What is Micro Fiber? | Properties of Microfibers

What is Micro Fiber? 

Microfiber or microfiber is synthetic fiber finer than one or 1.3 denier or decitex/thread. This is 1/100th the diameter of a human hair and 1/20th the diameter of a strand of silk. The most common types of microfibers are made from polyesters, polyamides (e.g., nylon, Kevlar, Nomex, trogamide), or a conjugation of polyester, polyamide, and polypropylene (Prolen). 

Microfiber combines two basic fibers, Polyester and Polyamide (a Nylon by-product). These fibers are usually “split” and formed into a woven fabric of 80% Polyester (the scrubbing and cleaning fiber), and 20% Polyamide (the absorbing and quick drying fiber). 

These threads are very small in diameter making them super soft. Rated in denier, the unit for measuring fineness of fabric, a strand of cotton has a rating of 200. A human hair has a denier of 20 and a strand of silk has a denier of 8. Microfiber has a denier of 0.01 to 0.02! At minimum, 100 times finer than a human hair. Softer than silk, yet bull-dog tough, split Microfiber cloth attracts dust, grime, oily films and salt residues like a magnet. 

The unique surface structure of split Microfiber cloth contains hundreds of thousands of micro fiber “hooks” per square inch! These micro-hooks grab, lift, and hold dust and grime without the need for cleaning solutions. Microfiber cloth can be used damp or dry. Used dry, Microfiber cloth works like a chamois. The super absorbent weaves holds up to seven times its weight in fluid and will not scratch paint, glass, acrylics or plastic window tint films.

Properties of Microfibres 
Microfibers are made solely from man-made fibers. They are the finest of all the fibers. Sportswear from microfibers functions particularly well. It is breathable and at the same time provides reliable protection against wind and rain. Fashionable apparels in microfibers have graceful flow, silk-like feel and are extremely comfortable. Microfiber clothing is not sensitive, retaining its positive qualities after washing or cleaning.

Comparison of microfiber with other textile fiber

General Properties of Microfibers 

1. Ultra-fine linear density (less than 0.1 dtex/f), finer than the most delicate silk.
2. Extremely drapeable & Durability.
3. Very soft, luxurious hand with a silken or suede touch.
4. Washable and dry-cleanable.
5. Shrink resistance.
6. High strength, although the filaments are super fine.
7. Insulates well against wind, rain and cold.
8. Anti-microbial agents help to protect both family members and work staff from the dangers of the bacteria that cause odor and mildew.
9. Microfibre is hypoallergenic, and so does not create problems for those suffering from allergies.
10. Microfibre is non-electrostatic.
11. Microfibres are super-absorbent, absorbing over 7 times their weight in water.
12. Microfiber dries in one-third of the time of ordinary fibres.
13. Microfibres are environmentally friendly
14. Improved breathability
15. Vivid prints with more clarity and sharper contrast
16. Appearance retention
17. Can be made windproof and water resistant
18. The greater fiber surface area also results in higher rates of dyeing at lower temperatures, and decreased fastness to light, crocking (fastness to rubbing), water & ozone. 

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Posted in: Manmade Fiber,Microfiber,Spinning

Milk or Casein Fiber | Manufacturing Process of Milk Fiber | Application of Milk Fiber

Milk Fiber:Milk fiber is a blend of casein protein and the chemical acrylonitrile, which is used to make acrylic. It’s made using a process that is similar to rayon/viscose, but because it’s a regenerated protein fiber and not a regenerated cellulose fiber, it reacts like wool. That means that it dyes like wool and even smells like wool when burned, according to Kiplinger. 

Milk fiber

Characteristics of Milk Fiber:

1. In milk fibre,the natural protein humectant factor is present,which makes the skin delicate and smooth...
2. It absorbs moisture very well as it is hygroscopic in nature.
3. It is antibacterial and antifungal as amino acids present in the fibre.
4. It is glossy and luxurious in appearance,feel and comfortability, just like silk..
5. It is very easy to dye and can be dyed under normal temperature.














































6. It can be blended well with other different fiares,such as tencel,cotton,bamboo,modal fibre.

History of Casein or Milk Fiber: 
According to Euroflax Industries, milk fiber was invented in 1930’s in both Italy and America and was called “milk casein.” Huh. Who knew? And here I thought it was some newfangled invention. But apparently it’s been around for a while. Whoa. For a longwhile! Crazily enough, casein was inventedway before the 1930s – apparently they’ve discovered that many churches from the 14th and 15th centuries were painted with casein-based paints – the colors are still bright and unfaded even to this day! Well, apparently this milk casein stuff is great for paint. But how does that connect with milk fiber?

Apparently “milk casein” fiber was used in many clothing and household items in America and Europe during the 1930s and ’40s, says Joan Kiplinger of Fabrics.net. It was substitute for wool, which was needed by men on the front lines. However, it fell out of use after WWII ended and newer, cheaper synthetics such as nylon grew in popularity. The fiber was blended with other natural fibers and known under the brand names of Aralac, Lanatil and Merinova, for those of you checking your vintage clothing labels. While these brands’ fabrics were very similar to wool and could be dyed by the same processes, apparently there were some flaws with the milk casein fiber – namely, that it was not as strong and firm, nor as elastic as wool, and the fibers mildewed easily when they got damp.

Production Process of Milk Fiber: 
Milk protein fiber production line application processing system can not do without the cooperation of the link. Shanghai is home on R & D Technology Co., Ltd. milk silk protein fibers, also engaged in spinning, dyeing and finishing of technical research, raw material quality, technology is complete, customers can better support the promotion of milk fiber.

Milk protein fiber can be used, in theory, cationic dyes, direct dyes, acid dyes, reactive dyes, neutral dyes, generally more than the actual cationic dye and reactive dye used is suitable for pure milk protein fiber and its products, such as staple fiber, yarn line, knitted fabrics, woven fabrics and garments. Period in order to milk protein fiber textiles as an example of pure cationic dyes and reactive dyes on the usage described as follows.

Flow chart of milk fiber

After Treatment of Milk Fiber: 
Cationic dyes and finishing the first treatment process, due to temperature and moisture absorption of the products are strong, so do not need special treatment. With 60 ?water, liquid running back 10s, and then the second can of cold wash. In the special white process, the use of prescription and bleaching conditions were as follows: 5% sodium hydrosulfite (95 ?with warm water even after accession); 5% of the standard soap powder (use warm water even after the accession), not alkaline , does not contain brighteners; bath ratio 1:20 ~ 30; temperature of 95 ~ 98 ? time is about 15s ~ 30s, but also according to liquor ratio, equipment and raw materials of different thickness to adjust. Note that, if so special white, raw materials without cooling; If the training is finished, then white, must be 2% to 3% of the HAC, 60 ?water running 5s ~ 10s, cold washed twice, and then softening. Prescription and use of the whitening process conditions: 1.6% cationic brighteners (Dilute with warm water even after accession); 3% HAC (Dilute with warm water even after accession); temperature of 95 ~ 98 ? time of 15s ~ 20s ; bath ratio 1:25 ~ 30. In the dyeing process, the basic cationic dye with the general approach, but not 1227, and NaAc. To liquor ratio 1:25 to 30, for example, dyeing conditions to control the following table. Cleaning, light to be 1 or 2 times the cold wash, cold wash in the dark to be 1 or 2 times and then wash with hot water, 70 ?10s, and finally cold wash 1 or 2 times. In the post-treatment processes, the use of softener 5% to 8%; temperature 45 ~ 50 ? time of 20s or so; bath ratio 1:20 ~ 25.

According to different requirements of customers can choose different softeners, such as the fabric soft, smooth, elastic anti-wrinkle, anti-contamination, etc. when requested, by the production units to decide. In the dehydration process, in order to reduce the discount video, dehydration, slower, time is shorter, usually 1 minute each time, while patients have to row together, try not to let cloth folded. In the drying process, the use of the cage drying temperature of 80 ? 5 ? time is 20s ~ 30s, speed too quickly, after drying grounds lit 12 to 24 hours after the stereotypes. Using rotary drying temperature of 90 ? 5 ? fast speed, the disadvantage is the easy bit like a very light, must be strictly controlled temperature.

In the setting process, the general shape of water rolling open sites, the effect is better than the cylindrical shape. Process parameters are 150 ? 5% overfeed of 10%, the line speed 15m / s, the pressure head of about 4kg. Reactive dyeing of basic aspects of pre-treatment with the former, but if the dye houses using recycled water, pH value may be unstable or reactive groups dealing with different materials, can be the first treatment bath by adding 1% of the HAC, it will give the pH value of the cloth evenly from the inside out, but also conducive to color dyes.

Proven, low temperature dyeing cotton used reactive dyes more suitable, light-colored soda instead of baking soda can be used as dyeing auxiliaries, the amount can be as long as required to achieve the color, the dark can be used for dyeing auxiliary sodium sulfate and soda ash , the amount of cotton fiber dyed with similar.

Uses of Milk or Casein Fiber: 
Because of the healthy & bacteriostatic nature of milk Fiber, it is being considered as a perfect material for manufacturing of underwear. As discussed above, milk casein proteins are considered as a main ingredient of milk protein Fiber, which can lubricate the skin. The milk protein contains the natural humectant factor which can help to maintain the skin moisture, to reduce the wrinkles & to smoothen the skin - which may help to realize the people of taking milk bath.

