Animal Fibre Wool The variety of fleece material

Animal Fibre Wool The variety of fleece material 1. 2. Fleece consists of two parts; an outer coat of long, course and hairy fibres, and a soft, downy under coat which is soft and fine. A wide variety of fibres can be found in a single ‘lock’ of wool. They also vary in character according to their position on the animal body. The shorter coat is valued for its softness, whiteness and warmth while outer coat because of its colour, harshness and unlikely feel is not so desirable. Therefore careful breeding is important to produce uniform quality of wool throughout the fleece. wool classing Wool classing is a process in which fleeces obtained are separated into different classes according to their character so that the maximum degree of uniformity can be achieved.

Type of wool Wool name Fleece Region Characteristics Length Crosssection uses Mohair Angora goat U. S. A. , South Africa, Turkey Long length, softness, Springy nature, excellent luster, very little ability to felt 4 -10 inches 25 -55µ vast variety of textiles Cashmere Tibetan goat Tibet Downy handle, fluffy nature, brown or grayish white colour 1. 5 – 3 inches 15 µ shawls Alpaca Peruvian goat or llama Peru, Bolivia Brown, gray or black in colour 10 inch 10– 35 µ lining or men’s wear

Wool fibre morphology Macro-structure of wool is a crimped, fine to thin, regular fibre. Finer wool has 10 crimps/10 centimeter while coarser wool has 4 crimps/10 centimeter. As diameter of the fibre increases the no of crimps per unit length decreases. Under the microscope the appearance of wool is over-lapping surface cell structure. These cells are known as epithelial cells and commonly called scales point towards the tip of the fibre. The scales give fibre a serrated surface. The cross-section of fibre is oval in shape. length of the fibre ranges from 5 cm for finer wool to 35 cm for longest and coarser wool. For textile manufacturing 5 – 12 cm is preferred. Fibre length to breath ratio is 2500: 1 for finer wool and 7500: 1 is for coarser wool fibre may vary from off-white to light cream in colour. This is due to the presence of disulphide bonds. When fibre is cream to dark in colour it is due to the degradation of fibre surface as wool fibre is very sensitive to atmospheric oxygen and air pollution.

Felting Irreversible shrinkage of length , breadth or thickness of material. It is done by agitation in an aqueous solution. Disadvantageous for woollen laundering. It is done by over lapping epithelial cells or scales. Less friction will result in rootward direction than in tipward direction.

DFE Difference in direction friction called DFE This movement caused by agitation and moisture. Felting can be enhanced by heat, acid and alkalis. Heat will make fiber elastic, plastic, distort and entangled itself with other fibers.

Micro-structure Wool fibre is a highly complex skin tissue. The micro structure consists of three main components; The cuticle the cuticle is the over-lapping epithelial cells surrounding the wool fibre. Epithelial cell is 1 µm thick, 30 µm long and 36 µm wide. It consists of epicuticle: out-most layer or sheath which covers the fibre, it is only a few molecules thick and is composed of a water repellent, wax-like substance. It also has countless microscopic pores which allows fibre to absorb moisture. exocuticle: the overlapping epithelial cells also form exocuticle. About 10 µm epithelial cell can be seen in finer fibre and 20 µm epithelial cell can be seen in coarser fibre. endocuticle. Is the cementing layer bonding the epithelial cells to the cortex of the wool fibre.

Cortex cortex or core of the fibre forms about 90 % of the fibre volume. It consists of long spindle-shaped cells; thick at the middle. These cells are about 100 – 200 µm in length, 2 -5 µm wide and 1 -3 µm thick. Finer wool have around 20 such cells while coarser wool has 50 cells across the diameter. Cortex is composed of two distinct sections. Ortho-cortex and para-cortex; para-cortex contains more cystine content than orthocortex. They spiral around one and other along the length of the wool fibre. Para-cortex tend to be on the inside of the spiral. This explains the crimp configuration of wool fibre. Para-cortex being rigid and stable tend to tighten the spiral while ortho-cortex elastic and flexable conforms spiral to the outer side.

Fibril The cortical part consists of number of macro-fibrils, each about 100 – 200 nm in diameter. These micro-fibril are held together by a protein matrix. Each macro-fibril is consists of hundred of micro-fibril each about 5 nm in diameter. Each micro-fibril consists of eleven protofibril about 500 nm in length and 2 nm in diameter. The proto-fibril spiral about each other. Finally each proto-fibril consists of three wool polymers which also spiral around each other. It is this spiraling structure which contribute towards the elasticity, flexibility and durability of wool fibre.

