Fibers microscopy

Examination. Specific questions arising in the study of textiles include the identification of the textile fiber. Microscopy is the most important approach. 

Microscopic techniques are extensively used to study the surface morphology of reinforcing fibers. The characterization of microstructure of polymer fibers provides an insight into stmcture-property relationship of the fiber. Microscopy techniques have been employed for the... 

Heyn, A.N.J. (1954). Fiber Microscopy. Interscience Publishers Inc., New York, NY. 

Try fiber microscopy longitudinal or cross-sectionah or both. 

Microscopy test. The optical microscope is a very useful tool in fiber testing and characterization laboratories. It is easier to identify natural fibers than synthetic ones because of the similarity in synthetic fiber appearance. Shape and cross section are common characteristics to examine under the microscope. Polyolefin fibers are usually characterized by a smooth and round cross section. Microscopy is not a definite technique to distinguish between PE and PP fibers. Microscopy is effective in telling whether the fiber is a mono-component filament or a bicomponent filament where two polymers are extruded in a sheath-core configuration. 

Natural and synthetic textile fibers were among the earliest materials studied by electron microscopy. Guthrie [1] and Stoves [2] described the techniques and applications of fiber microscopy to industrial practice. Somewhat later, evidence was provided for an oriented microfibrillar texture in polymer fibers [3]. X-ray diffraction suggested an arrangement of fine structures about 50 nm long and 5 nm wide in semicrystalline fibers [4, 5]. Peterlin [6, 7] observed the formation of fibrils and microfibrils by the deformation and transformation of spheru-lites using various nucroscopy techniques. 

Reviews of specimen preparation methods for fiber microscopy and instrumental techniques applied to fibers were published during the early 1970s [14-16]. This section contains applications of microscopy to the understanding of fiber microstructures used in the industrial laboratory for modification of fiber formation processes to... 

The fiber composition of paper is determined with a Hght microscope (fiber microscopy). Due to the varying fiber morphology, both the fiber raw material and the pulping process can be determined. Chemical dyeing methods are used for contrast enhancement and quantitative determination of fiber composition (ZM IV/ 55/74 TAPPI T 401 om-93, Harders-Steinhauser, Paseradas). 

Reviews of specimen preparation methods for fiber microscopy and instrumental tech-... 

Ren B, Li W H, Mao B W, Gao J S and Tian Z Q 1996 Optical fiber Raman spectroscopy combined with scattering tunneling microscopy for simultaneous measurements ICORS 96 XVth Int. Conf on Raman Spectroscopy ed S A Asher and P B Stein (New York Wley) pp 1220-1... 

Zong Q, inniss D, K]oiier K and Eiings V B 1993 Fractured poiymer/siiica fiber surface studied by tapping mode atomic force microscopy Surf. Sc/. Lett. 290 L688... 

General schemes for the identification of natural and synthetic fibers have been estabhshed by the Textile Institute and by the American Association of Textile Chemists and Colorists (8). A comprehensive treatment of burning, solvent, staining, microscopy, and density techniques has been given (9) and a general discussion of procedures for identifyiag synthetic fibers has been presented (10). 

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. 

Microscopy (qv) plays a key role in examining trace evidence owing to the small size of the evidence and a desire to use nondestmctive testing (qv) techniques whenever possible. Polarizing light microscopy (43,44) is a method of choice for crystalline materials. Microscopy and microchemical analysis techniques (45,46) work well on small samples, are relatively nondestmctive, and are fast. Evidence such as sod, minerals, synthetic fibers, explosive debris, foodstuff, cosmetics (qv), and the like, lend themselves to this technique as do comparison microscopy, refractive index, and density comparisons with known specimens. Other microscopic procedures involving infrared, visible, and ultraviolet spectroscopy (qv) also are used to examine many types of trace evidence. 

The crystal stmcture of PPT is pseudo-orthorhombic (essentially monoclinic) with a = 0.785/nm b = 0.515/nm c (fiber axis) = 1.28/nm and d = 90°. The molecules are arranged in parallel hydrogen-bonded sheets. There are two chains in a unit cell and the theoretical crystal density is 1.48 g/cm. The observed fiber density is 1.45 g/cm. An interesting property of the dry jet-wet spun fibers is the lateral crystalline order. Based on electron microscopy studies of peeled sections of Kevlar-49, the supramolecular stmcture consists of radially oriented crystaUites. The fiber contains a pleated stmcture along the fiber axis, with a periodicity of 500—600 nm. 

