Wool PDF

NATURAL - PROTEIN FIBER: WOOL & SILK Protein fibres are of animal origin and they include wool and specialty wool which are the hair and fur of the animal. In addition to this it also includes silk and spider silk which are the secretion of insects. The various animal breads for their hair include...

NATURAL - PROTEIN FIBER: WOOL & SILK Protein fibres are of animal origin and they include wool and specialty wool which are the hair and fur of the animal. In addition to this it also includes silk and spider silk which are the secretion of insects. The various animal breads for their hair include sheep, vicuna, alpaca, camel, llamas, cashmere goats, angora goats and also Angora rabbits. Silk is the secretion of the silkworm and spider silk that of spiders. Protein fibres are polypeptide chains formed in nature and are made up of various amino acids. Amino acids are in turn made up of carbon, hydrogen, oxygen and nitrogen. These fibres are amphoteric in nature i.e. they possess both acidic and basic groups. The protein present in hair fibres is keratin and in silk fibres in fibroins. The difference in the types and percentages of amino acids cause wool & silk to have different properties. WOOL Originally wool was born on wild sheep as a short, fluffy undercoat concealed by hair. When the primitive people killed the animal for meat they used the pelt to cover their bodies. The friction, pressure, heat, humidity caused due to everyday use may have caused wool to matt together, giving them the idea of felting it into crude cloth. This may have been the reason that sheep was one of the first animals to be domesticated. The fleece of the primitive sheep consisted of a long, hairy undercoat called Kemp and soft downy undercoat. The fleece of the present day sheep is primarily the soft undercoat and is a result of long continued selective breeding. Wool fibre is characterized by providing warmth, good moisture absorption without feeling wet, excellent heat retention, fantastic resiliency, water repellence, flame retardant and felt ability, making it a very sought after fibre. These properties along with the fact that it is produced in smaller amounts as compared to cellulose and synthetic fibres have made them valuable and expensive fibres. Major countries that breed sheep include Australia, New Zealand, England, Russia, Argentina, Uruguay, South Africa and The United States of America. PROCESSING OF WOOL The quality of wool fibre is determined by the breeding, climate, food, general care and health of the sheep. The sheep is generally sheared once a year. The Fleece is removed by experts using power shears and is done in deft strokes to get one continuous piece. Alternatives to shears are chemical feed  additives or injections that cause the wool to fall or be easily pulled out, once the chemical or injection goes into the sheep’s body This newly sheared wool is called raw or scoured wool and contains 30% to 70% by weight of impurities, such as sand, dirt, grease and dried swear. Removing these impurities produces clean or scoured wool, which has lots quite a lot of weight. The grease that is removed is purified to lanolin and is used for making creams, ointments, cosmetics and soaps. Shearing is followed by grading and sorting that helps group wools of common characteristics together, so that they can be put to the best use. Characteristics such as length, fineness, colour, crimp, strength and elasticity vary with the breed of the sheep. CLASSIFICATION OF WOOL This can be done in two methods: I) Sheep & II) Fleece I) CLASSIFICATION BY SHEEP Wool producing sheep are classified into four groups, according to the quality of the wool produced. CLASS I – Merino Wool Merino sheep produce the best wool. Length is short 1-5 inches; fibre is strong, elastic having the greatest amount of crimp and maximum number of scale, giving excellent spin ability and warmth. It is used in the best quality of clothing CLASS II In class II the fibre length is 2 – 8 inches in length, strong, fine elastic having good amount of crimp and scales, but not as good in quality as the first. Used in good quality clothing. CLASS III They are 4 – 18 inched in length, coarse, fewer scales and lesser crimp, causing them to be smoother and more lustrous. Good enough quality to produce clothing CLASS IV It is wool sheared from mongrel or half – breeds. They vary from 1 – 16 inches in length. They are coarse, hair – like, have fewer scales and crimp, making them smooth and lustrous. Used for carpets, rugs, blankets and low quality clothing. II) CLASSIFICATION BY FLEECE Wool differs depending upon the age of the sheep, also if the sheep were dead or alive during shearing and upon the purpose of breeding 1. LAMB’S WOOL It is the first wool sheared from lamb that is 6 – 8 months of age. It is off fine quality, having tapered ends. It produces soft fabric. However the wool is immature because of which it is not strong 2. HOGGET WOOL It is wool sheared for the first time from sheep which is 12 – 14 months. The fiber is fine, soft and resilient and with tapered ends. It is mature and is therefore strong. It is used for production of wrap yarns. 3. WETHER WOOL It is any wool that is sheared after the first clipping and form sheep which are older than 14 months of age. It contains soil & dirt. 4. PULLED WOOL When sheep are slaughtered for meat, their wool is pulled form their bodies after using chemical. It is inferior in quality as the sheep are bred for meat and not wool, due to action of pulling the wool and the use of chemicals. 5. DEAD WOOL It is wool that is recovered form sheep that have been killed accidently. It is inferior in grad and is used in inferior quality fabric. 