Rayon
Rayon is a regenerated natural fiber that is produced from 100% cellulose fiber. It has the same molecular structure as cellulose. The
many types and grades of rayon fibers can imitate the feel and texture of natural fibers such as silk, wool, cotton, and linen. The fiber is used to make textiles for clothing and other
purposes.
History of rayon
Rayon is the earliest regenerated fiber that was first patented in 1855 by the Swiss chemist Georges Audemars. It was also called artificial silk. Sir Joseph Swan, an English chemist was inspired by Thomas Edison's incandescent electric lamp to experiment with extruding Audemars's cellulose solution through fine holes into a coagulating bath in order to create filaments for the electric light. His fibers were used in Edison's invention as well as for an 1885 exhibition of textiles his wife crocheted from his new fiber. Artificial silk was also exhibited at the Paris Exhibition in 1889 by the French chemist Count Hilaire de Chardonnet who is known as the "father of the rayon industry" because he built the first plant for commercial production of Chardonnet silk in Besancon, France.
Rayon fiber properties
1.
Rayon is a regenerated natural fiber that is made from cellulose.
2.
The drape and slipperiness of rayon textiles are
often more like nylon.
3. The hand feels and texture of rayon like silk, wool, cotton, and linen.
4. Rayon fibers are easily dyed in a wide range
of colors.
5. Rayon fabrics are soft, smooth, cool, comfortable, and
highly absorbent.
6. The durability and appearance retention of regular rayons
are low, especially when it is wet.
7. Rayon has the lowest elastic recovery of any other fiber.
8. Regular rayon has lengthwise lines called striations and its cross-section is an indented circular shape.
9. Staple fibers range from 1.5
to 15 deniers and are mechanically or chemically crimped.
10. Rayon fibers are
naturally very bright.
Chemical composition of rayon
Rayon is 100% cellulose and
has the same chemical composition as the natural cell. The molecular structure
of rayon is the same as that of cotton and linen, except that the molecular
chains are shorter and do not form as many small crystals.
Spinning bath chemicals
Below chemical solvent is used in a spinning bath-
H2SO4 – 10%
Na2SO4 – 18%
Glucose – 02%
ZnSO4 – 01%
Water – 69%
Rayon production method
For
rayon production, the viscose method can use wood as a source of cellulose, whereas
other routes to rayon require lignin-free cellulose as a starting material.
The use of woody sources of cellulose makes viscose cheaper, so it was
traditionally used on a larger scale than the other methods. Mineral acids such
as sulfuric acid are used to make rain fibers from ripe solutions. In this
step, the xanthate groups are hydrolyzed to regenerate cellulose and carbon
disulfide.
The production process begins with cellulose obtained from wood pulp and plant
fibers. The cellulose content in the pulp should be about 87-97%.
The
steps of rayon production-
1.
At first, the cellulose is treated with caustic soda.
2.
The treated cellulose is then pressed between rollers to remove excess liquid.
3.
The pressed sheets are crumbled or shredded to produce what is known as a white
crumb.
4.
The white crumb is aged through exposure to oxygen. This is a depolymerization
step and is avoided in the case of polynosics.
5.
The aged white crumb is mixed in vats with carbon disulfide to form the
xanthate. This step produces an Orange-Yellow crumb.
6.
The yellow crumb is dissolved in a caustic solution to form viscose. Viscose
lets it ripen, standing for a certain period of time. At this stage the
molecular weight of the polymer changes.
7.
After ripening, the viscose is filtered, degassed, and then extruded through a
spinneret into a bath of sulfuric acid, resulting in the formation of rayon
filaments. The acid is used as a regenerating agent. It converts cellulose
xanthate back to cellulose. The regeneration step is fast which does not allow
the correct direction of the cellulose molecules. So to delay the process of
regeneration, zinc sulfate is used in the bath which converts cellulose
xanthate to zinc cellulose xanthate thus providing time for proper orientation
to take place before regeneration.
a.
Spinning: The spinning of rayon fiber is done using a wet-spinning process. The
filaments are allowed to pass through the frozen bath after coming out of the
spinrate hole. The two-way mass transfer takes place.
b.
Drawing: The rayon filaments are stretched, in a procedure known as drawing, to
straighten out the fibers.
c.
Washing: The fibers are then washed to remove any residual chemicals from them.
d.
Cutting: If filament fibers are desired, then the process ends here. The
filaments are cut during the production of the main fibers.
Advantages of rayon
1.
Rayon is a versatile and widely used fiber.
2.
The drape and slipperiness of the rayon are good.
3. Rayon fabrics are soft, smooth, cool,
comfortable, and highly absorbent.
4.
Stronger and exhibits higher durability and appearance retention.
5.
Rayon can be machine-washed.
6.
Rayon fibers are naturally very bright.
Disadvantages of rayon
1.
Highly toxic carbon disulfide is used in the production of rayon.
2.
Rates of disability in modern factories are unknown.
3.
The more water-repellent the rayon-based fabric, the more slowly it will
decompose.
4.
Rayon is weak when it is wet.
5.
Recommended care for regular viscose rayon is dry-cleaning only.
Conclusion
The future of rayon fabric is so bright. Not only
is there a growing demand for rayon worldwide, but there are many new
technologies that promise to make rayon even better and cheaper. Today there is
a strong trend toward blended fabrics. Blends offer the best of both worlds. With the present body of knowledge about the structure and chemical
reactivity of cellulose, some scientists believe it may soon be possible to
produce cellulose molecule directly from sunlight, water, and carbon dioxide.
If this technique proves to be cost-effective, such hydroponic factories could
represent a giant step forward in the quest to provide the raw materials
necessary to meet the worldwide demand for man-made fabric.
0 Comments