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Prepared By : Prepared By : Mazadul Hasan sheshir ID: 2010000400008 13thBatch (session 2009-2013) Department : Wet Processing Technology Email: mazadulhasan@yahoo.com Blog : www. Textilelab.blogspot.com (visit) Southeast University Department Of Textile Engineering I/A 251,252 Tejgaon Dhaka Bangladesh ©right
Viscose: Viscose is a regenerate cellulose fiber because it is produced from naturally occurring polymers .the raw materials of viscose rayon may be cotton linters ,the short staple fiber adhering to the cotton sheet, or wood pulp derivatives from northern spruce, western hemlock, eucalyptus, or southern slash pine. The pulps of these soft’s woods , containing 94% cellulose, are especially suited to fiber manufacturing.
Viscose: Viscose is a cellulosic man-made of artificial fiber. The starting material for the production of filaments and staple fibers is pulp, meanly produced from wood and linters, but also from annual plants (paper & pulp). Viscose rayon consists of cellulose of lower DP than cotton cellulose. The DP (degree of polymerization) of viscose polymer is (300- 450). Molecular weight of Viscose is 90,000 to 110,000 and number of glucose residues 550 to 680. According to ISO/TC6 the code of Viscose is CV. Since pulp fibers in their natural state are too short to be spun into yarns, they are dissolved and regenerated in filament form. The viscose fiber is made by solution wet spinning principal. Chemical Structure of Cellulose
DEFINITIONS OF VISCOSE: Definition by F T C : **rayon is a manufactured fiber composed of regenerated ,as well as manufactured fiber composed of regenerated cellulose in which substitutes have placed not more then 15% of hydrogen’s of the hydroxyl groups **
Chemistry of Viscose Rayon Cellulose, Soda Cellulose, Sodium Cellulose Xanthate, Regenerated Cellulose
History of Viscose: The great advances in chemistry and machine building at the end of the nineteenth and the beginning of the twentieth century have contributed to the development of the commercial manufacture of artificial fiber. A new era in the manufacture of manmade fibers began at the end of the thirties. In the course of the last 75 years about 100 different types of manmade fibers. However, comparatively small number of manmade fiber is produced in large commercial amounts and these are fibers of low manufacturing cost. Viscose fibers are made from regenerated cellulose. Since 1905 the viscose fiber is manufacture in England. The production has stabilized at approximately 2.7 million tons worldwide (Europe 600000 tons).
History of Viscose: Currently (2005), about 85 % of the total viscose fibre production is produced as staple fibers and about 15 % as filaments. In recent history in Europe, textile viscose filament end-users are receiving increased competition (resulting in phasing out of capacity) by cheaper competitive yarns based on polyester and polyamide, whereas viscose staple fibre and viscose try cord keep a strong position. Rayon is the oldest commercial manmade fiber. The U. S. Trade Commission defines rayon as "manmade textile fibers and filaments composed of regenerated cellulose". The process of making viscose was discovered by C.F.Cross and E.J.Bevan in 1891. The process used to make viscose can either be a continuous or batch process. The batch process is flexible in producing a wide variety of rayons, with broad versatility. Rayon's versatility is the result of the fiber being chemically and structurally engineered by making use of the properties of cellulose from which it is made.
History of Viscose: However, it is somewhat difficult to control uniformity between batches and it also requires high labor involvement. The continuous process is the main method for producing rayon. Three methods of production lead to distinctly different rayon fibers: viscose rayon, cuprammonium rayon and saponified cellulose acetate. Of the methods mentioned, the viscose method is relatively inexpensive and of particular significance in the production of nonwoven fabrics.
