Tuesday, July 23, 2019

CHEMICAL COMPOSITION OF WOOL FIBRE, CHEMICAL FORMULA OF WOOL, PHYSICAL STRUCTURE OF WOOL

     
CHEMICAL COMPOSITION OF WOOL FIBRE :

The chemical composition of wool fibre is given below:


Chemical Composition of Keratin:
The chemical composition of keratin is given below:



Chemical composition chart of wool fibre:




CHEMICAL FORMULA(STRUCTURE) OF WOOL FIBRE:
The chemical formula of wool fibre is given below:

The wool fibre is composed of a particular protein, this protein is known as “keratin”. This keratin  consists of long polypeptide chains. The polypeptide chains has  eighteen different amino acids. The most of these amino acids have the general formula H2N.CHR.COOH. In this formula R is a side chain of varying character. The structure of polypeptide chain is given below:



And at intervals bridges derived from the amino acid cystine connect the chains. Some of the side chains end in amino groups and others in carboxyl groups. Internal  salts are therefore formed and the

Molecules are bound together by electrovalent linkages. The molecules of keratin are very large, with and average molecular weight estimated at about 60,000.

      PHYSICAL STRUCTURE OF WOOL FIBRE:

 The cellular structure of wool fibre is given below:

Cuticle: 

“On the outside of the wool fibre is a protective layer of scales called cuticle cells”. They overlap like tiles on a roof. The exposed edges of the cells face away from the root end so there’s more friction when we rub the fibre in one direction than the other. This helps wool expel dirt and gives it the ability to felt. “Wool felts when fibres are aligned in opposite directions and they become entangled”.
The scales have a waxy coating chemically bound to the surface. This stops water penetrating the fibre but allows absorption of water vapour. “This makes wool water-repellent and resistant to water-based stains”.

Cortex:

The internal cell is called cortex. Almost ninety percent of the fibre is made of it. Two types of internal cells present in the fibre. One is ortho-cortical andother is  para-cortical. Each has a different type of chemical composition. In the finer fibres, these two types of cells form in two distinct halves. The cells expand differently when they absorb water and make the fibre bend. This creates the crimp in wool. In coarser fibres, the para-cortical and ortho-cortical cells form more randomly so there’s less crimp.
“Fibre crimp makes wool feel springy and provides insulation by trapping air”.

Cortical cell:

The cortical cells are surrounded and held together by a cell membrane complex and acting similarly to mortar holding bricks together in a wall.
The cell membrane complex is composed of proteins and waxy lipids,it runs through the whole fibre. The molecules in this area have fairly weak intermolecular bonds. These bonds can break down when exposed to continued abrasion and strong chemicals.The cell membrane complex allows easy uptake of dye molecules.

Macrofibril:

“The long filaments present inside the cortical cell are known as macrofibrils”. These consist of bundles of even finer filaments called microfibrils. They are surrounded by a matrix region.

Matrix:

The matrix is composed of sulphur proteins.These sulphur proteins improve  absorbency of wool because sulphur atoms attract water molecules. Wool can absorb up to 30% of its weight in water. This region also play important role to make wool fibre more fire-resistant and anti-static properties.

Microfibril:

Within the matrix region, there are embedded smaller units called microfibrils. The microfibrils in the matrix are rather similar to steel bars embedded in reinforced concrete to give strength and flexibility. The microfibrils have couples of twisted molecular chains. Protein chains are coiled in a helical shape like a spring. These protein chains construt twisted molecular chains. This structure is stiffened by hydrogen bonds and disulphide bonds within the protein chain. They link each coil of the helix, helping to prevent it stretching. The helical coil is the smallest part of the fibre. It gives flexibility, elasticity and resilience to wool which helps wool fabric to keep its shape unchanged and remain wrinkle-free in use.

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