Textile Fibers – a ubiquitous type of evidence. They are “common” in the sense that textiles surround us in our homes, offices, and vehicles. We are in constant contact with textiles daily.
Natural Fiber – any fiber that exists as a fiber in its natural state.
Manufactured Fiber – any fiber derived by a process of manufacture from any substance that, at any point in the manufacturing process, is not a fiber.
Fibers can also be designated by their chemical makeup:
Filaments – a type of fiber having indefinite or extreme length, such as silk or a manufactured fiber
Staple Fibers – natural fibers (except silk) or cut lengths of filament, typically being 7/8–8in (2.2–28.5cm) in length.
Denier – a direct numbering system in which the lower numbers represent the finer sizes and the higher numbers the larger sizes.
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Kind | Plant | Genus and Species | Characteristics |
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Bast (stem) fibers | Flax (linen) | Linum usitatissimum | The ultimates (individual fiber cells) are polygonal in cross-section, with thick walls and small lumina. Microscopically, the fibers have dark dislocations, which are roughly perpendicular to the long axis of the fiber. |
Jute | Corchorus capsularis | This fiber appears bundled microscopically and may have a yellowish cast. The ultimates are polygonal but angular with medium-sized lumina. It can be distinguished easily from flax by its counterclockwise twist. The dislocations appear as angular X or v’s and may be numerous. | |
Ramie | Boehmeria nivea | Ramie has very long and very wide ultimates. The walls are thick and, in cross-section, appear flattened. Ramie has frequent, short dislocations, and longer transverse striations. In cross-section, radial cracks may be present. | |
Hemp | Cannabis sativa | With the ultimates more bundled, a wider lumen, and fewer nodes, hemp is easy to distinguish from flax. Cross-sectioning hemp helps in distinguishing it from jute because hemp’s lumina are rounder and more flattened than jute’s. Hemp may also have a brownish cast to it. | |
Leaf fibers | Sisa | Agave siciliana | Sisal is relatively easy to identify due to its irregular lumen size, crystals, spiral elements, and annular vessels. In cross-section, sisal looks somewhat like cut celery |
Abaca | Musa textilis | Although potentially difficult to distinguish from sisal, abaca’s ultimates have a uniform diameter and a waxy appearance; often it is darker than sisal. Its ultimates are polygonal in cross-section and vary in size. Abaca may present spiral elements but often will have small crown-like structures | |
Seed fibers | Cotton | Genus Gossypium | Mature cotton has a flat, twisted, ribbon-like appearance that is easy to identify. Cotton fibers are made up of several spiraling layers around a central lumen. |
Kapok | Ceiba pentandra | Kapok fiber is used primarily for life preservers and upholstery padding because the fibers are hollow, producing very buoyant products. But they are brittle, which prevents spinning or weaving. | |
Coir | Coco Nucifera | Coir comes from the husk of the coconut and, accordingly, is a very dense, stiff fiber easily identified microscopically. On a slide mount, coir appears very dark brown or opaque with very large, coarse ultimates |
Polarized light microscope – the primary tool for the identification and analysis of manufactured fibers.
Delustrants – finely ground particles of materials, such as titanium dioxide, that are introduced into the spinning dope.
The examination of the optical properties of manufactured fibers can yield a tremendous amount of information about their chemistry, production, end-use, and environment.
If a fiber has a higher refractive index than the medium in which it is mounted, it acts as a converging lens, concentrating light within the fiber. If the fiber has a lower refractive index than the mounting medium, it acts as a “diverging” lens and the light rays diverge from the fiber.
Becke Line – a thin bright line that appears when light rays slightly converge or diverge.
One of the more distinctive traits of a fiber is its birefringence. The interference colors seen after crossing the polarizing filters relate to a fiber’s material nature, orientation, and crystallinity.
Many dyes used to color textiles have fluorescent components, and their response to certain wavelengths of light can be useful in comparing textile fibers.
Color is one of the most critical characteristics in a fiber comparison.
Simultaneous Contrast – the tendency of color to induce its opposite in hue, value, and intensity upon an adjacent color and be mutually affected in return.
Dye – an organic chemical that can absorb and reflect certain wavelengths of visible light.
Pigments – are microscopic, water-insoluble particles that are either incorporated into the fiber at the time of production or are bonded to the surface of the fiber by a resin.
Three main methods of analyzing the color of fibers:
Analyzing the fibers chemically offers not only a confirmation of the microscopic work but also may provide additional information about the specific polymer type or types that make up the fiber.
FTIR and PGC are both methods of assessing the chemical structure of polymers. FTIR is the preferred method because it is not destructive to the fibers.
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