Rayon Fiber - Types and Manufacturing Process Explained

Rayon is a regenerated cellulose fibre derived from natural cellulose derived from wood pulp or cotton linters. There are various types of rayon fibres, such as viscose, polynosic, and lyocell rayon. The viscose rayon fibre manufacturing process involves steeping, pressing, shredding, ageing, xanthation, dissolving, ripening, filtering, degassing, spinning, drawing, washing, cutting and many more.

Rayon is made of pure cellulose. Similar to rayon fabric, cellulose fabrics are produced from wood or plants. To make rayon fabric, a variety of cellulose ingredients, including bamboo, beech tree, and wood pulp, are frequently combined. Regenerated or re-formed cellulose fibres are used to create rayon fibre, known as regenerated cellulose fibres.Rayon, the first man-made fibre, was produced by English naturalist Robert Hooke in 1664. He felt an "artificial glutinous" composition could mimic silk-worm fibre. The Federal Trade Commission (FTC) granted the name "rayon" obtained from cellulose or its derivatives in 1925, legally recognising man-made textile fibres. In 1937, the FTC declared that any cellulose-based thread or yarn must be called rayon because of the rise in synthetic fibre manufacture.

Did you know? Rayon is the cellophane's sister. Despite being made from wood, it has such a soft texture that it is compared with silk and termed artificial silk.

History of Rayon 

French chemist Hilaire de Chardonnet invented rayon. Rayon is a synthetic textile that was developed in the late 19th century. It was initially known as "artificial silk," and it was produced by dissolving cellulose in a chemical solution and then extruding the resulting fibres through tiny holes.New production techniques and rayon fibre variants were created as the rayon manufacturing process quickly spread around the globe. When rayon with high tenacity was introduced in the 1930s, it was appropriate for use in tire cords and other commercial uses.Today, rayon is used in many different products, including bedding, curtains, and clothes. It is prized for its suppleness, drapeability, and adaptability and is more affordable than other natural fibres like silk.

Properties of Rayon Fibre

Wood pulp is used to make rayon synthetically. Rayon is frequently referred to as synthetic silk since it resembles silk. Rayon is substantially cheaper than silk and may be dyed in a variety of colours. 

Rayon fibre has the following properties:

Types of Rayon Fiber

Rayon is obtained from cellulose derived from cotton, wood pulp, and other natural sources. There are various types of rayon fibre, and each type has particular qualities all its own. 

Popular types of rayon fibre include:

1. Viscose Rayon

The most widely used type of rayon fibre is viscose, created from wood pulp. It is frequently used to make dresses, shirts, and other apparel because of its soft and silky feel.

2. Polynosic Rayon 

These fibres are stretched to an extremely high degree (up to 300%) during processing, which gives them an exceptionally high degree of orientation. They have a distinctive fibrillar structure, strong dry and wet strength, modest elongation (8 to 11%), only moderately high water retention, and extremely high wet modulus.

3. Lyocell Rayon

Eucalyptus trees create Lyocell rayon's soft and silky texture. It is frequently used to create textiles for homes and garments.

4. High Wet Modulus Rayon

Using natural cellulose fibres that have undergone chemical treatment to make them stronger when wet, high wet is called modulus rayon fabric. It is commonly used in products like towels and bathrobes where the fabric comes into contact with moisture.

5. Cuprammonium Rayon

Cuprammonium rayon is created by dissolving cellulose fibres in a copper and ammonia solution. Due to its softness and opulent feel, it is frequently used in textiles for apparel and household items.

6. Bamboo Rayon

 A soft and long-lasting fabric called bamboo rayon is manufactured from bamboo pulp that has undergone chemical treatment. Because it is hypoallergenic, moisture-wicking, and environmentally friendly, it is used in clothing and bedding.

Raw Materials Used in Rayon Preparation

Rayon is a very soft and comfortable material used in our daily lives. It is mixed with artificial fibres to make it soft and usable. Here are some of the components used in the preparation of rayon: 

1. Cellulose

Rayon is prepared by breaking down Cellulose, which is produced from wood pulp or cotton linters and is the main raw material for rayon.

2. Caustic Soda

Purified cellulose sheets are aged in metal containers for two to three days after being steeped in caustic soda, dried, and then shredded into crumbs to create rayon. The metal containers are meticulously regulated for humidity and temperature.

3. Carbon Disulfide 

Carbon disulfide, a colourless, extremely combustible, and deadly liquid, is employed as a solvent to create rayon fibres.

4. Sulfuric Acid 

When sulfuric acid is added to a cellulose solution in cuprammonium hydroxide, the cellulose precipitates out of the mixture. A complicated copper compound combines with sulfuric acid and dissolves. In rayon, tiny blue fibres are created.

5. Sodium Sulfate

It is a waste product from rayon manufacturing and is used to make detergent and other chemicals.

6. Water

Used to dissolve and dilute the process's chemical components.

Also Read: What is the Difference Between Weft and Warp Fabrics?

