Nonwoven Fabric

A non-woven cloth

Nonwoven Fabric is a fabric like material made from long fibers, bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabrics, such as felt, which are neither woven nor knitted. Nonwoven materials typically lack strength unless densified or reinforced by a backing. In recent years, nonwovens have become an alternative to polyurethane foam.

Applications

Nonwoven fabrics are broadly defined as sheet or web structures bonded together by entangling fiber or filaments (and by perforating films) mechanically, thermally or chemically. They are flat, porous sheets that are made directly from separate fibers or from molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibers to yarn. Typically, a certain percentage of recycled fabrics and oil-based materials are used in nonwoven fabrics. The percentage of recycled fabrics vary based upon the strengh of material needed for the specific use.

Nonwoven fabrics are engineered fabrics that may be a limited life, single-use fabric or a very durable fabric. Nonwoven fabrics provide specific functions such as absorbency, liquid repellency, resilience, stretch, softness, strength, flame retardancy, washability, cushioning, filtering, bacterial barrier and sterility. These properties are often combined to create fabrics suited for specific jobs, while achieving a good balance between product use-life and cost. They can mimic the appearance, texture and strength of a woven fabric and can be as bulky as the thickest paddings. In combination with other materials they provide a spectrum of products with diverse properties, and are used alone or as components of apparel, home furnishings, health care, engineering, industrial and consumer goods.

Non-woven materials are used in numerous applications, including:

Hygiene

baby diapers feminine hygiene adult incontinence products wipes bandages and wound dressings

Medical

isolation gowns surgical gowns surgical drapes and covers surgical scrub suits caps

Filters

gasoline, oil and air - including HEPA filtration water, coffee, tea bags liquid cartridge and bag filters vacuum bags allergen membranes or laminates with non woven layers

Geotextiles

soil stabilizers and roadway underlayment foundation stabilizers erosion control canals construction drainage systems geomeambranes protection frost protection agriculture mulch pond and canal water barriers sand infiltration barrier for drainage tile

Other

carpet backing, primary and secondary composites

o marine sail laminates o tablecover laminates o chopped strand mat

backing/stabilizer for machine embroidery packaging - to sterilize medical products insulation (fiberglass batting) pillows, cushions, and upholstery padding batting in quilts or comforters consumer and medical face masks mailing envelopes tarps, tenting and transportation (lumber, steel) wrapping disposable clothing (foot coverings, coveralls)

Manufacturing processes

Nonwovens are typically manufactured by putting small fibers together in the form of a sheet or web (similar to paper on a paper machine), and then binding them either mechanically (as in the case of felt, by interlocking them with serrated needles such that the inter-fiber friction results in a stronger fabric), with an adhesive, or thermally (by applying binder (in the form of powder, paste, or polymer melt) and melting the binder onto the web by increasing temperature).

Staple nonwovens

Staple nonwovens are made in 2 steps. Fibers are first spun, cut to a few centimeters length, and put into bales. These bales are then dispersed on a conveyor belt, and the fibers are spread in a uniform web by a wetlaid process or by carding. Wetlaid operations typically use 1/4" to 3/4" long fibers, but sometimes longer if the fiber is stiff or thick. Carding operations typically use ~1.5" long fibers. Rayon used to be a common fiber in nonwovens, now greatly replaced by PET and PP. Fiberglass is wetlaid into mats for use in roofing and shingles. Synthetic fiber blends are wetlaid along with cellulose for single-use fabrics. Staple nonwovens are bonded by using either resin or thermally. Bonding can be throughout the web by resin saturation or overall thermal bonding or in a distinct pattern via resin printing or thermal spot bonding. Conforming with staple fibers usually refers to a combination with meltblown, often used in high-end textile insulations. Melt Blown non wovens are produced by extruding melted polymer fibers through a spin net or die consisting of up to 40 holes per inch to form long thin fibers which are stretched and cooled by passing hot air over the fibers as they fall from the die.The resultant web is collected into rolls and subsequently converted to finished products.The extremely fine fibers typically polypropylene differ from other extrusions particularly spun bond in that they have low intrinsic strength but much smaller size offering key properties.Often melt blown is added to spun bond to form SM or SMS webs, which are strong and offer the intrinsic benefits of fine fibers such as fine filtration, low pressure drop as used in face masks or filters and physical benefits such as acoustic insulation as used in dishwashers. One of the largest users of SM and SMS materials is the disposable diaper and feminine care industry[1]

Spunlaid nonwovens

Spunlaid nonwovens are made in one continuous process. Fibers are spun and then directly dispersed into a web by deflectors or can be directed with air streams. This technique leads to faster belt speeds, and cheaper costs. Several variants of this concept are available, but the leading technology is the REICOFIL machinery[2]. PP spunbonds run faster and at lower temperatures than PET spunbonds, mostly due to the difference in melting points. Spunbond has been combined with meltblown nonwovens, conforming them into a layered product called SMS (spun-melt-spun). Meltblown nonwovens have extremely fine fiber diameters but are not strong fabrics. SMS fabrics, made completely from PP are water-repellent and fine enough to serve as disposable fabrics. Meltblown is often used as filter media, being able to capture very fine particles. Spunlaid is bonded by either resin or thermally. Regarding the bonding of Spunlaid, Rieter [3] has launched a new generation of nonwovens called Spunjet. In fact, Spunjet is the bonding of the Spunlaid filaments thanks to the hydroentanglement

Other

Nonwovens can also start with films and fibrillate, serrate or vacuum-form them with patterned holes. Fiberglass nonwovens are of two basic types. Wet laid mat or "glass tissue" use wet-chopped,

heavy denier fibers in the 6 to 20 micrometre diameter range. Flame attenuated mats or "batts" use discontinuous fine denier fibers in the 0.1 to 6 range. The latter is similar, though run at much higher temperatures, to meltblown thermoplastic nonwovens. Wet laid mat is almost always wet resin bonded with a curtain coater, while batts are usually spray bonded with wet or dry resin. An unusual process produces polyethylene fibrils in a Freon-like fluid, forming them into a paper-like product and then calendering them to create Tyvek.

Bonding

Both staple and spunlaid nonwovens would have no mechanical resistance, perse, without the bonding step. Several methods can be used:

thermal bonding o using a large oven for curing o calendering through heated rollers (called spunbond when combined with spunlaid),

calenders can be smooth faced for an overall bond or patterned for a softer, more tear resistant bond

hydro-entanglement: mechanical intertwining of fibers by water jets (called spunlace) ultrasonic pattern bonding, often used in high-loft or fabric insulation/quilts/bedding needlefelt: mechanical intertwining of fibers by needles chemical bonding (wetlaid process): use of binders (such as latex emulsion or solution

polymers) to chemically join the fibers. A more expensive route uses binder fibers or powders that soften and melt to hold other non-melting fibers together

one type of cotton staple nonwoven is treated with sodium hydroxide to shrink bond the mat, the caustic causes the cellulose-based fibers to curl and shrink around one another as the bonding technique

meltblown is very weakly bonded from the air attenuated fibers intertangling with themselves during web formation as well as the temporary tackiness when they are forming

one unusual polyamide spunbond (Cerex) is self-bonded with gas-phase acid

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CoirCoir (From Malayalam kayar, cord) is a coarse fiber extracted from the fibrous outer shell of a coconut.

Structure

Coir fibers are found between the husk and the outer shell of a coconut. The individual fiber cells are narrow and hollow, with thick walls made of cellulose. They are pale when immature but later become hardened and yellowed as a layer of lignin is deposited on their walls. There are two varieties of coir. Brown coir is harvested from fully ripened coconuts. It is thick, strong and has high abrasion resistance. It is typically used in mats, brushes and sacking. Mature brown coir fibers contain more lignin and less cellulose than fibers such as flax and cotton and so are stronger but less flexible. They are made up of small threads, each about 1 mm long and 10 to 20 micrometres in diameter. White coir fibers are harvested from the coconuts before they are ripe. These fibers are white or light brown in color and are smoother and finer, but also weaker. They are generally spun to make yarn that is used in mats or rope.

The coir fiber is relatively water-proof and is one of the few natural fibers resistant to damage by salt water. Fresh water is used to process brown coir, while sea water and fresh water are both used in the production of white coir.

Processing

Segregation of Coir fibre

Coconuts are the seed of the palm trees. These palms flower on a monthly basis and the fruit takes 1 year to ripen. A typical palm tree has fruit in every stage of maturity. A mature tree can produce 50–100 coconuts per year. Coconuts can be harvested from the ground once they have ripened and fallen or they can be harvested while still on the tree. A human climber can harvest approximately 25 trees in a day, while a knife attached to a pole can up the number to 250 trees harvested in a day. Monkeys can also be trained to harvest the coconuts, but this practice is less efficient than other methods. Green coconuts, harvested after about six to twelve months on the plant, contain pliable white fibres. Brown fibre is obtained by harvesting fully mature coconuts when the nutritious layer surrounding the seed is ready to be processed into copra and desiccated coconut. The fibrous layer of the fruit is then separated from the hard shell (manually) by driving the fruit down onto a spike to split it (De-husking). A well seasoned husker can manually separate 2,000 coconuts per day.

Machines are now available which crush the whole fruit to give the loose fibres. These machines can do up to 2,000 coconuts per hour.

Brown fibre

The fibrous husks are soaked in pits or in nets in a slow moving body of water to swell and soften the fibres. The long bristle fibres are separated from the shorter mattress fibres underneath the skin of the nut, a process known as wet-milling. The mattress fibres are sifted to remove dirt and other rubbish, dried in the sun and packed into bales. Some mattress fibre is allowed to retain more moisture so that it retains its elasticity for 'twisted' fibre production. The coir fibre is elastic enough to twist without breaking and it holds a curl as though permanently waved. Twisting is done by simply making a rope of the hank of fibre and twisting it using a machine or by hand. The longer bristle fibre is washed in clean water and then dried before being tied into bundles or hunks. It may then be cleaned and 'hackled' by steel combs to straighten the fibres and remove any shorter fibre pieces. Coir bristle fibre can also be bleached and dyed to obtain hanks of different colours.

White fibre

The immature husks are suspended in a river or water-filled pit for up to ten months. During this time micro-organisms break down the plant tissues surrounding the fibres to loosen them — a process known as retting. Segments of the husk are then beaten by hand to separate out the long fibres which are subsequently dried and cleaned. Cleaned fibre is ready for spinning into yarn using a simple one-handed system or a spinning wheel.

Uses

Brown coir is used in floor mats and doormats, brushes, mattresses, floor tiles and sacking. A small amount is also made into twine. Pads of curled brown coir fibre, made by needle-felting (a machine technique that mats the fibres together) are shaped and cut to fill mattresses and for use in erosion control on river banks and hillsides. A major proportion of brown coir pads are sprayed with rubber latex which bonds the fibres together (rubberised coir) to be used as upholstery padding for the automobile industry in Europe. The material is also used for insulation and packaging.

The major use of white coir is in rope manufacture. Mats of woven coir fibre are made from the finer grades of bristle and white fibre using hand or mechanical looms. White coir also used to make fishing nets due to its strong resilience to salt water.

In horticulture, coir is recommended as substitute for sphagnum moss because it is free of bacteria and fungal spores, and is sustainably produced without the environmental damage caused by peat mining.

Coconut coir from Mexico has been found to contain large numbers of colonies of the beneficial fungus Aspergillus terreus which acts as a biological control against plant pathogenic fungi. [2]

Major producers

Total world coir fibre production is 250,000 tonnes. The coir fibre industry is particularly important in some areas of the developing world. India, mainly the coastal region of Kerala State, produces 60% of the total world supply of white coir fibre. Sri Lanka produces 36% of the total world brown fibre output. Over 50% of the coir fibre produced annually throughout the world is consumed in the

countries of origin, mainly India. Together India and Sri Lanka produce 90% of the 250,000 metric tons of coir produced every year.

In the recent past, countries such as Mexico, Indonesia, Vietnam and certain Caribbean countries have started to supply to the global market in large scale.

Waste / By-products

Coir fibres make up about 1/3 of the coconut pulp. The other 2/3 is called the pith or dust, it is biodegradable but takes 20 years to decompose. Once considered as waste material , coir is now being used as mulch, soil treatment and a hydroponic growth medium.

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BananaBanana

'Cavendish' bananas

Scientific classification

Kingdom: Plantae

Family: Musaceae

Genus: Musa

Banana is the common name for a type of fruit and also the herbaceous plants of the genus Musa which produce this commonly eaten fruit. They are native to the tropical region of Southeast Asia. Bananas are likely to have been first domesticated in Papua New Guinea.[1] Today, they are cultivated throughout the tropics.[2]

Banana plants are of the family Musaceae. They are cultivated primarily for their fruit, and to a lesser extent for the production of fibre and as ornamental plants. As the banana plants are normally tall and fairly sturdy they are often mistaken for trees, but their main or upright stem is actually a pseudostem. For some species this pseudostem can reach a height of up to 2–8 m, with leaves of up to 3.5 m in length. Each pseudostem can produce a bunch of green bananas which when ripened often turn yellow or sometimes red. A variety was even recently discovered in a rainforest in Asia that turns purple. This then dies and is replaced by another pseudostem.

