Rayon Fiber
    (Viscose)

Rayon Staple Fiber
Rayon Textile Filament Fiber
Rayon Industrial Filament Fiber

First U.S. Commercial Rayon Fiber Production: 1910, Avtex Fibers Inc. (Formerly FMC Corporation and American Viscose)

Current U.S Rayon Fiber Producers: None currently

Federal Trade Commission Definition for Rayon Fiber: A manufactured fiber composed of regenerated cellulose, in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups. (Complete FTC Fiber Rules here.)   

Basic Principles of Rayon Fiber Production — In the production of rayon, purified cellulose is chemically converted into a soluble compound. A solution of this compound is passed through the spinneret to form soft filaments that are then converted or “regenerated” into almost pure cellulose. Because of the reconversion of the soluble compound to cellulose, rayon is referred to as a regenerated cellulose fiber.

There are several types of rayon fibers in commercial use today, named according to the process by which the cellulose is converted to the soluble form and then regenerated. Rayon fibers are wet spun, which means that the filaments emerging from the spinneret pass directly into chemical baths for solidifying or regeneration.

Viscose rayon is made by converting purified cellulose to xanthate, dissolving the xanthate in dilute caustic soda and then regenerating the cellulose from the product as it emerges from the spinneret. Most rayon is made by the viscose process.

Viscose Process

All of the early viscose production involved batch processing. In more recent times, processes have been modified to allow some semi-continuous production. For easier understanding, the viscose process is a batch operation. Click on each process step for a brief explanation.

Cellulose
Purified cellulose for rayon production usually comes from specially processed wood pulp. It is sometimes referred to as “dissolving cellulose” or “dissolving pulp” to distinguish it from lower grade pulps used for papermaking and other purposes. Dissolving cellulose is characterized by a high a -cellulose content, i.e., it is composed of long-chain molecules, relatively free from lignin and hemicelluloses, or other short-chain carbohydrates.

Steeping
The cellulose sheets are saturated with a solution of caustic soda (or sodium hydroxide) and allowed to steep for enough time for the caustic solution to penetrate the cellulose and convert some of it into “soda cellulose”, the sodium salt of cellulose. This is necessary to facilitate controlled oxidation of the cellulose chains and the ensuing reaction to form cellulose xanthate.

Pressing
The soda cellulose is squeezed mechanically to remove excess caustic soda solution.

Shredding
The soda cellulose is mechanically shredded to increase surface area and make the cellulose easier to process. This shredded cellulose is often referred to as “white crumb”.

Aging
The white crumb is allowed to stand in contact with the oxygen of the ambient air. Because of the high alkalinity of white crumb, the cellulose is partially oxidized and degraded to lower molecular weights. This degradation must be carefully controlled to produce chain lengths short enough to give manageable viscosities in the spinning solution, but still long enough to impart good physical properties to the fiber product.

Xanthation
The properly aged white crumb is placed into a churn, or other mixing vessel, and treated with gaseous carbon disulfide. The soda cellulose reacts with the CS₂ to form xanthate ester groups. The carbon disulfide also reacts with the alkaline medium to form inorganic impurities which give the cellulose mixture a characteristic yellow color – and this material is referred to as “yellow crumb”. Because accessibility to the CS₂ is greatly restricted in the crystalline regions of the soda cellulose, the yellow crumb is essentially a block copolymer of cellulose and cellulose xanthate.

Dissolving
The yellow crumb is dissolved in aqueous caustic solution. The large xanthate substituents on the cellulose force the chains apart, reducing the interchain 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”.

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.

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

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.

Spinning - (Wet Spinning)
The viscose is forced through a spinneret, a device resembling a shower head with many small holes. Each hole produces a fine filament of viscose. As the viscose exits the spinneret, it comes in contact with a solution of sulfuric acid, sodium sulfate and, usually, Zn⁺⁺ ions. Several processes occur at this point which cause the cellulose to be regenerated and precipitate from solution. Water diffuses out from the extruded viscose to increase the concentration in the filament beyond the limit of solubility. The xanthate groups form complexes with the Zn⁺⁺ which draw the cellulose chains together. The acidic spin bath converts the xanthate functions into unstable xantheic acid groups, which spontaneously lose CS₂ and regenerate the free hydroxyls of cellulose. (This is similar to the well-known reaction of carbonate salts with acid to form unstable carbonic acid, which loses CO₂). The result is the formation of fine filaments of cellulose, or rayon.

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 fiber axis. As the chains become more parallel, interchain hydrogen bonds form, giving the filaments the properties necessary for use as textile fibers.

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.

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

Other forms of regenerated cellulose fibers that are classified by the Commission as rayon without separate, distinctive names include high wet modulus rayon, cuprammonium rayon and saponified rayon.

High wet modulus rayon is highly modified viscose rayon that has greater dimensional stability in washing.

