CHAPTER TWO LECTURE 2 ON
NATURAL FIBERS OF VEGETABLE ORIGIN
BAHIR DAR UNIVERSITY (EiTEX)
By: Bademaw Abate(Lecturer)
NATURAL FIBERS OF VEGETABLE ORIGINCottonFlax JuteHemp Sisal
CottonAlmost pure cellulose, cotton is the world's most widely used natural fibre and still the undisputed "king" of the global textiles industry.
Thecottonfibre grows on the seed of a variety of plants of the genusGossypium. The most important Cottonspecies cultivated for fibre areG. hirsutum, which originated in Mexico and produces 90% of the world'scotton, G. barbadense, of Peruvian origin, which accounts for 5%. World averagecottonyields are around 800 kg per hectare.
ContCotton Fibres - the king of fibresCotton is a soft staple fibre that grown in a form known as a boll around the seeds of the cotton plant.
Cotton-cultivationCotton is grown in more than sixty countries of the world, but United States, India, Russia, Brazil, Egypt and China are some of the largest producers of cotton.The planting season varies depending on the geographical location. When the cotton bolls are ripe, they burst, exposing a soft mass of cotton fibres.
ContIn former times cotton harvesting was a hand operation, requiring considerable amount of hard labour. Now machine harvesting is also practised.In the picking method the cotton sections of the opened balls are removed from the burs leaving the burs on the stalk. In the pulling method, the open balls and burs are removed together. Sometimes leaves and other foreign matters also find their way in the cotton collected. Hence, pulled cotton is not as clean as picked cotton.
Ginning-Cotton The picked cotton contains about 66% seeds, 33% cotton fibers and small amounts of leaf and dirt. The separation of seeds and fibers is carried out by a process called ginning. The complete ginning process consists of :-preliminary cleaning and drying of cottonseparation of seeds from fibers, which are sometimes called cotton lint or linters, pressing and wrapping into a bale.
Cotton Fiber Structure and Components
Cont.Each cotton fiber is composed of concentric layers.
The cuticle layer on the fiber itself is separable from the fiber and consists of wax and pectin materials.
The primary wall, the most peripheral layer of the fiber, is composed of cellulosic crystalline fibrils.
The secondary wall of the fiber consists of three distinct layers. All three layers of the secondary wall include closely packed parallel fibrils with spiral winding of 25-35oand represent the majority of cellulose within the fiber.
Cont.The innermost part of cotton fiber- the lumen- is composed of the remains of the cell contents. Before boll opening, the lumen is filled with liquid containing the cell nucleus and protoplasm.
The twists and convolutions of the dried fiber are due to the removal of this liquid. The cross section of the fiber is bean-shaped, swelling almost round when moisture absorption takes place.
Raw Cotton Components:
80-90%Cellulose6-8%Water0.5 - 1%Waxes and fats0 - 1.5%Proteins4 - 6%Hemicelluloses and pectins1 - 1.8%Ash
Chemical structure of cottonCellulose is a polymer consisting of an hydroglucose units connected with 1,4 oxygen bridges in the beta position. The hydroxyl groups on the cellulose units enable hydrogen bonding between two adjacent polymer chains. The degree of polymerization of cotton is 9,000-15,000. Cellulose shows approximately 70% crystallinity.
PHYSICAL PROPERTIES OF COTTONFiber Length: Length of cotton fibre varies from 16mm to 52 mm depending upon the type of cotton.Fineness of cotton fiber: Longer the fibre, finer the fibre in case of cotton fibre. It is expressed in term of decitex and it varies from 1.1 to2.3 decitex.
Strength and extension of cotton fiber: Cotton fibre is fairly among natural fibres in relation to tenacity which is 3-5 g/den. disadvantage is low extension at break which is 5-7%.
ContThe fiber length to breadth ratio of cotton ranges from about 6000:1 for the longest and best types, to about 350:1 for the shortest coarsest cotton type. Elastic properties of cotton: Recovery from deformation of cotton fibre, yarn or fabric from applied load is very low. By applying heat it cant be achieved.
This property can be achieved by :-1.Chemical treatment to improve crease recovery, but the problem is the materials become harsher due to chemical treatment .2. blending or mixing of cotton with elastic fibre, e.g. polyester, blend ratio depends on the end use of the fabric.