Flow chart of viscose rayon manufacturing: • Preparation of wood pulp • Steeping & Pressing (Formation of Soda cellulose & excess alkali is pressed out) • Shredding (In two or three hours, formation “Crumbs”) • Ageing (In atmospheric oxygen, D.P. falls from 800 – 350) • Churning (Xanthation ) • Mixing (Solution) • Ripening • Spinning • Drying
STRUCTURE OF RAYON The unit cell of cellulose is shown in Fig. Fig . Structure of unit cell of cellulose
PHYSICAL PROPERTIES: Density: The density of Viscose rayon is 1.53 g/cc. Rayon filaments are available in three densities: 1.5, 3.0 and 4.5 Tensile Strength: The Tensile Strength of the fibre is less when the fibre is wet than when dry. It is 1.5-2.4 gpd in the dry state and 0.7-1.2 gpd in the wet state. Stiffness: Normally the stiffness of viscose fiver is 11.2 g/d. Moisture Absorption It absorbs more moisture than cotton. For Viscose Rayon is 13% moisture absorbs at 21˚C. Elasticity: The elasticity of Viscose Rayon is less than 2-3%. Action of Heat At 150˚C or more, Viscose Rayon loses its strength and begins to decompose at (175-204) ˚C.
Raw materials of viscose rayon fiber: 1. Wood 2. Seed hair 3. Bast 4. Grasses 5. Leaf 6. Bamboo
Manufacturing process of Viscose rayon: Preparation of wood pulp: Wood chips treated with calcium bic-sulphide, and the treated chips then cooked with steam under the pressure. Steeping: Soak cellulose in 17.5 percent sodium hydroxide for two hours and Produces soda cellulose Shredding: Soda cellulose is mechanically disintegrated in 2-3 hours to fine crumbs. Ageing: During ageing from 1-3 days at 20оC, the degree of polymerization (DP) falls from 800-350. Churning: Carbon disulfide added in deficiency only 70% of theory. The crumbs dissolve in 3 hours to produce sodium cellulose xanthenes. Mixing: Sodium cellulose xanthenes are treated with 3% NaOH for 4-5 hours to give a solution containing 715% cellulose and 6.5% NaOH. Ripening: The solution is stored for 2-5 days at (10-18)оC. The viscosity falls (degradation) and then rises. Spinning: Extruded into the bath containing 10% H2SO4 about 18% Na2SO4, 10% H2, 1% ZnSO4 at (40-55) C.
PHYSICAL PROPERTIES: Elongation at Break: High tenacity rayon has only 9-17% elongation at break but ordinary Viscose rayon has 15-30% elongation at break. Resiliency: The resiliency nature of viscose fiber is low. Dimensional stability for HWM is high. Colour & luster: The color of viscose is white & no colour. Luster is high. Softening temperature: At 149-163˚C viscose fiber will be soft. Specific gravity: The specific gravity of viscose rayon is 1.5.
CHEMICAL PROPERTIES: Effect of Acid: Similar to cotton fibre. Viscose rayon is attacked by hot dilute or cold concentrated mineral acids (H2SO4, HCl), which weaken and disintegrate the fibre. Effect of Alkalis: Like cotton, Viscose rayon has a high degree of resistance to dilute alkalis. Strong solutions of alkali cause swelling, with loss of tensile strength. [] Effect of Bleach: Viscose rayon is sensitive to oxidizing agents such as high-strength hydrogen peroxide5. As a result the bleaching of regenerated cellulose fibers may not always necessary before dying. Action of Microorganisms: Microorganisms (moulds, mildew, fungus, bacteria) affect the colour, strength, dyeing properties and luster of rayon. Clean and dry viscose rayon is rarely attacked by moulds and mildew. Effect of Iron: Viscose Rayon is attacked with iron in the form of ferrous hydroxide weakens the yarns. Therefore staining, marking or touching of rayon to iron or iron surface should be avoided. Action of Solvents: Textile solvents can be used on Viscose rayon without any deteriorating effect.
Rayon Fiber Characteristics 1. Highly absorbent 2. Soft and comfortable 3. Easy to dye 4. Drapes well The drawing process applied in spinning may be adjusted to produce rayon fibers of extra strength and reduced elongation. Such fibers are designated as high tenacity rayons, which have about twice the strength and two-third of the stretch of regular rayon. An intermediate grade, known as medium tenacity rayon, is also made. Its strength and stretch characteristics fall midway between those of high tenacity and regular rayon .
