Hemp Fiber

 

Hemp Fiber

Hemp belongs to the Angiosperm phylum since it has vessel elements in the woody core (xylem) like hardwood. It belongs to the eudicotyledons like hardwoods, numerous bushes, and herbs since it has two cotyledons (i.e. seed leaves).

The long and flexible hemp fibers are embedded in the bark (cortex) on
the surface of the stem. Hemp originates from Central Asia but can be cultivated from the Equator to the polar circle.

One of the reasons hemp fiber has been valued is because of its length. The primary bast fibers in the bark are 5–40 mm long, and are amalgamated in fiber bundles which can be 1–5 m long (secondary bast fibers are about 2 mm long). The woody core fibers are short—about 0.55 mm—and like hardwood fibers are cemented together with considerable lignin.

The core fibers are generally considered too short for high-grade paper applications (a length of 3 mm is considered ideal), and too much lignin is present. While the long bast fibers have been used to make paper almost for 2 millennia, the woody core fibers have rarely been so used.

Other desirable features of hemp fibers are strength and durability (particular resistance to decay), which made hemp useful in the past for rope, nets, sail-cloth, and oakum for caulking. During the age of sailing ships, Cannabis was considered to provide the very best of canvas, and indeed this word is derived from Cannabis.

The hemp fibers are present in bundles as long as the stems, which can easily be peeled off the xylem surface by hand or machine. The fresh stem consists of a hollow cylinder of 1-5 mm thick xylem covered by 10-50 µm cambium, 100-300 µm cortex, 20-100 µm epidermis and 2-5 µm cuticle. The pith is empty space in dry stems.

Hemp Plant

Highly selected forms of the fiber cultigen possess features maximizing fiber production. Since the nodes tend to disrupt the length of the fiber bundles, thereby limiting quality, tall, relatively unbranched plants with long internodes have been selected.

Another strategy has been to select stems that are hollow at the internodes, with limited wood, since this maximizes production of fiber in relation to supporting woody tissues.

Similarly, limited seed productivity concentrates the plant’s energy into production of fiber, and fiber cultivars often have a low genetic propensity for seed output. Selecting monoecious strains overcomes the problem of differential maturation times and quality of male (staminate) and female (pistillate) plants (males mature 1–3 weeks earlier).

Male plants, in general, are taller, albeit slimmer, less robust, and less productive. Except for the troublesome characteristic of dying after anthesis, male traits are favored for fiber production, in contrast to the situation for drug strains noted below. In former, labor-intensive times, the male plants were harvested earlier than the females, to produce superior fiber.

The limited branching of fiber cultivars is often compensated for by possession of large leaves with wide leaflets, which obviously increase the photosynthetic ability
of the plants. Since fiber plants have not generally been selected for narcotic purposes, the level of intoxicating constituents is usually limited.

Typical architecture of categories of cultivated Cannabis sativa. Narcotic plants are generally low, highly branched, and grown well-spaced. Plants were grown for oilseed was traditionally well-spaced, and the plants developed medium height and strong branching.

Fiber cultivars are grown at high density and are unbranched and very tall. “Dual purpose” plants are grown at moderate density, tend to be slightly branched and of medium to tall height. Some recent oilseed cultivars are grown at a moderate density and are short and relatively unbranched.

The degree of branching and height are determined both by the density of the plants and their genetic background.

Fiber Processing

Unlike flax, hemp long fiber requires water retting for preparation of high-quality spinnable fibers for production of fine textiles. Improved microorganisms or enzymes could augment or replace traditional water retting. Steam explosion is another potential technology that has been experimentally applied to hemp.

The traditional procedure for the production of fibers from hemp is field retting, a natural process which results in fibers of variable quality due to differences in weather conditions. During this process fungi and yeasts colonize the hemp and produce polysaccharide-degrading enzymes, which macerate and disrupt the parenchyma cells. This process can be replaced with the more controllable water retting procedure in which the plant stems are placed in tanks with 30-40°C hot water for 4 days.

After retting, the woody core is broken into small pieces that can be separated from the fibers by decertification. This is industrially done with pairs of rotating rollers, which crush the shives. In lab-scale, the fibres are isolated with hand peeling. The extracted fibres are in the form of large fibre bundles useful in non-woven fibre mats, which are made by air-drying and needle punching with uncontrolled and thereby random fiber orientation. Production of aligned fiber assemblies can also be done at laboratory scale by combing the fibers in water, stretching them and air-drying them.