6. COTTY WOOL Sheep that are exposed to several weather conditions or lack of nourishment produce wool that is matted together and is hard and brittle. It is poor grade wool. 7. TAGLOCKS The torn, ragged or discoloured parts of the fleece are called tag locks. It is of inferior quality PHYSICAL STRUCTURE OF WOOL The wool fibre has a complex structure made up of the outermost layer – cuticle, the second layer – cortex and the inner most layer medulla 1) CUTICLE: the cuticle is the outermost layer of the wool fibre. It is made up of 3 parts, the epicuticle, exocuticle & endocuticle. The cuticle also contains a dense non fibrous layer of scales. These scales are covered by the epicuticle which is a thin non protein membrane. This epicuticle gives the fibre its property of water repellence. The scales overlap each other and the tips of the scales point towards the tip of the fibre. The scales overlap each other and the tips of the scales point towards the tips of the fibre. The scales contribute to the wools abrasion resistance and felting property and can irritate sensitive skin. The exocuticle lies between the epicuticle and the endocuticle. The endocuticle lies just outside the second layer called the cortex. 2) CORTEX: it is the main part of the fibre. It is made up of long, tapered, flattered cells. In natural coloured wools, the corticular cells contain melanin, a coloured pigment. These corticular cells are  responsible for the crimp that is present in the fibre. Crimp is the most important feature of wool, as the cohesiveness, elasticity and loft of the fibre are because of this crimp. 3) MEDULLA: it is usually present only in coarse wools and is absent in fine wools. When present, it is a microscopic honeycomb like core containing air spaces that increase its insulation properties. CHEMICAL COMPOSITION Wool is a cross – linked protein called keratin consists of carbon, hydrogen, oxygen, nitrogen and sulphur. These combine to form 18 different amino acids, 17 of which are in measurable quantities. The molecular chains of wool are held together by natural crosslinks – cysteine or sulphur linkages and salt bridges that connect adjacent molecules. The structure of wool resembles a ladder – like helical structure. It is this structure that is responsible for its crimp and elasticity. The cysteine linkage is the most important part of the molecule. Any damage to this linkage causes wool to lose strength. PROPERTIES OF WOOL PHYSICAL PROPERTIES 1. LENGTH & DIAMETER The length of wool varies from 1.5 inches to 16 inches. The shorter fibres are used for the manufacture of woollen yarn and the fine and the long fibres (2.5 – 5 inches) are used for the manufacture of worsted yarns. The diameter varies from 10 – 50 microns 2. MICROSCOPIC VIEW The fibre has an uneven structure, which tapers to the tip. It has dark edges and the most prominent identification is the overlapping scales. 3. STRENGTH It is the weakest of the natural fibres and tends to lose strength when wet. Strength of woollen yarn can be improved by the use of ply yarns 4. ELASTICITY It has very good elasticity and compensates for its low strength. It can be stretched to 25 – 30% of its natural length and this reduces its chances of tearing under tension 5. RESILIENCE Its excellent crimp ensures that it wrinkles disappear quickly. Good wool is soft and resilient, poor wool is harsh and tends to hold wrinkles 6. DRAPABILITY It has excellent drapability due its properties of pliability, elasticity and resiliency. It has superior drape as compared to many man-made fibres 7. HEAT CONDUCTIVITY  Wool is a non-conductor of heat. It permits the body to retain its normal temperature. Thus it is an excellent fabric for winters on damp days. The scales and the crimp create air spaces, that serves as insulate barriers and help to keep the body warm. 8. ABSORBENCY Initially wool tends to be water repellent. Droplets on the surface can be easily brushed off. However, once water seeps in, its high capillary action results in very good absorption. Wool can absorb 20% of its weight in water without feeling wet. Wool also dries slowly. 9. CLEANLINESS & WASHABILITY Dirt tends to attract dirt. They need to clean thorough as they absorb odours. It needs frequent dry cleaning or laundering. Extreme care is required during laundering as it loses nearly 25% of its strength in water. Wool cannot be wrung or pulled when wet. It should be squeezed in a towel and pit flat to dry. 10.EFFECT OF HEAT It scorches at high temperature; however it is not easily combustible. It burns to give the odour of burning hair. 11.EFFECT OF SUNLIGHT It is weakened by long exposure to sunlight CHEMICAL PROPERTIES 1. REACTION TO ACIDS Although it is damaged by hot sulphuric acid, it is not affected by other acids even when hot. 2. REACTION TO ALKALIES It is quickly damaged by alkalis. Thus, if laundered at home, mild or neutral soaps have to be used. 3. RESISTANCE TO BLEACH Chlorine bleaches are extremely harmful to wool. Peroxide bleaches are safe to use. 4. AFFINITY TO DYES They have high affinity to dye thus they dye well 5. RESISTANCE TO PERSPIRATION Wool is weakened by alkaline perspiration. Perspiration tends to weaken fibre and cause discoloration. It also tends to retain odours. BIOLOGICAL PROPERTIES 1. RESISTANCE TO MILDEW It is affected by mildew if left in damp conditions. 2. RESISTANCE TO INSECTS They are easily affected by the larvae of moths and carpet beetles. They need to be stored with neem leaves, in newsprint or with moth balls of protection against moth. USES OF WOOL Wool is used for apparel and making blankets, rugs and carpets. Wool can also be blended easily because of its excellent cohesiveness. It is blended with cotton, silk, linen, polyester and rayon.