Fibrous analysis

Physical testing appHcations and methods for fibrous materials are reviewed in the Hterature (101—103) and are generally appHcable to polyester fibers. Microscopic analyses by optical or scanning electron microscopy are useful for evaluating fiber parameters including size, shape, uniformity, and surface characteristics. Computerized image analysis is often used to quantify and evaluate these parameters for quaUty control. 

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Fiber Analysis. Paper may be composed of one or several types of fibers, eg, animal, vegetable, mineral, and synthetic (see Eibers). Paper is generally composed of woody vegetable fibers obtained from coniferous (softwood) and deciduous (hardwood) trees. QuaUtative and quantitative methods have been developed to determine the fibrous constituents in a sheet of paper (see TAPPI T401). However, the proliferation in the number and types of pulping processes used have made the analysis of paper a much more complex problem. Comprehensive reviews of the methods are given in References 20 and 23. 

Close examination of the weld under a low-power stereoscopic microscope revealed small openings (Fig. 15.6). Probing these sites with a pin revealed a large pit that had been covered by a thin skin of weld metal. These sites contained fibrous, metallic remnants (Fig. 15.7). Examination under a scanning electron microscope further revealed the fibrous character of the material (Fig. 15.2) and also the convoluted shapes of the individual fibers (Fig. 15.21). Energy-dispersive spectrographic analysis of this material revealed the compositions in Table 15.1. 

Biological fibers, such as can be formed by DNA and fibrous proteins, may contain crystallites of highly ordered molecules whose structure can in principle be solved to atomic resolution by x-ray crystallography. In practice, however, these crystallites are rarely as ordered as true crystals, and in order to locate individual atoms it is necessary to introduce stereochemical constraints in the x-ray analysis so that the structure can be refined by molecular modeling. 

Gravimetric or] Fibrous filter good for gravimetric analysis chemical for a range of particle sizes... 

The standard unit normally used for measuring dust particles is the micron (pm one-thousandth of a millimeter). The smallest particle visible to the unaided eye is between 50 and 100 pm and the most dangerous sizes are between 0.2 and 5 pm. Particles larger than this are usually unable to penetrate the lung defenses and smaller ones settle out too slowly. Some dusts can be both toxic and fibrous (e.g. asbestos) and are therefore harmful even outside these parameters. It may therefore be assumed that dusts which are visible (i.e. between 50 and 100 pm), are quite safe. However, this is not the case, as dust clouds never consist solely of particles of one size. Analysis would show percentages of all sizes, and it is for this reason that special care is needed in measuring dust clouds and concentrations. 

Based on this analysis it is evident that materials which are biaxially oriented will have good puncture resistance. Highly polar polymers would be resistant to puncture failure because of their tendency to increase in strength when stretched. The addition of randomly dispersed fibrous filler will also add resistance to puncture loads. From some examples such as oriented polyethylene glycol terephthalate (Mylar), vulcanized fiber, and oriented nylon, it is evident that these materials meet one or more of the conditions reviewed. Products and plastics that meet with puncture loading conditions in applications can be reinforced against this type of stress by use of a surface layer of plastic with good puncture resistance. Resistance of the surface layer to puncture will protect the product from puncture loads. An example of this type of application is the addition of an oriented PS layer to foam cups to improve their performance. 

Acid anhydrides have been employed with, and without the use of a base catalyst. For example, acetates, propionates, butyrates, and their mixed esters, DS of 1 to ca. 3, have been obtained by reaction of activated cellulose with the corresponding anhydride, or two anhydrides, starting with the one with the smaller volume. In all cases, the distribution of both ester groups was almost statistic. Activation has been carried out by partial solvent distillation, and later by heat activation, under reduced pressure, of the native cellulose (bagasse, sisal), or the mercerized one (cotton linters). No catalyst has been employed the anhydride/AGU ratio was stoichiometric for microcrystalhne cellulose. Alternatively, 50% excess of anhydride (relative to targeted DS) has been employed for fibrous celluloses. In all cases, polymer degradation was minimum, and functionalization occurs preferentially at Ce ( C NMR spectroscopic analysis [52,56,57]). 

Filtration 1. Fibrous filter 1-50 85-100 Gravimetric or Fibrous filter good for gravimetric analysis... 