Defibration

During water retting, the hemp bast is separated into large fiber bundles. Additional treatment is required to defibrate the fiber bundles into single fibers and small fiber bundles useful for production of hemp yarn. It is done by degradation or disruption of the middle lamellae between the single fibres.

Enzyme treatment, wet oxidation and NaOH treatment can degrade pectin and lignin in the middle lamellae between the single fibres.

Yarn Formation

The retted fibre bundles of 0.5-2 m length are traditionally used directly for production of yarn for rope production. First hackling is done in two steps to straighten the fibers and remove short disordered fibers with a metal-pinned brush; this results in a sliver of parallel fibers useful for spinning.

At the industrial scale, the hackling is performed using metal-pinned brushes and rotating rollers to pull the fibres forward. This technique is basically also used to make sliver of shorter fibres like flax fibres.

By manual yarn spinning, some fibres from the sliver are mounted on a rotating hook. The fibres are stretched during the twisting process and more fibres are added, while the hand is moved backward to elongate the spun amount of yarn and keep a constant yarn thickness.

At industrial scale, the stretching part of this process is called drafting. In drafting, the fibres become straightened by passing the sliver through a series of rollers with increasing rotational speed in the forward direction.

The drafting process elongates the thick sections of the filament so they get the same thickness as the thinner sections, resulting in a uniform sliver ready for spinning.

The most common spinning method is ring spinning, in which slivers delivered from the drafting rollers become twisted by the traveller that is freely rotating on a ring. The ring distributes the yarn onto a rotating bobbin. Each traveller rotation introduces one twist. Increased delivering speed from the drafting rollers decreases the number of twists per length.

The twisting forces the fibers to take a helical structure and results in inherent sliding friction between the fibers and in axial strength in the yarn. The produced yarn can be wound on a metal frame to get aligned fiber assemblies, ready for composite production.

Hemp Product Usages

Hemp paper is useful for specialty applications such as currency and cigarette papers where strength is needed. The bast fiber is of greatest interest to the pulp and paper industry because of its superior strength properties compared to wood. However, the short, bulky fibers found in the inner part of the plant (hurds) can also be used to make cheaper grades of paper, apparently without greatly affecting quality of the printing surface. Hemp is not competitive for newsprint, books, writing papers, and general paper (grocery bags, coffee cups, napkins), although there is a specialty or novelty market for those specifically wishing to support the hemp industry by purchasing hemp writing or printing paper despite the premium price.

• Specialty pulp (cigarette paper, bank notes, technical filters, and hygiene products)
• Composites for autos
• Construction & thermal insulation materials
• Geotextiles
• Fiberboard
• Cement (Concrete) and Plaster
  

Acrylic Fibers

 

Acrylic Fibers

Acrylic fibres are polymers formed by addition polymerization of at least 85% by weight of a chemical called acrylonitrile or vinyl cyanide. To polymerize vinyl cyanide the double bond between the first two carbon atoms is broken and the molecules attach themselves to each other in a linear chain.

Acrylic is our final fiber. It can be thought of as artificial wool. It is made from the unlikely combination of coal, air, water, oil, and limestone. DuPont first made acrylic fibers in 1944 and began commercial production in 1950. It is spun by either dry spinning or wet spinning.

In dry spinning, the dissolved polymers are extruded into warm air. The fibers solidify by evaporation. In wet spinning, the polymer is dissolved and extruded into a bath and then dried.

In some ways, acrylic imitates wool. It has wool’s warmth and softness but does not absorb water. Instead, acrylic wicks moisture to the surface where it evaporates.

Acrylic is used in knitted apparels such as fleece, socks, sportswear, and sweaters. It is also used to create fake fur, craft yarns, upholstery fabric, carpet, luggage, awnings, and vehicle covers.

The acrylic fibers include acrylic, modacrylic, and other vinyl fibers containing cyanide groups as side chains. Among the major acrylic fibers used in commerce, acrylonitrile is the comonomer containing a cyanide group.