The banana fruit grow in hanging clusters, with up to 20 fruit to a tier (called a hand), and 3–20 tiers to a bunch. The total of the hanging clusters is known as a bunch, or commercially as a "banana stem", and can weigh from 30–50 kg. The fruit averages 125 g, of which approximately 75% is water and 25% dry matter content. Each individual fruit (known as a banana or 'finger') has a protective outer layer (a peel or skin) with a fleshy edible inner portion. Both skin and inner part can be eaten raw or cooked. Western cultures generally eat the inside raw and throw away the skin while some Asian cultures generally eat both the skin and inside cooked. Typically, the fruit has numerous strings (called 'phloem bundles') which run between the skin and inner part. Bananas are a valuable source of vitamin B6, vitamin C, and potassium.

Bananas are grown in at least 107 countries.[3] In popular culture and commerce, "banana" usually refers to soft, sweet "dessert" bananas. The bananas from a group of cultivars with firmer, starchier fruit are called plantains. Bananas may also be cut and dried and eaten as a type of chip. Dried bananas are also ground into banana flour.

Although the wild species have fruits with numerous large, hard seeds, virtually all culinary bananas have seedless fruits. Bananas are classified either as dessert bananas (meaning they are yellow and fully ripe when eaten) or as green cooking bananas. Almost all export bananas are of the dessert types; however, only about 10–15% of all production is for export, with the United States and European Union being the dominant buyers.

Botany

This section requires expansion.

Bananas displayed in a Singapore supermarket.

The banana plant is a pseudostem that grows to 6 to 7.6 metres (20–25 feet) tall, growing from a corm. Leaves are spirally arranged and may grow 2.7 metres (9 ft) long and 60 cm (2 ft) wide. The banana plant is the largest of all herbaceous flowering plants. The large leaves grow whole, but are easily torn by the wind, resulting in the familiar frond look.

A single, sterile, male banana flower, also known as the banana heart is normally produced by each stem (though on rare occasions more can be produced—a single plant in the Philippines has five[7]). Banana hearts are used as a vegetable in Southeast Asia, steamed, in salads, or eaten raw.[8] The female flowers are produced further up the stem and produce the actual fruit without requiring fertilization. The fruit has been described as a "leathery berry".[9] In cultivated varieties, the seeds have degenerated nearly to non-existence; their remnants are tiny black specks in the interior of the fruit. The ovary is inferior to the flower; because of their stiff stems and the positioning of the ovary and flower, bananas grow sticking up, not hanging down.

Some sources assert that the genus of the banana, Musa, is named for Antonio Musa, physician to the Emperor Augustus.[10] Others say that Linnaeus, who gave the genus its name in 1750, simply adapted an Arabic word for banana, mauz.[11] The word banana itself comes from the Arabic word banan, which means "finger".[11] The genus contains numerous species; several produce edible fruit, while others are cultivated as ornamentals.[12]

Properties

Banana, raw, edible partsNutritional value per 100 g (3.5 oz)

Energy 90 kcal   370 kJ

Carbohydrates     22.84 g

- Sugars  12.23 g

- Dietary fiber  2.6 g  

Fat 0.33 g

Protein 1.09 g

Vitamin A equiv.  3 μg  0%

Thiamine (Vit. B1)  0.031 mg   2%

Riboflavin (Vit. B2)  0.073 mg   5%

Niacin (Vit. B3)  0.665 mg   4%

Pantothenic acid (B5)  0.334 mg 7%

Vitamin B6  0.367 mg 28%

Folate (Vit. B9)  20 μg  5%

Vitamin C  8.7 mg 15%

Calcium  5 mg 1%

Iron  0.26 mg 2%

Magnesium  27 mg 7% 

Phosphorus  22 mg 3%

Potassium  358 mg   8%

Zinc  0.15 mg 1%

One banana is 100–150 g.

Percentages are relative to US

recommendations for adults.

Source: USDA Nutrient database

Bananas come in a variety of sizes and colors when ripe, including yellow, purple, and red. Bananas can be eaten raw though some varieties are generally cooked first. Depending upon cultivar and ripeness, the flesh can vary in taste from starchy to sweet, and texture from firm to mushy. Unripe or green bananas and plantains are used for cooking various dishes such as banana pudding and are the staple starch of many tropical populations. Banana sap is extremely sticky and can be used as a practical adhesive. Sap can be obtained from the pseudostem, from the fruit peelings, or from the fruit flesh.

Most production for local sale is of green cooking bananas and plantains, as ripe dessert bananas are easily damaged while being transported to market. Even when transported only within their country of origin, ripe bananas suffer a high rate of damage and loss.[citation needed]

The commercial dessert cultivars most commonly eaten in temperate countries (species Musa acuminata or the hybrid Musa × paradisiaca, a cultigen) are imported in large quantities from the tropics. They are popular in part because, being a non-seasonal crop, they are available fresh year-round. In global commerce, by far the most important of these banana cultivars is 'Cavendish', which accounts for the vast bulk of bananas exported from the tropics. The Cavendish gained popularity in the 1950s after the previously mass produced cultivar, Gros Michel, became commercially unviable due to Panama disease, a fungus which attacks the roots of the banana plant.

The most important properties making 'Cavendish' the main export banana are related to transport and shelf life rather than taste; major commercial cultivars rarely have a superior flavor[citation needed] compared to the less widespread cultivars. Export bananas are picked green, and then usually ripened in ripening rooms when they arrive in their country of destination. These are special rooms made air-tight and filled with ethylene gas to induce ripening. Bananas can be ordered by the retailer "ungassed", however, and may show up at the supermarket still fully green. While these bananas will ripen more slowly, the flavor will be notably richer[citation needed], and the banana peel can be allowed to reach a yellow/brown speckled phase, and yet retain a firm flesh inside. Thus, shelf life is somewhat extended.

The vivid yellow color normally associated with supermarket bananas is in fact a side-effect of the artificial ripening process. Cavendish bananas that have been allowed to ripen naturally on the plant have a greenish-yellow appearance which changes to a brownish-yellow as they ripen further. Although both the flavor and texture of "tree ripened" bananas is generally regarded as superior to any type green-picked fruit, once natural ripening has commenced the shelf life is typically only 7–10 days, making commercial distribution impractical. For most people the only practical means of obtaining such fruit is growing it themselves, however this is also somewhat problematic, as the bananas all tend to ripen at once and have very poor keeping properties.

The flavor and texture of bananas are also affected by the temperature at which they ripen. Bananas are refrigerated to between 13.5 and 15 °C (57 and 59 °F) during transportation. At lower temperatures, the ripening of bananas permanently stalls, and the bananas will eventually turn gray as cell walls break down. The skins of ripe bananas will quickly turn black in the 4°C environment of a domestic refrigerator, although the fruit inside remains unaffected.

It should be noted that Musa × paradisiaca is also the generic name for the common plantain, a coarser and starchier variant not to be confused with Musa acuminata or the Cavendish variety.

M. acuminata x balbisiana inflorescence, partially opened.

In addition to the fruit, the flower of the banana plant (also known as banana blossom or banana heart) is used in Southeast Asian, Telugu,Tamil, Bengali, and Kerala (India) cuisine, either served raw or steamed with dips or cooked in soups and curries. Banana flowers are somewhat similar in taste to artichokes and can be eaten in much the same way where one scrapes off the fleshy part of the petals and eats the whole of the heart. The tender core of the banana plant's trunk is also used in Telugu, Bengali and Kerala cooking, and notably in the Burmese dish mohinga. Bananas fried with batter is a popular dessert in Malaysia, Singapore, and Indonesia. Banana fritters can be served with ice cream as well. Bananas are also eaten deep fried, baked in their skin in a split bamboo, or steamed in glutinous rice wrapped in a banana leaf in Burma where bunches of green bananas surrounding a green coconut in a tray form an important part of traditional offerings to the Buddha and the Nats. The juice extract prepared from the tender core is used to treat kidney stones and Blood pressure.

The leaves of the banana plant are large, flexible, and waterproof. They are used many ways, including as umbrellas and to wrap food for cooking or storage. Banana leaves are also used to serve food in India and other Asian countries.

Banana chips are a snack produced from dehydrated or fried banana or plantain slices, which have a dark brown color and an intense banana taste. Bananas have also been used in the making of jam. Unlike other fruits, it is difficult to extract juice from bananas because when compressed a banana simply turns to pulp.

Seeded bananas (Musa balbisiana), the forerunner of the common domesticated banana, are sold in markets in Indonesia.

In India, juice is extracted from the corm and used as a home remedy for the treatment of jaundice, sometimes with the addition of honey, and for kidney stones.

Ripened bananas (left, under sunlight) fluoresce in blue when exposed to UV light.

A 2008 study reported that ripe bananas exhibit a blue fluorescence when exposed to ultraviolet light. This property is attributed to the degradation of chlorophyll giving rise to the accumulation of a fluorescent product in the skin of the fruit. The chlorophyll breakdown product is stabilized by a propionate ester group. Banana-tree leaves also fluoresce in the same way. Green bananas do not show any sign of fluorescence. The study suggested that this allows animals which are capable of seeing in the ultraviolet spectrum to detect ripened bananas.[16]

Banana output in 2005

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Top banana producing nations - 2007(in million metric tons)

 India 21.77

 China 8.04

 Philippines 7.48

 Brazil 7.10

 Ecuador 6.00

 Indonesia 5.46

 Tanzania 3.50

 Costa Rica 2.08

 Thailand 2.00

 Mexico 1.96

 Burundi 1.60

 Guatemala 1.57

 Vietnam 1.36

 Kenya 1.19

 Bangladesh 1.00

 Honduras 0.91

 Egypt 0.88

 Papua New Guinea 0.87

 Cameroon 0.86

 Uganda 0.62

World total 72.5

Source: Food and Agriculture Organization of the United Nations[3]

Bananas and plantains constitute a major staple food crop for millions of people in developing countries. In most tropical countries, green (unripe) bananas used for cooking represent the main cultivars. Cooking bananas are very similar to potatoes in how they are used. Both can be fried, boiled, baked, or chipped and have similar taste and texture when served. One green cooking banana has about the same calorie content as one potato.

In 2003, India led the world in banana production, representing approximately 23% of the worldwide crop, most of which was for domestic consumption. The four leading banana exporting countries were Ecuador, Costa Rica, the Philippines, and Colombia, which together accounted for about two-thirds of the world's exports, each exporting more than 1 million tons. Ecuador alone provided more than 30% of global banana exports, according to FAO statistics.

The vast majority of producers are small-scale farmers growing the crop either for home consumption or for local markets. Because bananas and plantains will produce fruit year-round, they provide an extremely valuable source of food during the hunger season (that period of time when all the food from the previous harvest has been consumed, and the next harvest is still some time away). It is for these reasons that bananas and plantains are of major importance to food security.

Women in Belize sorting bananas and cutting them from bunches.

Bananas are among the most widely consumed foods in the world. Most banana farmers receive a low unit price for their produce as supermarkets buy enormous quantities and receive a discount for that business. Competition amongst supermarkets has led to reduced margins in recent years which in turn has led to lower prices for growers. Chiquita, Del Monte, Dole, and Fyffes grow their own bananas in Ecuador, Colombia, Costa Rica, Guatemala, and Honduras. Banana plantations are capital intensive and demand high expertise, so the majority of independent growers are large and wealthy landowners of these countries. This has led to bananas being available as a "fair trade" or Rainforest Alliance certified item in some countries.

The banana has an extensive trade history beginning with the founding of the United Fruit Company (now Chiquita) at the end of the nineteenth century. For much of the 20th century, bananas and coffee dominated the export economies of Central America. In the 1930s, bananas and coffee made

up as much as 75% of the region's exports. As late as 1960, the two crops accounted for 67% of the exports from the region. Though the two were grown in similar regions, they tended not to be distributed together. The United Fruit Company based its business almost entirely on the banana trade, as the coffee trade proved too difficult for it to control. The term "banana republic" has been broadly applied to most countries in Central America, but from a strict economic perspective only Costa Rica, Honduras, and Panama were actual "banana republics", countries with economies dominated by the banana trade.

The countries of the European Union have traditionally imported many of their bananas from the former European island colonies of the Caribbean, paying guaranteed prices above global market rates. As of 2005, these arrangements were in the process of being withdrawn under pressure from other major trading powers, principally the United States. The withdrawal of these indirect subsidies to Caribbean producers is expected to favour the banana producers of Central America, in which American companies have an economic interest.

The United States has minimal banana production. 14,000 tons of bananas were grown in Hawaii in 2001. Bananas have also been grown in Florida and southern California.

History

Early cultivation

The domestication of bananas took place in southeastern Asia. Many species of wild bananas still exist in New Guinea, Malaysia, Indonesia, and the Philippines. Recent archaeological and palaeoenvironmental evidence at Kuk Swamp in the Western Highlands Province of Papua New Guinea suggests that banana cultivation there goes back to at least 5000 BCE, and possibly to 8000 BCE. This would make the New Guinean highlands the place where bananas were first domesticated. It is likely that other species of wild bananas were later also domesticated elsewhere in southeastern Asia. Southeast Asia is the region of primary diversity of the banana. Areas of secondary diversity are found in Africa, indicating a long history of banana cultivation in the region.

Actual and probable diffusion of bananas during Islamic times (700–1500 AD)

Some recent discoveries of banana phytoliths in Cameroon dating to the first millennium BCE have triggered an as yet unresolved debate about the antiquity of banana cultivation in Africa. There is linguistic evidence that bananas were already known in Madagascar around that time. The earliest evidence of banana cultivation in Africa before these recent discoveries dates to no earlier than late 6th century AD. In this view, bananas were introduced to the east coast of Africa by Muslim Arabs.