The major usages of milk Fiber are as given below: 

1. T-Shirts
2. Underwear
3. Sportswear
4. Ladies outerwear
5. Sweaters

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Posted in: Manmade Fiber,Milk Fiber,Spinning

Introduction of Glass Fiber | Types of Glass Fiber | Properties of Glass Fiber | Manufacturing Processes of Glass Fiber | Uses of Glass Fiber or Glass Yarn

Glass fiber

Glass fiber also called fiberglass. It is material made from extremely fine fibers of glass Fiberglass is a lightweight, extremely strong, and robust material. Although strength properties are somewhat lower than carbon fiber and it is less stiff, the material is typically far less brittle, and the raw materials are much less expensive. Its bulk strength and weight properties are also very favorable when compared to metals, and it can be easily formed using molding processes. Glass is the oldest, and most familiar, performance fiber. Fibers have been manufactured from glass since the 1930s.

Types of Glass Fiber 
As to the raw material glass used to make glass fibres or nonwovens of glass fibres, the following classification is known:

1. A-glass: With regard to its composition, it is close to window glass. In the Federal Republic of Germany it is mainly used in the manufacture of process equipment.

2. C-glass: This kind of glass shows better resistance to chemical impact.

3. E-glass: This kind of glass combines the characteristics of C-glass with very good insulation to electricity.

4. AE-glass: Alkali resistant glass.

Generally, glass consists of quartz sand, soda, sodium sulphate, potash, feldspar and a number of refining and dying additives. The characteristics, with them the classification of the glass fibres to be made, are defined by the combination of raw materials and their proportions. Textile glass fibres mostly show a circular

Properties of Glass Fiber
Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(mK).

The strength of glass is usually tested and reported for "virgin" or pristine fibers those which have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber. Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks. There is a correlation between bending diameter of the filament and the filament diameter. The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

Glass Fiber Manufacturing Processes
After the initial process of melting glass and passing it through spinnerets, continuous filaments or staple fibers of glass are manufactured by two different methods.

Continuous Filament Process
In this process, continuous filaments of indefinite length is produced. The molten glass passes through spinnerets having hundreds of small openings. These strands of multiple filaments are carried to winder revolving at very high speed of more than 2 miles per km. This process draws out the fibers in parallel filaments of the diameter of the openings. A sizing or a binder is applied to facilitate the twisting and winding process and to prevent breakage during yarn formation. After winding, filaments are further twisted and plied to make yarns by methods similar to those for making other continuous filament yarns. The sizing is removed through volatizing in an oven. These yarns are used for making such items as curtains and drapes.

Staple Fiber Process
Fibers with long-staple qualities are manufactured through staple fiber process. There are many methods for producing such fibers.

In one of such methods, the molten glass flows through the small holes of bushing, where jets of compressed air shake the thin streams of molten glass into fine fibers. These fibers vary in length ranging from 8 to 15 inches. The fibers fall through a spray of lubricant and a drying flame onto e revolving drum where they form into a thin web. These fibers in the form of web are gathered from the drum into a sliver. Yarn is then made from this sliver by similar methods that are adopted for making cotton or wool yarns. These yarns are used for fabrics for industrial purposes where insulation is required.

In yet another method, the ends of the glass rods are melted from which drops of glass fall away drawing off glass filaments after them onto a speedily revolving cylinder where they are wound parallel to each other. A web of sliver is formed if the cylinder moves sideways. Sometimes, the staple may be thrown off the cylinder onto a stationary sieve where it forms a sliver. In either conditions, the sliver is then converted into spun yarn.

The staple fiber, if subjected to oven, is compressed to the desired thickness and the binder which was earlier applied, is cured. This permanently binds the fibers.

Production:
The subsequent manufacture of glass fibres may be executed to the direct melting process. However, in most cases glass rods or balls are made first which then may undergo a variety of further processes.

Nozzle-Drawing:
As can be seen in Fig. 1-50, the glass fed in is melted in a heated melt tub at 1250–1400oC. Then, it emerges at the bottom of the melt tub from nozzle holes of 1–25 mm diameter and it is taken off and drawn. The filaments solidify and are finished and wound. One can find them in the shops as various kinds of “glass silk”. To make them into webs, the filaments are cut to length (mostly, between 6 and 25 mm).

Manufacture of glass melt

Processes to make glass fibres

Nozzle-Blowing: 
The same as with nozzle-drawing, glass balls are melted in the tub. The melt emerging from the nozzle holes is then taken by pressed air, which draws the liquid glass so as to make fibres of 6–10 um diameter. A fluttering effect is caused by the flow of pressed air, which results in fibres of lengths from 50 to 300 mm. A lubricant is put on and the fibres are laid down on a sieve drum which sucks them in. The dry web received is held together by the long fibres, the short ones lying in between them as a filling material. Then, the slivers of glass fibre material are cut.

Rod-Drawing: 
By means of a burner, bundles of glass rods are melted at their bottom ends. This results in drops which, as they fall down, draw filaments after them. The filaments are taken by a rotating drum, a squeegee laying them down onto a perforated belt. Thus, a dry web is received which can be wound as glass fibre slivers. – Machine performance being limited by the number of glass rods fed in, the rotating drum may be combined with nozzle-drawing, which results in drum-drawing. This multiplies machine performance. The dry web is again laid down onto a perforated belt and solidified or, after winding it so as to receive slivers, cut for further processing on machines producing wetlaid nonwovens. Using and processing glass fibres is not without any problems. For example, fine pieces of broken fibres may disturb if the work place is not well prepared for the purpose. Using the nonwovens to manufacture glass-fibre reinforced plastics, it is important the surface of the plastic material is fully even. Ends of fibre looking out may be pulled out or loosened by outward stress (temperature, gases, liquids), which may influence material characteristics. In some cases, it is
advisable to cover up such layers of glass fibre with suitable chemical fibres.

Uses of Glass Fiber or Glass Yarn
Glass fiber is manufactured in a wide range of fine diameters. Some of them are so fine that they can be seen only through a microscope. This quality of fineness contributes greatly to the flexibility of glass fibers. Various manufacturers produce different types of glass fibers for different end uses. Glass fibers them are used for various purpose.

1. For making home furnishings fabrics;
2. For making apparels and garments; and
3. For the purpose tires and reinforced plastics.

There are certain glass fibers that can resist heat upto 7200oC and can withstand forces having speed of 15,000 miles per hour. These types of glass fibers are used as

1. Filament windings around rocket cases;
2. Nose cones;
3. Exhaust nozzles; and
4. Heat shields for aeronautical equipment

Some other types of glass fibers are embedded into various plastics for strength. These are used in

1. Boat hulls and seats;
2. Fishing rods; and
3. Wall paneling

Some other types of glass fibers are used for reinforcing electrical insulation. Yet other types are used as batting for heat insulation in refrigerators and stoves.

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Posted in: Glass Fiber,Manmade Fiber,Spinning

Carbon Fiber | Characteristics/Properties of Carbon Fibers | Classification of Carbon Fiber | Application/Uses of Carbon Fibers

Carbon Fiber:

Weave of Carbon fiber

Carbon fiber is a high-tensile fiber or whisker made by heating rayon or polyacrylonitrile fibers or petroleum residues to appropriate temperatures. Fibers may be 7 to 8 microns in diameter and are more that 90% carbonized.

This fibers are the stiffest and strongest reinforcing fibers for polymer composites, the most used after glass fibers. Made of pure carbon in form of graphite, they have low density and a negative coefficient of longitudinal thermal expansion.
Carbon fibers are very expensive and can give galvanic corrosion in contact with metals. They are generally used together with epoxy, where high strength and stiffness are required, i.e. race cars, automotive and space applications, sport equipment.

Depending on the orientation of the fiber, the carbon fiber composite can be stronger in a certain direction or equally strong in all directions. A small piece can withstand an impact of many tons and still deform minimally. The complex interwoven nature of the fiber makes it very difficult to break. 

 

Characteristics/Properties of Carbon Fibers 

1. Physical strength, specific toughness, light weight.
2. Good vibration damping, strength, and toughness.
3. High dimensional stability, low coefficient of thermal expansion, and low abrasion.
4. Electrical conductivity.
5. Biological inertness and x-ray permeability.
6. Fatigue resistance, self-lubrication, high damping.
7. Electromagnetic properties.
8. Chemical inertness, high corrosion resistance.

Classification of Carbon Fiber:
Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories:

1. Based on carbon fiber properties,
2. Based on precursor fiber materials, 
3. Based on final heat treatment temperature,

1. Based on carbon fiber properties, carbon fibers can be grouped into:

• Ultra-high-modulus, type UHM (modulus >450Gpa)
• High-modulus, type HM (modulus between 350-450Gpa)
• Intermediate-modulus, type IM (modulus between 200-350Gpa)
• Low modulus and high-tensile, type HT (modulus < 100Gpa, tensile strength > 3.0Gpa)
• Super high-tensile, type SHT (tensile strength > 4.5Gpa)

2. Based on precursor fiber materials, carbon fibers are classified into:

• PAN-based carbon fibers
• Pitch-based carbon fibers
• Mesophase pitch-based carbon fibers
• Isotropic pitch-based carbon fibers
• Rayon-based carbon fibers
• Gas-phase-grown carbon fibers

3. Based on final heat treatment temperature, carbon fibers are classified into:  

• High-heat-treatment carbon fibers (HTT), where final heat treatment temperature should be above 2000°C and can be associated with high-modulus type fiber. 
• Intermediate-heat-treatment carbon fibers (IHT), where final heat treatment temperature should be around or above 1500°C and can be associated with high-strength type fiber.  
• Low-heat-treatment carbon fibers, where final heat treatment temperatures not greater than 1000°C. These are low modulus and low strength materials.

