponds and landfill pits. 

PVDC 340-550 0.1 -0.5 165 0 Oxygen and water barrier applications (food packaging)... 

Kum, O., Dickson, B.M., Stuart, S.J., Uberuaga, B.P., Voter, A.F. Parallel replica dynamics with a heterogeneous distribution of barriers application to n-hexadecane pyrolysis. J. Chem. Phys. 2004, 121(20), 9808-19. 

In order to get improved interlayer adhesion, the saponification degree must be 80-95 mol-%. For gas barrier applications, the saponification degree of the EVOH of 99 mol-% is required. When the saponification is insufficient, satisfactory gas barrier properties cannot be obtained (1). 

Copolymers of acrylonitrile are used in extmsion and molding applications. Commercially unportant comonomers for barrier applications include styrene and methyl acrylate. 

The use of safe materials is vital for barrier applications, particularly for food, medical, and cosmetics packaging. Suppliers of specific barrier polymers can provide the necessary details, such as material safety data sheets, to ensure safe processing and use of barrier polymers. 

Natural and engineered zeolites have been used extensively in wastewater treatment (e.g., Clifford, 1990). For in situ barrier applications, the focus of study has been a natural clihoptilolite supplied by Teague Mineral Products (Adrian, Oregon), primarily because of its low cost and strong affinity for Sr. 

Table 2 compares the cost of SMZ to other materials currently used or proposed for use in permeable reactive barriers. The most effective material for a particular barrier application will depend upon the material s unit cost and upon the contaminants to be controlled. Installation costs should be similar for each material. 

Vacuum Contamination of the A1 layer by residual gas components (mainly water vapor) affects the barrier substantially good vacuum (<5 x 104 mbar) in the evaporation chamber is therefore required for barrier applications. Contamination from the evaporation material and the evaporators must also be avoided as much as possible. 

The polymeric materials are used in (i) barrier applications (ii) self-supporting structures (tanks, piping, valves and pumps) (ii) column internals, seals, gaskets, adhesives and caulkings. An overview of polymeric materials used in corrosion control applications is given in Figure 4.8. 

Naftz, D., Morrison, S.J., Fuller, C.C., and Davis, J.A. (Eds.), Handbook of Groundwater Remediation Using Permeable Reactive Barriers - Applications to Radionuclides, Trace Metals, and Nutrients . Academic Press, San Diego (2002). 

The use of LCVD or LGT in membranes is aimed at increasing the value of a for a set of permeants of interest. The increase of a, however, is achieved at the expense of the permeant throughput, i.e.. Pa and Pb both decrease by the application of LCVD layer. Therefore, the use of high-flux membrane or substrate is mandatory. In barrier applications, the selection of good barrier (low values of Ps) is mandatory because the barrier characteristic of a film can be expressed by f/P, where t is the thickness of film, and there is a limit in the increase of barrier characteristics by application of nanofilm. 

Conca L, Strietelmeier E., Lu N., Ware S. D., Taylor T. P., Kaszuba L, and Wright 1. (2002) Treatability study of reactive materials to remediate groundwater contaminated with radionuclides, metals, and nitrates in a four-component permeable reactive barrier. In Handbook of Groundwater Remediation Using Permeable Reactive Barriers—Applications to Radionuclides, Trace Metals, and Nutrients (eds. D. L. Naftz, S. 1. Morrison, J. A. Davis, and C. C. Fuller). Academic Press, San Diego, CA, pp. 221-252. 

Blood Brain Barrier Application of Caco-2 Assay Measure LogPS (permeability x surface area) to estimate ability of compounds to cross blood brain barrier... 

Major polymer applications belting, steam hose, curing bladders, O-rings, shock and vibration products, structural caulks and sealants, water-barrier applications, roof coatings, and gas-metering diaphragms... 

Noble RD, Gin DL, Koval C (2007) Ionic liquid materials for barrier applications. Abstracts of Papers, 234th ACS National Meeting, Boston, MA, United States, 19-23 August 2007 COLL-401... 

Copolymers of acrylonitrile [107-13-1] are used in extmsion and molding applications. Commercially important comonomers for barrier applications include styrene and methyl acrylate. As the comonomer content is increased, the permeabilities increase as shown in Figure 3. These copolymers are not moisture-sensitive. Table 7 contains descriptions of three high nitrile barrier polymers. Barex and Cycopac resins are rubber-modified to improve the mechanical properties. 

Immiscible Blends. When two polymers are blended, the most common result is a two-phase composite. The most interesting blends have good adhesion between the phases, either naturally or with the help of an additive. The barrier properties of an immiscible blend depend on the permeabilities of the polymers, the volume fraction of each, phase continuity, and the aspect ratio of the discontinuous phase. Phase continuity refers to which phase is continuous in the composite. Continuous for barrier applications means that a phase connects the two surfaces of the composite. Typically, only one of the two polymer phases is continuous, with the other polymer phase existing as islands. It is possible to have both polymers be continuous. 

The unique molecular packing of rod-like chains in liquid crystalline polymers (LCP) closely resembles the extended chain structure of highly oriented flexible chain polymers, suggesting that these materials are good candidates for barrier applications. Thermotropic LCP s, first developed in the early 1970 s, have been the object of much interest because of their excellent mechanical properties and ease of product fabrication. Preliminary observations have shown that a commercially available wholly aromatic thermotropic copolyester has gas permeability coefficients that are lower than those of polyacrylonitrile (4.). These results raise some fundamental questions as to the nature of the mechanism for transport of small molecules through a matrix of ordered rigid rod-like chains. 

The potential advantage of crystalline polymers for barrier applications was recognized by Morgan (1) although, previous investigators had reported reduced permeabilities in semi-crystalline polymers (2,2) As will be discussed, the equilibrium concentration of sorbed penetrant and the diffusion process are affected by crystallinity in uniquely different ways. 

PrintPack, Inc. manufactures thin films for use in barrier applications. We used PrintPack EX429-325 coextruded film with the following layer distribution 1.8 mil LDPE // 0.3 mil tie // 0.3 mil EvOH - 32 // 0.3 mil tie //0.8 mil polycarbonate. The tie layer was Plexar 3342 from Quantum Chemical (The chemical composition of this tie layer material is proprietary and has not been disclosed by the manufacturer). 

The ability to fabricate the fluoropolymers in the required shape is also a consideration in its selection. As discussed in Ch. 2, Materials of Construction, fluoropol5miers are principally used in barrier applications. Selection and related testing discussed in this chapter concentrates heavily on that aspect. 

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