Description of Viscose manufacturing: Preparation of the wood pulp: The starting mtl is timber. It is floated on rivers to the mtls. Here the bark is removed and the wood is chipped into pieces about inches. The chips are treated with Calcium bi sulphite and the treated chips then cooked with steam under pressure for about 14 hrs. . These treatments do not greatly affect the cellulose but it decomposes and solubilizes the encrusting substances. So purifying the cellulose. Then bleached with hypochlorite and converted into paper boards or sheets.
Description of Viscose manufacturing: Steeping & Pressing: The flat, white sheets of board contain about 90 to 94% of pure cellulose. The sheets are then stacked vertically in the press and then soaked in a 17.5% solution of caustic soda for 1-4 hrs. This process is known as Steeping. Then the excess alkali is pressed out.
Description of Viscose manufacturing: Shredding: The shredding m/c consists of a drum inside which revolve a pair of blades with serrated edges. The shredders are water cooled and will take 200 lb of pressed soda cellulose at a time. In two or three hrs they break it up into fine “Crumbs” (break into very small pieces).
Description of Viscose manufacturing: Ageing: Description of Viscose manufacturing: After shredding, the crumbs are aged. Some de polymerization occurs and the degree of polymerization falls from about 800 to 350 in this process. The higher the temp, the more rapidly does ageing – which is mainly a process of depolymerisation. Churning: After ageing, the soda cellulose crumbs are introduced into rotating air-tight hexagonal churns. About 10% of their own (crumbs) weight of carbon disulphide is added and the crumbs and disulphide are churned up together, a deep orange, gelatinous mass of sodium cellulose Xanthate is formed.
Description of Viscose manufacturing: Mixing (Solution): In the mixers the sodium cellulose xanthate is stirred with dilute caustic soda for 4 to 5 hrs, the vessel being cooled. The xanthate dissolves to a clear-brown, viscous liquid, similar in appearance to honey this liquid is known as “Viscose” but is still too impure, too acetated and too young to spin. Ripening: The viscose solution is stored for 4 to 5 days at 10o-18oC and during storage it ripens. The test which is available to determine when viscose is ripe enough to be spun is as given below - Acetic acid test:
Description of Viscose manufacturing: Spinning: • Ripen viscose solnextruded through the spinneret mostly made of platinum alloys. The jet of viscose enters a co-agulating bath containing the followed composition of mixture- – Sulphuric acid. – Sodium sulphate. – Zinc sulphate Purification: The yarn collected in the Topham Box is impure and relatively weak, it has to be purified. Purification consists of 4- operation – Washing – Desulphurising, a process which is sometimes called sulphiding. – Bleaching – Washing.