Application/Uses of Carbon Fiber
The two main applications of carbon fibers are in specialized technology, which includes aerospace and nuclear engineering, and in general engineering and transportation, which includes engineering components such as bearings, gears, cams, fan blades and automobile bodies. Recently, some new applications of carbon fibers have been found. Such as rehabilitation of a bridge in building and construction industry. Others include: decoration in automotive, marine, general aviation interiors, general entertainment and musical instruments and after-market transportation products. Conductivity in electronics technology provides additional new application.

Application Carbon Fiber are given as Shortly:

• Aerospace, road and marine transport, sporting goods.
• Missiles, aircraft brakes, aerospace antenna and support structure, large telescopes, optical benches, waveguides for stable high-frequency (GHz) precision measurement frames.
• Audio equipment, loudspeakers for Hi-fi equipment, pickup arms, robot arms.
• Automobile hoods, novel tooling, casings and bases for electronic equipments, EMI and RF shielding, brushes.
• Medical applications in prostheses, surgery and x-ray equipment, implants, tendon/ligament repair.
• Textile machinery, genera engineering.
• Chemical industry; nuclear field; valves, seals, and pump components in process plants.
• Large generator retaining rings, radiological equipment.

Carbon fibre is sometimes used in conjunction with fiberglass because of their similar manufacturing processes, an example of this would be the Corvette ZO6 where the front end is carbon fibre and the rear is fibreglass. Carbon fiber is however, far stronger and lighter than fiberglass.

Carbon fibre can be found in a wide range of performance vehicles including sports cars, superbikes, pedal bikes (where they are used to make frames), powerboats and it is often used in the tuning and customising industry where attractive woven panels are left unpainted to 'show off' the material. 

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Posted in: Carbon Fiber,Manmade Fiber,Spinning

Introduction of Acrylic Fibers | Properties of Acrylic Fiber | Production Process of Acrylic Fiber | Uses of Acrylic Fiber

A manufactured fiber in which the fiber-forming substance is any long chain synthetic polymer composed of at least 85% by weight of acrylonitrile units [-CH2-CH(CN)-] (FTC definition). Acrylic fibers are produced by two basic methods of spinning (extrusion), dry and wet. In the dry spinning method, material to be spun is dissolved is a solvent. After extrusion through the spinneret, the solvent is evaporated, producing continuous filaments which later may be cut into staple, if desired. In wet spinning, the spinning solution is extruded into a
liquid coagulating bath to form filaments, which are drawn, dried, and processed.

Acrylic fibers are synthetic fibers made from a polymer (polyacrylonitrile) with an average molecular weight of ~100,000, about 1900 monomer units. To be called acrylic in the U.S, the polymer must contain at least 85% acrylonitrile monomer. Typical comonomers are vinyl acetate or methyl acrylate. The Dupont Corporation created the first acrylic fibers in 1941 and trademarked them under the name "Orlon".

Raw Material 
Acrilonitrile is the main main raw material for the manufacture of acrylic fibres. It is made by different methods. In one commercial method, hydrogen cyanide is treated with acetylene:
1st Method

Acetylene + Hydrogen cyanide --> Acrilonitrile

2nd Method
Ethylene--Air Oxidation--> Ethylene oxide + HCN--> Ethylene cyanahydrin--Dehydration at 300 deg C (catalyst)--> Acrylonitrile

Production Process of Acrylic Fiber
The acrylic process is a "one step technology", with the following main characteristics:

1. polymerization in solution
2. direct feeding of the dope to spinning
3. wet spinning
4. DMF as solvent for both polymerization and spinning

Production Process of Acrylic Fiber

In a continuous polymerisation process, 95% acrylonitrile and 6% methyl acrylate (400 parts) 0.25% aqueous solution of K2S2O8(600 parts), 0.50 % Na2S2O5 solution ( 600 Parts) and 2N sulphuric acid (2.5 Parts) are fed into the reaction vessel at 52 deg C under nitrogen atmosphere giving a slurry with 67% polymer. The slurry is continuously withdrawn, filtered and washed till it is free from salts and dried.

Acrilonitrile is dry spun. The material is dissolved in dimethyl formamide, the solution contains 10-20 polymers. It is heated and extruded into a heated spinning cell. A heated evaporating medium such as air, nitrogen or steam moves counter current to the travel of filaments and removes the solvent to take it to a recovery unit. The filaments are hot stretched at 100 to 250 C depending on the time of contact in the hot zone, to several times their original length.

Properties of Acrylic Fibers

1. Acrylic has a warm and dry hand like wool. Its density is 1.17 g/cc as compared to 1.32 g/cc of wool. It is about 30% bulkier than wool. It has about 20% greater insulating power than wool.

2. Acrylic has a moisture regain of 1.5-2% at 65% RH and 70 deg F.

3. It has a tenacity of 5 gpd in dry state and 4-8 gpd in wet state.

4. Breaking elongation is 15% ( both states)

5. It has a elastic recovery of 85% after 4% extension when the load is released immediately.

6. It has a good thermal stability. When exposed to temperatures above 175 deg C for prolonged periods some discolouration takes place.

7. Acrylic shrinks by about 1.5% when treated with boiling water for 30 min. 

8. It has a good resistance to mineral acids. The resistance to weak alkalies is fairly good, while hot strong alkalies rapidly attack acrylic.

9. Moths, Mildew and insects do not attack Acrylic.

10. It has an outstanding stability towards commonly bleaching agents.

Uses of Acrylic Fiber

1. Knit Jersey, Sweater, blankets

2. Wrinkle resistant fabrics.

3. Pile and Fleece fabrics

4. Carpets and rugs.

Precaution of Acrylic Fiber 

• Wash delicate items by hand in warm water. Static electricity may be reduced by using a fabric softener in every third or fourth washing. Gently squeeze out water, smooth or shake out garment and let dry on a non-rust hanger. (Sweaters, however, should be dried flat.) 
• When machine washing, use warm water and add a fabric softener during the final rinse cycle. 
• Machine dry at a low temperature setting. Remove garments from dryer as soon as tumbling cycle is completed. 
• If ironing is required, use a moderately warm iron. (For specific instructions, refer to garment's sewn-in care label.)

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Posted in: Acrylic,Manmade Fiber,Spinning

Preparation, Properties and Applications of Nylon 6,6 Fibers

ABSTRACT 

Here in this term paper description is given about a type of polyamide fibre i.e. Nylon-66. Here in this paper the methods of preparation of monomers, polymerisation, manufacturing methods of nylon-66, spinning process to obtain fibres, different properties and wide range of applications and uses of nylon-66 are discussed. In this paper data are represented in the form of flow charts, histogram and pie charts for easy understandings. This paper covers all the processes related to nylon-66.

1. Introduction 
There are several polyamides, which have been developed as fibres. The generic word for these products is 'Nylon'. Nylon is defined as a generic term for any long chain synthetic polymeric amide which has recurring amide groups as an integral part of the main polymer chain and which is capable of being formed into a filament in which the structural elements are oriented in the direction of the axis.

DuPont researchers led by Dr. Wallace Carothers, invented nylon-66 polymer in the 1930s. Nylon, the generic name for a group of synthetic fibers, was the first of the “miracle” yarns made entirely from chemical ingredients through the process of polymerization. Nylon 66 polymer chip can be extruded through spinnerets into fiber filaments or molded and formed into a variety of finished engineered structures.Nylon-66 fibre is a member of the large group of polycondensation products of dicarboxylic acids and diamines with fibre forming properties. The individual member refers to the number of carbon atoms respectively in the diamine and dicarboxylic acid chains.

Nylon-66 (polyhexamethylene diamine adipamide) is a polyamide made from adipic acid and hexamethylenediamine by polycondensation. The resulting polymer is extruded into a wide range of fiber types. The fibers are drawn, or stretched, in a process that increases their length and reorients the material’s molecules parallel to one another to produce a strong, elastic filament. The thermo-plasticity of nylon permits permanent crimping or texturing of the fibers and provides bulk and stretch properties.

The nylon developed by Carothers at Du Pont was nylon 66. Because of the importance of starting out with equal amounts of the two reactants, salts of the diamine and of the diacid are made and then used in the commercial synthesis of nylon 66.

2. HISTORY 
The development of nylon was started from 1927 by means of many researchers, notably among them W.H.Carothers and P.Schlack. The research activities preceding the manufacture of nylon yarn can be divided into the following categories:

(a) Fundamental research activities which provided the foundation for the development.

(b) Different types of polyamides, their synthesis, manufacture and their suitability for use as a new fibre. This includes all types of polyamides like aliphatic, aliphatic-aromatic and fully aromatic polyamides.

(c) Commercial production of the fibres.

(d) Development of the properties and serviceability of the fibres.

