Barrier property improvement

Barrier property Improved greatly Negligible improvement... 

The arrangement of the layers themselves also has an impact. The self-extinguishing properties of these materials, for instance, have been described qualitatively. A protective char layer forms and acts as a diffusion barrier to further combustion. Likewise, before the advents of nanocomposites, models of the barrier properties of glass-ribbon reinforced composites foreshadowed the increased tortuosity arguments often heard with regard to nanocomposite barrier properties. Improvements on these first approximations of bar-... 

A variety of discontinuous (short) functional fillers may be combined with thermoplastic or thermoset matrices to produce composites. The fillers may differ in shape (fibers, platelets, flakes, spheres, or irregulars), aspect ratio, and size. When the fully dispersed (exfoliated or deagglomerated) fillers are of nanoscale dimensions, the materials are known as nanocomposites. They differ from conventional microcomposites in that they contain a significant number of interfaces available for interactions between the intermixed phases. As a result of their unique properties, nanocomposites have great potential for applications involving polymer property modification utilizing low filler concentrations for minimum weight increase examples include mechanical, electrical, optical, and barrier properties improvement and enhanced flame retardancy. 

Polymer nanocomposites are an important class of materials, which are an alternative to the conventionally tilled polymers. These are materials in which nanosized inorganic fillers, typically 1-100 nm in at least one dimension, are individually dispersed in a polymer matrix. Because of the nanometer sizes of the filler, nanocomposites exhibit markedly improved properties as compared to the pure polymers or their conventional composites. These include increased modulus and strength, outstanding barrier properties, improved solvent and heat resistance, and decreased flammability (Lagashetty and Venkataraman, 2005). 

The primary motivation for blending immiscible polymers is to create materials with combinations of properties superior to its components [1], Cocontinuous morphologies are characterized by the mutual interpenetration of phases and can form over a range of compositions, depending largely on the relative polymer viscosities, elasticity, and interfacial tension. These morphologies offer a variety of applications mechanical property enhancement, electrically conductive blends, barrier property improvement, and tissue scaffolds. 

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... 

Some cast (unoriented) polypropylene film is produced. Its clarity and heat sealabiUty make it ideal for textile packaging and overwrap. The use of copolymers with ethylene improves low temperature impact, which is the primary problem with unoriented PP film. Orientation improves the clarity and stiffness of polypropylene film, and dramatically increases low temperature impact strength. BOPP film, however, is not readily heat-sealed and so is coextmded or coated with resins with lower melting points than the polypropylene shrinkage temperature. These layers may also provide improved barrier properties. 

Considerable amounts of polyethylene film are produced using coaxial extrusion processes in which two or more melt streams are combined in the die to produce extruded film of two or more layers of plastics materials. Layers in such a composite may be included, for example, to improve barrier properties, to enhance sealability or even simply to act as an adhesive between dissimilar layers. 

In order to reduce the tendency of the film to shrink oriented film may be annealed at about 100°C whilst under tension immediately after drawing. The film is often coated with another polymer sueh as a vinylidene ehloride-based copolymer. This both improves the barrier properties and improves the heat scalability. 

The quality of blends is strongly dependent on mixing techniques but encouraging results have been obtained, particularly in respect of improving barrier properties. 

Certain polymers have come to be considered standard building blocks of the polyblends. For example, impact strength may be improved by using polycarbonate, ABS and polyurethanes. Heat resistance is improved by using polyphenylene oxide, polysulphone, PVC, polyester (PET and PBT) and acrylic. Barrier properties are improved by using plastics such as ethylene vinyl alchol (EVA). Some modem plastic alloys and their main characteristics are given in Table 1.2. 

Orientation Control of CVD TiN Films. The crystal orientation of TiN deposited by CVD can be controlled by the partial pressure of TiCl4 to improve the diffusion barrier properties.1 1 The bond... 

In devices with geometry below the 0.25 im level, titanium nitride will likely replace titanium-tungsten, since it has better barrier properties. The process of choice will likely be CVD, which offers improved uniformity and step coverage, although improvements in collimated sputtering may keep that process on line for a while. 

PP is probably the most thoroughly investigated system in the nanocomposite field next to nylon [127-132]. In most of the cases isotactic/syndiotactic-PP-based nanocomposites have been prepared with various clays using maleic anhydride as the compatibilizer. Sometimes maleic anhydride-grafted PP has also been used [127]. Nanocomposites have shown dramatic improvement over the pristine polymer in mechanical, rheological, thermal, and barrier properties [132-138]. Crystallization [139,140], thermodynamic behavior, and kinetic study [141] have also been done. 

Polyimide-clay nanocomposites constitute another example of the synthesis of nanocomposite from polymer solution [70-76]. Polyimide-clay nanocomposite films were produced via polymerization of 4,4 -diaminodiphenyl ether and pyromellitic dianhydride in dimethylacetamide (DMAC) solvent, followed by mixing of the poly(amic acid) solution with organoclay dispersed in DMAC. Synthetic mica and MMT produced primarily exfoliated nanocomposites, while saponite and hectorite led to only monolayer intercalation in the clay galleries [71]. Dramatic improvements in barrier properties, thermal stability, and modulus were observed for these nanocomposites. Polyimide-clay nanocomposites containing only a small fraction of clay exhibited a several-fold reduction in the... 

The ability to downgauge, decrease part weight, improve barrier properties and reach new levels of product performance are propelling polyolefins into new markets previously dominated by other plastics. The high growth rate in PP production capacity is mainly being driven by the ability of PP to replace other resins on a cost/performance basis. For example, functionalisation of PP by incorporation of acrylic functionality has extended its weatherability performance. Interpolymer competition will have a significant impact on the amount and type of additives used. 

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