ACRYLIC

Acrylic fibers are formed from the wet or dry spinning of copolymers containing at least 85% acrylonitrile units. After texturizing, acrylic fibers have a light bulky wool-like hand and overall wool-like aesthetics. The fibers are resilient and possess an excellent acid resistance and sunlight resistance. Acrylics have been used extensively in applications formerly reserved for wool or other keratin fibers.

Common trade names for acrylic fibers include Acrilan, Creslan, Orlon, Sayelle, and Zefran. Since the acrylic fibers are usually texturized, they have a bulky wool-like hand and possess a moderate degree of luster.

MODACRYLIC

The modacrylics generally resemble acrylics and have a warm pleasing hand and good drapability, resiliency and wrinkle resistance. They are more heat sensitive but more flame resistant than acrylics and have generally been used in specialty applications.

Modacrylic fiber trade names include Elura, SEF, Verel, and Zefran. Production of Dynel modacrylic fibers was discontinued in 1975. Modacrylics possess warm wool-like aesthetics and a generally bright luster. The fiber exhibits fair pilling and abrasion resistance. It has good wrinkle resistance and crease retention if the fiber has been properly heating set.

Nytril

Nytril fibers are made up of polymers containing at least 85% vinylidene dinitrile units, which appear at least every other unit in the polymer chain. The comonomer used in Nytril synthesis is vinyl acetate.

Lastrile

Lastrile fibers are fibers formed from copolymers of acrylonitrile and a diene such as butadiene and contain 10%-50% acrylonitrile units. Lastrile fibers have not been commercially produced.

Sisal Fibers

 

Sisal Fibers

Sisal-fiber-reinforced composites that are traditionally used for making ropes, mats, carpets, fancy articles and others.

Sisal fiber is a hard fiber extracted from the leaves of the sisal plant (Agave sisalana). Though native to tropical and sub-tropical North and South America, sisal plant is now widely grown in tropical countries of Africa, the West Indies, and the Far East. Sisal fibers are extracted from the leaves.

Sisal fiber is one of the most widely used natural fibers and is very easily cultivated. It has short renewal times and grows wild in the edges of fields. Tanzania and Brazil are the two main producing countries.

A sisal plant produces about 200-250 leaves and each leaf contains 1000-1200 fiber bundles which are composed of 4% fiber, 0.75% cuticle, 8% dry matter and 87.25% water. So normally a leaf weighing about 600 g will yield about 3% by weight of fiber with each leaf containing about 1000 fibers.

The sisal leaf contains three types of Fibres, namely (1) mechanical, (2) ribbon, and (3) xylem.

1. The mechanical fibers are mostly extracted from the periphery of the leaf. They have a roughly thickened-horseshoe shape and seldom divide during the extraction processes. They are the most commercially useful of the sisal fiber.
2. Ribbon fibers occur in association with the conducting tissues in the median line of the leaf. They are the longest fibers and compared with mechanical fibers they can be easily split longitudinally during processing.
3. Xylem fibers have an irregular shape and occur opposite the ribbon fibers through the connection of vascular bundles They are composed of thin-walled cells and are therefore easily broken up and lost during the extraction process.

Sisal Fiber Processing

The processing methods for extracting sisal fibers include (1) retting followed by scraping and (2) mechanical means using decorticators. the mechanical process yields about 2-4% fiber (15 kg per 8 h) with good quality having a lustrous color while the retting process yields a large number of poor quality fibers. After extraction, the fibers are washed thoroughly with plenty of clean water to remove the surplus wastes such as chlorophyll, leaf juices, and adhesive solids.

Properties of Sisal Fiber

The length of sisal fiber is between 1.0 and 1.5 m and the diameter is about 100-300 mm. The fiber is actually a bundle of hollow sub-fibers. Their cell walls are reinforced with spirally oriented cellulose in a hemicellulose and lignin matrix. So, the cell wall is a composite structure of lignocellulosic material reinforced by helical microfibrillar bands of cellulose.

The composition of the external surface of the cell wall is a layer of ligneous material and waxy substances which bond the cell to its adjacent neighbors. Hence, this surface will not form a strong bond with a polymer matrix. Also, cellulose is a hydrophilic glucan polymer consisting of a linear chain of 1, 4-b-bonded an-hydro glucose units and this large amount of hydroxyl groups will give sisal fiber hydrophilic properties. This will lead to a very poor interface between sisal fiber and the hydrophobic matrix and very poor moisture absorption resistance.