Microscopists in every technical field use the microscope to characterize, compare, and identify a wide variety of substances, eg, protozoa, bacteria, vimses, and plant and animal tissue, as well as minerals, building materials, ceramics, metals, abrasives, pigments, foods, dmgs, explosives, fibers, hairs, and even single atoms. In addition, microscopists help to solve production and process problems, control quaUty, and handle trouble-shooting problems and customer complaints. Microscopists also do basic research in instmmentation, new techniques, specimen preparation, and appHcations of microscopy. The areas of appHcation include forensic trace evidence, contamination analysis, art conservation and authentication, and asbestos control, among others. 

Plant-fiber identification is described in TAPPI T8 and TIO. In order to identify synthetic fibers, it usually is necessary to conduct solubihty and physical properties tests in addition to light microscopy observations. Systematic sampling is required to obtain quantitative information on sample composition. Because different types of pulps contain varying numbers of fibers per unit weight, it is necessary to multiply the total number of each kind of fiber by a relative weight factor, thereby the weight percentage that each fiber type contributes to the sample can be deterrnined. 

Combination techniques such as microscopy—ftir and pyrolysis—ir have helped solve some particularly difficult separations and complex identifications. Microscopy—ftir has been used to determine the composition of copolymer fibers (22) polyacrylonitrile, methyl acrylate, and a dye-receptive organic sulfonate trimer have been identified in acryHc fiber. Both normal and grazing angle modes can be used to identify components (23). Pyrolysis—ir has been used to study polymer decomposition (24) and to determine the degree of cross-linking of sulfonated divinylbenzene—styrene copolymer (25) and ethylene or propylene levels and ratios in ethylene—propylene copolymers (26). 

Optical properties of fibers are measured by light microscopy methods. ASTM D276 describes the procedure for fiber identification using refractive indexes and birefringence. Other methods for determining fiber optical properties have been discussed (3,38—44). However, different methods of determining optical properties may give different results (42). 

Asbestos fiber identification can also be achieved through transmission or scanning electron microscopy (tern, sem) techniques which are especially usefiil with very short fibers, or with extremely small samples (see Microscopy). With appropriate peripheral instmmentation, these techniques can yield the elemental composition of the fibers using energy dispersive x-ray fluorescence, or the crystal stmcture from electron diffraction, selected area electron diffraction (saed). 

Progress in deducing more structural details of these fibers has instead been achieved using NMR, electron microscopy and electron diffraction. These studies reveal that the fibers contain small microcrystals of ordered regions of the polypeptide chains interspersed in a matrix of less ordered or disordered regions of the chains (Eigure 14.9). The microcrystals comprise about 30% of the protein in the fibers, are arranged in p sheets, are 70 to 100 nanometers in size, and contain trace amounts of calcium ions. It is not yet established if the p sheets are planar or twisted as proposed for the amyloid fibril discussed in the previous section. 

Regarding a historical perspective on carbon nanotubes, very small diameter (less than 10 nm) carbon filaments were observed in the 1970 s through synthesis of vapor grown carbon fibers prepared by the decomposition of benzene at 1100°C in the presence of Fe catalyst particles of 10 nm diameter [11, 12]. However, no detailed systematic studies of such very thin filaments were reported in these early years, and it was not until lijima s observation of carbon nanotubes by high resolution transmission electron microscopy (HRTEM) that the carbon nanotube field was seriously launched. A direct stimulus to the systematic study of carbon filaments of very small diameters came from the discovery of fullerenes by Kroto, Smalley, and coworkers [1], The realization that the terminations of the carbon nanotubes were fullerene-like caps or hemispheres explained why the smallest diameter carbon nanotube observed would be the same as the diameter of the Ceo molecule, though theoretical predictions suggest that nanotubes arc more stable than fullerenes of the same radius [13]. The lijima observation heralded the entry of many scientists into the field of carbon nanotubes, stimulated especially by the un-... 

Oshida, K., Kogiso, K., Matsubayashi, K., Takeuchi, K., Kobayashi, S., Endo, M., Dressclhaus, M. S., Drcsselhaus, G., Analysis of pore structure of activated carbon fibers using high resolution transmission electron microscopy and image processing, 7. Mater. Res., 1995, 10(10), 2507 2517. 

Economy, J., Daley, M., Hippo, E. J. and Tandon, D., Elucidating the pore structure of activated carbon fibers through direct imaging using scanning tunneling microscopy (STM), Carbon, 1995, 33(3), 344 345... 

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