Wool: Manufacturing Process, Features, and Fabric Good Washing

By Eman Abdallah Kamel

December 19, 2022

Eman is a writer and textile engineer. She received her bachelor’s degree in textile science from the Faculty of Applied Arts, Egypt.

Natural wool textiles are the best fabrics used during the winter to provide warmth. In this article, you will learn the history of wool, its features, wool fiber microstructure, sheep wool types, manufacturing process, uses, and the good washing of wool fabrics. Image source: istockphotos.com

What is wool?

Natural wool is a fiber obtained from sheep and other animals. Examples are cashmere and the mohair of goats, qiviut of muskoxen, angora of rabbits, and camelid wool. There are different characteristics associated with each type of wool.

The wool consists of protein with a low proportion of fat.

Global raw wool production is approximately 3.1 million tons per year. The most important wool-producing countries are Australia, New Zealand, China, Russia, Uruguay, Argentina, Turkey, Iran, the United Kingdom, India, Sudan, and South Africa.

There is currently a global interest in reviving the use of organic wool. This initiative is funded by wool producers in Australia, Britain, and New Zealand to encourage more carpet and clothing producers to use wool instead of synthetic fibers.

Woman spinning wool. Detail from an Ancient Greek Attic white-ground, 490 BC, from Locri, Italy. British Museum, London.
wikimedia.org

History

Wool fibers were important to primitive human tribes for more than 10,000 BC. Wool was woven and coordinated by the Babylonians and northern European tribes. Textile tools were relatively basic.

The Persians, the Greeks, and the Romans were interested in raising sheep and weaving wool.

The Romans built a wool factory in Winchester, England, in 50 AD.

Following the Norman invasions of Greece in the 12th century, Greek weavers were sent to Italy as slaves, stimulating the Italian textile industry. In the 14th century, the Flemish weavers escaped from the Spanish invasion of England, leading to the flourishing of the wool industry.

Moroccan Arabs used to breed sheep and produce fine wool. They invented many wool-weaving processes and transported them to Andalusia (Spain).

During the fifteenth and eighteenth centuries, sheep and wool were important economic forces. Countries like England and Spain, for example, banned the export of sheep and raw wool. Woolen textile exports accounted for two-thirds of England’s foreign trade in 1660.

Spanish Merino Rams and Spanish Merino Ewes arrived in South Africa after being granted by the Spanish king access to the Dutch Orange House, where they could not cope with the cold and rainy climate. The Spanish Merino sheep flourished in South Africa. Later, some descendants of the Spanish Merino sheep were sent to Australia.

The first Merino sheep arrived in Australia in 1797. The sheep were descendants of the Royal Merino herd of Spain. After selective breeding, Australian farmers produced soft Australian Merino wool. And then it was shipped to England for industrialization.

Native Women Washing Wool in a Spring Near Jenin, Palestine. A photograph by William H. Rau shows women washing wool near the city of Jenin, circa 1903. wikimedia.org

The Arabs of the Levant also cared about raising sheep and wool yarn.

The Wool Products Classification Act was passed by the United States Congress in 1941. In this act, producers and consumers were protected from unknown substitutes and mixtures in wool products. The law required that all wool-containing products (except upholstery and floor coverings) include information about their wool content.

The decline in wool prices began in late 1966 due to a decrease in demand for natural wool with the increased use of synthetic fibers, resulting in a sharp drop in production.

Washable wool machines first appeared in the early 1970s.

The General Assembly of the United Nations declared 2009 to be the International Year of Natural Fibers, including wool.

Features

Wool fiber has many characteristics, including:

Dimensions: Wool fibers have three-dimensional crimps with 25 waves per 10 cm in fine fiber and 4 waves per 10 cm in coarse fiber.
Length: The fiber length ranges from 3.8 to 38 cm. The fiber length of 5–12 cm is used in the garment industry because this length allows the yarn to be manufactured with greater precision.
Diameter: The diameter of the fiber varies from 14 micrometers to more than 45 micrometers. The fibers of some sheep may be up to 70 micrometers in diameter, and these fibers are used in the manufacture of carpets. A higher price is paid for fibers with a fine diameter, especially if they are identical in diameter.
Color: The color of sheep’s wool varies from white to brown and black. White is more desirable than other colors. The dark fibers cannot be successfully dyed because of the difficulty of removing or hiding the natural color.
Absorption: Wool fibers absorb water from the surrounding atmosphere better than other fabric fibers because they have pores and interstitial spaces in their composition. Wool fibers absorb about 18% of their weight in moisture. But this moisture is not felt. It is an important hygienic factor that must be provided in clothes.
Warmth: Fabric made from woolen fibers gives a warmer feel than industrial fibers.
Insulation: Wool is good insulation for heat, preventing heat from leaking out and cold air from leaking inside. Therefore, woolen textiles are used as a protective covering for heat in hot and cold places in the winter.
Flexibility: Wool fibers are very flexible; they increase about 30% of their length under simple tensile strength and return to normal condition when removing the tensile strength.
Flammable: Woolen fabrics are non-flammable and stop burning when the fire source is removed.
Ultraviolet rays: Wool transfers ultraviolet rays to the body.
Dissolving: Wool fibers dissolve in base (alkaline) solutions and are fixed in acidic solutions.

Schematic diagram of wool fiber structure.
scienceimage.csiro.au

Wool Fiber Microstructure

Wool fibers consist of protein molecules. Keratin protein is a crystalline copolymer; the repeated units are amino acids.