Sisal and synthetic hybrid-fiber composites

Reinforcement by two or more fibers in a single matrix leads to hybrid composites with a great diversity of material properties. It appears that the behavior of hybrid composites is simply a weighted sum of the individual components so that there is a more favorable balance of properties in the resultant composite material. Sisal and glass fibers are one good example of
hybrid composites possessing very good combined properties.

Sisal fiber is an effective reinforcement of polymer, rubber, gypsum and cement matrices. This has created a range of technological applications beyond its traditional usage as ropes, carpets, mats, etc.

The mechanical and physical properties of sisal fiber not only depend on its source, position, and age which will affect the structure and properties but also depend on the experimental conditions, such as fiber diameter, gauge length, strain rate and test temperature.

Sisal and glass fibers can be combined to produce hybrid composites which take full advantage of the best properties of the constituents. Almost all the mechanical properties show `positive’ hybrid effects.

Banana Fibers

 

Banana Fibers

Banana fibre, a ligno-cellulosic fibre, obtained from the pseudo-stem of banana plant (Musa sepientum), is a bast fibre with relatively good mechanical properties.

Banana fiber is a natural fiber with high strength, which can be blended easily with cotton fiber or other synthetic fibers to produce blended fabric & textiles. Banana Fiber also finds use in high-quality security/ currency paper, packing cloth for agriculture produce, ships towing ropes, wet drilling cables etc.

Banana fiber, a lignocellulosic fiber, obtained from the pseudo-stem of banana plant (Musa sepientum), is a bast fiber with relatively good mechanical properties.

Plant fibers are sclerenchymatous cells with heavily lignified cell walls having a narrow lumen in cross section. Fiber cells are dead at maturity and serve as a support tissue.

Natural fibers possess several advantages over synthetic fibers such as low density, appropriate stiffness and mechanical properties and also high disposability and renewability. Also, they are recyclable and biodegradable.

Banana fibers can be used for various purposes such as in textile, paper or handicrafts industry. Banana paper is versatile as it is waterproof and stronger than wood-pulp paper, meaning it can be used in packaging and even as a basis for building materials.

Technology / Process

There are two methods for extraction of Banana fiber, namely Bacnis method and Loenit method.

• In the Bacnis method, Banana Fiber is produced from the waste stalk of Banana plant. The outer sheath is tightly covered layers of fiber. The fiber is located primarily adjacent to the outer surface of the sheath and can be peeled-off readily in ribbons of strips of 5 to 8 cm wide and 2-4 mm thick, the entire length of the sheath.
• This stripping process is known as tuxying the strips being called tuxies. Two methods of tuxying are employed in the Philippines. In the first method called Bacnis method, the trunks are pulled apart and the sheath separated according to their position in the stalk. They are then flattened and the fiber is stripped from the stem by cutting the pulpy portion and pulling away from the tuxy.
• In the Loenit method, the tuxies are pulled off the stalk from one sheath at a time. In either of these methods, tuxies are tied into bundles of 23 to 27 kg and brought to the stripping knife for cleaning. In this process, tuxies are pulled under a knife blade, which is pressed tightly against the tuxy in order to scrape away the plant tissue between the fibers. The clean fiber is then air dried and made up into bundles for subsequent grading and bailing.
• In addition to hand stripping, machines are used where the trunks from which the dark outer sheaths have been removed, are cut into sections of 120 to 180 cm in length. The sections are then crushed between rolls and the pulpy tissues are scraped away, one half the length at a time, by two large revolving drums, the rim of which is fitted with scrapping blade which scrapes the sheath while it is pressed against a bed plate, oven dried, graded and baled.

Banana Fiber – Structure and Usage

Banana fibers can be extracted by employing chemical, mechanical or biological methods. The chemical method causes environmental pollution, while mechanical method fails to remove the gummy material from the fiber bundle surface. Biological procedures yield more fiber bundles than the other two procedures without any harm to the environment. The extraction of banana fibers using biological natural retting has already been reported. After extracting the fibers, degumming is essential prior to the utilization of fibers. The removal of heavily coated, non-cellulosic gummy material from the cellulosic part of plant fibers is called degumming.