Wool polymer system Wool polymer is linear, keratin polymer, with some very short side groups and has normally a helical configuration. The repeating unit of wool is amino acid. Amino acids are linked to each other by peptide bond i. e. –CO-NH- to form wool polymer. The wool polymer is composed of twenty amino acids; so the general formula for wool polymer is R-CH(NH 2)-COOH. In general, arginine, cystine, glutamic acid constitute the one-third of wool polymer. Helical configuration is called alpha-keratin and extended configuration is called beta-keratin. Hydrogen bonding is the inner polymer forces of attraction. Secondly, salt linkages or ionic bonds also form between side groups such as between carboxylate group (-COOˉ) and amino group -NH 3+ The cystine; sulpher containing amino acid forms cystine linkages or disulphide bonds. These linkages are very strong as they are covalent bonds. They occur within and between wool polymers. There also van der Waals forces present but other forces tend to make these forces insignificant. Each proto-fibril consists of three alpha-keratin spiraling about each other. Eleven proto-fibril spiral about to form one micro-fibril while hundreds of micro-fibril spiral about each other to form one macrofibril The polymer system is 70 -75 % amorphous and 25 -30 % crystalline, the spiraling does not indicate a well aligned polymer system.

Properties Tenacity The low tensile strength of wool is due to relatively weak hydrogen bonding. The lack of strength is compensated by alpha/beta keratin configuration. When wool fiber absorb moisture, the water molecules force sufficient polymers apart to cause a significant number of hydrogen bonds to break. In addition the water molecules also hydrolyse the salt linkages. The breakage of hydrogen bonding and hydrolysis of salt linkages cause wool fibre to swell and result in loss in tenacity of wet wool textile material. Elastic nature Wool has good elastic recovery and excellent resilience. The ability of wool fiber to recover is partly due to its crimped configuration and partly due to its alpha-keratin configuration of polymer. The ability of polymer to return its alpha-keratin configuration is due to inter-polymer disuliphide bonds, salt linkages and hydrogen bonding. Hygroscopic nature The absorbent nature of wool is due to the polarity of peptide group, the salt linkages and the amorphous nature of its polymer. The peptide group and salt linkages attract water which readily entres the amorphous region of wool fibre. The dry wool may develop static electricity. This is because there is not enough water molecules present in the polymer system to dissipate static charge.

Heat of setting Wool is renowned to give up small steady amount of heat while absorbing moisture. This is know as heat of setting. This is due to the energy given up by the collision between polar molecules and water. Wool fabric have much less chilling effect on the skin in comparison with other textile materials. This is because wool polymer will continue to give off heat until it become saturated with water molecules. Thermal properties wool is poor conductor of heat and has low heat resistance. There is no satisfactory explanation for this except that when wool absorb large amount of heat the disulphide linkages break. And polymer fragmentation occur. Initially this fragmentation will only result in discoloration of wool fibre. Prolong exposure to heat can result in scorching. The brown and black colour of wool fibre is due to formation of minute particles of carbon. Wool smoulders rather than burns. This seems to be due the water molecules held by hydrogen bonds to the polymer sites on the keratin polymer. Therefore if wool is exposed to naked flame, much of the heat or kinetic energy is consumed in producing steam.

Chemical properties Effect of acids Wool is more resistant to acids than to alkalis. Acid hydrolyze the peptide group but leaves the disulphide group. The polymer weakens but does not dissolve though it become very vulnerable to further degradation. it is essential to neutralize wool after acid treatment. Effect of alkalis Wool dissolve readily in alkaline solution. Alkali dissolve the hydrogen bonds, disulphide bonds and salt linkages. Prolong exposure to alkies cause fragmentation and complete destruction of wool fibres. Effect of bleaches No method is known for bleaching wool permanently. The effective method of bleaching wool is to use a reducing bleach followed by an oxidizing bleach. Reducing bleach such as sodium bisulphite, sodium sulphite converts discoloration on the fibre surface to colourless compounds. Due to the application of oxidizing bleach the colourless compounds are converted into water soluble compounds and then can be rinsed off. Effect of sunlight and weather Sunlight cause yellowing or dullness of wool fabric. The ultraviolet rays of sunlight degrade the peptide and disulphide linkages; degradation products cause wool fibre to absorb more light and to scatter the incident light even more to give yellowing or dulling effect on fabric.