Particulate fiber

Over the last decade advances have occurred very rapidly in the area identified as composite materials. In general, a composite material is the combination of any two or more materials, one of which has superior mechanical properties but is in a difficult to use form (e.g. fiber, powder, etc.). The superior component is usually the reinforcement while the other component serves as the matrix in which the reinforcement is dispersed. The resultant composite is a material whose properties are near those of the reinforcement element but in a form which can be easily handled and can easily function as a structural element. Included in this definition are all of the reinforced materials including particulate, fiber, flake and sheet reinforcements. Adhesive joints for, example, would be a planar or two dimensional composite 1). 

Classification by particle size is helpful in classification since particle size will affect performance but, by itself, falls short as a criterion when selecting fillers for applications which require certain levels of conductivity (thermal or electric) or of chemical interaction, etc. In one publication, materials were divided into particulates, fibers, and colorants. These distinctions are not helpful for a material designer. For a classification to be useful in filler applications, it must include the most important properties of fillers which affect the resultant material. The eight most important are as follows ... 

Difficult-to-process composites can be readily produced by thermal spray forming, and plasma spray is the process of choice for the most reactive matrix materials. Particulate-, fiber-, and whisker-reinforced composites have all been produced and used in various applications. Particulate-reinforced wear-resistant coatings such as WC/Co, Cr3C2/NiCr, and TiC/NiCr are the most common applications. Figure 8 illustrates the diverse forms of composites that can be thermally spray formed. Whisker particulates can be incorporated into sprayed deposits using so-called engineered powders, mechanical blending, or by... 

The appearance testing of a parenteral solution has additional focus on the presence of particulates, fibers, or flecks in the solution. Parenteral appearance should be assessed while the solution is in its original container against a white and/or black background. Vials should be held up in front of the background with indirect white fluorescent lighting. The vials should be examined for about 5-15 s. Typical observations are The solution in the vial was clear, colorless, and free of particulates, fibers and any other foreign material . When the analyst is presented with a... 

For DR values between 10 and 50, a decrease in elastic modulus with DR is observed. In the case of a polymer blend, such as PA6/LDPE, there is an almost independent behavior of the tensile properties in the MD of noncompatibilized blends as a function of the dispersed phase concentration. However, in the TD, a clear dependence of the elastic modulus is observed. It is also observed that compatibilized films have higher modulus compared to noncompatibilized films. For the films presented in Table 24.4, PA6 particulate fibers... 

This book chapter evaluates the definition, classification, and scope of POCs in different applications. POCs represent one of the most widely used polymeric materials. Synergistic reactions between the polymer matrix and filler materials (particulate, fiber, and structural fillers) result in modified properties. This book chapter contributes a brief introduction followed by a definition of processing and an extensive illustration of the different applications of POCs in a variety of fields (consumer, medical, agricultural, packaging, transportation, electrical, construction, and textile). POCs with natural wood fiber are widely used in consumer applications. They result in wood-like texture and properties with the cost of plastic. 

As previously mentioned, in the uncured state, thermosetting materials are generally mixtures of small reactive molecules that form networks catalysts, initiators and/or accelerators and particulate, fiber-based, or nanosize fillers. There... 

The procedures UNE-77250 and EPA TO-13A described a sampling system to determine PAHs in ambient air based on the utilization of a particulate fiber filter followed by a PUF eartridge or a XAD-2 resin [85,86]. Table 5 shows several sampling devices utilized in standard methods. 

Nonvolatile compounds are normally present either as solid particulates or bound to solid particulates. Samples are collected by pulling large volumes of gas through a filtering unit where the particulates are collected on glass fiber filters. 

Particulate gravimetry is commonly encountered in the environmental analysis of water, air, and soil samples. The analysis for suspended solids in water samples, for example, is accomplished by filtering an appropriate volume of a well-mixed sample through a glass fiber filter and drying the filter to constant weight at 103-105 °C. 

Total airborne particulates are determined using a high-volume air sampler equipped with either cellulose fiber or glass fiber filters. Samples taken from urban environments require approximately 1 h of sampling time, but samples from rural environments require substantially longer times. 

Mesh beds of knitted wire mesh, plastic, or glass fibers are used for the removal of Hquid particulates and mist. They will also remove soHd particles, but win plug rapidly unless irrigated or flushed with a particle-dissolving solvent. 

Venturi scmbbers can be operated at 2.5 kPa (19 mm Hg) to coUect many particles coarser than 1 p.m efficiently. Smaller particles often require a pressure drop of 7.5—10 kPa (56—75 mm Hg). When most of the particulates are smaller than 0.5 p.m and are hydrophobic, venturis have been operated at pressure drops from 25 to 32.5 kPa (187—244 mm Hg). Water injection rate is typicaUy 0.67—1.4 m of Hquid per 1000 m of gas, although rates as high as 2.7 are used. Increasing water rates improves coUection efficiency. Many venturis contain louvers to vary throat cross section and pressure drop with changes in system gas flow. Venturi scmbbers can be made in various shapes with reasonably similar characteristics. Any device that causes contact of Hquid and gas at high velocity and pressure drop across an accelerating orifice wiU act much like a venturi scmbber. A flooded-disk scmbber in which the annular orifice created by the disc is equivalent to a venturi throat has been described (296). An irrigated packed fiber bed with performance similar to a... 

Extrusion. The filtered, preheated polymer solution is deHvered to the spinneret for extmsion at constant volume by accurate metering pumps. The spinnerets are of stainless steel or another suitable metal and may contain from thirteen to several hundred precision-made holes to provide a fiber of desired si2e and shape. AuxUiary filters are inserted in front of the fixture that holds the spinneret and in the spinneret itself to remove any residual particulate matter in the extmsion solution. 

Traditional appHcations for latices are adhesives, binders for fibers and particulate matter, protective and decorative coatings (qv), dipped goods, foam, paper coatings, backings for carpet and upholstery, modifiers for bitumens and concrete, and thread and textile modifiers. More recent appHcations include biomedical appHcations as protein immobilizers, visual detectors in immunoassays (qv), as release agents, in electronic appHcations as photoresists for circuit boards, in batteries (qv), conductive paint, copy machines, and as key components in molecular electronic devices. 

Binders. Latices are used as fiber binders by the paper and textile industries. The two principal methods of appHcation are (/) wet-end addition, wherein the ionic latex is added to a fiber slurry and then coagulated in the slurry prior to sheet formation, and (2) saturation of the latex into a formed fiber web wherein the latex is coagulated by dehydration. Latices are also used as binders for particulate matter such as mbber scrap. 

Fig. 23. Two types of hollow-fiber modules used for gas separation, reverse osmosis, and ultrafiltration applications, (a) Shell-side feed modules are generally used for high pressure appHcations up to - 7 MPa (1000 psig). Fouling on the feed side of the membrane can be a problem with this design, and pretreatment of the feed stream to remove particulates is required, (b) Bore-side feed modules are generally used for medium pressure feed streams up to - 1 MPa (150 psig), where good flow control to minimise fouling and concentration polarization on the feed side of the membrane is desired.

A second factor determining module selection is resistance to fouling. Membrane fouling is a particularly important problem in Hquid separations such as reverse osmosis and ultrafiltration. In gas separation appHcations, fouling is more easily controlled. Hollow-fine fibers are notoriously prone to fouling and can only be used in reverse osmosis appHcations if extensive, costiy feed-solution pretreatment is used to remove ah. particulates. These fibers caimot be used in ultrafiltration appHcations at ah. 

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