Barrier Properties and Chemical Resistance

Barrier Properties and Chemical Resistance 7.1 Gas Barrier Properties... 

Acrylonitrile Copolymer A thermoplastic prepared by copolymerization of acrylonitrile with small amounts of other unsaturated monomers. Has good gas barrier properties and chemical resistance. Processed by extrusion, inj ection molding, and thermo forming. Used in food packaging. 

The properties of SAN resins depend on their acrylonittile content. Both melt viscosity and hardness increase with increasing acrylonittile level. Unnotched impact and flexural strengths depict dramatic maxima at ca 87.5 mol % (78 wt %) acrylonitrile (8). With increasing acrylonitrile content, copolymers show continuous improvements in barrier properties and chemical and uv resistance, but thermal stabiUty deteriorates (9). The glass-transition... 

Very good water and vapor barrier properties Good chemical resistance but poor solvent resistance Poor heat resistance... 

Refractory Barrier Materials of the Cell Lining. Dry Barrier Mixes and Bricks. Properties and Chemical Resistance. The Processes During Service. Interactions with Infiltrated Electrolyte. Change of Properties. Lenses... 

The principal monomer of nitrile resins is acrylonitrile (see Polyacrylonitrile ), which constitutes about 70% by weight of the polymer and provides the polymer with good gas barrier and chemical resistance properties. The remainder of the polymer is 20 to 30% methylacrylate (or styrene), with 0 to 10% butadiene to serve as an impact-modifying termonomer. 

TPX is used in mold-releasing films, printed circuit mold-releasing materials, various containers, etc., because of its heat resistance, chemical resistance, mold-releasing properties, transparency and other properties (4). In application areas, which require mechanical strength, gas barrier properties and high temperature mechanical strength, among other properties, composites are needed. 

Multilayer flat films and sheets can be formed by coextrusion, consisting of two layers (AB), three (such as ABA), five (such as ABCBA), and up to eleven layers. Each layer and particular multilayer configuration is selected for its contribution to one or more film/sheet product properties, such as gas barrier, adhesion, abrasion, and chemical resistance. 

Talcs are either platy or acicular in particle shape. Thin platelet particles have aspect ratios varying from 20 1 to 5 1. Coarse particle sizes (10 to 75 im) are commonly used in these applications at loading levels of 5 to 30 percent. Fine talcs (1 to 10 im) are more expensive and require intensive dispersion processes. Platy grades enhance barrier properties and air, water, and chemical resistance. 

Use In packaging applications where a transparent, vapor, and/or gas barrier is required, as in packaging of foods for astronauts. Used in electronic and electrical applications because of insulating and heat-resistant properties. Extreme chemical resistance and ability to seal make it useful as a tank lining, etc. 

In addition, PCTFE has exceptional barrier properties and superb chemical resistance. It is attacked by a number of organic solvents. It has low thermal stability and degrades upon reaching its melting point, requiring special care during processing. 

Composite Particles, Inc. developed two methods of surface modification of polymeric materials which are used for materials of different shapes and compositions. Here, only the spherical, non-rubber particles are discussed. Further information is included in the section on rubber particles below. One method of surface modification is based on exposing the polymeric powder to a chemically reactive gas atmosphere which oxidizes surface groups to form OH and COOH functionalities. These functionalities are then available for reaction with the components of the matrix into which modified particles are introduced. Vistamer HD and UH are manufactured by this method from polyethylenes of different molecular weights. Two factors can be regulated here the properties of the core particle and the type and density of functional groups on the surface of these particles. Polyethylene is a material, which without this modification, will not be compatible with most systems. The surface modification allows the incorporation of the material into resins. This improves abrasion resistance, tear strength, and moisture barrier properties and reduces the fiiction coefficient. 

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