Chemicals Used in the Rayon Manufacturing Process

The fundamentals of viscose rayon production have not changed in modern times. The process of making caustic soda (sodium hydroxide) begins with purified cellulose. Carbon disulfide is added to alkali cellulose after it has aged, creating cellulose xanthate, which is then dissolved in sodium hydroxide. Rayon characteristics are altered using additional compounds like zinc and sodium sulfates.

Manufacturing Process of Viscose Rayon Fiber

The manufacturing process of viscose rayon fibre involves several steps:

1. Steeping

The initial step in the production of viscose is steeping. In this procedure, NaOH treats the pulp for mercerization at mercerizing strength. Then, 18% NaOH is steeped (immersed) into the pulp sheets. Alkali cellulose is produced during the process as a by-product.

2. Pressing

The removal of extra liquid from the viscose solution is done by pressing. After steeping, a machine presses the viscous solution to remove extra water, producing a more concentrated solution. To create fibres, this concentrated solution is pushed through a spinneret.

3. Shredding

The cellulose sheet is then broken up into tiny bits known as "white crumbs." The alkali cellulose's surface area is enhanced at this stage, which enhances its capacity to react in later procedures.

4. Ageing

The white crumb is then aged for a few days so that it can mature and have a more consistent texture. To depolymerise alkali cellulose to the required polymerisation level, it is aged at a controlled time and temperature settings (between 18 and 30° C).

5. Xanthation

The aged white crumb is then subjected to a chemical reaction with carbon disulfide (CS2) to produce cellulose xanthate, a yellowish-orange material.

Formula: (C6H10O5)n nCS2 → [C6H10O5-SC-S]n nCS2

6. Dissolving

The cellulose xanthate is dissolved in a NaOH solution to provide viscose, a viscous, transparent solution. Aqueous caustic dissolves yellow crumbs. Due to the high concentration of xanthate substituents on cellulose, which pull the chains apart and lessen inter-chain hydrogen bonding, cellulose solutions are created when water molecules solvate and separate the cellulose chains.

Formula: [C6H10O5-SC-S]n nNaOH → [C6H9O4ONa]n nCS2 H2S

7. Ripening

The viscose solution is then given time to ripen for a number of hours to enhance its quality and guarantee uniformity. Viscose may "ripen" if desired. During ripening, the xanthate group is redistributed and lost. Reversible xanthation converts specific xanthate groups into cellulosic hydroxyls and free CS2 molecules.

8. Filtration

Any contaminants or undissolved particles are subsequently removed from the matured viscose solution.

9. Degassing

To remove air bubbles, the filtered viscose solution is degassed.

10. Spinning

To produce long filaments of viscose rayon, the degassed viscose solution is extruded through tiny holes in a machine known as a spinneret. Rayon products are strong because they were tried and failed. Slow cellulose regeneration and rayon stretching promote crystallinity in high-tenacity rayons.

11. Drawing 

The cellulose molecules are then aligned, and the viscose rayon filaments are drawn or stretched to increase the strength and durability of the fibres. As chains lengthen, they become more parallel, which results in inter-chain hydrogen bonding, which gives the filaments their characteristics as textile fibres.

12. Washing

Any remaining impurities or chemicals are rinsed out of the viscose rayon fibres. Removing salts and other water-soluble contaminants from newly made rayon is necessary. There are many washing methods.

13. Cutting

Viscose rayon fibres are then packaged for use in various applications after being trimmed to the correct length. If rayon is to be used as a staple, the group of filaments (known as "tow") is run through a rotary cutter to create a fibre that can be processed similarly to cotton. Overall, viscose rayon fibre production entails a number of intricate procedures that necessitate exact control and oversight. This is to guarantee the consistent quality and performance of the finished product.

Uses of Rayon Fiber

Rayon fibre is a versatile material with many industrial uses. 

Here are some additional applications for rayon fibre:

1. Clothing: Rayon Fibre makes shirts, dresses, blouses, and skirts.

2. Home Furnishings: Curtains, bedspreads, and upholstery are made from rayon fibre. Its lustre and drape ability make it a popular choice for these applications.

3. Medical Textiles: Rayon Fibre makes surgical dressings, gauze, and other medical fabrics. Medical applications are ideal because it is absorbent and sterilisable.

4. Industrial Applications: Tire ropes, conveyor belts, and industrial hoses are made from rayon fibre. These applications take advantage of their strength and durability.

5. Filters: Air and water filters are made of rayon fabric. 

6. Products for Personal Care: Tampons, sanitary towels, and other personal care items are made from rayon fibre. Due to its great absorption capacity, it is the appropriate substance for various uses.

Also Read: Fashion Forward: Manufacturing Garments for a Better Future

Conclusion

Rayon fibre is a type of cellulose fibre regenerated from natural cellulose acquired from cotton linters or wood pulp. Consumers may confidently choose the products they buy if they are aware of the different varieties of rayon fibre and how they are made.

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