Cellulose fiber preparation

The predominant cellulose ester fiber is cellulose acetate, a partially acetylated cellulose, also called acetate or secondary acetate. It is widely used in textiles because of its attractive economics, bright color, styling versatiUty, and other favorable aesthetic properties. However, its largest commercial appHcation is as the fibrous material in cigarette filters, where its smoke removal properties and contribution to taste make it the standard for the cigarette industry. Cellulose triacetate fiber, also known as primary cellulose acetate, is an almost completely acetylated cellulose. Although it has fiber properties that are different, and in many ways better than cellulose acetate, it is of lower commercial significance primarily because of environmental considerations in fiber preparation. 

Cellulose triacetate is obtained by the esterification of cellulose (qv) with acetic anhydride (see Cellulose esters). Commercial triacetate is not quite the precise chemical entity depicted as (1) because acetylation does not quite reach the maximum 3.0 acetyl groups per glucose unit. Secondary cellulose acetate is obtained by hydrolysis of the triacetate to an average degree of substitution (DS) of 2.4 acetyl groups per glucose unit. There is no satisfactory commercial means to acetylate direcdy to the 2.4 acetyl level and obtain a secondary acetate that has the desired solubiUty needed for fiber preparation. 

Refining and Fractionation. These processes are used to alter and select cellulose properties so the final sheet has the desired properties (51). Properties of recycled fibers differ from those of fibers prepared directly from wood. For example, recovered chemical fibers have lower freeness, an apparent viscosity leading to different water drainage characteristics on paper machines. Recovered fibers also have iacreased apparent density, lower sheet strength, iacreased sheet opacity, inferior fiber—fiber bonding properties, lower fiber sweUiag, lower fiber flexibiUty, lower water reteatioa, reduced fiber fibrillatioa, and much lower internal fiber delamination. 

Anth nthrones. Halogenated derivatives have been developed to improve the dyeing properties of anthanthrones, which have low tinctorial strength and poor affinity to cellulose fibers. The only example of commercial significance is Cl Vat Orange 3 [4378-614] (4) Cl 59300). This compound is prepared from l,l -dinaphthyl-8,8 -dicarboxyhc acid (173) with oleum and bromine as follows ... 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Investigators of cellulosic liquid crystals have two main motivations to study mesophase formation primarily from a scientific viewpoint or a technolomcsd vie oint. The main focus of the latter has been on the potential of preparing high strength/high modulus regenerated cellulose fibers. Another potentim use of cellulosic liquid crystal derivatives is as chiroptical filters (S,lfi). 

Cellulose powder is a mechanically shortened cellulosic fiber, whereby the degree of polymerization remains almost intact. Microcrystalline cellulose is a partially purified and depolymerized cellulose, prepared by treating a-cellulose obtained from fibrous plant material with mineral acids. It occurs as a fine white odorless and... 

A series of water-soluble fiber-reactive xanthene dyes has been prepared from the reaction of benzoxanthenedicarboxylic acid anhydride disulfonic acid with, for example, 3-aminophenyl- 3-hydroxyethyl sulfone to yield dyes, with high brilliance and good fastness properties for dyeing of or printing on leather, wool, silk, or cellulosic fibers (53). 

Elastomers. Ethyl acrylate has been copolymerized onto cellulose fibers, preirradiated by high energy radiation, to prepare elastomers (43,... 

Corrections of the apparent crystallinity values of fibers materials have been carried out by taking into account a disorder parameter k, following Ruland s method. Peculiar care was taken about samples preparation (cutting and pelleting of fibers), data collection and reduction, which will be briefly described. Crystallinity and disorder parameter measurements have been performed on main textile fibers (polyester, polyamide, aramid, polypropylene, cellulosic fibers) and the results will be discussed comparatively, with those got by more conventional x-ray crystallinity determinations. The complementarities of these different approaches will be illustrated with several examples. For instance,... 

With a few exceptions, sulfur dyes are used for dyeing cellulosic fibres. They are insoluble in water and are reduced to the water-soluble leuco form for application to the substrate by using sodium sulfide solution. The sulfur dye proper is then formed within the fiber pores by atmospheric or chemical oxidation. Sulfur dyes constitute an important class of dye for producing cost-effective tertiary shades, especially black, on cellulosic fibers. One of the most important dyes is C.I. Sulphur Black 1, prepared by heating 2,4-dinitrophenol with sodium polysulfide. 

It should also be mentioned that the application of wood nanocellulose prepared by the described techniques - where the cell wall is further disintegrated by mechanical treatment - leads to lower-strength cellulose fiber-reinforced composites than in the corresponding BC materials [34]. 

In Japan, pilot plant quantities of rayon and cotton grafted with styrene and other monomers have been prepared and evaluated. Improvements in the flex abrasion resistance and good water repellency were obtained. In addition, thermoplasticity was imparted plus an improved adhesion to rubber. Arthur et al. have also studied this type of grafted cellulose fibers. Again, the work has not led to any large scale developments. Research into grafting to textiles is continuing, but the prospects for any early successful industrialization seem remote. 

Viscose rayon is but one variety of rayon, a more general term for derivatized or reconstituted cellulose. Other rayons include fiber prepared from collodion, cellulose acetate, and cellulose fiber regenerated from a cellulose-copper ammonium solution cuprammonium rayon) (Kauffman 1993). 

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