The banana may have been present in isolated locations of the Middle East on the eve of the rise of Islam. There is some textual evidence that the prophet Muhammad was familiar with it. The spread of Islam was followed by the far reaching diffusion of bananas. There are numerous references to it in Islamic texts (such as poems and hadiths) beginning in the ninth century. By the tenth century the banana appears in texts from Palestine and Egypt. From there it diffused into north Africa and Muslim Iberia. In fact, during the medieval ages, bananas from Granada were considered amongst the best in the Arab world. In 650, Islamic conquerors brought the banana to Palestine.

Bananas were introduced to the Americas by Portuguese sailors who brought the fruits from West Africa in the 1500s. The word banana is of West African origin, from the Wolof language, and passed into English via Spanish or Portuguese.

Plantation cultivation

In the 15th and 16th century, Portuguese colonists started banana plantations in the Atlantic Islands, Brazil, and western Africa. As late as the Victorian Era, bananas were not widely known in Europe, although they were available via merchant trade. Jules Verne references bananas with detailed descriptions so as not to confuse readers in his book Around the World in Eighty Days (1872).

In the early 20th century, bananas began forming the basis of large commercial empires, exemplarized by the United Fruit Company, which created immense banana plantations especially in Central and South America. These were usually extremely commercially exploitative, and the term "Banana republic" was coined for states like Honduras and Guatemala, representing the fact that "servile dictatorships" were created and abetted by these companies and their political backers, for example in the USA.

Cultivation

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Fruits of wild-type bananas have numerous large, hard seeds.

Banana corms, used in the propagation of domesticated bananas.

While the original bananas contained rather large seeds, triploid (and thus seedless) cultivars have been selected for human consumption. These are propagated asexually from offshoots of the plant. The plant is allowed to produce 2 shoots at a time; a larger one for fruiting immediately and a smaller "sucker" or "follower" that will produce fruit in 6–8 months time. The life of a banana plantation is 25 years or longer, during which time the individual stools or planting sites may move slightly from their original positions as lateral rhizome formation dictates.

Cultivated bananas are parthenocarpic, which makes them sterile and unable to produce viable seeds. Lacking seeds, another form of propagation is required. This normally involves removing and transplanting part of the underground stem (called a corm). Usually this is done by carefully removing a sucker (a vertical shoot that develops from the base of the banana pseudostem) with some roots intact. However, small sympodial corms, representing not yet elongated suckers, are

easier to transplant and can be left out of the ground for up to 2 weeks; they require minimal care and can be boxed together for shipment.

Contrary to what is widely believed, it is not actually necessary to include any of the corm or root structure to propagate bananas; severed suckers with no root material attached can be successfully propagated in damp sand, although this takes somewhat longer.

In some countries, bananas are also commercially propagated by means of tissue culture. This method is preferred since it ensures disease-free planting material. When using vegetative parts such as suckers for propagation, there is a risk of transmitting diseases (especially the devastating Panama disease).

Pests, diseases, and natural disasters

Main article: List of banana and plantain diseases

Banana bunches are sometimes encased in plastic bags for protection. The bags may be coated with pesticides.

Inspecting bananas for fruit flies

While in no danger of outright extinction, the most common edible banana cultivar 'Cavendish' (extremely popular in Europe and the Americas) could become unviable for large-scale cultivation in the next 10–20 years. Its predecessor 'Gros Michel', discovered in the 1820s, has already suffered this fate. Like almost all bananas, it lacks genetic diversity, which makes it vulnerable to diseases, which threaten both commercial cultivation and the small-scale subsistence farming. Some commentators have further remarked that those variants which could replace what much of the world considers a "typical banana" are so different that most people would not consider them the

same fruit, and blame the decline of the banana on monogenetic cultivation driven by short-term commercial exploitation motives.[27]

Major diseases

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Major afflictions of bananas include:

Panama Disease (Race 1): fusarium wilt (a soil fungus). The fungus enters the plants through the roots and moves up with water into the trunk and leaves, producing gels and gums. These plug and cut off the flow of water and nutrients, causing the plant to wilt. Prior to 1960 almost all commercial banana production centered on the cultivar 'Gros Michel', which was highly susceptible to fusarium wilt and collapse, exposing the rest of the plant to lethal amounts of sunlight.[30] The cultivar 'Cavendish' was chosen as a replacement for 'Gros Michel' because out of the resistant cultivars it was viewed as producing the highest quality fruit. However, more care is required for shipping the 'Cavendish' banana, and its quality compared to 'Gros Michel' is debated.

However, according to current references, a deadly form of Panama disease is infecting the world's Cavendish banana plants. All are genetically identical, which causes problems when it comes to disease resistance. However, researchers are experimenting with hundreds of feral varieties to find out which one(s) are resistant.[30]

Tropical Race 4: a reinvigorated strain of Panama disease first discovered in 1993. This is a virulent form of fusarium wilt that has wiped out 'Cavendish' in several southeast Asian countries. It has yet to reach the Americas; however, soil fungi can easily be carried on boots, clothing, or tools. This is how Tropical Race 4 moves from one plantation to another and is its most likely route into Latin America. The Cavendish cultivar is highly susceptible to TR4, and over time, Cavendish is almost certain to be eliminated from commercial production by this disease. Unfortunately, the only known defense to TR4 is genetic resistance.

Black Sigatoka : a fungal leaf spot disease first observed in Fiji in 1963 or 1964. Black Sigatoka (also known as Black Leaf Streak) has spread to banana plantations throughout the tropics due to infected banana leaves being used as packing material. It affects all of the main cultivars of bananas and plantains, impeding photosynthesis by turning parts of their leaves black, and eventually killing the entire leaf. Being starved for energy, fruit production falls by 50% or more, and the bananas that do grow suffer premature ripening, making them unsuitable for export. The fungus has shown ever increasing resistance to fungicidal treatment, with the current expense for treating 1 hectare exceeding $1000 per year. In addition to the financial expense there is the question of how long such intensive spraying can be justified environmentally. Several resistant cultivars of banana have been developed, but none has yet received wide scale commercial acceptance due to taste and texture issues.

Banana Bunchy Top Virus (BBTV): this virus is spread from plant to plant by aphids. It causes stunting of the leaves resulting in a "bunched" appearance. Generally, a banana plant infected with the virus will not set fruit, although mild strains exist in many areas which do allow for some fruit production. These mild strains are often mistaken for malnourishment, or a disease other than BBTV. There is no cure for BBTV, however its effect can be minimised by planting only tissue cultured plants (In-vitro propagation), controlling the

aphids, and immediately removing and destroying any plant from the field that shows signs of the disease.

Even though it is no longer viable for large scale cultivation, 'Gros Michel' is not extinct and is still grown in areas where Panama disease is not found. Likewise, "Cavendish" is in no danger of extinction, but it may leave the shelves of the supermarkets for good if diseases make it impossible to supply the global market. It is unclear if any existing cultivar can replace 'Cavendish' on a scale needed to fill current demand, so various hybridisation and genetic engineering programs are working on creating a disease-resistant, mass-market banana.

In Australia

Banana plants destroyed after Cyclone Larry in 2006

Australia is relatively free of plant diseases and therefore prohibits imports. When Cyclone Larry wiped out Australia's domestic banana crop in 2006, bananas became relatively expensive, due to both low supply domestically and the existence of laws prohibiting banana imports. Prices have since fallen as production has reverted back to a steady rate.

In East Africa

Most bananas grown worldwide are used for local consumption. In the tropics, bananas, especially cooking bananas, represent a major source of food, as well as a major source of income for smallholder farmers. It is in the East African highlands that bananas reach their greatest importance as a staple food crop. In countries such as Uganda, Burundi, and Rwanda per capita consumption has been estimated at 450 kg per year, the highest in the world. Ugandans use the same word "matooke" to describe both banana and food.

In the past, the banana was a highly sustainable crop with a long plantation life and stable yields year round. However with the arrival of the Black sigatoka fungus, banana production in eastern Africa has fallen by over 40%. For example, during the 1970s, Uganda produced 15 to 20 tonnes of bananas per hectare. Today, production has fallen to only 6 tonnes per hectare.

The situation has started to improve as new disease resistant cultivars have been developed by the International Institute of Tropical Agriculture and NARO such as the FHIA-17 (known in Uganda as the Kabana 3). These new cultivars taste different from the traditionally grown banana which has slowed their acceptance by local farmers. However, by adding mulch and animal manure to the soil around the base of the banana plant, these new cultivars have substantially increased yields in the areas where they have been tried.

The International Institute of Tropical Agriculture and NARO, funded by the Rockefeller Foundation and CGIAR have started trials for genetically modified banana plants that are resistant

to both Black sigatoka and banana weevils. It is developing cultivars specifically for smallholder or subsistence farmers.

Health benefits

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Potential health benefits of banana consumption.[31][32]

By a high potassium to sodium content, bananas may prevent high blood pressure and its complications. High fiber content may also contribute to this effect. High potassium may also prevent renal calcium loss, in effect preventing bone breakdown. In diarrhea, it contributes with electrolyte replacement, as well as increased absorption of nutrients. Bananas also have some antacid effect, protecting from peptic ulcers. Pectin content, a hydrocolloid, can ease constipation by normalizing movement through the intestine. The low glycemic index in unripe bananas is of particular benefit to people with diabetes. High fructooligosaccharide content may work as a prebiotic, nourishing the intestinal flora to produce beneficial vitamins and enzymes.[31] Carotenoid content has antioxidant effects, and protects against vitamin A deficiency, resulting in e.g. night blindness. Moderate consumption decreases risk of kidney cancer, possibly due to antioxidant phenolic compounds. In contrast, large consumption of highly processed fruit juice increases the risk of kidney cancer. In a 2001 study <Hamilton & Jensen> it was established that all bananas contain the same number of calories. The study determined that the calorific density varied depending on the size of banana to keep the calorific value at a constant 163 Kcal.

Fruit consumption in general decreases the risk of age-related macular degeneration.[31]

Allergic reactions

There are two forms of banana allergy. One is oral allergy syndrome which causes itching and swelling in the mouth or throat within one hour after ingestion and is related to birch tree and other pollen allergies. The other is related to latex allergies and causes urticaria and potentially serious upper gastrointestinal symptoms.[33]

Fibre

Textiles

The banana plant has long been a source of fibre for high quality textiles. In Japan, the cultivation of banana for clothing and household use dates back to at least the 13th century. In the Japanese system, leaves and shoots are cut from the plant periodically to ensure softness. The harvested shoots must first be boiled in lye to prepare the fibres for the making of the yarn. These banana shoots produce fibres of varying degrees of softness, yielding yarns and textiles with differing qualities for specific uses. For example, the outermost fibres of the shoots are the coarsest, and are suitable for tablecloths, whereas the softest innermost fibres are desirable for kimono and kamishimo. This traditional Japanese banana cloth making process requires many steps, all performed by hand.

In another system employed in Nepal, the trunk of the banana plant is harvested instead, small pieces of which are subjected to a softening process, mechanical extraction of the fibres, bleaching, and drying. After that, the fibres are sent to the Kathmandu Valley for the making of high end rugs with a textural quality similar to silk. These banana fibre rugs are woven by the traditional Nepalese hand-knotted methods, and are sold RugMark certified.

Paper

Main article: Banana paper

Banana fibre is also used in the production of banana paper. Banana paper is used in two different senses: to refer to a paper made from the bark of the banana plant, mainly used for artistic purposes, or paper made from banana fiber, obtained from an industrialized process, from the stem and the non usable fruits. This paper can be either hand-made or made by industrialized machine.

Storage and transport

Banana storage room, , 1913

In the current world marketing system, bananas are grown in the tropics. The fruit therefore has to be transported over long distances and storage is necessary. To gain maximum life, bunches are harvested before the fruit is fully mature. The fruit is carefully handled, transported quickly to the seaboard, cooled, and shipped under sophisticated refrigeration. The basis of this procedure is to prevent the bananas producing ethylene which is the natural ripening agent of the fruit. This sophisticated technology allows storage and transport for 3–4 weeks at 13 degrees Celsius. On arrival at the destination, the bananas are held at about 17 degrees Celsius and treated with a low concentration of ethylene. After a few days, the fruit has begun to ripen and it is distributed for retail sale. It is important to note that unripe bananas can not be held in the home refrigerator as

they suffer from the cold. After ripening some bananas can be held for a few days at home. They can be stored indefinitely frozen, then eaten like an ice pop or cooked as a banana mush.

Recent studies have suggested that the presence of carbon dioxide (which is produced by the fruit) extends the life and the addition of an ethylene absorbent further extends the life even at high temperatures. This effect can be exploited by packing the fruit in a polyethylene bag and including an ethylene absorbent, potassium permanganate, on an inert carrier. The bag is then sealed with a band or string. This treatment has been shown to more than double the life of the bananas at a range of temperatures and can give a life of up to 3–4 weeks without the need for refrigeration.

Usage in culture

Peels

The depiction of a person slipping on a banana peel has been a staple of physical comedy for generations. An 1898 comedy recording features a popular character of the time, "Cal Stewart", claiming to describe his own such incident, saying:[38]

Now I don't think much of the man that throws a banana peelin' on the sidewalk, and I don't think much of the banana peel that throws a man on the sidewalk neither ... my foot hit the bananer peelin' and I went up in the air, and I come down ker-plunk, jist as I was pickin' myself up a little boy come runnin' across the street ... he says, "Oh mister, won't you please do that agin? My little brother didn't see you do it."