Polyamides are characterized according to the number of carbon atoms present in the structural unit of the molecule. These are:

(a) Nylon made from condensation of a diamine and a dicarboxylic acid is classified according to the number of carbon atoms present in the amine and acid respectively. Thus nylon formed by hexamethylene diamine (NH2 (CH2)6-NH2) having 6 carbon atoms and sebacic acid (COOH-(CH2)8-COOH) having 10 carbon atoms is generally referred to as nylon 6,10

(b) Nylon, made from amino acid, is classified according to the number of carbon atoms present in the acid. It will have only one number. For example, Nylon 6 can be made from amino acid having 6 carbon atoms i.e., amino caproic acid or its condense product caprolactum.

So the numbers indicate the number of carbon atoms in the monomer taking part in the polymerisation. In general,

Table 12.1 Raw materials of different Nylons 

Nylon	Raw materials
Nylon 4,6    Nylon 6,6   Nylon 6, 1 0   Nylon 6,12     Nylon 3    Nylon 4    Nylon 6   Nylon 7   Nylon 11    Nylon 12	1 ,4 diamino butane, Adipic acid Hexamethylene diamine, Adipic acid              Hexamethylene diamine, Sebacic acidHexamethylenediamine, Dodecanedioic acid Acrylamide 2-pyrolidane Caprolactum  Lactum of heptonoic acid  W-amino-cendecanoic acid  Dodelactum

3. The Nylon Fiber Design Advantage 
In 1939, the introduction of nylon into sheer stockings revolutionized the women’s hosiery market. Silk and cotton were quickly replaced by this more durable and easy-care product. Nylon soon found its way into other end uses. In parachutes and fishing line, nylon provided a moisture- and mildew-resistant replacement for silk. In flak vests, nylon offered a strength and durability previously unattainable for protection against shell fragments. And, when used as aircraft tire reinforcement, nylon enabled heavy bombers to land safely on improvised air strips. Today, as the global leader in nylon polymer, DuPont offers a wide range of nylon-66 polymer types for use in industrial, textile, and furnishing/floor covering applications.

4. Advantages of Nylon-66 
Nylon 66 is superior in many applications to nylon 6—the other large volume nylon—due to its outstanding dimensional stability, higher melting point, and more compact molecular structure (see Figure 1). Nylon 66 exhibits only about half the shrinkage of nylon 6 in steam, for instance. And, with a less open structure, the 66 fiber has good dye wash fastness and UV light-fastness, and excellent performance in high-speed spinning processes. Typical advantages of nylon 66 over nylon 6 are its

• Higher tensile strength in use,
• Excellent abrasion resistance, and
• Higher melting point. 

Nylon 66 provides high tensile strength for

• Tough fibers at fine deniers,
• Excellent performance for tyre applications, and
• High-speed mill processing.

Excellent abrasion resistance makes nylon-66 polymer ideal for use in

• Carpets,
• Upholstery, and
• Conveyor belts.

The rubber industry takes advantage of the higher melting point of nylon 66 in high-temperature tire curing. A high melting point also results in a fiber with

• High stretch and recovery in false-twist textured Yarns (e.g., hosiery and socks) and
• Thermal stability in high-temperature coating operations.

5. Use of Nylon-66 in Fiber Manufacturing 
The processing of nylon usually begins by conditioning the received chip, with or without an increase in the asreceived molecular weight. The chip is then melted, usually in a screw-type extruder, and spun into filament form. The filamentsare then packaged in a process that may include drawing, bulking, or cutting into lengths of staple.

6. Preparing Nylon-66 Chip 
Chip is normally conditioned in an inert atmosphere at temperatures in the 120–180°C (248–356°F) range. Processors may employ higher temperatures to increase molecular weight, especially for industrial uses. Both batch- and continuous-type conditioners may be used. It is important to avoid excessive exposure of the chip to oxygen, which may lead to degradation and yellowing of the product.

7. Remelting Nylon 66 Chip 
Remelting is normally performed in a single or twin screw-type extruder, although the melting can be done in a heated grid-type melter. Single screws are preferred for smaller spinning plants because of their simplicity. Twin screws are preferred for larger installations or when more extensive mixing during remelt is required. Equipment must have the capability of heating the polymer to 280–290°C (536–554°F). Handling of the Molten Polymer Nylon 66 may produce undesirable cross-linked material (gel) if processing temperatures and holdup times are not properly maintained. Care must be taken to eliminate areas of stagnation in the screw and in the polymer piping. Good engineering practices require the application of optimum shear rates and frequent mixing of the melt. Conversion—Molten Polymer to Final Product Form Due to the wide variety of nylon 66 products that can be produced and the range of processing equipment available, it is beyond the scope of this bulletin to specify ideal processing conditions. In general, most modern filament-producing equipment will process nylon 66 polymer adequately.

8. PREPARATION of the Monomer 
Adipic Acid (ADA) and Hexamethylene diamine (HMD) are used as raw materials for Nylon-66 Polymer. The schemes of preparation of adipic acid and hexamethylene diamine are shown in Figure.

8.1. ADIPIC ACID MANUFACTURE 

8.1.1 FROM CYCLOHEXANOL 
Mostly cyclohexane (CH), cyclohexanol (CHL) and cyclohexanone (CNH) are used to obtain adipic acid (ADA). For oxidation, only nitric acid and oxygen can be used economically. The most important process is the oxidation of cyclohexanol with 50% nitric acid at 60-70°C. In a stainless steel kettle the cyclohexanol is added to the acid under cooling and stirring, the acid is crystallized from water. The yield exceeds 85%.

8.1.2. From Cyclohexanone 
The oxidation of cyclohexanone with nitric acid requires higher temperatures. Also cyclohexanone is oxidized in the presence of acetic acid as diluent and with 0.1% manganese acetate or nitrate at 80-1.00°C. The yield is about 70%.

8.1.3 From Cyclohexane 
The simplest method for the production of adipic acid is direct oxidation of cyclohexane. Most useful is the catalytic oxidation with air by soluble Mn or Co catalysts at 120-150°C. The reaction is interrupted at a conversion of 10-15% and leads away to a mixture of cyclohexanol and cyclohexanone in equal amounts with adipic acid, cyclohexanol adipate, and lower aliphatic acids. The unchanged product is recycled and the crude oxidation product fractionated. Since cyclohexane is an important petrochemical product, production of cyclohexanol and cyclohexanone is based on this process.

8.2. ADIPONITRILE Manufacture 
Adiponitrile is the intermediate for the production of hexamethylene diamine. It can be produced by different methods:

8.2.1. VAPOUR PHASE FROM ADIPIC ACID AND AMMONIA

This method involves condensation from ammonia and adipic acid in the vapor phase. Adipic acid is vaporized with an excess of ammonia gas (mol. ratio 20:1) at 350°C over a catalyst of boron phosphate. The reaction is endothermic at 57 cal/mole. The yield is 88%.

8.2.2. Liquid Phase Process 
In a liquid phase process, ammonia is introduced in molten adipic acid at 200-250 in the presence of such alkyl or alkyl phosphates catalysts like 0.1 -0.5% phosphonic acid or boron phosphate. The yield is around 88%.

8.3. 1, 4 DlCHLOROBUTANE AND SODIUM CYANIDE 
1, 4 Dichlorobutane can be obtained by addition of chlorine to butadiene. This can be converted to 1, 4 dicyanobutane by NaCN. Dry NaCN is mixed with adiponitrile as diluent and the calculated amount of 1, 4 dichlorobutane is added at 185-190°C. By addition of water, the oily layer is distilled. The yield is about 95%.

8.4. ELECTROHYDRO DIMERISATION OF ACRYLONITRILE

By electrohydro dimerisation, yield will be 82%. The pH will be 9 and the current density will be 2 to 30 MA/dm2. The cathode potential was found to be independent of pH above 2.5. The overall reaction will be

2 CH2 CHCN + 2 H+ + 2e- → NC (CH2)4CN

8.5. Hexamethylene Diamine - Manufacture 
HMD is manufactured exclusively by the hydrogenation of the dinitriles. Palladium is used as catalyst. Another effective catalyst is cobalt oxide mixed with calcium oxide. In all cases, the reaction must be carried out in the presence of excess ammonia. Pure HMD is a colourless crystal, melting at 40°C, B.P. 100°C, soluble in water, and alcohol.

9. POLYMERISATION 
Nylon-66 production from adipic acid and hexamethylene diamine comprises four steps: (1) Salt preparation (2) Polycondensation (3) Melting. (4) Extrusion. A schematic diagram of Nylon 66 polymer formation process is shown in Figure.

10. Nylon 66 Salt (NH salt) 
High molecular weight nylon 66 is only obtained if equimolecular amounts of the components are used. An excess of the components would terminate the chain by formation of an acid or amino end group. So stoichiometric portions of hexamethylene diamine and adipic acid must be used (amine to acid of 1:1). For this reason, the salt of 1 mole adipic acid and hexamethylene diamine (AH salt) is used as intermediate. The hexamethylene diamine is used as a 60-70% solution and the adipic acid as a 20% solution. The monomers are fed and mixed in the mixer and transferred to the prepolymeriser. Methanol is added and the reaction takes place. Methanol can be refluxed. The separated salt is centrifuged and washed with methanol. It is stored as a 60% solution in distilled water. It is a snow white crystal (mp - 190°C). Owing to all these constraints, batch processing is used.