Cont...Color: There is five recognized groups of color: white, gray, spotted, tinged, and yellow stained. As the color of cotton deteriorates, the process ability of the fibers decreases.Trash: A trash measurement describes the amount of non-lint materials (such as parts of cotton plant) in the fiber.
The values of trash content should be within the range from 0 to 4%.
CHEMICAL PROPERTIES OF COTTONCotton swells in a high humidity environment, in water and in concentrated solutions of certain acids, salts and bases. The swelling effect is usually attributed to the sorption of highly hydrated ions.
The moisture regain for cotton is about 7.1~8.5%.
Cotton is attacked by hot dilute or cold concentrated acid solutions. Acid hydrolysis of cellulose produces hydro-celluloses. Cold weak acids do not affect it.
Cont..The fibers show excellent resistance to alkalis.
There are a few other solvents that will dissolve cotton completely. One of them is a copper complex of cupramonium hydroxide and cupriethylene diamine.
Cotton degradation is usually attributed to oxidation, hydrolysis or both.
Uses of cotton
An estimated 60% ofcottonfibre is used as yarn and threads in a wide range of clothing, most notably in shirts, T-shirts and jeans, but also in coats, jackets, underwear and foundation garments.
Cottonis also used to make home furnishings, such as draperies, bedspreads and window blinds, and is the most commonly used fibre in sheets, pillowcases, towels.
Medical: bandages, sanitary towels. Industrial products containingcottoninclude book bindings and tarpaulins.
One of nature's strongest vegetable fibres, flax was also one of the first to beextracted, spun and woven into textilesThe plant
Flaxfibres obtained from the stems of the plantLinum usitatissimumare used mainly to make linen.The fibre
Like cotton,flaxfibre is a cellulose polymer, but its structure is more crystalline, making it stronger and stiffer to handle, and more easily wrinkled.Flaxfibres range in length up to 90 cm, and average 12 to 16 microns in diameter. They absorb and release water quickly, making linen comfortable to wear in hot weather.
Microscopic appearance of flax-
The cross markings, known as nodes, on flax fibers give them their characteristic microscopic appearance.
Production of Flax FiberRetting- this is an important process. The fleshy part of the stem is rotted by contact with water. Retting is a ferment process where the Pectin Ovurum(Pectin eater) bacteria eat the gum(pectin) which bind the fiber to the stem. There are 5 method of retting-
A. Dew retting-stems are spread out in fields and are exposed to rain, sun and dew for several weeks, until, the stalk begins to separate from the fiber. It takes around 15-30 days. Because of long exposure to the sun and other natural conditions, causes to discoloration of the fiber.
B. Water retting- the bundle of the stems are kept in running orsegmented water for about 2weeks . Swift running of watercarries away the bacteria andthus slow down the fermentation. The stem bundlesare covered with straw and stones are put on thestraw to give extra weight. After 2 weeks the stalks(upper portion of stem) separates out from the fiberand the bundles are taken out of the water and left todry.
C. Wooden vat retting- the stems are steeped in water at the controlled temperatur 75-90 in a Vat or in a container until the stems get soft. This is a fast process and the easiest method of retting and the quality of the fibers are good from this process.
D. Chemical retting- in this process the stems are treated with mild/dilute conc. Acid and alkalis then the fibers are easily removed from the stems.
E. Enzyme retting- enzyme retting is the safest and fastest process of retting, in this process the fibers can be taken out from the stems within few hours.
Uses of flax
Fine and regular longflaxfibres are spun into yarns for linen textiles. More than 70% of linen goes to clothing manufacture, where it is valued for its exceptional coolness in hot weather.
Linen fabric maintains a strong traditional niche among high quality household textiles - bed linen, furnishing fabrics, and interior decoration accessories.
ContShorterflaxfibres produce heavier yarns suitable for kitchen towels, sails, tents and canvas.
Lower fibre grades are used as reinforcement and filler in thermoplastic composites and thermoset resins used in automotive interior substrates, furniture and other consumer products.
/flax fabric is used around the home in curtains, bed linen, upholstery(COVERING ON FURNITURE ) , table dressings and soft furnishings(RUGS , MATS ).25
The strong threads made from jute fibre are used worldwide in sackcloth - and help sustain the livelihoods of millions of small farmers.The plant
Juteis extracted from the bark of the whitejuteplant,Corchorus capsularisand to a lesser extent from tossa