Arts

The poet Bashō is named after the Japanese word for a banana plant. The "bashō" planted in his garden by a grateful student became a source of inspiration to his poetry, as well as a symbol of his life and home.[39]

The song Yes! We Have No Bananas was written by Frank Silver and Irving Cohn and originally released in 1923; for many decades, it was the best-selling sheet music in history. Since then the song has been rerecorded several times and has been particularly popular during banana shortages.

The Japanese novelist Banana Yoshimoto (real name: Mihoko Yoshimoto) changed her name because she liked banana flowers.

Symbols

Bananas are also humorously used as a phallic symbol due to similarities in size and shape. This is typified by the artwork of the debut album of The Velvet Underground, which features a banana on the front cover, yet on the original LP version, the design allowed the listener to 'peel' this banana to find a pink, phallic structure on the inside.

Gallery

Traditional offerings of bananas and coconut at a Nat spirit shrine in Myanmar.

Certain banana cultivars turn red or purplish instead of yellow as they ripen.

Bananas are often sold in bunches, as shown above.

Banana pudding.

Banana plant, Luxor, Egypt - Bananas are continually cropped, fruits from higher in the inflorescence being taken before the lower part opens.

Banana tree.

From the left: bananas as commonly eaten by peeling the skin in thick strips; banana fruit; banana cross section.

Banana leaves can be used for packaging food, such as with the Malaysian dish 'nasi lemak'.

Fiberglass

Bundle of fiberglass

Fiberglass, (also called fibreglass and glass fibre), is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymer (FRP) or glass-reinforced plastic (GRP), is called "fiberglass" in popular usage. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of fiberglass was only made possible with the invention of finer machine tooling. In 1893, Edward Drummond Libbey exhibited a dress at the World's Columbian Exposition incorporating glass fibers with the diameter and texture of silk fibers. This was first worn by the popular stage actress of the time Georgia Cayvan.

What is commonly known as "fiberglass" today, however, was invented in 1938 by Russell Games Slayter of Owens-Corning as a material to be used as insulation. It is marketed under the trade name Fiberglas, which has become a genericized trademark. A somewhat similar, but more expensive technology used for applications requiring very high strength and low weight is the use of carbon fiber.

Formation

Glass fiber is formed when thin strands of silica-based or other formulation glass is extruded into many fibers with small diameters suitable for textile processing. The technique of heating and drawing glass into fine fibers has been known for millennia; however, the use of these fibers for textile applications is more recent. Until this time all fiberglass had been manufactured as staple. When the two companies joined to produce and promote fiberglass, they introduced continuous filament glass fibers.[1] The first commercial production of fiberglass was in 1936. In 1938 Owens-Illinois Glass Company and Corning Glass Works joined to form the Owens-Corning Fiberglas Corporation. Owens-Corning is still the major fiberglass producer in the market today.[2]

The types of fiberglass most commonly used are mainly E-glass (alumino-borosilicate glass with less than 1 wt% alkali oxides, mainly used for glass-reinforced plastics), but als A-glass (alkali-lime glass with little or no boron oxide), E-CR-glass (alumino-lime silicate with less than 1 wt% alkali oxides, has high acid resistance), C-glass (alkali-lime glass with high boron oxide content, used,e.g., for glass staple fibers), D-glass (borosilicate glass with high dielectric constant), R-glass (alumino silicate glass without MgO and CaO with high mechanical requirements), and S-glass (alumino silicate glass without CaO but with high MgO content with high tensile strength).[3]

Chemistry

The basis of textile-grade glass fibers is silica, SiO2. In its pure form it exists as a polymer, (SiO2)n. It has no true melting point but softens at 2,000 °C (3,630 °F), where it starts to degrade. At 1,713 °C (3,115 °F), most of the molecules can move about freely. If the glass is then cooled quickly, they will be unable to form an ordered structure.[4] In the polymer, it forms SiO4 groups which are configured as a tetrahedron with the silicon atom at the center and four oxygen atoms at the corners. These atoms then form a network bonded at the corners by sharing the oxygen atoms.

The vitreous and crystalline states of silica (glass and quartz) have similar energy levels on a molecular basis, also implying that the glassy form is extremely stable. In order to induce

crystallization, it must be heated to temperatures above 1,200 °C (2,190 °F) for long periods of

time.

Molecular Structure of Glass

Although pure silica is a perfectly viable glass and glass fiber, it must be worked with at very high temperatures, which is a drawback unless its specific chemical properties are needed. It is usual to introduce impurities into the glass in the form of other materials to lower its working temperature. These materials also impart various other properties to the glass which may be beneficial in different applications. The first type of glass used for fiber was soda lime glass or A glass. It was not very resistant to alkali. A new type, E-glass was formed that is alkali free (< 2%) and is an alumino-borosilicate glass.[5] This was the first glass formulation used for continuous filament formation. E-glass still makes up most of the fiberglass production in the world. Its particular components may differ slightly in percentage, but must fall within a specific range. The letter E is used because it was originally for electrical applications. S-glass is a high-strength formulation for use when tensile strength is the most important property. C-glass was developed to resist attack from chemicals, mostly acids which destroy E-glass.[5] T-glass is a North American variant of C-glass. A-glass is an industry term for cullet glass, often bottles, made into fiber. AR-glass is alkali-resistant glass. Most glass fibers have limited solubility in water but are very dependent on pH. Chloride ions will also attack and dissolve E-glass surfaces.

Since E-glass does not really melt, but soften, the softening point is defined as "the temperature at which a 0.55–0.77 mm diameter fiber 235 mm long, elongates under its own weight at 1 mm/min when suspended vertically and heated at the rate of 5°C per minute". The strain point is reached when the glass has a viscosity of 1014.5 poise. The annealing point, which is the temperature where the internal stresses are reduced to an acceptable commercial limit in 15 minutes, is marked by a viscosity of 1013 poise.

Properties

Glass fibers are useful because of their high ratio of surface area to weight. However, the increased surface area makes them much more susceptible to chemical attack. By trapping air within them, blocks of glass fiber make good thermal insulation, with a thermal conductivity of the order of 0.05 W/(m·K).

The strength of glass is usually tested and reported for "virgin" or pristine fibers—those which have just been manufactured. The freshest, thinnest fibers are the strongest because the thinner fibers are more ductile. The more the surface is scratched, the less the resulting tenacity. Because glass has an amorphous structure, its properties are the same along the fiber and across the fiber.[4] Humidity is an important factor in the tensile strength. Moisture is easily adsorbed, and can worsen microscopic cracks and surface defects, and lessen tenacity.

In contrast to carbon fiber, glass can undergo more elongation before it breaks. There is a correlation between bending diameter of the filament and the filament diameter. The viscosity of the molten glass is very important for manufacturing success. During drawing (pulling of the glass to reduce fiber circumference), the viscosity should be relatively low. If it is too high, the fiber will break during drawing. However, if it is too low, the glass will form droplets rather than drawing out into fiber.

Glass-reinforced plastic

Main article: Glass-reinforced plastic

Glass-reinforced plastic (GRP) is a composite material or fiber-reinforced plastic made of a plastic reinforced by fine glass fibers. Like graphite-reinforced plastic, the composite material is commonly referred to by the name of its reinforcing fibers (fiberglass). Thermosetting plastics are normally used for GRP production—most often unsaturated polyester (using 2-butanone peroxide aka MEK peroxide as a catalyst), but vinylester or epoxy are also used. Traditionally, styrene monomer was used as a reactive diluent in the resin formulation giving the resin a characteristic odor. More recently alternatives have been developed. The glass can be in the form of a chopped strand mat (CSM) or a woven fabric.

As with many other composite materials (such as reinforced concrete), the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in compressive loading and relatively weak in tensile strength, the glass fibers are very strong in tension but have no strength against compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well. The two materials may be used uniformly or the glass may be specifically placed in those portions of the structure that will experience tensile loads.

Uses

Uses for regular fiberglass include mats, thermal insulation, electrical insulation, reinforcement of various materials, tent poles, sound absorption, heat- and corrosion-resistant fabrics, high-strength fabrics, pole vault poles, arrows, bows and crossbows, translucent roofing panels, automobile bodies and boat hulls. It has been used for medical purposes in casts. Fiberglass is extensively used for making FRP tanks and vessels.

JuteThis article is about vegetable fibre. For the Germanic people, see Jutes.

Bundles of jute, showing the fibres of Corchorus olitorius (tossa jute fibre) and Corchorus capsularis (white jute fibre)

Jute is a long, soft, shiny vegetable fiber that can be spun into coarse, strong threads. It is produced from plants in the genus Corchorus, family Tiliaceae.

Jute is one of the cheapest natural fibres and is second only to cotton in amount produced and variety of uses. Jute fibres are composed primarily of the plant materials cellulose (major component of plant fibre) and lignin (major components wood fibre). It is thus a ligno-cellulosic fibre that is partially a textile fibre and partially wood. It falls into the bast fibre category (fibre collected from bast or skin of the plant) along with kenaf, industrial hemp, flax (linen), ramie, etc. The industrial term for jute fibre is raw jute. The fibres are off-white to brown, and 1–4 meters (3–12 feet) long.

Jute plants (Corchorus olitorius and Corchorus capsularis)

Jute fibre is often called hessian; jute fabrics are also called hessian cloth and jute sacks are called gunny bags in some European countries. The fabric made from jute is popularly known as burlap in North America.

Cultivation

Main article: Jute cultivation

Jute needs a plain alluvial soil and standing water. The suitable climate for growing jute (warm and wet climate) is offered by the monsoon climate during the monsoon season. Temperatures ranging 20˚ C to 40˚ C and relative humidity of 70%–80% are favourable for successful cultivation. Jute requries 5–8 cm of rainfall weekly with extra needed during the sowing period.

White jute (Corchorus capsularis)

Several historical documents (especially, Ain-e-Akbari by Abul Fazal in 1590) during the era of Mughal Emperor Akbar (1542–1605) state that the poor villagers of India used to wear clothes made of jute. Simple handlooms and hand spinning wheels were used by the weavers, who used to spin cotton yarns as well. History also states that Indians, especially Bengalis, used ropes and twines made of white jute from ancient times for household and other uses.

Tossa jute (Corchorus olitorius)

Tossa jute (Corchorus olitorius) is an Afro-Arabian variety. It is quite popular for its leaves that are used as an ingredient in a mucilaginous potherb called molokhiya (ملوخية a word of uncertain

etymology), popular in certain Arab countries. The Book of Job in the Hebrew Bible mentions this vegetable potherb as Jew's mallow.

Tossa jute fibre is softer, silkier, and stronger than white jute. This variety astonishingly showed good sustainability in the climate of the Ganges Delta. Along with white jute, tossa jute has also been cultivated in the soil of Bengal where it is known as paat from the start of the 19th century. Currently, the Bengal region (West Bengal, India, and Bangladesh) is the largest global producer of the tossa jute variety.

History

For centuries, jute has been an integral part of Bengali culture, which is shared by both Bangladesh and West Bengal of India. In the 19th and early 20th centuries, much of the raw jute fibre of Bengal was exported to the United Kingdom, where it was then processed in mills concentrated in Dundee ("jute weaver" was a recognised trade occupation in the 1901 UK census), but this trade had largely ceased by about 1970 due to the appearance of synthetic fibres.

Margaret Donnelly, a jute mill landowner in Dundee in the 1800s, set up the first jute mills in India. In the 1950s and 1960s, when nylon and polythene were rarely used, Pakistan, then the world leader in jute products, was earning exchange from jute grown in East Pakistan, now Bangladesh. It was called the "Golden Fibre of Bangladesh," and it used to bring the major portion of foreign currency reserve for the country. However, as the use of polythene and other synthetic materials as a substitute for jute increasingly captured the market, the jute industry in general experienced a decline.

During some years in the 1980s, farmers in Bangladesh burnt their jute crops when an adequate price could not be obtained. Many exporters that were dealing with jute found other commodities in which to deal. Jute-related organisations and government bodies also experienced closures, change, and fund cutting. The long decline in demand forced the largest jute mill in the world (Adamjee Jute Mills) to close. Latif Bawany Jute Mills, the second largest, is still running but was nationalized by the government from prominent businessman, Yahya Bawany. Farmers in Bangladesh have not completely ceased growing jute, however, mainly due to demand in the internal market. Recently (2004–2009), the jute market began to recover and the price of raw jute increased more than 200%.

Jute has entered many diverse sectors of industry, where natural fibres are gradually becoming better substitutes. Among these industries are paper, celluloid products (films), non-woven textiles, composites (pseudo-wood), and geotextiles.

In December 2006 the General Assembly of the United Nations proclaimed 2009 to be the International Year of Natural Fibres, so as to raise the profile of jute and other natural fibres.

Description

Jute matting being used to prevent flood erosion while natural vegetation becomes established. For this purpose, a natural and biodegradable fibre is essential.