Cuprammonium rayon is made by converting the cellulose into a soluble compound by combining it with copper and ammonia. The solution of this material in caustic soda is passed through the spinneret and the cellulose is regenerated in the hardening baths that remove the copper and ammonia and neutralize the caustic soda. Cuprammonium rayon is usually made in fine filaments that are used in lightweight summer dresses and blouses, sometimes in Combination with cotton to make textured fabrics with clubbed, uneven surfaces.

When extruded filaments of cellulose acetate are reconverted to cellulose, they are described as saponified rayon, which dyes like rayon instead of acetate.

Rayon Fiber Characteristics

•  
  • Highly absorbent
  • Soft and comfortable
  • Easy to dye
  • 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-thirds 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.

Some Major Rayon Fiber Uses

• Apparel: Accessories, blouses, dresses, jackets, lingerie, linings, millinery, slacks, sportshirts, sportswear, suits, ties, work clothes
• Home Furnishings: Bedspreads, blankets, curtains, draperies, sheets, slipcovers, tablecloths, upholstery
• Industrial Uses: Industrial products, medical surgical products, nonwoven products, tire cord
• Other Uses: Feminine hygiene products

General Rayon Fiber Care Tips — Most rayon fabrics should be dry-cleaned, but some types of fabric and garment construction are such that they can be hand or machine washed. For washable items, use the following as a guide:

•  
  • Fabrics containing rayon can be bleached; some finishes, however, are sensitive to chlorine bleach.
  • Use mild lukewarm or cool suds. Gently squeeze suds through fabric and rinse in lukewarm water. Do not wring or twist the article.
  • Smooth or shake out article and place on a non-rust hanger to dry. Rayon sweaters should be dried flat.
  • Press the article while damp on the wrong side with the iron at a moderate setting. If finishing on the right side is required, a press cloth should be used.
  • Between wearings, rayon articles may be pressed with a cool iron. (For specific instructions, refer to garment's sewn-in care label.)

Polyester Fiber 

(Polyethyleneterephthalate) (Polyethylene Naphthalate)

Polyester Tow Fiber
Polyester Staple Fiber
Polyester Fiberfill
Polyester Textile Filament Fiber
Polyester Industrial Filament Fiber
PEN Fiber (Polyethylene Naphthalate) more

First U.S. Commercial Polyester Fiber Production: 1953, DuPont Company

Current U.S. Polyester Fiber Producers: Color-Fi; Dak Fibers; Fiber Science, Inc.; Foss Manufacturing Co.; INVISTA LLC; Nan Ya Plastics Corp.; Palmetto Synthetics; Performance Fibers Inc.; Premiere Fibers, Inc.; Universal Fiber Systems LLC; Wellman, Inc.

Federal Trade Commission Definition for Polyester Fiber: A manufactured fiber in which the fiber forming substance is any long-chain synthetic polymer composed of at least 85% by weight of an ester of a substituted aromatic carboxylic acid, including but not restricted to substituted terephthalic units, p(-R-O-CO- C₆H₄-CO-O-)_x and parasubstituted hydroxy-benzoate units, p(-R-O-CO-C₆H₄-O-)_x. (Complete FTC Fiber Rules here.)

Basic Principles of Polyester Fiber Production — The most common polyester for fiber purposes is poly (ethylene terephthalate), or simply PET. This is also the polymer used for many soft drink bottles and it is becoming increasingly common to recycle them after use by remelting the PET and extruding it as fiber. This saves valuable petroleum raw materials, reduces energy consumption, and eliminates solid waste sent to landfills.

PET is made by reacting ethylene glycol with either terephthalic acid or its methyl ester in the presence of an antimony catalyst. The reaction is carried out at high temperature and vacuum to achieve the high molecular weights need to form useful fibers. PET is melt spun. For a detailed production flowchart, go here.

Polyester Fiber Characteristics

•  
  • Strong
  • Resistant to stretching and shrinking
  • Resistant to most chemicals
  • Quick drying
  • Crisp and resilient when wet or dry
  • Wrinkle resistant
  • Mildew resistant
  • Abrasion resistant
  • Retains heat-set pleats and crease
  • Easily washed

Some Major Polyester Fiber Uses

• Apparel: Every form of clothing
• Home Furnishings: Carpets, curtains, draperies, sheets and pillow cases, wall coverings, and upholstery
• Other Uses: hoses, power belting, ropes and nets, thread, tire cord, auto upholstery, sails, floppy disk liners, and fiberfill for various products including pillows and furniture

General Polyester Fiber Care Tips

•  
  • Most items made from polyester can be machine washed and dried. Use warm water and add a fabric softener to the final rinse cycle. Machine dry at a low temperature and remove articles as soon as the tumbling cycle is completed.
  • If ironing is desired, use a moderately warm iron.
  • Most items made from polyester can be dry-cleaned. (For specific instructions, refer to garment's sewn-in care label.)