Banana fiber is multiple celled structures. The lumens are large in relation to the wall thickness. Cross markings are rare and fiber tips pointed and flat, ribbons like individual fiber diameter range from 14 to 50 microns and the length from 0.25 cm to 1.3 cm, showing the large oval to round lumen.

The ‘‘pseudo-stem’’ is a clustered, cylindrical aggregation of leaf stalk bases. Banana fiber at present is a waste product of banana cultivation and either not properly utilized or partially done so.

The extraction of fiber from the pseudostem is not a common practice and much of the stem is not used for the production of fibers. The buyers for banana fibers are erratic and there is no systematic way to extract the fibers regularly. Useful applications of such fibers would regularize the demand which would be reflected in a fall in the prices.

Bast fibers, like banana, are complex in structure. They are generally lignocellulosic, consisting of helically wound cellulose microfibrils in an amorphous matrix of lignin and hemicellulose. The cellulose content serves as a deciding factor for mechanical properties along with microfibril angle.

A high cellulose content and low microfibril angle impart desirable mechanical properties for bast fibers. Lignins are composed of nine carbon units derived from substituted cinnamyl alcohol; that is, coumaryl, coniferyl, and syringyl alcohols. Lignins are associated with the hemicelluloses and play an important role in the natural decay resistance of the lignocellulosic material.

Coconut or coir Fiber

 

Coconut or coir Fiber

Coir or coconut fiber belongs to the group of hard structural fibers. It is an important commercial product obtained from the husk of the coconut. Industries based on coir have developed in many coconut producing countries especially India, Tanzania, Kenya, Bangladesh, Burma, Thailand, Sri Lanka, Nigeria, Ghana etc.

Coir or coconut fiber belongs to the group of hard structural fibers. It is an important commercial product obtained from the husk of the coconut.

Industries based on coir have developed in many coconut producing countries especially India, Tanzania, Kenya, Bangladesh, Burma, Thailand, Sri Lanka, Nigeria, Ghana etc. In India, coir manufacture is a traditional industry, which has taken deep roots in the economic structure of the rural areas in the coastal states.

The industry sustains over half a million people and contributes substantial foreign exchange to the national exchequer. India was ranked first among the coconut producing countries of the world until 1921, since then, the position has changed. Indonesia and Philippines have increased their production and India now occupy the third place. These three countries together account nearly 65 percent of the world production (4.5 m mt) out of which India’s share is about 25 percent.

Harvesting and Processing

The fruits are harvested when still green to obtain the best quality coir. Husk usually forms 35.45 percent of the weight of the whole nut, when ripe. Husks from ten to eleven-month-old nuts have been found to give superior quality fiber possessing a golden yellow color. The fiber from the husk is extracted on a commercial scale, either by natural retting process or by mechanical decortication.

Mechanical Methods

Mechanical methods of retting are employed in areas where facilities for natural retting do not exist. Either dry or green husks are soaked in cement tanks for a period varying from a few hours to three weeks and the fiber extracted manually or mechanically. In one method, the husks are first crushed through a series of corrugated iron rollers, a machine called husk crusher. Then the husks are thrown into a retting tank where they undergo fermentation for a minimum period of 72 hours. This process, however, does not yield fiber of spinnable quality as in the case of natural retting, but yields only bristles and mattress fibers.

Chemical Methods

Various chemical methods have also been developed for the retting of husk. The advantages claimed includes higher yield of uniform quality fiber and a considerable saving of time.

1. Nanji Process. The green or dry husks are partially crushed and treated under the steam pressure of 36.4-45.4 kg/sq. inch. With sodium sulfate or sodium carbonate containing traces of aluminum sulfate for 1-2 hours. During this process, the pith is loosened from the fiber and removed by washing. The fiber obtained is of good quality but slightly darker than that of natural retting.
2. Elod and Thomas Process. The crushed husks are immersed in hot water twice. Slaked lime or similar substance is added during the second immersion in order to avoid discoloration. Subsequently, the fiber is extracted mechanically.
3. Rowel Process. The crushed husks are subjected to a high steam pressure and the fiber come out loose from the steaming chambers.
4. