Viscose rayon modifiers

Other investigations of the porosity of activated carbon cloth explored the effects of impregnation with certain transition metal salts and oxo-complexes (Freeman etal., 1989) and of activation in ammonia (Tomlinson etai, 1993). In the latter case it was found that ammonia reacts with the viscose rayon chars to form various nitrogen-containing microporous products. An early study by Barton and Koresh (1983) had also demonstrated that the pore structure of carbon cloth and its affinity for water vapour can be modified by HN03 activation. 

The various TEX-WETS are colloidal aqueous silica dispersions widely used in textile finishing to control yarn slippage, modify hand, and control luster. However applied, these products can be used to stabilize weave and to impart special finish effects to fabrics made of cotton, wool, synthetic fibers and filaments, and to mixtures. Treatment gives outstanding finishes on nylon and Dacron marquisettes, rayon fabrics and viscose rayon suitings. Application requires no special equipment nor curing. The dispersions are not cationic and, therefore, cannot be applied by exhaustion onto the fabric. 

Viscose and modified viscose are composed of cellulose and like cotton they are polymer of anhydroglucose unit. The significant physical differences between various regenerated cellulose and cotton polymers are listed in Table 1.14. HWM viscose rayon may appear nearly round in cross-section. Viscose polymers are very amorphous and have high moisture absorption capacity of 11 to 16%. Vis-... 

Interest in the manufacture of different forms of rayon has resulted in the production of regular rayon, hollow viscose, spun-dyed filaments and staple rayon, crimped rayon and surface modified fibers, high tenacity rayon and high wet modulus (polynosic) rayon fibers. In chemical composition, viscose rayon and cotton are alike they are both cellulose. 

A viscose process additive is a surfactant that disperses hydrophobic particles in the viscose, for example, insoluble resins or other insoluble hydrophobic material. The dosage used is 0.5-3 kg/ton cellulose. A modifier is an additive, not always a surfactant, that decreases the regeneration speed. This leads to viscose/rayon fibres with higher wet strengths when modifiers are used at dosages of 5-30 kg/ton cellulose. 

There are a number of different ways to classify polymers but perhaps the simplest division is between natural polymers (biopolymers) which include proteins (polypeptides), polysaccharides, and poly(nucleotides) and synthetic polymers which include polyethylene, poly(vinyl chloride) and nylon some natural polymers are synthetically modified as in the formation of viscose rayon from cellulose or vulcanized rubber from natural rubber [largely poly(isoprene)]. 

Modified Viscose Processes. The need for ever stronger yams resulted in the first important theme of modified rayon development and culminated, technically if not commercially, ia the 0.88 N/tex (10 gf/den) high wet modulus iadustrial yam process. 

Plate pr esses. Sometimes called sheet filters, these are assemblies of plates, sheets of filter media, and sometimes screens or frames. Thev are essentially modified filter presses with practically no cakeholding capacity. A press may consist of many plates or of a single filter sheet between two plates, the plates may be rectangular or circular, and the sheets may lie in a horizontal or vertical plane. The operation is similar to that of a filter press, and the flow rates are about the same as for disk filters. The operating pressure usually does not exceed 138 kPa (20 psig). The presses are used most frequently for low-viscosity liqmds, but an ordinaiy filter press with thin frames is commonly used as a clarifier for 100-Pa s (1000-P) rayon-spinning solution. Here the filtration pressure may be 6900 kPa (1000 psig). 

Cellulose is sometimes used in its original or native form as fibers for textile and paper, but is often modified through dissolving and reprecipitation or through chemical reaction. The xanthate viscose process, which is used for the production of rayon and cellophane, is the most widely used regeneration process. The cellulose obtained by the removal of lignin from wood pulp is converted to alkali cellulose. The addition of carbon disulfide to the latter produces cellulose xanthate. 

Regenerated proteins from casein (lanital), peanuts (ardil), soybeans (aralac), and zine (vicara) are used as specialty fibers. Regenerated and modified cellulose products, including acetate, are still widely used today and the production of fibers is similar to that described above for synthetic fiber production. Most regenerated cellulose (rayon) is produced by the viscose process where an aqueous solution of the sodium salt of cellulose xanthate is precipitated in an acid bath. The relatively weak fibers produced by this wet spinning process are stretched to produce strong rayon. 

Natural fibers such as cotton can be chemically modified to form rayon or acetate. Rayon was first called artificial silk. In the viscose process, cellulose is dissolved in sodium hydroxide, pushed through spinnerets, and treated with acid to harden. Treatment with copper compounds and ammonia is used to form hosiery yams. Acetate (or cellulose acetate), produced by treating cotton with acetic acid and acetic anhydride, is also used in production of clothing. 

Modified rayon is made principally of regenerated cellulose and contains nonregenerated cellulose fiber-forming material, for example, a fiber spun from viscose containing casein or other protein (ASTM). This greatly increases both dry and wet strength and also permits mercerization. Rayon is readily dyed by standard methods. 

In the period 1965-1980 a wide variety of new, stronger, and more durable rayon fibers were developed. Rayon variants are now produced which utilize the comfort and aesthetic qualities of cellulose to compliment synthetic fibers in many textile applications. Considerable emphasis has been placed on the economics and ways to meet environmental and safety standards. Special effects, such as crimp or hollow filaments, may be obtained by appropriate viscose formulations, point-of-stretch applications, spin-bath compositions, and modifiers. Flame-retardant (FR), acid-dyeable, and superabsorbent rayons are typical of the properties that can be attained by incorporating various materials in the fiber structure. Rayon is unique in the respect that the fiber can be permanently modified for a wide variety of end uses simply by adding the appropriate material to viscose. 

Cellophanes. Cellophane looks and acts like a hydrocarbon-based plastic material, but is not one. The viscose process is used to extract cellulose as cellulose xanthate, which is then treated and processed to regenerate the cellulose as Rayon, a material used extensively as fibers. The same material, however, can be made in sheet form, in which it is essentially a modified cellulose paper. 

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