Wool Fiber

Updated: Jan 8, 2021


Introduction :

Wool is a natural fiber attained from the Hair of sheep. The wool comes under the category of Natural-Animal-Protein. The history of wool begins in stone age i.e., before 10,000 BC in Europe, primitive humans collected wool by handpicking. India produces about 2% of wool in world production and it is the 7th largest manufacturer with the product range of 43-46 million kgs per year. India has 3rd largest population of sheep in the entire world with 71 million sheep. The Indian wool industry is growing at a healthy rate. With an increase in technology into the wool industry and due to various government schemes and other capacity-building initiatives, increased exports, besides domestic consumption.

Sheep Shearing:

It is the process of cutting the woolen fleece of the sheep. The persons who collect/ remove wool from sheep is called Shearer. On average an adult sheep can be shorn once a year. After shearing the sheep is called shorn or sheared. Shearing is done by using Wool scissor or by hair clipper machine.


Classification of wool:

Classification based on the type of sheep:

  • Merino wool

  • Class-two wool

  • Class-three wool

  • Class-four wool

Merino Wool:

  • 40% of world production is Merino wool.

  • Australia merino wool quality is Best.

  • This type of wool has a fine size and has good uniformity.

  • This type of wool is fine with good Strength, elasticity, and wicking property.



Class-Two Wool:

  • This is not quite good as Merino wool.

  • Class-two Wool has a large number of scales per inch.

  • Class-Two Wool has a good crimp.

  • Class-Two Wool is Strong, Fine, and Elastic.

  • Class-Two Wool also has food working properties.

Class-Three Wool:

  • Class-Three Wool is Courser than merino and class-two wool.

  • Class-Three Wool has a lesser number of scales than merino and Class-Two Wool.

  • Class-Three Wool is less crimp than merino and Class-Two Wool.

  • Class-Three Wool is smooth and has more luster.

  • Class-Three Wool is less elastic and resilient.

  • Class-Three Wool is nevertheless of good enough quality to be used for clothing.

Class-Four Wool:

  • Class-Four Wool is coarser.

  • Class-Four Wool has few scales.

  • Class-Four Wool has a little crimp.

  • Class-Four Wool is smoother and lustrous.

  • Class-Four Wool has less strength and the least elasticity.

  • Class-Four Wool is used to manufacturing carpets, rugs, and inexpensive low-grade clothing.

Classification based on Fleece:

  1. Lambs Wool

  2. Hogget Wool

  3. Whether Wool

  4. Pulled Wool

  5. Dead Wool

  6. Cotty wool

  7. Tag locks Wool

Lamb’s Wool:

The wool obtained by shearing the 6-8 moths old sheep is known as Lamb’s wool. Generally, this is obtained by the first shearing. Sometimes this is also called “Fleece Wool or First Clip”. This type of wool is very fine and the fibers are tapered as the ends are never trimmed before. Fabrics produced by this type of wool has a very soft texture.


Hogget Wool: This type of wool is obtained by shearing the 12-14 months old sheep. This is also obtained from the first shearing. This type of wool is also called as Teg-wool. This is very fine, soft, resilient, and matured with tapered ends. Hog wool is a very desirable wool that is used as warp yarns in fabric manufacturing.

Weather Wool: The second shearing of wool is called weather wool. This is generally obtained from more than 14 months of old sheep. This kind of wool will be of soil and dirt.

Pulled wool: This type of wool is obtained after slaughtering the sheep. Wool is pulled from the dead sheep by the use of line, by sweating, or by chemical depilatory. The quality of the pulled wool is not good.

Dead wool: This type of wool is obtained from the sheep which is accidentally killed i.e., dead by accident or by any other disease. This type of wool is used for low-grade clothing.

Cotty wool: This type of wool is obtained by exposing sheep to different weather conditions. This is hard and brittle and this is a very poor quality of wool.

Tag-locks wool: This is obtained from discolored parts of the sheep. This type of wool is sold separately as an inferior grade of wool.

Grading of wool: Based on the length and diameter of the wool grading is done. 1. Fine 2. Medium 3. Long 4. Cross bread 5. Mixed

Morphological Structure of Wool:


Technically wool contains three layers.