Production

Jute is a rain-fed crop with little need for fertilizer or pesticides. The production is concentrated in India and Bangladesh. The jute fibre comes from the stem and ribbon (outer skin) of the jute plant. The fibres are first extracted by retting. The retting process consists of bundling jute stems together and immersing them in low, running water. There are two types of retting: stem and ribbon. After the retting process, stripping begins. Women and children usually do this job. In the stripping process, non-fibrous matter is scraped off, then the workers dig in and grab the fibres from within the jute stem.[1]

India with overall of ~66% of worlds production tops the production of jute. Bangladesh with ~25% lies at second position followed way behind by China with ~3%.

Uses

Jute is the second most important vegetable fibre after cotton; not only for cultivation, but also for various uses. Jute is used chiefly to make cloth for wrapping bales of raw cotton, and to make sacks and coarse cloth. The fibres are also woven into curtains, chair coverings, carpets, area rugs, hessian cloth, and backing for linoleum.

While jute is being replaced by synthetic materials in many of these uses, some uses take advantage of jute's biodegradable nature, where synthetics would be unsuitable. Examples of such uses include containers for planting young trees which can be planted directly with the container without

Top Ten Jute Producers — 11 June 2008

CountryProduction (Tonnes)

Footnote

 India 2140000 F

 Bangladesh 800000 F

 People's Republic of China

99000

 Côte d'Ivoire 40000 F

 Thailand 31000 F

 Myanmar 30000 F

 Brazil 26711

 Uzbekistan 20000 F

 Nepal 16775

 Vietnam 11000 F

 World 3225551 ANo symbol = official figure, F = FAO estimate, A = Aggregate(may include official, semi-official or estimates);Source: Food And Agricultural Organization of United Nations: Economic And Social Department: The Statistical Devision

disturbing the roots, and land restoration where jute cloth prevents erosion occurring while natural vegetation becomes established.

The fibres are used alone or blended with other types of fibres to make twine and rope. Jute butts, the coarse ends of the plants, are used to make inexpensive cloth. Conversely, very fine threads of jute can be separated out and made into imitation silk. As jute fibres are also being used to make pulp and paper, and with increasing concern over forest destruction for the wood pulp used to make most paper, the importance of jute for this purpose may increase. Jute has a long history of use in the sackings, carpets, wrapping fabrics (cotton bale), and construction fabric manufacturing industry.

Traditionally jute was used in traditional textile machineries as textile fibres having cellulose (vegetable fibre content) and lignin (wood fibre content). But, the major breakthrough came when the automobile, pulp and paper, and the furniture and bedding industries started to use jute and its allied fibres with their non-woven and composite technology to manufacture nonwovens, technical textiles, and composites. Therefore, jute has changed its textile fibre outlook and steadily heading towards its newer identity, i.e. wood fibre. As a textile fibre, jute has reached its peak from where there is no hope of progress, but as a wood fibre jute has many promising features.[2]

Jute can be used to create a number of fabrics such as Hessian cloth, sacking, scrim, carpet backing cloth (CBC), and canvas. Hessian, lighter than sacking, is used for bags, wrappers, wall-coverings, upholstery, and home furnishings. Sacking, a fabric made of heavy jute fibres, has its use in the name. CBC made of jute comes in two types. Primary CBC provides a tufting surface, while secondary CBC is bonded onto the primary backing for an overlay. Jute packaging is used as an eco-friendly substitute.

Diversified jute products are becoming more and more valuable to the consumer today. Among these are espadrilles, floor coverings, home textiles, high performance technical textiles, Geotextiles, composites, and more.

Jute Bags

Jute bags are used for making fashion bags & promotional bags. The eco-friendly nature of jute make its ideal for corporate gifting.

Jute floor coverings consist of woven and tufted and piled carpets. Jute Mats and mattings with 5 / 6 mts width and of continuous length are easilly being woven in Southern parts of India, in solid and fancy shades, and in different weaves like, Boucle, Panama, Herringbone, etc. Jute Mats & Rugs are made both through Powerloom & Handloom, in large volume from Kerala, India. The traditional Satranji mat is becoming very popular in home décor. Jute non-wovens and composites can be used for underlay, linoleum substrate, and more.

Jute has many advantages as a home textile, either replacing cotton or blending with it. It is a strong, durable, color and light-fast fibre. Its UV protection, sound and heat insulation, low thermal conduction and anti-static properties make it a wise choice in home décor. Also, fabrics made of jute fibres are carbon-dioxide neutral and naturally decomposable. These properties are also why jute can be used in high performance technical textiles [1].

Moreover, jute can be grown in 4–6 months with a huge amount of cellulose being produced from the jute hurd (inner woody core or parenchyma of the jute stem) that can meet most of the wood

needs of the world. Jute is the major crop among others that is able to protect deforestation by industrialisation.

Thus, jute is the most environment-friendly fibre starting from the seed to expired fibre, as the expired fibres can be recycled more than once.

Jute is also used in the making of ghillie suits which are used as camouflage and resemble grasses or brush.

Another diversified jute product is Geotextiles, which made this agricultural commodity more popular in the agricultural sector. It is a lightly woven fabric made from natural fibres that is used for soil erosion control, seed protection, weed control, and many other agricultural and landscaping uses. The Geotextiles can be used more than a year and the bio-degradable jute Geotextile left to rot on the ground keeps the ground cool and is able to make the land more fertile. Methods such as this could be used to transfer the fertility of the Ganges Delta to the deserts of Sahara or Australia[citation

needed].

Food

Jute leaves are consumed in various parts of the world. It is a popular vegetable in West Africa. The Yoruba of Nigeria call it "ewedu" and the Songhay of Mali call it "fakohoy." It is made into a common mucilaginous (somewhat "slimy") soup or sauce in some West African cooking traditions, as well as in Egypt, where it is called mulukhiyya and is often considered the national dish. It is also a popular dish in the northern provinces of the Philippines, where it is known as saluyot. Jute leaves are also consumed among the Luyhia people of Western Kenya, where it is commonly known as 'mrenda' or 'murere'. It is eaten with 'ugali', which is also a staple for most communities in Kenya. The leaves are rich in betacarotene, iron, calcium, and Vitamin C. The plant has an antioxidant activity with a significant α-tocopherol equivalent Vitamin E.

Other

Diversified byproducts which can be cultivated from jute include uses in cosmetics, medicine, paints, and other products.

Features

Picture of cutting lower part of the long jute fibre. The lower part is hard fibre, which is called jute cuttings in Bangladesh and India (commonly called jute butts or jute tops elsewhere). Jute cuttings are lower in quality, but have commercial value for the paper, carded yarn, and other fibre processing industries. Jute fibres are kept in bundles in the background in a warehouse in Bangladesh.

Jute fibre is 100% bio-degradable and recyclable and thus environmentally friendly. It is a natural fibre with golden and silky shine and hence called The Golden Fibre. It is the cheapest vegetable fibre procured from the bast or skin of the plant's stem. It is the second most important vegetable fibre after cotton, in terms of usage, global

consumption, production, and availability. It has high tensile strength, low extensibility, and ensures better breathability of fabrics.

Therefore, jute is very suitable in agricultural commodity bulk packaging. It helps to make best quality industrial yarn, fabric, net, and sacks. It is one of the most

versatile natural fibres that has been used in raw materials for packaging, textiles, non-

textile, construction, and agricultural sectors. Bulking of yarn results in a reduced breaking tenacity and an increased breaking extensibility when blended as a ternary blend.

Unlike the hemp fiber, jute is not a form of cannabis. The best source of jute in the world is the Bengal Delta Plain in the Ganges Delta, most of

which is occupied by Bangladesh. Advantages of jute include good insulating and antistatic properties, as well as having low

thermal conductivity and a moderate moisture regain. Other advantages of jute include acoustic insulating properties and manufacture with no skin irritations.

Jute has the ability to be blended with other fibres, both synthetic and natural, and accepts cellulosic dye classes such as natural, basic, vat, sulfur, reactive, and pigment dyes. As the demand for natural comfort fibres increases, the demand for jute and other natural fibres that can be blended with cotton will increase. To meet this demand, it has been suggested that the natural fibre industry adopt the Rieter's Elitex system, in order to modernize processing. The resulting jute/cotton yarns will produce fabrics with a reduced cost of wet processing treatments. Jute can also be blended with wool. By treating jute with caustic soda, crimp, softness, pliability, and appearance is improved, aiding in its ability to be spun with wool. Liquid ammonia has a similar effect on jute, as well as the added characteristic of improving flame resistance when treated with flameproofing agents.

Some noted disadvantages include poor drapability and crease resistance, brittleness, fibre shedding, and yellowing in sunlight. However, preparation of fabrics with castor oil lubricants result in less yellowing and less fabric weight loss, as well as increased dyeing brilliance. Jute has a decreased strength when wet, and also becomes subject to microbial attack in humid climates. Jute can be processed with an enzyme in order to reduce some of its brittleness and stiffness. Once treated with an enzyme, jute shows an affinity to readily accept natural dyes, which can be made from marigold flower extract. In one attempt to dye jute fabric with this extract, bleached fabric was mordanted with ferrous sulphate, increasing the fabric's dye uptake value. Jute also responds well to reactive dyeing. This process is used for bright and fast coloured value-added diversified products made from jute.

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Metallic fiberMetallic fibers are manufactured fibers composed of metal, plastic-coated metal, metal-coated plastic, or a core completely covered by metal[1]. Gold and silver have been used since ancient times as yarns for fabric decoration. More recently, aluminum yarns, aluminized plastic yarns, and aluminized nylon yarns have replaced gold and silver. Metallic filaments can be coated with transparent films to minimize tarnishing. A common film is Lurex polyester.[2]

History

Gold and silver have been used since ancient times as decoration in the clothing and textiles of kings, leaders, nobility and people of status. Many of these elegant textiles can be found in museums around the world.[3] Historically, the metallic thread was constructed by wrapping a metal strip around a fiber core (cotton or silk), often in such a way as to reveal the color of the fiber core to enhance visual quality of the decoration.[4] Ancient textiles and clothing woven from wholly or partly gold threads is sometimes referred to as Cloth of Gold. They have been woven on Byzantine looms from the 7th to 9th Centuries, and after that in Sicily, Cyprus, Lucca, and Venice.[5] Weaving also flourished in the 12th Century during the legacy of Genghis Khan when art and trade flourished under Mongol rule in China and some Middle Eastern areas.[6] The Dobeckmum Company produced the first modern metallic fiber in 1946.[3] In the past, aluminum was usually the base in a metallic fiber. More recently stainless steel has become a base as well. It is more difficult to work with but provides properties to the yarn that allows it to be used in more high tech[clarification needed] applications .[3]

Fiber properties

Coated metallic filaments help to minimize tarnishing. When suitable adhesives and films are used, they are not affected by salt water, chlorinated water in swimming pools or climatic conditions.[7] If possible anything made with metallic fibers should be dry-cleaned, if there is no care label. Ironing can be problematic because the heat from the iron, especially at high tempatures, can melt the fibers.

Production method

There are two basic processes that are used in manufacturing metallic fibers. The most common is the laminating process, which seals a layer of aluminum between two layers of acetate or polyester film. These fibers are then cut into lengthwise strips for yarns and wound onto bobbins. The metal can be colored and sealed in a clear film, the adhesive can be colored, or the film can be colored before laminating. There are many different variations of color and effect that can be made in metallic fibers, producing a wide range of looks.

Metallic fibers can also be made by using the metalizing process. This process involves heating the metal until it vaporizes then depositing it at a high pressure onto the polyester film . This process produces thinner, more flexible, more durable, and more comfortable fibers.

Producers

Currently metallic fibers are manufactured primarily in Europe with only three manufacturers still producing metallic yarn in the United States. Metlon Corporation is one of the remaining manufacturers in the U.S. that stocks a wide variety of laminated and non-laminated metallic yarns.]

Trademarks

The Lurex Company has manufactured metallic fibers in Europe for over fifty years. They produce a wide variety of metallic fiber products including fibers used in apparel fabric, embroidery, braids, knitting, military regalia, trimmings, ropes, cords, and lace surface decoration. The majority of Lurex fibers have a polyamdie film covering the metal strand but polyester and viscose are also used. The fibers are also treated with a lubricant called P.W., a mineral-based oil, which helps[clarification needed] provide ease of use.

Metlon Corporation is a trademark of Metallic Yarns in the United States and has been producing metallic yarns for over over sixty years. Metlon produces their metallic yarn by wrapping single slit yarns with two ends of nylon. One end of nylon is wrapped clockwise and the other end is wrapped counterclockwise around the metallic yarn. The most commonly used nylon is either 15 denier or 20 denier, but heavier deniers are used for special purposes.

Uses

The most common uses for metallic fibers is upholstery fabric and textiles such as lamé and brocade. Many people also use metallic fibers in weaving and needlepoint. Increasingly common today are metaillic fibers in clothing, anything from party and evening wear to club clothing, cold weather and survival clothing, and everyday wear. Metallic yarns are woven, braided, and knit into many fashionable fabrics and trims. For additional variety, metallic yarns are twisted with other fibers such as wool, nylon, cotton, and synthetic blends to produce yarns which add novelty effects to the end cloth or trim. Stainless steel and other metal fibers are used in communication lines such as phone lines and cable television lines. Stainless steel fibers are also used in carpets. They are dispersed throughout the carpet with other fibers so they are not detected. The presence of the fibers helps to conduct electricity so that the static shock is reduced. These types of carpets are often used in computer-use areas where the chance of producing static is much greater. Other uses include tire cord, missile nose cones, work clothing such as protective suits, space suits, and cut resistant gloves for butchers and other people working near bladed or dangerous machinery.