• . 9. Top godet 10.Funnel 11.Topham Box 12. Drive for topham box 13. Traverse 14. Fresh air Inlet 15. Fumes sucked out 17. Cake 1. 2. 3. 4. 5. 6. Selection of main viscose feed. Pump Candle filter Glass rounder end Coagulating bath Selection of acid replenishing pipe 7.Spinneret 8. Bottom godet
Recipe Reaction - • . Na2SO4 Used as coagulant; The Na2SO4precipitates the Na- cellulose Xanthate from the viscose solution into the form of filaments. 18% → - Regenerating agent and also neutralizes the alkali. Converts Na- cellulose Xanthate to regenerated H2SO4 10% → Proper recipe of a coagulating bath during spinning cellulose. - Causes variation in strength, excess use degrades quality of viscose. It causes serrated X- section so that the dye absorbency increased. ZnSO4 1% → - Given pliability and softness of the yarn, increase viscosity of bath, control cellulose formation. Glucose 2% → - Water 69% - Temperature 40o-55oC
Four regenerated cellulose fibres: 1. Cuprammonium or cupro rayon: Cuprammonium or cupro regenerated cellulose obtained by the cuprammonium process. The cuprammonium is obtained from the aqueous cuprammonium hydroxide solvent and the 1stbath contains warm water where the filaments are stretched and the second bath containing dilute H2SO4completes the coagulation. So Cellulose + Cuprammonium hydroxide CuproThe international organization standardization prefers the name cupro. Properties: 1. Tenacity: 1.7-2.3 g/d (dry), 1.1-1.35 g/d (wet) 2. Elongation at break: 10-19% (dry), 17-33% (wet) 3. D.P.: 500 4. Cross section: Round 5. Recovery from stretch: Good 6. MR%: 11%
CUPRAMMONIUM RAYON It is produced by a solution of cellulosic material in cuprammonium solution at low temperature in a nitrogen atmosphere, followed by extruding through a spinnerette into a sulphuric acid solution necessary to decompose cuprammonium complex to cellulose. hydroxide This is a more expensive process than that of viscose rayon. Its fiber cross section is almost round. Fig. : Cupro flow chart
Four regenerated cellulose fibres: 2. Polynosic: Polynosic or modal regenerated cellulose obtained by process giving a high tenacity and high wet modulus. In other words, Polynosic is a regenerated cellulose fibre which, when wet remains stronger and distorts less than either Cuprammonium or Viscose. The Intl. Organization for standardization prefers the name modal. Properties: 1. Tenacity: 3.9 g/d (dry), 2.9 g/d (wet) 2. Elongation at break: 11% (dry), 13 %(wet) 3. D.P.: 450-500 4. Cross section: Round 5. Recovery from stretch: Good 6. MR%: 11.8%
Four regenerated cellulose fibres: 3. Tancel: General name is Lyocel. Tancel is solvent spun cellulosic fibre of new generic class produce a clear viscose solution which is treated and spun into a bath contain dilute solution of the solvent. Tencel is the best fibre among regenerated cellulose fibres. The fibre is called CF0001 in USA. Properties: – Tenacity: 3.5 (dry), 2.5 (wet) – longation: 11.8% – X-section: Round – MR%: 11.5
DIFFERENT TYPES OF RAYONS Rayon fibers are engineered to possess a range of properties to meet the demands for a wide variety of end uses. Some of the important types of fibers are briefly described. High wet modulus rayon: These fibers have exceptionally high wet modulus of about 1 g/den and are used as parachute cords and other industrial uses. Fortisan fibers made by Celanese (saponified acetate) has also been used for the same purpose. Polynosic rayon: These fibers have a very high degree of orientation, achieved as a result of very high stretching (up to 300 %) during processing. They have a unique fibrillar structure, high dry and wet strength, low elongation (8 to 11 %), relatively low water retention and very high wet modulus.
Specialty rayons: Flame retardant fibers: Flame retardance is achieved by the adhesion of the correct flame- retardant chemical to viscose. Examples of additives are alkyl, aryl and halogenated alkyl or aryl phosphates, phosphazenes, phosphonates and polyphosphonates. Flame retardant rayons have the additives distributed uniformly through the interior of the fiber and this property is advantageous over flame retardant cotton fibers where the flame retardant concentrates at the surface of the fiber. Super absorbent rayons: This is being produced in order to obtain higher water retention capacity (although regular rayon retains as much as 100 % of its weight). These fibers are used in surgical nonwovens. These fibers are obtained by including water- holding polymers (such as sodium polyacrylate or sodium carboxy methyl cellulose) in the viscose prior to spinning, to get a water retention capacity in the range of 150 to 200 % of its weight.
Specialty rayons: Micro denier fibers: rayon fibers with deniers below 1.0 are now being developed and introduced into the market. These can be used to substantially improve fabric strength and absorbent properties. Cross section modification: Modification in cross sectional shape of viscose rayon can be used to dramatically change the fibers' aesthetic and technical properties. One such product is Viloft, a flat cross sectional fiber sold in Europe, which gives a unique soft handle, pleasing drape and handle. Another modified cross section fiber called Fibre ML(multi limbed) has a very well defined trilobal shape. Fabrics made of these fibers have considerably enhanced absorbency, bulk, cover and wet rigidity all of which are suitable for usage as nonwovens .