11. POLYCONDENSATION 
The concentrated salt solution is then fed to the polymerisation reactor, where the second-stage of the reaction begins (Fig 12.5 c). 60% Aq. Solution of the salt in distilled water, 0.5% acetic acid (stabilizer) is pumped into an autoclave. Increased temperature and pressure are used to initiate the polymerisation reaction. So the autoclave is heated to 275°C. The pressure is generally kept constant (1.8 MPa). Before the reaction, the autoclave is purged with very pure nitrogen (less than 0.005% oxygen) to avoid degradation and discoloration of the polymer. When the temperature of the batch reaches 275°C, the pressure is allowed to fall to atmospheric pressure. The batch is held at 270°C and atmospheric pressure for half an hour to allow removal of the water vapor. The heating is continued until all water has been distilled off. Towards the end of the distillation, the autoclave is evacuated. The polymer is obtained as a clear, low-viscous melt which is removed from the autoclave by pressure with pure nitrogen. The melt is extruded through the bottom of the reactor to form a ribbon. It is solidified and cooled in cold water cut into chips and dried. The dried chips are stored in a storage hopper in a similar manner like that of Nylon 6.

12. SPINNING 
Nylon has sufficient stability of the melt and adequate viscosity. So it can be spun in the molten state with usual velocity (upto 2000 m/min). The polymer chips are fed to the hopper and then it is melted and homogenized in an extruder. The molten polymer after filtration is passed to the spinnerets. The melt is pumped through this system and solidifies immediately on contact with air. Cross air flow is used for solidification. The melting temperature for spinning is around 300°C. After spinning like nylon 6, the flows are stretched to get the desired elongation. Details of spinning and stretching processes are discussed in Chapter - 2 (Fig 2.1 and 2.6). The different parameters which can be varied to influence fibre properties are: (a) Mass output, (b) Winding speed, (c) Spin draw ratio, (d) Draw ratio and (e) Draw temperature. The properties which will be considered are: tensile strength, elongation, modulus, crystallinity and orientation.

13. PROPERTIES 

13.1. PHYSICAL PROPERTIES 
Like Nylon 6, different types of Nylon 66 fibre exhibit different physical properties.

Physical Properties	Staple Fibre	Normal Filament	High Tenacity Filament
Density (gm/cc)	1.13	1.14	1.15
Moisture (%) at   65% rh 100% rh	4.0-4.5 6.0-8.0	4.0-4.5 6.0-8.0	4.0-4.5 6.0-8.0
Tenacity (g/d)      Dry Wet	3.0-6.8 2.5-6.1	2.3-6.0 2.0-5.5	6.0-10.0 5.1-8.0
Elongation (%)	16-75	25-65	15-28
Stiffness (g/d)	10-45	5-24	21-58

13.2. Thermal Properties 
Because of different structure, the melting point will occur in the range of 249°C to 260°C. The glass transition temperature of this fibre is in the range of 29°C- 42°C. The softening temperature i.e., the sticking temperature is 230°C. The fibre discolors, when kept at 150°C for 5 hours. The heat deflection temperature is 70°C. The decomposition of this fibre starts at 350°C.

13.3. Chemical Properties 
Nylon 6, 6 fibres is more resistant to acids or alkalis in comparison with nylon 6 fibre because of light intermolecular forces present in the structure. The fibre is unaffected by most mineral acids, except hot mineral acids. The fibre dissolves with partial decomposition in concentrated solutions of hydrochloric acid, sulphuric acid and nitric acid. The fibre is soluble in formic acid. In a similar way, the fibre is attacked by strong alkalies under extreme conditions otherwise it is inert to alkalis. The fibre can be bleached by most of the bleaching agents. The fibre is mostly insoluble in all organic solvents except some phenolic compounds.

The fibre has excellent resistance to biological attacks. Prolonged exposure to sunlight causes fibre degradation and loss in strength.

The fibre can be dyed by almost all type of dyestuffs like direct, acid, metal-complex, chrome, reactive, disperse and pigments. However only acid and metal complex dyes are preferred because of higher fastness properties.

14. Types of Nylon-66 products Manufactured 

1. Nylon 66/6
2. Nylon 66/6, 10% Glass Fiber Reinforced
3. Nylon 66/6, 20% Glass Fiber Reinforced
4. Nylon 66/6, 30% Glass Fiber Reinforced
5. Nylon 66/6, 40% Glass Fiber Reinforced
6. Nylon 66/6, Mineral Reinforced
7. Nylon 66/6, 60% Glass Fiber Reinforced
8. Nylon 66/Nylon 6 Blend, Glass Fiber Filled
9. Nylon 66, Unreinforced
10. Nylon 66, Impact Grade
11. Nylon 66, Unreinforced, Flame Retardant
12. Nylon 66, Heat Stabilized
13. Nylon 66, Extruded
14. Nylon 66, Film
15. Nylon 66, Nucleated
16. Nylon 66, PTFE Filled
17. Nylon 66, MoS2 Filled
18. Nylon 66, Glass Bead Filled
19. Nylon 66, 30% glass filled, extruded
20. Nylon 66, Mineral Filled, NCG Fiber Filled

15. Advantages of DuPont Nylon 66 in Specific Fiber Applications

When processed into fiber form, nylon 66 polymer offers many advantages for customer applications.

Hosiery 

• Excellent high-speed processing
• High stretch and recovery
• High durability and strength
• Good hand

Weaving and Warp Knitting 

• High fiber modulus

           – minimizes yarn distortion possible during winding, warping, knitting, and weaving processes

           – minimizes barré and streaks during dyeing

• Wide operating window for heat setting, dyeing, and processing, this is especially important for fabric combinations with spandex
• Very good resistance to photo degradation
• Good dye light-fastness
• Good dye wet-fastness

Tires and Conveyor Belts 
Heavy-duty tires and belts reinforced with nylon 66 polymer are capable of withstanding high temperatures and fast curing cycles. The superior performance is due to the high strength and modulus of nylon 66. Woven and modified nylon 66 tire cord provides aircraft and off-road vehicle tires with long life and high fatigue resistance. Nylon 66 has particular advantages in industrial products as a result of the polyamide’s

• High melting point,
• Superior dimensional stability, and
• Reduced moisture sensitivity.

Coated Fabrics 
Nylon 66 fabrics withstand coating temperatures with PU, PVC, and rubber up to 200°C (392°F) and display good dimensional stability for coating integrity.

Carpeting 
During the late 1950s, two new developments opened up a new era for the carpet industry. First, equipment was developed to tuft carpet yarn into a backing material to produce pile carpeting. At the same time, DuPont invented a technique to impart bulk or “loft” to nylon by a fluid-texturing process called Bulk Continuous Filament (BCF). The combination of nylon 66 yarns, textured by the BCF process, yields carpets with

• High abrasion resistance,
• High resistance to pile crushing and Matting,
• Ease of level dyeing,
• High dye light-fastness, and
• High dye wet/wash-fastness.

Carpets of nylon now account for nearly 70% in a market that was once the exclusive domain of wool yarns.

Furnishings/Floor Coverings 
Nylon 66 offers the furnishings/floor coverings industry

• A complete line of luster (from 0.0 to 1.0% TiO2),
• Products for direct use and post-polymerization Feed,
• Products intended for color addition during remelt, and
• A full line of dye variant polymers for yarn styling formulations.

Nylon is a material that runs from combs to ship propellers to ladies stockings. The applications can be summarized as follows:

Airbags in automobile

• Textiles: Apparel, tooth brushes, Tyre cord
• Automotive: Bearings, slides, door handles, door & window stops.
• Furniture: Locks, hangers, chairs etc.,
• Packaging: Film sheet
• Mech. Engg.: Drive gears, bearings, fish plates for railways lines tubing.

16. Product Specification Parameters 
Relative Viscosity (RV) 
The degree of polymerization of a polymer is directly proportional to molecular weight and is commonly measured by a solution viscosity technique. Methods of Measurement Common solvents used for viscosity measurements of nylon 66 include both formic and sulfuric acids. The details of these procedures are summarized in Table.

RV is determined by comparing the time required for a specific volume of polymer solution to flow through a capillary tube with the corresponding flow time of the same volume of pure solvent. Results are corrected for moisture content of the sample; alternatively, the sample is dried to a low moisture level.

Values quoted in specifications are those measured in 90% formic acid. Figure.6 shows the typical relationship between RV in 90% formic acid versus 98% sulfuric acid.

Amine End Groups (AEG) 
A major nylon asset is its ability to accept a wide range of dyestuffs. These include both acid and premetallized dyestuffs that associate with the terminal amine groups of the polymer. The concentration of these end groups is an important factor in controlling dye ability (see Figure7).

Analysis Method 
The technique commonly used for measuring AEG involves dissolution of polymer in 68/32 wt% phenol/methanol solvent and potentiometric titration with 0.05 m hydrochloric acid using commercially available equipment. Results are corrected for moisture and titanium dioxide content.

For typical textile grade products, amine end Group concentration is usually within the range of 35–50 and is expressed as gram equivalents/106 g of polymer.