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Optical fiber

A bundle of optical fibers

A TOSLINK fiber optic audio cable being illuminated on one end

An optical fiber (or fibre) is a glass or plastic fiber that carries light along its length. Fiber optics is the overlap of applied science and engineering concerned with the design and application of optical fibers. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those which can only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 550 metres (1,800 ft).

Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with an electric arc. Special connectors are used to make removable connections.

Daniel Colladon first described this "light fountain" or "light pipe" in an 1842 article entitled On the reflections of a ray of light inside a parabolic liquid stream. This particular illustration comes from a later article by Colladon, in 1884.

History

Fiber optics, though used extensively in the modern world, is a fairly simple and old technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London a dozen years later.[1] Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: "When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface.... The angle which marks the limit where total reflexion begins is called the limiting angle of the medium. For water this angle is 48°27', for flint glass it is 38°41', while for diamond it is 23°42'."[2][3]

Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. In 1952, physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[1] Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed.

Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, was the first to propose the use of optical fibers for communications in 1963.[4] Nishizawa invented other technologies that contributed to the development of optical fiber communications as well.[5] Nishizawa invented the graded-index optical fiber in 1964 as a channel for transmitting light from semiconductor lasers over long distances with low loss.[6]

In 1965, Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), allowing fibers to be a practical medium for communication.[7] They proposed that the attenuation in fibers available at the time was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. The crucial attenuation level of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuations ushered in optical fiber telecommunications and enabled the Internet. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.[8]

Attenuations in modern optical cables are far less than those in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometres (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or even in many cases eliminating the need for optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton, and Emmanuel Desurvire at Bell Laboratories in 1986. The more robust optical fiber commonly used today utilizes glass for both core and sheath and is therefore less prone to aging processes. It was invented by Gerhard Bernsee in 1973 of Schott Glass in Germany.[9]

In 1991, the emerging field of photonic crystals led to the development of photonic-crystal fiber [10] which guides light by means of diffraction from a periodic structure, rather than total internal reflection. The first photonic crystal fibers became commercially available in 2000.[11] Photonic crystal fibers can be designed to carry higher power than conventional fiber, and their wavelength dependent properties can be manipulated to improve their performance in certain applications.

Applications

Optical fiber communication

Main article: Fiber-optic communication

Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. This allows long distances to be spanned with few repeaters. Additionally, the per-channel light signals propagating in the fiber can be modulated at rates as high as 111 gigabits per second,[12] although 10 or 40 Gb/s is typical in deployed systems.[citation needed] Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing (WDM)). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008).

Over short distances, such as networking within a building, fiber saves space in cable ducts because a single fiber can carry much more data than a single electrical cable.[vague] Fiber is also immune to electrical interference; there is no cross-talk between signals in different cables and no pickup of environmental noise. Non-armored fiber cables do not conduct electricity, which makes fiber a good solution for protecting communications equipment located in high voltage environments such as power generation facilities, or metal communication structures prone to lightning strikes. They can

also be used in environments where explosive fumes are present, without danger of ignition. Wiretapping is more difficult compared to electrical connections, and there are concentric dual core fibers that are said to be tap-proof.

Although fibers can be made out of transparent plastic, glass, or a combination of the two, the fibers used in long-distance telecommunications applications are always glass, because of the lower optical attenuation. Both multi-mode and single-mode fibers are used in communications, with multi-mode fiber used mostly for short distances, up to 550 m (600 yards), and single-mode fiber used for longer distance links. Because of the tighter tolerances required to couple light into and between single-mode fibers (core diameter about 10 micrometers), single-mode transmitters, receivers, amplifiers and other components are generally more expensive than multi-mode components.

Examples of applications are TOSLINK, Fiber distributed data interface, Synchronous optical networking.[jargon]

Fiber optic sensors

Fibers have many uses in remote sensing. In some applications, the sensor is itself an optical fiber. In other cases, fiber is used to connect a non-fiberoptic sensor to a measurement system. Depending on the application, fiber may be used because of its small size, or the fact that no electrical power is needed at the remote location, or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor, or by sensing the time delay as light passes along the fiber through each sensor. Time delay can be determined using a device such as an optical time-domain reflectometer.

Optical fibers can be used as sensors to measure strain, temperature, pressure and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity, phase, polarization, wavelength or transit time of light in the fiber. Sensors that vary the intensity of light are the simplest, since only a simple source and detector are required. A particularly useful feature of such fiber optic sensors is that they can, if required, provide distributed sensing over distances of up to one meter.

Extrinsic fiber optic sensors use an optical fiber cable, normally a multi-mode one, to transmit modulated light from either a non-fiber optical sensor, or an electronic sensor connected to an optical transmitter. A major benefit of extrinsic sensors is their ability to reach places which are otherwise inaccessible. An example is the measurement of temperature inside aircraft jet engines by using a fiber to transmit radiation into a radiation pyrometer located outside the engine. Extrinsic sensors can also be used in the same way to measure the internal temperature of electrical transformers, where the extreme electromagnetic fields present make other measurement techniques impossible. Extrinsic sensors are used to measure vibration, rotation, displacement, velocity, acceleration, torque, and twisting.

Other uses of optical fibers

A frisbee illuminated by fiber optics

Fibers are widely used in illumination applications. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-of-sight path. In some buildings, optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics). Optical fiber illumination is also used for decorative applications, including signs, art, and artificial Christmas trees. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fiber is an intrinsic part of the light-transmitting concrete building product, LiTraCon.

Optical fiber is also used in imaging optics. A coherent bundle of fibers is used, sometimes along with lenses, for a long, thin imaging device called an endoscope, which is used to view objects through a small hole. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach, such as jet engine interiors.

In spectroscopy, optical fiber bundles are used to transmit light from a spectrometer to a substance which cannot be placed inside the spectrometer itself, in order to analyze its composition. A spectrometer analyzes substances by bouncing light off of and through them. By using fibers, a spectrometer can be used to study objects that are too large to fit inside, or gasses, or reactions which occur in pressure vessels.[13][14][15]

An optical fiber doped with certain rare-earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line. The doped fiber is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. Both wavelengths of light are transmitted through the doped fiber, which transfers energy from the second pump wavelength to the signal wave. The process that causes the amplification is stimulated emission.

Optical fibers doped with a wavelength shifter are used to collect scintillation light in physics experiments.

Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Examples of this are electronics in high-powered antenna elements and measurement devices used in high voltage transmission equipment.

Principle of operation

An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis, by the process of total internal reflection. The fiber consists of a core surrounded by a cladding layer. To confine the optical signal in the core, the refractive index of the core must be greater than that of the cladding. The boundary between the core and cladding may either be abrupt, in step-index fiber, or gradual, in graded-index fiber.

Index of refraction

Main article: Refractive index

The index of refraction is a way of measuring the speed of light in a material. Light travels fastest in a vacuum, such as outer space. The actual speed of light in a vacuum is about 300 million meters (186 thousand miles) per second. Index of refraction is calculated by dividing the speed of light in a vacuum by the speed of light in some other medium. The index of refraction of a vacuum is therefore 1, by definition. The typical value for the cladding of an optical fiber is 1.46. The core value is typically 1.48. The larger the index of refraction, the slower light travels in that medium. From this information, a good rule of thumb is that signal using optical fiber for communication will travel at around 200 million meters per second. Or to put it another way, to travel 1000 kilometres in fiber, the signal will take 5 milliseconds to propagate. Thus a phone call carried by fiber between Sydney and New York, a 12000 kilometre distance, means that there is an absolute minimum delay of 60 milliseconds (or around 1/16th of a second) between when one caller speaks to when the other hears. (Of course the fiber in this case will probably travel a longer route, and there will be additional delays due to communication equipment switching and the process of encoding and decoding the voice onto the fiber).

Total internal reflection

Main article: Total internal reflection

When light traveling in a dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary), the light will be completely reflected. This effect is used in optical fibers to confine light in the core. Light travels along the fiber bouncing back and forth off of the boundary. Because the light must strike the boundary with an angle greater than the critical angle, only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. This range of angles is called the acceptance cone of the fiber. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding.

In simpler terms, there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate, or travel, in the core of the fiber. The sine of this maximum angle is the numerical aperture (NA) of the fiber. Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA. Single-mode fiber has a small NA.

Multi-mode fiber

The propagation of light through a multi-mode optical fiber.

A laser bouncing down an acrylic rod, illustrating the total internal reflection of light in a multi-mode optical fiber.Main article: Multi-mode optical fiber

Fiber with large core diameter (greater than 10 micrometers) may be analyzed by geometric optics. Such fiber is called multi-mode fiber, from the electromagnetic analysis (see below). In a step-index multi-mode fiber, rays of light are guided along the fiber core by total internal reflection. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary), greater than the critical angle for this boundary, are completely reflected. The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. Rays that meet the boundary at a low angle are refracted from the core into the cladding, and do not convey light and hence information along the fiber. The critical angle determines the acceptance angle of the fiber, often reported as a numerical aperture. A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles, allowing efficient coupling of light into the fiber. However, this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore take different times to traverse the fiber. A low numerical aperture may therefore be desirable.

Optical fiber types.

In graded-index fiber, the index of refraction in the core decreases continuously between the axis and the cladding. This causes light rays to bend smoothly as they approach the cladding, rather than reflecting abruptly from the core-cladding boundary. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core, rather than the high-index center. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis.

Single-mode fiber

The structure of a typical single-mode fiber.1. Core: 8 µm diameter2. Cladding: 125 µm dia.3. Buffer: 250 µm dia.4. Jacket: 400 µm dia.Main article: Single-mode optical fiber

Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. Instead, it must be analyzed as an electromagnetic structure, by solution of Maxwell's equations as reduced to the electromagnetic wave equation. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. As an optical waveguide, the fiber supports one or more confined transverse modes by which light can propagate along the fiber. Fiber supporting only one mode is called single-mode or mono-mode fiber. The behavior of larger-core multi-mode fiber can also be modeled using the wave equation, which shows that such fiber supports more than one mode of propagation (hence the name). The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics, if the fiber core is large enough to support more than a few modes.

The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. Instead, especially in single-mode fibers, a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave.

The most common type of single-mode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrared. The mode structure depends on the wavelength of the light used, so that this fiber actually supports a small number of additional modes at visible wavelengths. Multi-mode fiber, by comparison, is manufactured with core diameters as small as 50 micrometers and as large as hundreds of micrometres. The normalized frequency V for this fiber should be less than the first zero of the Bessel function J0 (approximately 2.405).

Special-purpose fiber

Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer, usually with an elliptical or rectangular cross-section. These include polarization-maintaining fiber and fiber designed to suppress whispering gallery mode propagation.

Photonic crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). Such fiber uses diffraction effects instead of or in addition to total internal reflection, to confine light to the fiber's core. The properties of the fiber can be tailored to a wide variety of applications.

Mechanisms of attenuation

Light attenuation by ZBLAN and silica fibersMain article: Transparent materials

Attenuation in fiber optics, also known as transmission loss, is the reduction in intensity of the light beam (or signal) with respect to distance travelled through a transmission medium. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission media. The medium is typically usually a fiber of silica glass that confines the incident light beam to the inside. Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.

Light scattering

Specular reflection

Diffuse reflection

The propagation of light through the core an optical fiber is based on total internal reflection of the lightwave. Rough and irregular surfaces, even at the molecular level, can cause light rays to be reflected in random directions. This is called diffuse reflection or scattering, and it is typically characterized by wide variety of reflection angles.

Light scattering depends on the wavelength of the light being scattered. Thus, limits to spatial scales of visibility arise, depending on the frequency of the incident lightwave and the physical dimension (or spatial scale) of the scattering center, which is typically in the form of some specific microstructural feature. Since visible light has a wavelength of the order of one micron (one millionth of a meter) scattering centers will have dimensions on a similar spatial scale.

Thus, attenuation results from the incoherent scattering of light at internal surfaces and interfaces. In (poly)crystalline materials such as metals and ceramics, in addition to pores, most of the internal surfaces or interfaces are in the form of grain boundaries that separate tiny regions of crystalline order. It has recently been shown that when the size of the scattering center (or grain boundary) is reduced below the size of the wavelength of the light being scattered, the scattering no longer occurs to any significant extent. This phenomenon has given rise to the production of transparent ceramic materials.

Similarly, the scattering of light in optical quality glass fiber is caused by molecular level irregularities (compositional fluctuations) in the glass structure. Indeed, one emerging school of thought is that a glass is simply the limiting case of a polycrystalline solid. Within this framework, "domains" exhibiting various degrees of short-range order become the building blocks of both metals and alloys, as well as glasses and ceramics. Distributed both between and within these domains are micro-structural defects which will provide the most ideal locations for the occurrence of light scattering. This same phenomenon is seen as one of the limiting factors in the transparency of IR missile domes. At high optical powers, scattering can also be caused by nonlinear optical processes in the fiber.

UV-Vis-IR absorption

In addition to light scattering, attenuation or signal loss can also occur due to selective absorption of specific wavelengths, in a manner similar to that responsible for the appearance of color. Primary material considerations include both electrons and molecules as follows:

1) At the electronic level, it depends on whether the electron orbitals are spaced (or "quantized") such that they can absorb a quantum of light (or photon) of a specific wavelength or frequency in the ultraviolet (UV) or visible ranges. This is what gives rise to color.

