Tuesday, June 13, 2017

Wool Fiber: Production, Classification, Properties and Application

Wool Fiber:
Wool is the natural highly crimped textile fiber obtained from a variety of sheep. These crimps or curls create pockets and give the wool a spongy feel and create insulation for the wearer. Wool is possibly the oldest fibre know to humans. It was the first fibers to be spun into yarn and into fabric. For thousands of year, wool has been used for clothing and other purpose by different tribes and nations around the world. The sheep’s fleece is removed once a year by power operated clippers. Wool fibre is composed of very complicated protein known as keratin along with many active side groups. Wool producing countries are Australia, China, Former USSR, New Zealand, Argentina, Uruguay, South Africa, Turkey, Great Britain, and Pakistan.
wool fiber
Fig: Wool fiber
Classification of wool according to source and animal breed:
There are hundreds of different types and breeds of sheep. Major varieties of wool come from Merino, Lincoln, Leicester, Sussex, Cheviot and other breeds of sheep.

Typography of wool:
The interior of the wool fiber, called the cortex, is made up of long tapering cells tht overlap and are surrounded by the cuticle cells membrane complex (CMC). The CMC runs throughout the fiber and is made up of proteins and waxy lipids. The cuticle cells provide a tough exterior, protecting the fiber from damage.

The scales on the fiber surfaces are capable of hooking onto one another to cause felting, under the influence of water, heat and mechanical action.

The chemical composition of the cells of the ortho and paracortex is different i.e. the paracortex contains more cystine groups that cross-link the chain molecules and therefore more stable. It is this difference between the ortho and paracortex that brings about the spiral form of the fiber. In addition, these two parts react differently to changes in the environment, which leads to the spontaneous curling and twisting of wool. This is the bilateral structure of wool, which causes the fibers to be crimped and natural waviness which are distinct sharp and clear.

Wool production process:
Collection and processing of wool fiber is done by following steps:

Shearing: Sheep shearing is the process by which the woolen fleece of a sheep is cut off. A ram or male sheep have 20 pounds of raw wool of which 30-70% are contaminants.

Sorting: In sorting, the wool is classified, marking and divided according to fibers quality from different parts of the body.

Cleaning and scouring: Scouring is the process of removal of impurities from greasy wool using water, detergent and mild alkali.

Carbonizing: Wool clips are contaminated with excessive vegetable matter, such as burrs and thorny branch segments, are carbonized using an aqueous sulfuric acid treatment, which is followed by heating to convert the defective material into carbon. The carbon is then crushed and shaken from the wool.

Grading: After shearing, the fleece is graded into essentially four qualities (1=best, 4=worst). The grader classifies the wool according to fineness, crimp, length, impurities and color.

Bailing: A wool bale is a standard sized and weighted pack of graded and sorted wool compressed by the mechanical means of a wool press. Each bale contains 330 Kg of graded wool, wrapped in plastic and tied by wire.

Physical and chemical properties of wool:

  • Length: 60-100mm sometimes it goes 250mm.
  • Diameter: 20µm to 40µm
  • Strength: 1.0-1.7 gm/den
  • Elongation: 25-35% under standard condition.
  • Resiliency: Excellent
  • Hygroscopic (Moisture capacity 14-18%): Higher than other fibers
  • Hand feel: Soft
  • Specific gravity: 1.32 and so fabrics feel lighter than cellulose.
  • Wool dissolved in alkali solution
  • Abrasion resistance: Good
  • Dimensional stability: Bad
  • Color: White to light cream in color.
  • Effect of alkalis: Wool is easily and extremely vulnerable attacked by alkalis even by weak bses at low dilutions.
  • Effect of acids: Wool is more resistant to acids.
Uses of wool fiber:
Wool is extensively used in textile applications where comfort and aesthetics are important. It is used in men’s and women’s apparel, outer wear and cold weather clothing, suits, blankets, felts and carpeting. It is often used in blends with cellulosic and man-made fibers.

Identification of wool fiber:

I have already published an article on wool fiber identification. 

You can follow this: Identification of Cotton, Jute, Flax, Wool and Silk Fiber