Specialty rayons: Tencel rayon: Unlike viscose rayon, Tencel is produced by a straight solvation process. Wood pulp is dissolved in an amine oxide, which does not lead to undue degradation of the cellulose chains. The clear viscous solution is filtered and extruded into an aqueous bath, which precipitates the cellulose as fibers. This process does not involve any direct chemical reaction and the diluted amine oxide is purified and reused. This makes for a completely contained process fully compatible with all environmental regulations.
Specialty rayons: Lyocell: A new form of cellulosic fiber, Lyocell, is starting to find uses in the nonwovens industry. Lyocell is manufactured using a solvent spinning process, and is produced by only two companies -- Acordis and Lenzing AG. To produce Lyocell, wood cellulose is dissolved directly in n-methyl morpholine n-oxide at high temperature and pressure. The cellulose precipitates in fiber form as the solvent is diluted, and can then be purified and dried. The solvent is recovered and reused. Lyocell has all the advantages of rayon, and in many respects is superior. It has high strength in both dry and wet states, high absorbency, and can fibrillate under certain conditions. In addition, the closed-loop manufacturing process is far more environmentally friendly than that used to manufacture rayon, although it is also more costly.
Differentiate between four re-generated fibers: Properties Viscose rayon Polynosic Cupro Cotton 1.7-2.3 (dry) 1.1-1.35 (wet) 1. Tenacity 1.5-2.4 (dry) 0.7-1.2 (wet) 15-30% (dry) 20-35% (wet) 3.9 (dry) 2.9 (wet) 11% (dry) 13% (wet) 3-5 (dry) 3.6-6 (wet) 2. Elongation at break 10-19% (dry) 17-33% (wet) 3-7% 5000 450-500 3. D.P. 250-300 500 Flat/kidney shaped. Round 4. Cross section Serrated Round Good 5. Recovery from stretch Poor Good Good 11.8% 6. MR% 13% 11% 8.5%
End use of Viscose Rayon: 1. Some major Rayon fiber uses include apparel (e. g. Blouses, dresses, jaket, lingerie, scarves, suits, hats, socks). 2. The home furnishings (e. g. bedspreads, window treatments, upholstery, slipcovers). 3. Industrial uses (e. g. medical surgery products, non-woven products, tire cord). 4. The lower tensile strength high extension at brake its use limited. 5. The filling in Zippo lighters. 6. Other Uses: Feminine hygiene products.
Some Major Rayon Fiber Uses Apparel: Accessories, blouses, dresses, jackets, lingerie, linings, millinery, slacks, sportshirts, sportswear, suits, ties, work clothes; Home Furnishings: Bedspreads, blankets, curtains, draperies, sheets, slipcovers, tablecloths, upholstery; Industrial Uses: Industrial products, medical surgical products, nonwoven products, tire cord Other Uses: Feminine hygiene products
Uses: Some major rayon fiber uses include apparel (e.g. Aloha shirts, blouses, dresses, jackets, lingerie, linings, scarves, suits, neckties, hats, socks), the filling in Zippo lighters, furnishings (e.g. bedspreads, bedsheets, blankets, window treatments, upholstery, slipcovers), industrial uses (e.g. medical surgery products, non-woven products, tire cord), and other uses (e.g. yarn, feminine hygiene products, diapers, towels). Rayon is a major feedstock in the production of carbon fiber. In early 2010, the U.S. Federal Trade Commission warned several retailers that six major manufacturers were falsely labeling rayon products as "bamboo", in order to appeal to environmentally conscious consumers. While rayon may be produced with bamboo as a raw material, and the two may be used for similar fabrics (though natural bamboo is not as smooth), rayon is so far removed from bamboo by chemical processing that the two are entirely separate.
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