Cellulose fiber orientation

Milwich et al. (2006) combined ideas of cellulose fiber orientation in wood with the structure of the stem of giant reeds to create a hybrid model realized using advanced braid protrusion machinery at the Institute of Textile Technology and Process Engineering (ITV) Germany. The outcome called Technical Plant Stem is a commercially scalable architectural textile composite that demonstrates excellent strength and impact resistance with the minimal material use (Speck and Speck, 2006). 

Textured samples are the better suitable to measure the size of crystallites. To determine the lateral dimensions of the crystallites is recommended use the cellulose fibers oriented parallel to plane of the sample. On the other hand, the samples for measuring the length of the crystallites should be prepared so that the fiber axis would be perpendicular to plane of the sample. Preliminary it is necessary to find such azimuthal position of the sample in order to get the most intensity of the studied peak Three to five X-ray diffractograms are recorded by reflection using a step-scan mode, 0.05° step, and with the accumulation of pulses at the each step. 

PH Hermans and D Heikens, Orientation in cellulose fibers as derived from measurements of dichroism of dyed fibers, Reel. Trav. Chim. Pays-Bas, 71 49-55, 1952. 

Cellulose fibers are in fhe form of hollow fubes of several hundreds of micromefers long and with a cavity mouth of several micrometers wide. The fiber wall section consists of densely packed cellulose microfibrils, wifh a preferential orientation along the fiber axis. Cellulose microfibrils consisf of glucose units bounded in a /i-conformation favoring straight... 

FIGURE 1.9 The different structural levels of a typical cellulose fiber the fiber wall consists of closely packed cellulose microfibrils oriented mainly in the direction of the fiber. 

FIGURE 20-29 Cellulose structure. The plant cell wall is made up in part of cellulose molecules arranged side by side to form paracrys-talline arrays—cellulose microfibrils. Many microfibrils combine to form a cellulose fiber, seen in the scanning electron microscope as a structure 5 to 12 nm in diameter, laid down on the cell surface in several layers distinguishable by the different orientations of their fibers. 

The composition of the solution and its interaction with irradiated cellulosic fibers determine the increase in accessibility of these radicals. The life-times of trapped radicals in irradiated, dried (less than about 2 percent moisture) cellulose appear to be indefinite. Immersion in solutions that strongly interact with cellulosic fibers in which both their morphology and molecular orientation are changed does not necessarily scavenge or terminate all of the trapped radicals. However, immersion of irradiated cellulose in liquid ammonia reduced molecular orientation and terminated all of the trapped radicals (21, 24, 25). ... 

Molecular orientations of grafted celluloses can be changed to a small extent. Interactions of monomer solutions with cellulosic fibers to decrease crystallinities and to change lattice type of the products from those of unmodified fibers have been reported. X-ray diffraction methods are used to determine the changes (24). 

The large-production reinforcing agent used today is primarily glass. Other fibers include cotton, cellulosic fiber, sisal, polyamide, jute, carbon, graphite, boron, whiskers, steel, and other synthetic fibers.10 12> 289 291, 466 They all offer wide variations in composition, properties, fiber orientation/construction, weight, and cost (Tables 15.4 and 15.5... 

Crystallinity indexes calculated according to the method described by Segal et al. (32) showed that the old cotton has a crystallinity of about 38 . Aqueous treatments increased the crystallinity of the historic cotton sample to about 45 . However, the crystallinity of contemporary cotton, which is about 70 , was not reached (30). This increase suggests that water acts as an internal plasticizer and allows a segmental reorientation which leads to an increase in crystallinity. Water-induced crystallization of amorphous cellulose fibers has been reported (17). Kalyanaraman (33) investigated orientation factors of cotton fibers from historic samples and found that the orientation values of the museums samples are smaller than the values of present-day cottons. He opined that cotton may have lost its orientation over time. In view of this... 

The woody part of a tree provides both mechanical support to hold the tree upright for optimum exposure of the leaves to sunlight and air, and serves as a conduit to carry water and trace nutrients from the roots to the leaves and photosynthetic products to where needed. Hollow and interconnected fibers composed mostly of cellulose and oriented along the axis of the tree provide both of these functions (Fig. 15.1). 

The orientation of cellulosic fibers has some effect on the conductivity of the paper. The conductivity in the XY plane of the sheet (surface conductivity parallel to most of the fibers) may be quite different from the conductivity along the Z direction (bulk conductivity perpendicular to the fibers). Comparison of surface and bulk conductivity for a given paper sheet can thus yield information which reflects the anisostropy in the structural morphology due to fiber orientation. Bulk conductivity measurements are also important since many paper sheets used in reprographic processes are composed of a conductive base sheet coated with a dielectric material 16. One important specification for these types of papers is the value of the bulk conductivity of the base paper. 

Cellulosic fibers may also be pressed into transparent films without the addition of any medium. Such samples are randomly oriented. A further method for investigating cellulosic fibers involves pressing out a very thin layer of contiguous filaments. Under favorable conditions, there results a thin, cohesive layer of oriented fibers that is sufficiently transparent for study in the infrared, without the need for any liquid or solid embedding medium. The purpose in preparing such a sample is to try to extend the use of polarized infrared spectroscopy beyond the field of films. Films are eminently suitable as samples, but information is sometimes required on the fibrous form itself and this must be obtained directly. 

U.S. Pat. No. 5,863,480 [12] (by SRP Industries Ltd., Nexwood) discloses a thermoplastic composite of polyethylene, polypropylene, vinyls or other extrudable plastics, cellulosic fiber such as sawdust, wood flour, ground rice hulls, and so on, fillers, and lubricanfs. The pafenfees describe fhe exfrusion occurring through a die at a temperature below the melting point of the polymer, so that the deformation of the polymer takes place in the solid phase, making the product biaxially oriented. 

Physical objects can be isotropic or anisotropic by their nature. Isotropic objects expand and contract equally in all directions. Anisotropic objects expand and contract differently in length, width, and/or depth. A piece of wood is anisotropic in terms of expansion-contraction as a result of orientation of cellulose fiber. That is why wood is characterized by three linear coefficients of expansion-contraction, of... 

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