1. Cuticle (or) epidermis

2. Cortex

3. Medulla.

Cuticle:

1) This is the outermost layer of the wool fiber. 2) This layer is made of flat, irregular horny scales with projecting edges that are pointing toward the fiber tip. 3) Cuticle acts as the protection to the main parts of fiber. 4) This layer gives the rigidity to the wool fibers. 5) Cell width – 36 microns 6) Thickness – 0.5-1.0 microns. 7) Visible length – 16 microns. 8) With an increase in diameter, the number of scales also increases. Cortex:

1) This layer forms the body of the fiber.

2) This layer contains long, slightly flattened and twisted spindle-shaped cells. 3) The cell length is 80 – 110 microns. 4) This layer is responsible for strength, elasticity, and dyeing behavior. Medulla: 1. This is the central core which runs lengthwise through the fiber. 2. This layer occupies a 10 – 80% volume in fiber. Detailed structures are shown in the fig. below


Chemical structure of Wool:

Physical properties of wool:

Length:

3.6 cm to 35 cm

Based on length wool is classified into Fine : 3.2 cm to 10 cm Medium: 5 cm to 20 cm Coarse: 15 cm & more Fineness: 10–70 microns Merino wool: 10-30 micron Carpet wool: 20-70 micron Cross-section: Circular to Elliptical Crimp : 0-30 crimps/inch For Fine wool- 14 to 22 crimps/inch For Medium wool- 8 to 14 crimps/inch For Coarser wool- 0 to 8 crimps/inch. Strength : Wool fiber has low strength due to its low orientation. Strength of different types of wool 1. Fine wool – 4.8 to 7.1 gm. 2. Medium wool – 10 to 16 gm. 3. Coarser wool – 20 to 24 gm. Tensile strength of wool : 1600 to 2150 kg/cm2 Elasticity :

Wool has good Elasticity with 90% recovery and wool fiber can be elongated up to 30% Hygroscopic property : · Wool fiber is hygroscopic than any other natural fiber. · Wool can absorb 25% of moisture at normal conditions it can absorb 12-15% of moisture and at 70-80% Rh wool can absorb 15-18% of moisture. Specific gravity : 1.30 gm/cc Electrical property: Wool is a bad conductor of electricity. Thermal properties : · There is no effect up to 130oc until it is exposed for a long time. · When Wool is heated in dry air it feels harsh and brittle at 115oc and Scorch at above 200oc. Effect of sunlight : · When wool exposed to sunlight keratin will decompose. · Under the action of sunlight sulfur in wool converted to H2SO4. · Under the action of sunlight, the fiber becomes discolored and develops a harsh feel. Luster : The luster of coarser fiber is higher than fine fibers. Storage : There is no effect on storage. Chemical properties : Effect of Acid : · In Conc. Sulphuric acid wool decomposes. · Wool has resistance to mineral acid. · Under the action of Nitric acid wool Oxidizes. Effect of Alkalis : · Wool is sensitive to alkalis · Wool dissolves in caustic acid. · Effect of strong alkali is significant and weak alkalies will not effect on wool. Effect of organic solvents : · Organic solvents will not effect wool Effect of insects : Wool is effected by insects. Effect of micro-organisms : Wool is effected by mildew if it remains wet for a long time. Dyeing ability : Wool can be dyed with Basic dyes, Direct dyes, and Acid dyes. Chemical composition of Wool :

Grease :

· Grease is an impurity in the wool with an composition of 5-15%

· This is insoluble in water and cause emulsion.

· This is soluble in organic solvents.

· Wool grease is an ester of high molecular weight fatty acids and a monohydric alcohol i.e., ichloesterol (C27H45OH) or isocholesterol.

· Grease is not fat but it is wax

· Wool wax absorbs a large quantity of water.

Suint :

· This is soluble in water and can be isolated from raw wool by aqueous extraction.

· It consist of potassium salts of fatty acids and organic amino acids and it is a complex mixture.

Sand and Dirt :

· In the natural state of wool, it contains some amount of dirt.

· Wool keratin is composed of fine elements like


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