Viscose - Definition of 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 adherin

Prepared By : Mazadul Hasan sheshir ID: 2010000400008

13th Batch (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 Banglade sh Prepared By :

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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

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 **

DEFINITIONS OF VISCOSE:

Chemistry of Viscose Rayon

Cellulose, Soda Cellulose, Sodium Cellulose Xanthate, Regenerated Cellulose

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 100different 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:

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

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

History of Viscose:

• Preparation of wood pulp

(Formation of Soda cellulose & excess alkali is pressed out)

STRUCTURE OF RAYON

Fig Structure of unit cell of cellulose The unit cell of cellulose is shown in Fig.

Chemical Composition of Viscose

Preparation of wood pulp:

Wood chips treated with calcium bic-sulphide, and the treated chips then cooked with steam under the pressure.

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.

Colour & luster:

The color of viscose is white & no colour Luster is high

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.

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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.

CHEMICAL PROPERTIES:

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

Rayon Fiber Characteristics

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

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:

In two or three hrs they break it up into fine

“Crumbs” (break into very small pieces).

Description of Viscose manufacturing:

Description of Viscose manufacturing:

Ageing:

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:

• Ripen viscose soln extruded 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

12 Drive for topham box

13 Traverse

14 Fresh air Inlet

15 Fumes sucked out

17 Cake

Proper recipe of a coagulating bath during spinning

H2SO4

Regenerating agent and also neutralizes the alkali

Converts Na- cellulose Xanthate to regenerated cellulose.

ZnSO4

Causes variation in strength, excess use degrades quality

of viscose It causes serrated X- section so that the dye absorbency increased.

Glucose

-2% → Given pliability and softness of the yarn, increase

viscosity of bath, control cellulose formation.

Water - 69%

Temperature -

40o-55oC

Figure : Process of manufacture of viscose rayon fiber

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 1st bath contains warm water where the filaments are stretched and the second bath containing dilute H2SO4 completes 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%

Four regenerated cellulose fibres:

CUPRAMMONIUM RAYON

It is produced by a solution of cellulosic

material in cuprammonium hydroxide

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

This is a more expensive process than that

of viscose rayon Its fiber cross section is

almost round

Fig : Cupro flow chart

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.

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

DIFFERENT TYPES OF 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

Specialty rayons: