Chopped natural fibers

It is the length of a particle divided by its diameter. For spherical or cubical particles, the aspect ratio equals to one. For calcium carbonate particles, the aspect ratio is typically 1-3. For talc, the aspect ratio is typically in the range of 5-20. For milled glass fiber, it is between 3 and 25. For mica, it is 10-70. For wollastonite, it is between 4 and 70. For chopped glass fiber, it is between 250 and 800. For natural fibers, such as cellulose, the aspect ratio can be from 20-80 to thousands. Low aspect ratio is below 10. However, the above figures are given for fillers not processed in a compounder and/or an extruder. Upon processing, aspect ratio can decrease from dozens and hundreds to as low as 3-10. 

The demands of staple fiber are different from those of filament yarns. Staple fiber is a continuous filament cut into short lengths in centimeters. Staple fibers are discontinuous and are crimped and chopped to the desired staple fiber length to blend at the carding stage with cotton (short staple), wool (long staple), or other natural fibers. The raw polyester fibers are... 

Recently, new compounding methods have been investigated to produce long, natural fiber-reinforced thermoplastic pellets and improve composite mechanical properties [31, 32]. For example, pellets have been formed by melt impregnation of continuous natural fiber yarns by pultrusion followed by cooling and chopping. Another method involves commingling of continuous forms of natural and synthetic fibers that are then heated, consolidated, and chopped. 

It was found by Cho s research group [24] that the thermal expansion of neat poly(butylene succinate) dramatically reduced by reinforcing it with chopped silk fibers, which are animal-based natural fibers, without any surface treatment or modification, indicating much improved dimensional stability of silk/PBS biocomposites, as seen in Figure 4.19. The linear coefficients of thermal expansion (GTE) were 294 x 10 for neat PBS and 10 x 10 to 52 x 10 °G for silk/PBS biocomposites, depending on the fiber content incorporated. This result implied that such a reduction of the GTE may be further performed by enhancing the fiber-matrix adhesion through optional surface modification of raw silk fibers. 

A fiber is often defined as an object with a length-to-diameter ratio of at least 100. Synthetic fibers are spun (Chapter 17) in the form of continuous /amcn/5, but may be chopped to much shorter staple, which is then twisted into thread before weaving. Natural fibers, with the exception of sUk, are initially in staple form. The thickness of a liber is most commonly expressed in terms of denier, which is the weight in grams of a 9000-m length of the fiber. Stresses and tensile strengths are reported in terms of tenacity, with units of grams/denier. 

Of all the fibers that have (and are still) evaluated in rubber compounds over the last 30 years, only treated imregenerated cellulose fibers and chopped aramid fibers have really achieved a certain industrial importance. The current research efforts being made, essentially by university groups in the producing countries, on natural fibers such as jute, sisal, kenaf, etc., are not (yet) leading to documented industrial applications, at least to the author s knowledge. Actual reasons for this situation are imclear, except maybe that industrial applications for treated imregenerated cellulose fibers were inherited from the important preliminary works by former Monsanto s scientists, prior to the commercial development of Santoweb fibers. When... 

Natural fibers were already being used as reinforcement materials in ancient Egypt. House walls there used a mixture of clay, sand, and chopped straw, which... 

The fiber content in mat or random fiber RPs is usually somewhat lower than for an isotropic laminate which is comprised of a number of unidirectional plies. Both laminates may, for example, be planar-isotropic. The random criss-cross nature of chopped fibers in a mat does not permit close packing of the bundles, and thus the fiber content is usually lower. With a lay-up of unidirectional plies, the packing of fibers within a ply may be very close, and the fiber content can be very high. The higher fiber content made from individual plies tends to make it stiffer and stronger than the mat construction. 

The reinforcements amenable to RTM are similar to those used for pultrusion, except that they need not be continuous in nature. Thus, E-glass, S-glass, aramid, and carbon fibers are commonly used, as are discontinuous filaments such as wood fiber and polyesters. Even metal and ceramic fibers can be used in this technique. In one method, the preform is fabricated by spraying 12- to 75-mm-long chopped fiber rovings onto a preshaped screen. A binder sprayed with the fibers keeps them in place and holds the preform shape, which is then placed in the mold. 

The basic raw material is cellulose, a major constituent of sawdust, straw, cardboard or paper wastes, wood chips, or other natural plant fibers. Any of these materials should be chopped or shredded, but never so finely as to eliminate their inherent structural qualities. This cellulosic base comprises approximately 80% of the total substrate mixture. 

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