Fibers optical retardation

The optical behavior of asbestos fibers viewed with crossed polars has been described. Crystalline fibers have positions of extinction 90° apart. The fact that crystalline fibers have retardation has also been mentioned. With crossed polars and a first order red plate in place, asbestos fibers will go from yellow to extinction to blue, back to yellow, etc., upon rotation of the stage. If the fiber bends, this is equivalent to a rotation of the stage and the color will change. If the fiber... 

Figure 3. Images of a cross-section of carbon fibers after propylene pyrolysis. 3a Scanning Electron Microscopy of a piece of the carbon cloth. 3b optical microscopy (crossed polarizers with a wave retarding plate).

The lateral texture can be studied by measuring the lateral birefringence in a thin fiber cross section [132, 134], or by registration of the retardation profile across the diameter of a whole filament with an optical interference microscope... 

Kimura [37] selected three kinds of thermosetting resins—furan, diphenylether-formaldehyde and polyimide resins—as matrix precursors to fabricate carbon fiber reinforced carbon composites (C/C composites). After heat treatment at 2000-3000°C, the graphitization process of the matrix was examined by optical microscopy and X-ray diffraction. In the C/C composite derived from a polyimide, the graphite structure was not as well developed as the others. This retarded development is attributed to less internal stress between fibers and matrix as well as to less stretching of the matrix. 

Fiber additives are chemicals such as flame retardants, delustrants, ultraviolet (UV)-radiation absorbers, and optical brighteners which are incorporated into manufactured fibers to provide properties such as enhanced flame resistance, dullness, decreased rate of degradation from incident UV radiation, or enhanced whiteness and brightness. The chemicals are added to the polymer solution or melt so that they become embedded and locked between the fiber s polymers as the solution coagulates or the melt solidifies. Lists of specific additive chemicals are available from manufacturers such as ICI Corporation (1987). There have been few reports of fiber additives causing skin reactions, a situation that would be expected because these compounds are not readily available for transfer to the skin. 

For this test, align the fiber at 45° to the polarization directions in order to maximize the contribution to each of the optical axes. The colors seen are called retardation colors. They arise from the recombination of light which has traveled through the two separate directions of the crystal. One of the rays is retarded behind the other since the light in that direction travels slower. On recombination, some of the colors which make up white light are enhanced by constructive interference and some are suppressed by destructive interference. The result is a color... 

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. 

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