Moisture Content 
Nylon is a relatively hygroscopic polymer. Nylon 66 leaves our production plant with low moisture content (typically <0.3 wt %). However, the product can absorb more moisture (up to8 wt %) depending on the relative humidity (see Figure 8) and length of exposure time (see Figure 9). Customers must take precautions to keep the product free of moisture.

17. CONCLUSION 
After all the research works and information in this term paper we conclude that Nylon 6,6 is a semi-crystalline, off-white engineering thermoplastic that is the strongest and most abrasion resistant unreinforced aliphatic nylon with better low temperature toughness than Nylon 6 or acetal. Its very low melt viscosity can give industrial processing difficulties and weathering can cause embrittlement and color change unless it is stabilized or protected. Available with a wide range of fillers notably glass fibre, which gives a marked increase in stiffness, and solid and liquid (oil) lubricants. Super-tough grades are also available whose impact properties and low notch sensitivity are amongst the best of all engineering thermoplastics.

Applications include mainly engineering components eg gears, bearings, nuts, bolts, rivets and wheels and power tool casings and rocker box covers. Widely used as monofilament for brushes etc and fibre - notable for its resilience and high abrasion resistance - for apparel, carpet and industrial end-uses. 

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Viscose Rayon Manufacturing Process | Manufacturing Process of Viscose Rayon Fiber

1. Introduction 

Rayon is the oldest fibre, is the regenerated cellulose fibre with a wide spectrum properties. Cellulose is to be one of the most useable natural polymers worldwide. It is biodegradable & renewable polymer. The common source for industrial purpose are wood pulp and cotton lint. Highly purified wood pulp consists of 95 – 99% cellulose. It is called ‘chemical cellulose’ & ‘dissolving pulp’. Those chemical cellulose or dissolving pulps are use to manufacture man-made fibres (e.g. viscose rayon, cellulose acetate). 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 having broad Rayon's versatility is the result of the fibre 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 labour involvement. The continuous process is the main method for producing rayon. Three methods of production lead to distinctly different types of rayon fibres, viscose rayon, cuprammonium rayon and saponified cellulose acetate.

Its hygroscopicity and easy dyeability are additional assets. Rayon fibre can be produced with a wide properties particularly mechanical properties.

Method of dissolving cellulose were first discovered in the late 19th century and first fibre were made by dissolving cellulose in cuprammoniumm hydroxide and then forcing the solution through tinny orifice into a bath containing reagent to remove solvent to regenerate cellulose in filament form. Problem associated with lack of stability and considerations of cost competitiveness soon pushed this method into background. With the discovery of the cellulose the cellulosic have been and still are predominantly produced by this process. Due to the strong intermolecular bonds, cellulose does not melt and does not dissolve readily in ordinarily available solvents; chemists have resorted to the derivatization of cellulose to render it soluble and process-able. Specifically, the viscose process was developed. It converted cellulose into sodium cellulose xanthate, which was soluble in a caustic solution, making it possible to wet-spin the polymer into a fibre or film. This technique was accepted worldwide and has prospered. The process, however, consists of multiple steps and causes pollution. As a result, end users have looked for alternate methods of processing cellulose.

2. Different types of rayons

Rayon fibres 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 fibres are briefly described-

a. High wet modulus yarn- These fibres have exceptionally high wet modulus of about 1 g/den and are used as parachute cords and other industrial uses. Fortisan fibres made by Celanese (saponified acetate) has also been used for the same purpose.

b. Polynosic rayon-These fibres 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.

3. Specialty rayons
3.1 Flame retardant fibres- 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 fibre and this property is advantageous over flame retardant cotton fibres where the flame retardant concentrates at the surface of the fibre.

3.2 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 fibres are used in surgical nonwovens. These fibres 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.

3.3 Micro denier fibres- rayon fibres 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.

3.4 Cross section modification- Modification in cross sectional shape of viscose rayon can be used to dramatically change the fibres' aesthetic and technical properties. One such product is Viloft, a flat cross sectional fibre sold in Europe, which gives a unique soft handle, pleasing drape and handle. Another modified cross section fibre called Fibre ML(multi limbed) has a very well defined trilobal shape. Fabrics made of these fibre have considerably enhanced absorbency, bulk, cover and wet rigidity all of which are suitable for usage as nonwovens [10].

3.5 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 fibre. 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.

3.6 Lyocell- A new form of cellulosic fibre, 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 fibre 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.

Uses-Some major uses in apparel like as shirts, blouses, blankets, window treatment dresses, jackets, hats ,socks, bedsheets & industrial uses such as tire cord, non- woven product,& also medical surgery product and other uses as hygiene product ,diapers, towels. Rayon is the major feedstock in the production of carbon fibre.

4. Manufacturing Process of Viscose Rayon Fiber

The process of manufacturing viscose rayon consists of the following steps mentioned, in the order that they are carried out: (1) Steeping, (2) Pressing, (3) Shredding, (4) Aging, (5) Xanthation, (6) Dissolving, (7)Ripening, (8) Filtering, (9) Degassing, (10) Spinning, (11) Drawing, (12) Washing, (13) Cutting. The various steps involved in the process of manufacturing viscose are shown in Fig. and clarified below.

Manufacturing of Viscose Rayon

(1) Steeping: Cellulose pulp is immersed in 17-20% aqueous sodium hydroxide (NaOH) at a temperature in the range of 18 to 25°C in order to swell the cellulose fibres and to convert cellulose to alkali cellulose.

(C6H10O5)n + nNaOH ---> (C6H9O4ONa)n + nH2O

(2) Pressing: The swollen alkali cellulose mass is pressed to a wet weight equivalent of 2.5 to 3.0 times the original pulp weight to obtain an accurate ratio of alkali to cellulose.

(3) Shredding: The pressed alkali cellulose is shredded mechanically to yield finely divided, fluffy particles called "crumbs". This step provides increased surface area of the alkali cellulose, thereby increasing its ability to react in the steps that follow.

(4) Aging: The alkali cellulose is aged under controlled conditions of time and temperature (between 18 and 30° C) in order to depolymerize the cellulose to the desired degree of polymerization. In this step the average molecular weight of the original pulp is reduced by a factor of two to three. Reduction of the cellulose is done to get a viscose solution of right viscosity and cellulose concentration.

(5) Xanthation: In this step the aged alkali cellulose crumbs are placed in vats and are allowed to react with carbon disulphide under controlled temperature (20 to 30°C) to form cellulose xanthate.

(C6H9O4ONa)n + nCS2 ----> (C6H9O4O-SC-SNa)n

Side reactions that occur along with the conversion of alkali cellulose to cellulose xanthate are responsible for the orange colour of the xanthate crumb and also the resulting viscose solution. The orange cellulose xanthate crumb is dissolved in dilute sodium hydroxide at 15 to 20 °C under high-shear mixing conditions to obtain a viscous orange coloured solution called "viscose", which is the basis for the manufacturing process. The viscose solution is then filtered (to get out the insoluble fibre material) and is deaerated.

(6) Dissolving: The yellow crumb is dissolved in aqueous caustic solution. The large xanthate substituents on the cellulose force the chains apart, reducing the inter-chain hydrogen bonds and allowing water molecules to solvate and separate the chains, leading to solution of the otherwise insoluble cellulose. Because of the blocks of un-xanthated cellulose in the crystalline regions, the yellow crumb is not completely soluble at this stage. Because the cellulose xanthate solution (or more accurately, suspension) has a very high viscosity, it has been termed "viscose".

(7) Ripening: The viscose is allowed to stand for a period of time to "ripen". Two important process occur during ripening: Redistribution and loss of xanthate groups. The reversible xanthation reaction allows some of the xanthate groups to revert to cellulosic hydroxyls and free CS2. This free CS2 can then escape or react with other hydroxyl on other portions of the cellulose chain. In this way, the ordered, or crystalline, regions are gradually broken down and more complete solution is achieved. The CS2 that is lost reduces the solubility of the cellulose and facilitates regeneration of the cellulose after it is formed into a filament.

(C6H9O4O-SC-SNa)n + nH2O ---> (C6H10O5)n + nCS2 + nNaOH

(8) Filtering: The viscose is filtered to remove undissolved materials that might disrupt the spinning process or cause defects in the rayon filament.

(9) Degassing: Bubbles of air entrapped in the viscose must be removed prior to extrusion or they would cause voids, or weak spots, in the fine rayon filaments.

(10) Spinning - (Wet Spinning): Production of Viscose Rayon Filament: The viscose solution is metered through a spinnerette into a spin bath containing sulphuric acid (necessary to acidify the sodium cellulose xanthate), sodium sulphate (necessary to impart a high salt content to the bath which is useful in rapid coagulation of viscose), and zinc sulphate (exchange with sodium xanthate to form zinc xanthate, to cross link the cellulose molecules). Once the cellulose xanthate is neutralized and acidified, rapid coagulation of the rayon filaments occurs which is followed by simultaneous stretching and decomposition of cellulose xanthate to regenerated cellulose. Stretching and decomposition are vital for getting the desired tenacity and other properties of rayon. Slow regeneration of cellulose and stretching of rayon will lead to greater areas of crystallinity within the fibre, as is done with high-tenacity rayons.

The dilute sulphuric acid decomposes the xanthate and regenerates cellulose by the process of wet spinning. The outer portion of the xanthate is decomposed in the acid bath, forming a cellulose skin on the fibre. Sodium and zinc sulphates control the rate of decomposition (of cellulose xanthate to cellulose) and fibre formation.

