GROWTH AND MOLECULAR STRUCTURE OF WOOL FIBRE ; PHYSICAL AND CHEMICAL PROPERTIES OF WOOL.

By: Supriya S.Deokar M.V.Sc Scholar

Department of Livestock Products Technology

INTRODUCTION Fleece obtained from sheep =Raw/Grease

wool. It is the animal fibre which grows from

follicles in the skin . Indian needs good wool & increased supply of

mutton . Population of sheep -71.6 million (4th rank) The yield of wool -350 gm to

1800gm/sheep/yearMohair-Straight ,uneven ,translucent fibre

obtained from Goat.

CHEMICAL STRUCTURE OF WOOL FIBRE Wool fibre is a protein known as keratin. Keratin is

made up of amino-acids joined by peptide linkages. In addition to carbon, hydrogen, oxygen and

nitrogen it also contains sulfur. These 5 elements are combined into 19amino acids linked together in ladder-like polypeptide chains.

The amino-acids present in wool are mainly bulky, while silk has chiefly small amino-acids. Due to this wool is relatively amorphous. The polymer system of wool is highly amorphous that is 75%

Wool fibres-2 cell typesCuticle and cortex cellCentral medulla is present .

COMPOSITION OF WOOL

CHARACTERISTICS OF WOOL Elastic

Hygroscopic

Durable

Non-inflammab

le

Transmits UV light

Warmth retainin

g

Hold body heat

GROWTH AN MOLECULAR STRUCTURE OF WOOL

DEVELOPMENT OF WOOL FOLLICLE

Stage F1: Follical plug –A plug of cells from Epidermis into Dermis -This stage begins when a localized thickening of the basal of the epidermis can be recognized.

Stage F2: Pre-papilla- The base of epidermal plug flattens prior to invagination

Stage F3: Papilla –epidermal plug invaginated and dermal papilla is formed.

Stage F4: Hair cone –The elongated the cells of Henle’s layer of the inner root sheath are recognized, forming a cone which is directed along the axis of the follicle towards the skin surface.

Stage F5: Advanced hair cone –The tip of the hair cone reaches the deepest level of sebaceous gland

Stage F6: Hair formation –The tip of keratinized hair fibre inside the hair cone.

Stage F7: Hair in epidermis-The tip of the keratinized hair reaches beyond the base of eipdermis above the follicle . A hair canal has usually been formed in the epidermis before the hair tip reaches the level

Stage F8: Hair emerged –The tip of the hair has been penetrated the superficial layers of the epidermis .

PHYSICAL PROPERTIES OF WOOL Hydroscopic nature:-It has the very absorbent nature because of the polarity of the peptide group, the salt linkages and the amorphous nature of the polymer system. The peptide groups and salt linkages easily attract water molecules which enter the amorphous polymer system of the fibre. Density:-It has a comparatively low density and therefore fibres are light with regard to their visible weight. Luster:

It is ability of wool to reflect light. Softness:

-Soft wool produces fabrics softer to touch . Non-Inflammable:

-Slower to burn and on burning it gives off a pungent odour and forms bead where burning ceases.

Elasticity and resiliency:-This is elastic and resilient. Covalent bonds can stretch, but they are strong. The disulphide bonds in the amorphous parts of the strand or fibre are able to stretch when the strand is extended. When the strand is released the disulphide bonds pull the protein molecules back into their original positions. Conductivity:

-is best of fibre holding in body heat and also keeping heat out.-It has a low conductivity of heat and therefore makes it ideal for cold weather.

Strength :-Wool fibres and fabrics are usually strong and durable.

CHEMICAL PROPERTIES OF WOOL Effect of acids:-Concentrated acids damage it since they hydrolyze the salt linkages and hydrogen bonds. Dilute acids do not affect it. Effect of alkali:-It easily dissolves in alkaline solutions. Alkalis hydrolyze the disulphide bonds; hydrogen bonds and salt linkages of wool and cause the polymers to separate from each other, which is looked as dissolution of the fibres.Prolonged exposure of Alkalis On wool Hydrolysis of peptide bonds polymers Fragmentation destruction of the fibre

Effect of bleach:-Chlorine bleach is ordinary harmful to the wool. KMnO4, Na2O2 are utilized for bleaching. Effect of sunlight and weather:-Effect of sunlight’s ultra-violate radiation tends to yellow white or dull colored fabrics. -The UV cause the peptide and di-sulphide bonds to sever. This leads to polymer degradation products on the surface of the fibre. As a consequence the strand not only absorbs more light but scatters the incident light to a greater extent. -Prolonged exposure sunlight weakens the fibres very much.

Colorfastness/Dyeing properties :-Like cotton wool is easy to dye. Acid dyes, chrome and mordant dyes are utilized to dye this. The dye molecules are attracted into the amorphous areas of wool.

Thank you