VISCOSE VS RAYON - Ideal Semi-Synthetic fiber - Materials Today

VISCOSE VS RAYON – Ideal Semi-Synthetic fiber

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Rayon and viscose are cellulose-based semi-synthetic fabrics. Both the artificial fabric provides comfort like natural fiber, easily breathable features, and smooth texture. The “Viscose VS Rayon” is difficult to postulate but one thing which appears foremost is the ability of Rayon to absorb oil and body sweat which leave spots on Fabric. Rayon, on one side, shrinks while washing in the water while Viscose, on the other hand, stretches. Topic covered here are; Manufacturing Methods, Advantages, and Disadvantages, Environmental Impacts to a clear difference between Viscose and Rayon.

Overview

Both types under discussion are cellulose synthesized semi synthetic fiber. The origin of cellulose in these fabrics is from wood pulp, bamboo trees or directly from cotton. The natural source of the raw material makes it difficult to characterize it as either a natural or synthetic fabric even though the manufacturing process is man-driven.

Rayon and viscose are very inexpensive fabrics and, they are known for their soft and silky touch. The manufacturing process of Rayon was patented in 1855 by a well-known Swiss chemist, Georges Audemars. The commercial production of these fibres started in 1905 by Samuel Courtaulds and Company, Ltd. The cellulose in these fabrics is depolymerized and then regenerated again through chemical reactions. We have detailed their benefits and drawbacks to compare both the fabrics.

Cellulose structural formula is given below;

Cellulose Structure
Cellulose Structure

Viscose VS Rayon

  1. Viscose, as synthetic fabric, is manufactured by driving cellulose only from the pulp, while Rayon drives cellulose from wood pulp, cotton litter, and a bamboo tree.
  2. Rayon is flammable fabric, while Viscose characterizes as inflammable.
  3. Viscose fabric feels like silk and difficult to die while Rayon is easy to die.
  4. Body sweat does not leave spots on Viscose, on the other hand, it gets absorbed into Rayon fabric and leaves visible spots.
  5. Rayon shrinks on washing while Viscose stretches in water.

What is Rayon Fabric

Rayon fabrics
Rayon fabrics

Manufacturing Process

The primary ingredient is cellulose, cellulose is a linear polymer of β-D-glucose repeating units with the empirical formula (C6H10O5)n. The following manufacturing method of Rayon has been in use since the early 1900s. The manufacturing process starts with processed cellulose which is extracted from wood pulp. The wood pulp must contain 87% to 97% cellulose. The cellulose is immersed in caustic soda to remove impurities and convert it into alkali cellulose.

Manufacturing process of Rayon
Manufacturing process of Rayon

Manufacturing of these semi-synthetic fabric follows concepts of polymers. You can study about common polymerization techniques used in Aramid in Article, “Aramid Synthesis”.

The reaction for this conversion is as follows:

(C6H10O5)n + nNaOH → (C6H9O4ONa)n + nH2O

This solution is pressed between two rollers to remove the excess liquid. The pressed sheets are shredded to form a white crumb. This white crumb is depolymerized to an extent. The rate of depolymerization is controlled by temperature, air and the presence of other additives like metallic oxides and hydrides. It is then reacted with Carbon Disulfide to form Sodium Cellulose Xanthate. This process is called Xanthation and it takes place in vats under controlled temperatures of 20OC to 30OC.

(C6H9O4ONa)n + nCS2 → (C6H9O4O−SC−SNa)n

The color of Sodium Xanthate Cellulose is yellow and it is called Yellow Crumb. The yellow crumb is then dissolved in Sodium Hydroxide solution and allowed to age for 4 to 5 days.

Rayon filaments are produced from the aged Yellow crumb solution by treatment with a mineral acid, for example, Sulfuric Acid. In this reaction, the xanthate groups are hydrolyzed to recover cellulose and discharge dithiocarbonic acid that later breaks down to carbon disulfide and water.

[C6H9O4-OCS2Na]2n + nH2SO4  → [C6H9O4-OH]2n +2nCS2 + nNa2SO4

H2COS2 → H2O + CS2

The filaments are then washed and bleached to remove any remaining acid or impurities and are converted into a fabric that can be cut to desired shapes and size.

Advantages of Rayon

Rayon provides comfort just like natural fabric, with a smooth texture and soft-touch, rayon has other advantages as well as some limitations.