(C6H9O4O-SC-SNa)n + (n/2)H2SO4 --> (C6H10O5)n + nCS2 + (n/2)Na2SO4

Elongation-at-break is seen to decrease with an increase in the degree of crystallinity and orientation of rayon.

In standard viscose of 30-50 poise viscosity made with 32% CS2 is spun into an aqueous acid salt spin bath of the following type at a temperature of 40-50 0c .

• H2SO4-8-10%
• Na2SO4-16-24%
• ZnSO4-1-2%

Spinning speed may be high as 120m/min.

(11) Drawing: The rayon filaments are stretched while the cellulose chains are still relatively mobile. This causes the chains to stretch out and orient along the fibre axis. As the chains become more parallel, inter-chain hydrogen bonds form, giving the filaments the properties necessary for use as textile fibres.

(12) Washing: The freshly regenerated rayon contains many salts and other water soluble impurities which need to be removed. Several different washing techniques may be used.

(13) Cutting: If the rayon is to be used as staple (i.e., discreet lengths of fibre), the group of filaments (termed "tow") is passed through a rotary cutter to provide a fibre which can be processed in much the same way as cotton.

5. Structure of Rayon

Figure 1: Structure of cellulose structure

In regenerated celluloses, the unit cell structure is an allotropic modification of cellulose I, designated as cellulose II (other allotropic modifications are also known as cellulose III and cellulose IV). The structure of cellulose derivatives could be represented by a continuous range of states of local molecular order rather than definite polymorphic forms of cellulose which depend on the conditions by which the fibre is made. Rayon fibre properties will depend on: how cellulose molecules are arranged and held together; the average size and size distribution of the molecules.

1. Cellulose I is shown in native cellulose.
2. Cellulose II has been seen in regenerated cellulose or and mercerized cellulose.
3. Cellulose III is produce when treat with liquid ammonia (NH3) or organic amines (RNH2).
4. Cellulose IV is generate when we treat cellulose with heat and glycerol (CH2(OH)CH(OH)CH2(OH)). 

Many models describe ways in which the cellulose molecules may be arranged to form fibre fine structure. The most popular models of fibre fine structure are the fringed micelle and fringed fibrillar structures. Essentially, they all entail the formation of crystallites or ordered regions.

The skin-core effect is very prominent in rayon fibres. Mass transfer in wet spinning is a slow process (which accounts for the skin-core effect) compared to the heat transfer in melt spinning. The skin contains numerous small crystallites and the core has fewer but larger crystallites. The skin is stronger and less extensible, compared to the core. It also swells less than the core; hence, water retention is lower in the skin than in the core although moisture regain is higher in the skin. This is explained by an increased number of hydroxyl groups available for bonding with water as a result of a larger total surface area of the numerous small crystallites.

Fig. 5: Cellulose structure

When rayon fibres are worked in the wet state,the filament structure can be made to disintegrate into a fibrillar texture. The extent to which this occurs reflects the order that exists in the fibre structure, as a consequence of the way in which the cellulose molecules are brought together in spinning. Another important structural feature of rayon fibre is its cross-sectional shape. Various shapes include round, irregular, Y-shaped, E-shaped, U-shaped, T-shaped and flat.


6. Properties of Rayon

Variations during spinning of viscose or during drawing of filaments provide a wide variety of fibres with a wide variety of properties. These include:

1. Fibres with thickness of 1.7 to 5.0dtex, particularly those between 1.7 and 3.3 dtex, dominate large scale production.
2. Tenacity ranges between 2.0 to 2.6 g/den when dry and 1.0 to 1.5 g/den when wet.
3. Wet strength of the fibre is of importance during its manufacturing and also in subsequent usage. Modifications in the production process have led to the problem of low wet strength being overcome.
4. Dry and wet tenacity extend over a range depending on the degree of polymerization and crystallinity. The higher the crystallinity and orientation of rayon, the lower is the drop in tenacity upon wetting.
5. Percentage elongation-at-break seems to vary from 10 to 30 % dry and 15 to 40 % wet. Elongation-at-break is seen to decrease with an increase in the degree of crystallinity and orientation of rayon.
6. Thermal properties: Viscose rayon loses strength above 149°C; chars and decomposes at 177 to 204°C. It does not melt or stick at elevated temperatures.
7. Chemical properties: Hot dilute acids attack rayon, whereas bases do not seem to significantly attack rayon. Rayon is attacked by bleaches at very high concentrations and by mildew under severe hot and moist conditions. Prolonged exposure to sunlight causes loss of strength because of degradation of cellulose chains.
8. Abrasion resistance is fair and rayon resists pill formation. Rayon has both poor crease recovery and crease retention.

7. Role of Zinc in Spinning Bath
In the non-zinc spinning process under normal conditions of acid concentrated in the spinning bath ,cellulose xanthate gel is converted into cellulose xanthic acid and then to cellulose .The process is very fast and regeneration takes place before the cellulose molecules can properly oriented .This result in a rather disorientation matrix with poor crystalline organization .The net result is a regenerated cellulose filament with poor dry strength and a very interior wet strength. So the zinc result in a transient zinc cellulose xanthate complex which is more stable against acid induced regeneration. Zinc being bivalent form a transient cross link between the adjustment xanthate groups. Coupled with crosslinkg the strong deswelling action of zinc xanthate gel which can be stretched to a highly oriented structure with small crystal size and relatively large crystals.

8. Spinning with Modifiers
It should be recognized that in the presence of zinc, modifiers enhance the action of zinc in spinning bath. It do not effect the viscose. Its mechanism is the formation of a semipermeable membrane by the combined action of zinc ions by the product trithiocarbamate ions from the viscose and the modifiers .This semipermeable retards the diffusion of both Zn+ and H+ ions in the filament ,but actual ratio Zn+ to H+ ion penetration is markedly increased in the presence of modifiers. Hense its act as barrier for proton diffusion .Hense its acidification boundary shift further away from the spinning nozzle in the presence of modifiers.

Types of modifiers 

1. Tertiary amine
2. Quaternary ammonium salt
3. Polyoxyalkylene derivative
4. Polyoxyhydroxy polyamide
5. Dithiocarbamates

8.1 Tyre yarn 
A viscose solution of viscosity 100 poise containing modifiers 1-3% by weight of cellulose and with a CS2 content of 40% is spun underripe (salt index-6-15) into a aqueous spinning bath containing –

• H2SO4 8-10%
• Na2SO4 16-24%
• ZnSO4 6%

The spin bath temperature is kept around 550c and the spinning speed is between 40 and 60 m/min. The stretch applied is 75-125%

8.2 Modified high wet-modulus yarns 
The condition of viscose solution and spinning bath composition are generally similar to those tyre yarns.

Spinning bath temperature-350c is kept lower because it gives more deformable gel necessitating a slower spinning speed 20-40 m/min The result is that gel fibres are stretched at an earlier state of the gel dehydration and decomposition when the gel is more plastic and can be stretched more(125%-150%).

8.3 Polynosic fibre 
Polynosic is similar rayon fibre but difference in process of manufacturing than viscose rayon. Since the manufacturing process is different so their morphological structure also different. Generally polynosic fibre has high crystallinity and high orientation. This give high mechanical strength and chemical resistant, high wet modulus and more dimension stable.

NOTE- In polynosic process we eliminated the Ageing stage, Ripening stage ,Diluted acid concentration & zinc sulphate.

Viscose solution: 

• 6% cellulose
• 4.4% NaOH
• 500-600 D.P
• 500 poise viscosity

Spinning bath:

• H2SO4-2-3%
• Na2SO4-4-6%
• Temp-250c
• Spinning speed-20-30m/min
• Stretch-150-300%

	Crystallinity(%)	Birefringence
Standard Viscose	45.2	0.027
Tyre yarn	41.5	0.037
Polynosic	55.2	0.046

8.4 Super high wet modulus rayon
By adding 1% formaldehyde to spin bath or to the viscose substantially increases the toughness and plasticity of viscose gel. We can get the stretch of 500-600% .Disadvantage of this compound is that it is very toxic.

9. Fibre variant for improved bulk & handle
Approaches has been to produce high performance crimped fibres where the bulk is due to the interaction between the fibres, creating bulk in resultant yarns and fabric. The second approach has been to produce an inherently bulky fibre using an inflation technique during fibre production.

Composition for producing high wet performance fibres, 

Cellulose	7-7.5
NaOH	6-7.5
CS2	30-32
Modifiers: Dimetylamine	.8-1.5
Polyethylene  glycol	.8-1.5

9.1 High performance crimped fibres
For many years standard crimped fibres have been available which are produced by altering the regeneration condition so that the skin of the fibre burst while still in spin bath. The liquid viscose thus processed is regenerated under slightly different conditions and a bicomponent structure result. The two parts of the fibre shrink differently in subsequently washing and drying processes and the fibre develops a permanent crimp as a result.

9.2 Inflated fibres 
In this a range of fibres cross-section can be produced ,but a tubular structure provide the best combination of bulk and handle while still retaining the physical properties and processing performance of standard viscose rayon.