The contributions to this volume demonstrate that structural studies of fibrous /1-proteins, as well as prion and amyloid fibrils, have advanced rapidly thanks in large part to improved experimental techniques and better theoretical analysis of the ever-increasing structural data. It is also possible to learn from studies of naturally occurring silks (Dicko et al., this volume) howvariations in the conditions of production of silk threads from the same protein can produce a variety of /1-structures with very distinct... 

Wilkins, D.J. (1983). Failure analysis and mechanisms of failure of fibrous composite structures. NASA CP-2278, 67-93. 

A formal description of a mineral presents all the physical and chemical properties of the species. In particular, distinctive attributes that might facilitate identification are noted, and usually a chemical analysis of the first or type specimen on which the name was originally bestowed is included. As an example, the complete description of the mineral brucite (Mg(OH)2), as it appears in Dana s System of Mineralogy, is presented as Appendix 3. Note the complexity of this chemically simple species and the range of information available. In the section on Habit (meaning shape or morphology) both acicular and fibrous forms are noted. The fibrous variety, which has the same composition as brucite, is commonly encountered (see Fig. I.ID) and is known by a separate name, nemalite. ... 

In the remainder of this chapter, specific examples of fibrous minerals are presented. The chemical formulas are given as well as the mineral names. A formula is a shorthand notation that describes the elemental composition of the compound plus the specific ion associations, as determined by three-dimensional structure analysis of the species. Because every mineral sample is not completely analyzed, an ideal formula—one that summarizes the chemistry and associations of the ions—is usually presented. 

When crystalline cellulose I is treated with aqueous alkali solutions of sufficient strength, a process known as mercerization takes place. As a result of it, cellulose I is converted to cellulose II, the most stable or the four crystalline cellulose polymorphs. The conversion proceeds in the solid state, without apparent destruction or change in the fibrous morphology of the cellulose. As our diffraction analysis indicates, however, it is accompanied by a reversal of the chain packing polarity—from the parallel-chain cellulose I to the... 

Van Soest, P.J. and Wine, R.H. (1967) Use of detergents in the analysis of fibrous feeds. IV. Determination of plant cell-wall constituents. Journal of the Association of Official Analytical Chemists 50(1), 50-55. 

Fibrous mat type filters include the frequently used paper (cellulose) fiber filter, for example, the Whatman paper filter, and glass fiber filters. A common fibrous mat filter used for sample collection and air cleaning is known as the HEPA filter (/zigh efficiency particulate air filter) and is made of a combination of cellulose and mineral fibers. A widely used type of fibrous mat filter is the high-volume filter, commonly referred to as Hi-Vol, shown in Fig. 11.56. A modification of the Hi-Vol filter to increase the total air flow allows the collection of sufficient particulate matter in relatively short time periods (e.g., 2 h) to cany out chemical analysis this is important for studies of the diurnal variation of various chemical components of the aerosol as well as for minimizing sampling artifacts (Fitz el ai, 1983). 

Figure 5 presents the results of tensile tests for the HPC/OSL blends prepared by solvent-casting and extrusion. All of the fabrication methods result in a tremendous increase in modulus up to a lignin content of ca. 15 wt.%. This can be attributed to the Tg elevation of the amorphous HPC/OSL phase leading to increasingly glassy response. Of particular interest is the tensile strength of these materials. As is shown, there is essentially no improvement in this parameter for the solvent cast blends, but a tremendous increase is observed for the injection molded blend. Qualitatively, this behavior is best modeled by the presence of oriented chains, or mesophase superstructure, dispersed in an amorphous matrix comprised of the compatible HPC/OSL component. The presence of this fibrous structure in the injection molded samples is confirmed by SEM analysis of the freeze-fracture surface (Figure 6). This structure is not present in the solvent cast blends, although evidence of globular domains remain in both of these blends appearing somewhat more coalesced in the pyridine cast material.

Quantitative trace element analysis of diamond by LA-ICP-MS using different synthetic multielement carbon based standards (e.g., cellulose pellets) is discussed by Rege et al 2, whereby 13C was used for internal standardization. Concentrations of 41 elements were determined in two fibrous diamonds from Jwaneng Botswana (JWA 110 and 115) by relative sensitivity coefficients measured using the synthetic cellulose standard. The analytical data were verified by means of instrumental neutron activation analysis (INAA) and proton induced X-ray emission (PIXE).72... 

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