  • Inexpensive fabric
  • Smooth texture and silk-like touch
  • Very comfortable
  • Breathable fabric
  • Easily dyed
  • Blended with other fabrics
  • Highly absorbent fabric
  • Drapes well

Disadvantages

Some of the limitations of th is semi synthetic fiber are:

  • It wrinkles easily unless treated
  • Difficult to iron
  • Sensitive to heat and Is very flammable
  • Washing it is difficult because it shrinks
  • May always need dry cleaning
  • It weakens when it is wet
  • Toxic chemicals are used during its manufacturing

Disposal and biodegradability

The biodegradability study of various fabrics containing cellulose in aerobic soil was conducted by Mary Warnock. The study concluded that the rate of biodegradation depends on the crystallinity of Cellulose.

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Pure rayon, being the least crystalline out of pure Cotton and pure Tencel®, degraded at a much higher rate. The presence of air also increased the rate of degradation. In 2007, 10 million tons of textile waste was buried in landfills, the anaerobic conditions in these sites resulted in slow degradation rates of the fabrics.

A survey in 2014 found that 56.9% of the total fabrics in the ocean were Rayon. It was found in the deep ocean areas. In oceans, the degradation rate depends on the wettability of the fiber, the more hydrophobic it is, lesser will be the degradation rate.

Enviromental effects

Highly toxic chemicals are used during the manufacturing process of Rayon for depolymerizing and regeneration of cellulose. Even though the CS2, NaOH and H2SO4 are removed before it reaches the customer but the removal process of these toxic chemicals is very hazardous for the workers in Rayon producing factories. They are at a high risk of brain damage, heart diseases, stroke and nerve damage. Once these chemicals are dumped into waterways, then the whole community is at a risk of being poisoned.

You can purchase Rayon Jersey being supplied by Amazon by following the link below;

Telio Softique Rayon Spandex Jersey Knit Black Fabric

What is Viscose Fabric

Viscose Fabric - Viscose VS Rayon
Viscose Fabric

Manufacturing Process

To make viscose fibre, sheets of pure cellulose are immersed in NaOH to form alkali cellulose. The solution is pressed between rollers to remove excess liquid. It is then shredded and left to depolymerize in the presence of air and heat in metal containers. The crumbled substance is called white crumb which is then reacted with CS2 to produce yellow crumb. The yellow crumb is known as Cellulose Xanthalate.

Product is then reacted with NaOH to form a honey-like viscous substance known as viscose. This viscose is allowed to age for some time. After ageing the viscose is filtered and degassed to remove any impurity and undissolved particles. It is then extruded through a spinneret; upon exit it reacts with H2SO4 to form viscose filaments.

Manufacturing process of Viscose - Viscose VS Rayon
Manufacturing process of Viscose – Viscose VS Rayon

Viscose VS Rayon comparison | One has singular source while Rayon has multiple cellular source.

Advantages of Viscose

  • Silk-like feel
  • Lightweight
  • Breathable, even better than cotton
  • Very luxurious and cheaper
  • Vivid colors on dying
  • No trapped body heat
  • Soft and comfortable
  • Less sensitive to heat
  • Biodegradable

Disadvantages

Some of the limitations associated with this fabric are:

  • difficult to wash
  • weaker when wet
  • vulnerable to stretching and difficult to recover
  • not recommended for use in home furnishings because it stretches
  • absorbs sweat, body oils, and water, which leaves spots on the fabric
  • Shrinks when washed

Disposal and Biodegradation

The biodegradation of viscose was studied by many researchers in different media including freshwater, soil, marine water etc. A recent study conducted in marine water conditions showed that viscose fully degraded after 35 days. But it can take much more time if disposed in landfills.

Environmental Effects

In 2017, a researcher reported that manufacturers of viscose fabrics were dumping untreated wastewater in local lakes which had a devastating effect on local people. CS2, which is used during the manufacturing of viscose, is considered as a powerful solvent. It will cause very serious health issues like insanity. Moreover, NaOH can cause corrosion, skin burn and eye damaged if inhaled, ingested or if it makes any contact with skin.

FAQ – Viscose VS Rayon

Viscose VS Cotton

Viscose fibre shares many properties of cotton, for example, its comfort and touch are like cotton but it is much cheaper than cotton.
Viscose differs from cotton in many regards, viscose is not as strong as cotton, its wet strength is much weaker than cotton, viscose is semi-synthetic but cotton is completely natural fabric

How to wash Viscose

Washing viscose fabric is a bit tricky. The safest method of washing is hand washing in cold water. Evenly agitate soap in cold water and immerse the fabric for 30 minutes. Press the water out of the fabric and let it dry in its natural shape. Normal cleaning mostly requires dry cleaning as it is a very delicate fabric

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Is rayon breathable?

Rayon has very thin fibers that allow air to pass through easily, preventing the fabric to stick to your body during hot and humid weather

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