9.3 Spinning specifications 

Xanthate sulphur (%)	.8-1.2
Viscosity (poise)	80-100
Salt index(NaCl)	4-6
DP(fibre)	400-600

	Primary Bath	Secondary Bath
H2SO4	5-5.5	2.5-4.5
Na2SO4	15
ZnSO4(%)	2-3
Temp.(0c)	35-45	95+
Stretch(%)	90-100	25-30
Take-up speed(m/min)	30-50	30-50

9.4 Super absorbent fibres
These fibres are used in sanitary protection and in surgical dressing. For these end uses high absorbency and purity. For these fibre highly hydrophilic polymers that are also compatible with viscose are added to the spinning solution. Chemicals such as sodium polyacrylate, carboxymetyl cellulose,acrylamide-2-metylpropne sulphonic acid.

9.5 Flame retardant fibres
Flame retardant additives are added in the viscose dope. Some of compound used are halogenized triaryl ,halogenized alkyl phosphate ,halogenized alkyl thiophosphate, aloxyphosphopanzenes. A flame retardant fibre using a flame retardant compound is phosphorous. The flame retardant compound is mixed with viscose solution prior to spinning.

Limiting oxygen index (LOI) of more than 26% qualifies a material for flame retardency, Tufban’s LOI value of 30-32% makes it an excellent fire resistant material. It is claimed that normal washing and dry –cleaning do not effect its flame retardant characteristics.

Material	LOI(%)
Tufban	30-32
Cotton	18-20
Polyester	20-22
Acryllic	19-20
Nylon	20-22

10. Incorpation of carbon in viscose fiber 

(a) Incorporation of carbon black for antistatic properties-Electrically conductive carbon is used for the production of electrically conductive viscose fibre. The conductivity increases with decreasing particle size of carbon. For the production of electrically conductive viscose fibres, a slightly alkaline , electric conductive carbon black with a particle size of 20 nm is dispersed in water and mixed in viscose solution prior to spinning. It is found that a loss of about 50% in tenacity of this fibre compared with the tenacity of regular viscose fibre. On the other hand electricity conductive is increased by five orders of magnitude.

(b) Incorporation of activated carbon-Activated carbon containing fibre with outstanding adsorption properties. For the production of activated carbon-containing viscose fibres, activated carbon from coconut with a very fine pores is used .This activated carbon is has to be aground to a very fine particle size and thoroughly dispersed in water in order to be incorporated in viscose fibre in a satisfactory way. These fibres are used in application in such as protective clothing against gases, flat structure for industrial gas adsorportion, shoe insoles odour-absorbing and antimicrobial wound dressing.

(c) Incorporation of graphite-Incorporating 40% of lubricating graphite with a purity 99.5% into viscose yields fibres with excellent lubricating properties which as packing and sealing for crankshafts. Packings from graphite containing viscose fibres may be used to a temperature of 180-2000c.They are stable in the Ph range 5-9 and predominantly used to seal pumps and fitting for water, salt solutions, weak organic and inorganic acids.

11. Alternative to the viscose process
The viscose process provides inexpensive route to regenerate cellulose in fibrous form it constituent a health hazard due to toxic pollutants. Two major route which are much easier and less polluting than the old viscose process.

1. In which dissolution involves nearly simultaneous derivative formation for example metal-amine solvents, N2O4-DMF,DMSO-PF SYSTEM.

2. That produces a derivative from which cellulose can be easily generated for example-liquid ammonia salt system.


Organic solvent (Direct solvent) 

1. Ammonia-ammonium thiocyanate- The solvent is prepared by condensing NH3 to a predetermined weight with a known amount of NH4SCN. Solution of cellulose in NH3-NH4SCN are prepared by making a slurry of cellulose and solvent and stirring at- 10 0c.Fibres have been spun using wet spinning ,dry spinning and dry-jet wet spinning containing 14% cellulose at a solvent composition of 24.5:75.5 (wt%) NH3:NH4SCN

2. N-Methylmorpholine N-Oxide and Water-

1. It is the best solvent to dissolve viscose fibre.
2. Its having strong oxidant property due to which it can dissolve cellulose. 
3. During the dissolving step time and temp. are maintained properly otherwise thermal degradation takes place. Generally temp. is around 1300c
4. If the temp. is goes above 150 0 c ,DP of cellulose goes down for this we add some phenolic oxidant .It stabilize the solution and finally oxidize the colour compound.

Note-Its having high potential to dissolve cellulose up to 50%.

3. N-N Dimethyl acetamide and lithium chloride 

1. It is another solvent which dissolve cellulose. It directly linked with very high reproducible.
2. It was observed that fibres from wet spinning process exhibited superior properties. 
3. It makes an complex with OH-group of cellulose & help to dissolve cellulose. 

Solution process

1. Take mixture of DMAc and dried cellulose. The mixture is distilled at 1650c for 30 min. in N2 atmosphere 
2.  Mixture is then cool down at 100 0c can add required amount of LiCl stirred at 80 0 c for 40 min. 
3. Generally this solvent can dissolve upto 15% (w/w) for DP-130 & 4% (w/w) for DP-1700.

4. Ionic liquid
Salt that melt at temp. below 1000c called ionic liquid. It can be used as green solvent. Or reaction media. Generally contain imidazolium, pyridinium or organic ammonium salt. The anions could be chloride, bromide. Room temp. have more complex structure .The polymer can be regenerated by precipitation with water. They are able to achieve a very high polymer concentration of up to 25%.

5. Amine salt
Two component system (amine salt) consisting of hydrazine (NH2-NH2) or ethylenediamine (NH2-CH2-CH2-NH2) and various thiocyanate salt such as LISCN,NASCN or KSCN that dissolve cellulose pump. However a high concentration 40-50% . Salt is generally required to obtain high concentration (upto 18-20% w/w) spinning dope.

Hydrazine is a good solvent swelling agent, similar to ammonia . Its boiling point 113.50c which is much higher than (-33.40c ) .So that due to high boiling point its offer same potential advantages for investigating the solubility and behaviour of cellulose.

property	cotton	Ordinary viscose	HWM	polynosic
Average Dp	1600-2000	300	400	500
Dry tear strength(cn/tex)	22	22	35	38
Wet tear strength(cn/tex)	28	12	20	30
Water retention(%)	50	90-100	75	50-70
Degree  of fibrillation	2	1	1	3

12. Development in process technology 

Difficulties

1. Old batch-wise process to continuous or semi-continuous system. In the batch wise process the sequence of steeping ,pressing and ageing took up to 40 hr. to produce alkali cellulose.
2. Difficulties in ensuring contact temp. and equal ageing time, because a large no. of bins involved ,frequently resulted in a variable degree of polymerization in the resultant viscose.

Process

1. In the modern plants bales of wood pulp are automatically fed into continuously sulrry. 
2.  By the use of catalyst and elevated temp during ageing have reduced to time 4-5 hr. 
3. Xanthation process has been improved with the use of wet churns. In which both xanthation and mixing carried out.
4. More recently the introduction of back flush filters with non-woven metal screens has improved the filtration efficiency with the new non- woven metal screens the filtration amount has increased 50 fold. Thus the filtration size could be decreased.
5. Completely automatization.

Development in process chemistry 
Reduction in chemical used such as CS2,NaOH and H2SO4. There are number of ways to achieve reduction in the amount of CS2 used in viscose & also allow a substantial reduction in viscose alkali content. Process-SINI process-Its also known as double steeping process operation of aged alkali cellulose at lower alkali concentration (10-12%).A second steeping after ages reduces the amount of free alkali in the crumb with out changing the bound alkali. This reduces the formation of by-product and improves distribution of xanthate group to get a stable viscose.

Advantages

1. This process yield a 30% reduction in CS2 usuage, reducing CS2 emission. 
2. It is claimed that even interior-grade pulp can be used with this process to yield a good quality of viscose fibre. 
3. Due to removal of low molecular weight fractions. In the second steeping as well as increased rate of swelling of alkali cellulose which increases the reactivity to CS2 during xanthation .With this process a higher CS2:NaOH ratio (9:4.5) can be used in viscose solution which result in a substantial reduction in H2SO4.

Other process

1. Activation of cellulose with liquid ammonia prior to xanthation also reduces CS2 consumption by as much as 33%.
2. Xanthation in the presence of surfactants like Berol spin decreases CS2 consumption without effecting the quality of rayon produced.The addition of urea to the steeping solution result in change viscosity of viscose, the ripening time decreases and a high degree of xanthate substitution is obtained.It is presumed that complex with the alkali cellulose is formed which control the side reactions occurring during xanthation process.
3. A reduction in viscosity of viscose allow for an increases in α-cellulose content & leads to reduction in consumption of H2SO4 & also less amount of energy is required for transport, filtration, deaeration.

13. Conclusion

1. Development in process technology & process chemistry are much environment friendly
2. Polynosic fibre show high crystallinity ,high resistant ,high dimension stability.
3. By different solvent ,spinning specifications ,modifiers . We can make end use product.
4. Solvent is very costly so need to recycle it.
5. Ethylenediamine/NaSCN System is the best solvent

14. References

1. Spinning of cellulose from N-methyl morpholine N-oxide in the presence of additives, polymer 1990,vol 31,march.
2. Structure formation of regenerated cellulose materials from NMMO solutions, progress in polymer science 26(2001). 3. Novel cellulose solvent system and dry jet wet spinning of cellulose ED/KSCN solution, by hyun jik cel (thesis)

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