2) At the atomic or molecular level, it depends on the frequencies of atomic or molecular vibrations or chemical bonds, how close-packed its atoms or molecules are, and whether or not the atoms or molecules exhibit long-range order. These factors will determine the capacity of the material transmitting longer wavelengths in the infrared (IR), far IR, radio and microwave ranges.

The design of any optically transparent device requires the selection of materials based upon knowledge of its properties and limitations. The lattice absorption characteristics observed at the lower frequency regions (mid IR to far-infrared wavelength range) define the long-wavelength transparency limit of the material. They are the result of the interactive coupling between the motions of thermally induced vibrations of the constituent atoms and molecules of the solid lattice and the incident light wave radiation. Hence, all materials are bounded by limiting regions of absorption caused by atomic and molecular vibrations (bond-stretching)in the far-infrared (>10 µm).

Normal modes of vibration in a crystalline solid.

Thus, multi-phonon absorption occurs when two or more phonons simultaneously interact to produce electric dipole moments with which the incident radiation may couple. These dipoles can absorb energy from the incident radiation, reaching a maximum coupling with the radiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole (e.g. Si-O bond) in the far-infrared, or one of its harmonics.

The selective absorption of infrared (IR) light by a particular material occurs because the selected frequency of the light wave matches the frequency (or an integral multiple of the frequency) at which the particles of that material vibrate. Since different atoms and molecules have different natural frequencies of vibration, they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light.

Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural resonant frequencies of vibration of the objects. When IR light of these frequencies strike an object, the energy is either reflected or transmitted.

Manufacturing

Materials

Glass optical fibers are almost always made from silica, but some other materials, such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, are used for longer-wavelength infrared applications. Like other glasses, these glasses have a refractive index of about 1.5. Typically the difference between core and cladding is less than one percent.

Plastic optical fibers (POF) are commonly step-index multi-mode fibers with a core diameter of 0.5 millimeters or larger. POF typically have higher attenuation co-efficients than glass fibers, 1 dB/m or higher, and this high attenuation limits the range of POF-based systems.

Silica

Tetrahedral structural unit of silica (SiO2).

The amorphous structure of glassy silica (SiO2). No long-range order is present, however there is local ordering with respect to the tetrahedral arrangement of oxygen (O) atoms around the silicon (Si) atoms.

Silica exhibits fairly good optical transmission over a wide range of wavelengths. In the near-infrared (near IR) portion of the spectrum, particularly around 1.5 μm, silica can have extremely low absorption and scattering losses of the order of 0.2 dB/km. A high transparency in the 1.4-μm region is achieved by maintaining a low concentration of hydroxyl groups (OH). Alternatively, a high OH concentration is better for transmission in the ultraviolet (UV) region.

Silica can be drawn into fibers at reasonably high temperatures, and has a fairly broad glass transformation range. One other advantage is that fusion splicing and cleaving of silica fibers is relatively effective. Silica fiber also has high mechanical strength against both pulling and even bending, provided that the fiber is not too thick and that the surfaces have been well prepared during processing. Even simple cleaving (breaking) of the ends of the fiber can provide nicely flat surfaces with acceptable optical quality. Silica is also relatively chemically inert. In particular, it is not hygroscopic (does not absorb water).

Silica glass can be doped with various materials. One purpose of doping is to raise the refractive index (e.g. with Germanium dioxide (GeO2) or Aluminium oxide (Al2O3)) or to lower it (e.g. with fluorine or Boron trioxide (B2O3)). Doping is also possible with laser-active ions (for example, rare earth-doped fibers) in order to obtain active fibers to be used, for example, in fiber amplifiers or laser applications. Both the fiber core and cladding are typically doped, so that the entire assembly (core and cladding) is effectively the same compound (e.g. an aluminosilicate, germanosilicate, phosphosilicate or borosilicate glass).

Particularly for active fibers, pure silica is usually not a very suitable host glass, because it exhibits a low solubility for rare earth ions. This can lead to quenching effects due to clustering of dopant ions. Aluminosilicates are much more effective in this respect.

Silica fiber also exhibits a high threshold for optical damage. This property ensures a low tendency for laser-induced breakdown. This is important for fiber amplifiers when utilized for the amplification of short pulses.

Because of these properties silica fibers are the material of choice in many optical applications, such as communications (except for very short distances with plastic optical fiber), fiber lasers, fiber amplifiers, and fiber-optic sensors. The large efforts which have been put forth in the development

of various types of silica fibers have further increased the performance of such fibers over other materials. [19] [20] [21] [22] [23] [24] [25] [26] [27]

Fluorides : Fluoride glass is a class of non-oxide optical quality glasses composed of fluorides of various metals. Due to their low viscosity, it is very difficult to completely avoid crystallization while processing it through the glass transition (or drawing the fiber from the melt). Thus, although heavy metal fluoride glasses (HMFG) exhibit very low optical attenuation, they are not only difficult to manufacture, but are quite fragile, and have poor resistance to moisture and other environmental attacks. Their best attribute is that they lack the absorption band associated with the hydroxyl (OH) group (3200–3600 cm−1), which is present in nearly all oxide-based glasses.

An example of a heavy metal fluoride glass is the ZBLAN glass group, composed of zirconium, barium, lanthanum, aluminum, and sodium fluorides. Their main technological application is as optical waveguides in both planar and fiber form. They are advantageous especially in the mid-infrared (2000–5000 nm) range.

HMFG's were initially slated for optical fiber applications, because the intrinsic losses of a mid-IR fiber could in principle be lower than those of silica fibers, which are transparent only up to about 2 μm. However, such low losses were never realized in practice, and the fragility and high cost of fluoride fibers made them less than ideal as primary candidates. Later, the utility of fluoride fibers for various other applications was discovered. These include mid-IR spectroscopy, fiber-optic sensors, thermometry, and imaging. Also, fluoride fibers can be used to for guided lightwave transmission in media such as YAG (yttria-alumina garnet) lasers at 2.9 μm, as required for medical applications (e.g. ophthalmology and dentistry).

Phosphates :

The P4O10 cagelike structure—the basic building block for phosphate glass.

Phosphate glass constitutes a class of optical glasses composed of metaphosphates of various metals. Instead of the SiO4 tetrahedra observed in silicate glasses, the building block for this glass former is Phosphorus pentoxide (P2O5), which crystallizes in at least four different forms. The most familiar polymorph (see figure) comprises molecules of P4O10.

Phosphate glasses can be advantageous over silica glasses for optical fibers with a high concentration of doping rare earth ions. A mix of fluoride glass and phosphate glass is fluorophosphate glass. [30] [31]

Chalcogenides : The chalcogens—the elements in group 16 of the periodic table—particularly sulphur (S), selenium (Se) and tellurium (Te)—react with more electropositive elements, such as silver, to form chalcogenides. These are extremly versatile compounds, in that they can be crystalline or amorphous, metallic or semiconducting, and conductors of ions or electrons.

Process:

Illustration of the modified chemical vapor deposition (inside) process

Standard optical fibers are made by first constructing a large-diameter preform, with a carefully controlled refractive index profile, and then pulling the preform to form the long, thin optical fiber. The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition, outside vapor deposition, and vapor axial deposition.[32]

With inside vapor deposition, the preform starts as a hollow glass tube approximately 40 centimetres (16 in) long, which is placed horizontally and rotated slowly on a lathe. Gases such as silicon tetrachloride (SiCl4) or germanium tetrachloride (GeCl4) are injected with oxygen in the end of the tube. The gases are then heated by means of an external hydrogen burner, bringing the temperature of the gas up to 1900 K (1600 °C, 3000 °F), where the tetrachlorides react with oxygen to produce silica or germania (germanium dioxide) particles. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume, in contrast to earlier techniques where the reaction occurred only on the glass surface, this technique is called modified chemical vapor deposition.

The oxide particles then agglomerate to form large particle chains, which subsequently deposit on the walls of the tube as soot. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as

thermophoresis). The torch is then traversed up and down the length of the tube to deposit the material evenly. After the torch has reached the end of the tube, it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. This process is repeated until a sufficient amount of material has been deposited. For each layer the composition can be modified by varying the gas composition, resulting in precise control of the finished fiber's optical properties.

In outside vapor deposition or vapor axial deposition, the glass is formed by flame hydrolysis, a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H2O) in an oxyhydrogen flame. In outside vapor deposition the glass is deposited onto a solid rod, which is removed before further processing. In vapor axial deposition, a short seed rod is used, and a porous preform, whose length is not limited by the size of the source rod, is built up on its end. The porous preform is consolidated into a transparent, solid preform by heating to about 1800 K (1500 °C, 2800 °F).

The preform, however constructed, is then placed in a device known as a drawing tower, where the preform tip is heated and the optic fiber is pulled out as a string. By measuring the resultant fiber width, the tension on the fiber can be controlled to maintain the fiber thickness.

Practical issues

Optical fiber cables

An optical fiber cableMain article: Optical fiber cable

In practical fibers, the cladding is usually coated with a tough resin buffer layer, which may be further surrounded by a jacket layer, usually plastic. These layers add strength to the fiber but do not contribute to its optical wave guide properties. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers, to prevent light that leaks out of one fiber from entering another. This reduces cross-talk between the fibers, or reduces flare in fiber bundle imaging applications.

Modern cables come in a wide variety of sheathings and armor, designed for applications such as direct burial in trenches, high voltage isolation, dual use as power lines,[35][not in citation given] installation in conduit, lashing to aerial telephone poles, submarine installation, and insertion in paved streets. The cost of small fiber-count pole-mounted cables has greatly decreased due to the high Japanese and South Korean demand for fiber to the home (FTTH) installations.

Fiber cable can be very flexible, but traditional fiber's loss increases greatly if the fiber is bent with a radius smaller than around 30 mm. This creates a problem when the cable is bent around corners or wound around a spool, making FTTX installations more complicated. "Bendable fibers", targeted towards easier installation in home environments, have been standardized as ITU-T G.657. This type of fiber can be bent with a radius as low as 7.5 mm without adverse impact. Even more bendable fibers have been developed.[36] Bendable fiber may also be resistant to fiber hacking, in which the signal in a fiber is surreptitiously monitored by bending the fiber and detecting the leakage.

Termination and splicing

ST connectors on multi-mode fiber.

Optical fibers are connected to terminal equipment by optical fiber connectors. These connectors are usually of a standard type such as FC, SC, ST, LC, or MTRJ.

Optical fibers may be connected to each other by connectors or by splicing, that is, joining two fibers together to form a continuous optical waveguide. The generally accepted splicing method is arc fusion splicing, which melts the fiber ends together with an electric arc. For quicker fastening jobs, a "mechanical splice" is used.

Fusion splicing is done with a specialized instrument that typically operates as follows: The two cable ends are fastened inside a splice enclosure that will protect the splices, and the fiber ends are stripped of their protective polymer coating (as well as the more sturdy outer jacket, if present). The ends are cleaved (cut) with a precision cleaver to make them perpendicular, and are placed into special holders in the splicer. The splice is usually inspected via a magnified viewing screen to check the cleaves before and after the splice. The splicer uses small motors to align the end faces together, and emits a small spark between electrodes at the gap to burn off dust and moisture. Then the splicer generates a larger spark that raises the temperature above the melting point of the glass, fusing the ends together permanently. The location and energy of the spark is carefully controlled so that the molten core and cladding don't mix, and this minimizes optical loss. A splice loss estimate is measured by the splicer, by directing light through the cladding on one side and measuring the light leaking from the cladding on the other side. A splice loss under 0.1 dB is typical. The complexity of this process makes fiber splicing much more difficult than splicing copper wire.

Mechanical fiber splices are designed to be quicker and easier to install, but there is still the need for stripping, careful cleaning and precision cleaving. The fiber ends are aligned and held together by a precision-made sleeve, often using a clear index-matching gel that enhances the transmission of light across the joint. Such joints typically have higher optical loss and are less robust than fusion splices, especially if the gel is used. All splicing techniques involve the use of an enclosure into which the splice is placed for protection afterward.

Fibers are terminated in connectors so that the fiber end is held at the end face precisely and securely. A fiber-optic connector is basically a rigid cylindrical barrel surrounded by a sleeve that holds the barrel in its mating socket. The mating mechanism can be "push and click", "turn and latch" ("bayonet"), or screw-in (threaded). A typical connector is installed by preparing the fiber end and inserting it into the rear of the connector body. Quick-set adhesive is usually used so the fiber is held securely, and a strain relief is secured to the rear. Once the adhesive has set, the fiber's end is polished to a mirror finish. Various polish profiles are used, depending on the type of fiber and the application. For single-mode fiber, the fiber ends are typically polished with a slight curvature, such that when the connectors are mated the fibers touch only at their cores. This is known as a "physical contact" (PC) polish. The curved surface may be polished at an angle, to make

an "angled physical contact" (APC) connection. Such connections have higher loss than PC connections, but greatly reduced back reflection, because light that reflects from the angled surface leaks out of the fiber core; the resulting loss in signal strength is known as gap loss. APC fiber ends have low back reflection even when disconnected.

Free-space coupling

It often becomes necessary to align an optical fiber with another optical fiber or an optical device such as a light-emitting diode, a laser diode, or an optoelectronic device such as a modulator. This can involve either carefully aligning the fiber and placing it in contact with the device to which it is to couple, or can use a lens to allow coupling over an air gap. In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens.