Wool fibers are cross-linked through the disulfide bonds present in the amino acid cysteine.

Wool has two structures. One is alpha-keratin, and the second is beta-keratin, obtained through X-ray diffraction.

The microstructure of wool fibers consists of three basic parts: the cuticle, cortex, and medulla.

The cuticle (epidermis) is a layer of overlapping cells surrounding wool fibers. There are three cuticles (epicuticle, exocuticle, and endocuticle).

The cortex is the internal cell that forms 90% of the wool fiber. There are two basic types of cortical cells: orthocortical and paracortical, each with a different chemical composition.

In superior fibers, these two types of cells are of distinct halves. The cells expand differently when the moisture is absorbed, making the fiber curve, which creates a crease in the wool. Rough fibers have less curl because the ortho- and paracortical-chemical cells are more random. The curliness of the fibers also makes wool insulating against the air.

The medulla is a mass of degenerated cells in the central part of the fiber. This layer may disappear or be difficult to see in the fine wool.

Wool Sheep Types

Four types of wool fibers come from sheep:

Fine (Soft wool): In this type, the fiber diameter does not exceed 25 microns, and the average length of wool is 9–6 cm. Wool fibers are very wavy, the fiber density is large, the fat ratio is high, and the wool is white. This type of wool can be obtained from Merino sheep breeds.
Medium (semi-soft wool): Wool is white and has average fat. The thickness of wool fiber ranges from 25 to 55 microns, and wool length ranges from 8 to 10 cm. This type of wool can be obtained from the Tsigai, Suffolk, Hampshire, and Tunis sheep breeds.
Longwool: This type of wool is white and has a coarse and dry feel. This wool can be obtained from the Awassi and Lincoln sheep breeds.
Carpet wool: This type of wool contains more fat than coarse wool, as well as more softness. This wool can be obtained from the Marco Polo sheep and Karakul sheep. This kind of wool is more suitable for the carpet industry.

Image source: researchgate.net

Manufacturing Process

The production stages of wool involve:

Shearing,
Sorting,
Scouring,
Carding,
Spinning,
Weaving,
Finishing.

1. Shearing: The process of cutting wool from sheep is called sheep shearing. Each sheep is sheared once a year. Shearing can take place at any time of year, but spring is the best time to do it. There are two ways to shear:

Hand shearing: In this method, different types of scissors are used, requiring a long time and a large number of workers, and it may cause injury to the animals as well as irregular shearing of wool.
Automatic shearing: It is made by electric machines, spread in many countries because of the saving of time and effort, in addition to getting good quality shearing, and does not cause any injuries to sheep when carried out by trained shearers.

2. Sorting: In sorting, wool is divided into four sections of different quality fibers (fleece, broken, bellies, and locks). Sheep’s shoulders and sides are the best sources of wool for clothing. The lower quality comes from the bottom legs and is used for carpet making.

3. Scouring: This is a process of cleaning the greasy wool because it contains a high level of lanolin, the sheep’s dead skin, sweat residue, pesticides, and vegetable matter from the animal’s environment. It is a water bath that contains alkaline, soda ash, and soap. The rollers of the cleaning machines press the excess water from the wool, but the wool is not allowed to dry completely. After this process, wool is processed with oil to make it easier to manage.

4. Carding: In this stage, short fibers are removed and replaced with long parallel fibers, forming a loose rope (sliver). Comb machines consist of a giant roller surrounded by smaller ones. All cylinders are covered with small metal teeth; when the wool reaches more, the teeth become finer.

5. Spinning: The thread is formed by spinning the fibers together to form the strand. The plexus is woven with at least two other threads. Because the wool fibers cling to each other, it is easy to expand and spin the wool into yarns. Woolen yarns can be spun on any number of spinning machines. The spun threads are then wound around rollers or commercial drums.

6. Weaving: There are two basic types of weave: plain and twill. The most common method is plain weaving, which produces soft-surface textiles. Wool textiles made using the twill method are more beautiful and precise, but they are also more expensive.

7. Finishing: Wool fabrics undergo a series of final processes after weaving, including fulling or tucking, which involves cleaning the cloth to remove oils, dirt, and other impurities. The process of cribbing controls the expansion or relaxation of the fabric and ensures its thickness. By cribbing, wrinkles and uneven contractions are prevented. Wool fibers can be dyed before carding (combing) or after weaving into fabrics.

Uses

There are many uses for wool, including clothing, blankets, insulation, upholstery, and saddle cloth.
Merino wool is used to make baby blankets and infant sleeping bags.
Preliminary studies of woolen underwear have found that they prevent heat and rashes because they absorb moisture more than other fibers.
Researchers at the Royal Melbourne School of Technology of Fashion and Textiles have discovered a blend of wool and Kevlar (a synthetic fiber used in body armor). The wet Kevlar loses about 20% of its effectiveness. So it requires expensive waterproofing. Mixing wool with Kevlar reduced the cost of using Kevlar alone.

Good Washing of Wool

The best way to wash woolen fabrics is by hand. Wash the wool with a large amount of warm water by pressing it.
Do not use hot water, as it changes the properties of wool.
As a result of rubbing wool with soap, it shrinks and wrinkles.
When soap dissolves in water, it produces an alkaline effect, so it is not necessary to add more soap. Soap will have more negative effects on wool fabrics if its concentration increases.
It is best to change the washing water at least twice and to maintain the same temperature.

Sources

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