In a laboratory environment, the fiber end is usually aligned to the device or other fiber with a fiber launch system that uses a microscope objective lens to focus the light down to a fine point. A precision translation stage (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized.

Fiber fuse

At high optical intensities, above 2 megawatts per square centimeter, when a fiber is subjected to a shock or is otherwise suddenly damaged, a fiber fuse can occur. The reflection from the damage vaporizes the fiber immediately before the break, and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second (4−11 km/h, 2–8 mph). The open fiber control system, which ensures laser eye safety in the event of a broken fiber, can also effectively halt propagation of the fiber fuse. In situations, such as undersea cables, where high power levels might be used without the need for open fiber control, a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage.

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Polypropylene

Polypropylene

IUPAC name [show]

Other names

Polypropylene; Polypropene;Polipropene 25 [USAN];Propene polymers;Propylene polymers; 1-Propene

IdentifiersCAS number 9003-07-0

PropertiesMolecular formula (C3H6)x

Density0.855 g/cm3, amorphous0.946 g/cm3, crystalline

Melting point ~ 160 °CExcept where noted otherwise, data are given for materials in

their standard state (at 25   °C, 100   kPa) Infobox references

Polypropylene or polypropene (PP) is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles (e.g. ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.

In 2007, the global market for polypropylene had a volume of 45.1 million tons which led to a turnover of about 65 billion US $ (47,4 billion €).

Chemical and physical properties

Micrograph of polypropylene

Most commercial polypropylene is isotactic and has an intermediate level of crystallinity between that of low density polyethylene (LDPE) and high density polyethylene (HDPE); its Young's modulus is also intermediate. PP is normally tough and flexible, especially when copolymerised with ethylene. This allows polypropylene to be used as an engineering plastic, competing with materials such as ABS. Polypropylene is reasonably economical, and can be made translucent when uncolored but is not as readily made transparent as polystyrene, acrylic or certain other plastics. It is often opaque and/or coloured using pigments. Polypropylene has good resistance to fatigue.

Polypropylene has a melting point of ~160°C (320°F), as determined by Differential scanning calorimetry (DSC).

The MFR (Melt Flow Rate) or MFI (Melt Flow Index) is a measure of PP's molecular weight. This helps to determine how easily the melted raw material will flow during processing. Higher MFR PPs fill the plastic mold more easily during the injection or blow molding production process. As the melt flow increases, however, some physical properties, like impact strength, will decrease.

There are three general types of PP: homopolymer, random copolymer and block copolymer. The comonomer used is typically ethylene. Ethylene-propylene rubber or EPDM added to PP homopolymer increases its low temperature impact strength. Randomly polymerized ethylene monomer added to PP homopolymer decreases the polymer crystallinity and makes the polymer more transparent.

Degradation

Polypropylene is liable to chain degradation from exposure to UV radiation such as that present in sunlight. For external applications, UV-absorbing additives must be used. Carbon black also provides some protection from UV attack. The polymer can also be oxidized at high temperatures, a common problem during moulding operations. Anti-oxidants are normally added to prevent polymer degradation.

History

Polypropylene was first polymerized by Karl Rehn and Giulio Natta in March 1954,[1] serving as a preliminary work for large scale synthesis from 1957 onwards. At first it was thought that it would be cheaper than polyethylene

Synthesis

Short segments of polypropylene, showing examples of isotactic (above) and syndiotactic (below) tacticity.

An important concept in understanding the link between the structure of polypropylene and its properties is tacticity. The relative orientation of each methyl group (CH3 in the figure at left) relative to the methyl groups on neighboring monomers has a strong effect on the finished polymer's ability to form crystals, because each methyl group takes up space and constrains backbone bending.

Like most other vinyl polymers, useful polypropylene cannot be made by radical polymerization due to the higher reactivity of the allylic hydrogen (leading to dimerization) during polymerization. Moreover, the material that would result from such a process would have methyl groups arranged randomly, so called atactic PP. The lack of long-range order prevents any crystallinity in such a material, giving an amorphous material with very little strength and only specialized qualities suitable for niche end uses.

A Ziegler-Natta catalyst is able to limit incoming monomers to a specific orientation, only adding them to the polymer chain if they face the right direction. Most commercially available polypropylene is made with such Ziegler-Natta catalysts, which produce mostly isotactic polypropylene (the upper chain in the figure above). With the methyl group consistently on one side, such molecules tend to coil into a helical shape; these helices then line up next to one another to form the crystals that give commercial polypropylene many of its desirable properties.

A ball-and-stick model of syndiotactic polypropylene.

More precisely engineered Kaminsky catalysts have been made, which offer a much greater level of control. Based on metallocene molecules, these catalysts use organic groups to control the monomers being added, so that a proper choice of catalyst can produce isotactic, syndiotactic, or atactic polypropylene, or even a combination of these. Aside from this qualitative control, they allow better quantitative control, with a much greater ratio of the desired tacticity than previous Ziegler-Natta techniques. They also produce narrower molecular weight distributions than traditional Ziegler-Natta catalysts, which can further improve properties.

To produce a rubbery polypropylene, a catalyst can be made which yields isotactic polypropylene, but with the organic groups that influence tacticity held in place by a relatively weak bond. After the catalyst has produced a short length of polymer which is capable of crystallization, light of the proper frequency is used to break this weak bond, and remove the selectivity of the catalyst so that the remaining length of the chain is atactic. The result is a mostly amorphous material with small crystals embedded in it. Since each chain has one end in a crystal but most of its length in the soft, amorphous bulk, the crystalline regions serve the same purpose as vulcanization.

Mechanism of metallocene catalysts

The reaction of many metallocene catalysts requires a co catalyst for activation. One of the most common co catalysts for this purpose is Methylaluminoxane (MAO). Other co catalysts include, Al(C2H5)3There are numerous metallocene catalysts that can be used for propylene polymerization. (Some metallocene catalysts are used for industrial process, while others are not, due to their high cost.) One of the simplest is Cp2MCl2 (M = Zr, Hf). Different catalyst can lead to polymers with different molecular weights and properties. Active research is still being conducted on metallocene catalyst.

In the mechanism the metallocene catalyst first reacts with the co catalyst. If MAO is the co catalyst, the first step is to replace one of the Cl atoms on the catalyst with a methyl group from the MAO. The methyl group on is replaced by the Cl from the catalyst. The MAO then removes another Cl from the catalyst. This makes the catalyst positively charged and susceptible to attack from propyleneOnce the catalyst is activated, the double bond on the propene coordinates with the metal of the catalyst. The methyl group on the catalyst then migrates to the propene, and the double bond is broken. This starts the polymerization. Once the methyl migrates the positively charged catalyst is reformed and another propene can coordinate to the metal. The second propene coordinates and the carbon chain that was formed migrates to the propene. The process of coordination and migration continues and a polymer chain is grown off of the metallocene catalyst.[6][7]

Manufacturing

Melt processing of polypropylene can be achieved via extrusion and molding. Common extrusion methods include production of melt blown and spun bond fibers to form long rolls for future conversion into a wide range of useful products such as face masks, filters, nappies and wipes.

The most common shaping technique is injection molding, which is used for parts such as cups, cutlery, vials, caps, containers, housewares and automotive parts such as batteries. The related techniques of blow molding and injection-stretch blow molding are also used, which involve both extrusion and molding.

The large number of end use applications for PP are often possible because of the ability to tailor grades with specific molecular properties and additives during its manufacture. For example, antistatic additives can be added to help PP surfaces resist dust and dirt. Many physical finishing techniques can also be used on PP, such as machining. Surface treatments can be applied to PP parts in order to promote adhesion of printing ink and paints.

Uses

Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap

Since polypropylene is resistant to fatigue, most plastic living hinges, such as those on flip-top bottles, are made from this material. However, it is important to ensure that chain molecules are oriented across the hinge to maximise strength.

Very thin sheets of polypropylene are used as a dielectric within certain high performance pulse and low loss RF capacitors.

High-purity piping systems are built using polypropylene. Stronger, more rigid piping systems, intended for use in potable plumbing, hydronic heating and cooling, and reclaimed water applications, are also manufactured using polypropylene.[8] This material is often chosen for its resistance to corrosion and chemical leaching, its resillience against to most forms of physical damage, including impact and freezing, and its ability to be joined by heat fusion rather than gluing.[2][citation needed]

Many plastic items for medical or laboratory use can be made from polypropylene because it can withstand the heat in an autoclave. Its heat resistance also enables it to be used as the manufacturing material of consumer-grade kettles. Food containers made from it will not melt in the dishwasher, and do not melt during industrial hot filling processes. For this reason, most plastic tubs for dairy products are polypropylene sealed with aluminium foil (both heat-resistant materials). After the product has cooled, the tubs are often given lids made of a less heat-resistant material, such as LDPE or polystyrene. Such containers provide a good hands-on example of the difference in modulus, since the rubbery (softer, more flexible) feeling of LDPE with respect to PP of the same thickness is readily apparent. Rugged, translucent, reusable plastic containers made in a wide variety of shapes and sizes for consumers from various companies such as Rubbermaid and Sterilite are commonly made of polypropylene, although the lids are often made of somewhat more flexible LDPE so they can snap on to the container to close it. Polypropylene can also be made into disposable bottles to contain liquid, powdered or similar consumer products, although HDPE and polyethylene terephthalate are commonly also used to make bottles. Plastic pails, car batteries, wastebaskets, cooler containers, dishes and pitchers are often made of polypropylene or HDPE,

both of which commonly have rather similar appearance, feel, and properties at ambient temperature.

Polypropylene is a major polymer used in nonwovens, with over 50% used[citation needed] for diapers or sanitary products where it is treated to absorb water (hydrophillic) rather than naturally repelling water (hydrophobic). Other interesting non woven uses include filters for air, gas and liquids where the fibers can be formed into sheets or webs that can be pleated to form cartridges or layers that filter in various efficiencies in the 0.5 to 30 micron range.Such applications could be seen in the house as water filters or air conditioning type filters. The high surface area and naturally hydrophobic polypropylene nonwovens are ideal absorbers of oil spills with the familiar floating barriers near oil spills on rivers.

A common application for polypropylene is as Biaxially Oriented polypropylene (BOPP). These BOPP sheets are used to make a wide variety of materials including clear bags. When polypropylene is biaxially oriented, it becomes crystal clear and serves as an excellent packaging material for artistic and retail products.

Polypropylene, highly colorfast, is widely used in manufacturing rugs and mats to be used at home. In New Zealand, in the US military, and elsewhere, polypropylene, or 'polypro' (New Zealand 'polyprops'), has been used for the fabrication of cold-weather base layers, such as long-sleeve shirts or long underwear (More recently, polyester replace polypropylene in these applications in the U.S. military, such as in the ECWCS [10]). Polypropylene is also used in warm-weather gear such as some Under Armour clothing, which can easily transport sweat away from the skin. These polypropylene clothes are not easily flammable, however, they can melt, which may result in severe burns if the service member is involved in an explosion or fire of any kind.[11]

Polypropylene is widely used in ropes, distinctive because they are light enough to float in water.[12]

Polypropylene is also used as an alternative to polyvinyl chloride (PVC) as insulation for electrical cables for LSZH cable in low-ventilation environments, primarily tunnels. This is because it emits less smoke and no toxic halogens, which may lead to production of acid in high temperature conditions.

Polypropylene is also used in particular roofing membranes as the waterproofing top layer of single ply systems as opposed to modified bit systems.

Its most common medical use is in the synthetic, nonabsorbable suture Prolene, manufactured by Ethicon Inc.

Polypropylene is most commonly used for plastic moldings where it is injected into a mold while molten, forming complex shapes at relatively low cost and high volume, examples include bottle tops, bottles and fittings.

Recently it has been produced in sheet form and this has been widely used for the production of stationary folders, packaging and storage boxes. The wide colour range, durability and resistance to dirt make it ideal as a protective cover for papers and other materials. It is used in Rubik's cube stickers because of these characteristics.

The availability of sheet polypropylene has provided an opportunity for the use of the material by designers. The light weight, durable and colourful plastic makes an ideal medium for the creation of light shades and a number of designs have been developed using interlocking sections to create elaborate designs.

Polypropylene sheets are a popular choice for trading card collectors; these come with pockets (nine for standard size cards) for the cards to be inserted and are used to protect their condition and are meant to be stored in a binder.

Polypropylene has been used in hernia repair operations to protect the body from new hernias in the same location. A small patch of the material is placed over the spot of the hernia, below the skin, and is painless and is rarely, if ever, rejected by the body.

The material has recently been introduced into the fashion industry through the work of designers such as Anoush Waddington who have developed specialized techniques to create jewelry and wearable items from polypropylene.

Researchers in Canada recently asserted that quaternary ammonium biocides and oleamide were leaking out of polypropylene labware, affecting experimental results.[13] Since polypropylene is used in a wide number of food containers such as those for yogurt, the problem is being studied.[14]

Expanded Polypropylene (EPP) is a foam form of polypropylene. EPP has very good impact characteristics due to its low stiffness, this allows EPP to resume its shape after impacts. EPP is extensively used in model aircraft and other radio controlled vehicles by hobbyists. This is mainly due to its ability to absorb impacts, making this an ideal material for RC aircraft for beginners and amateurs.

Recycling

Polypropylene is commonly recycled, and has the number "5" as its resin identification code: .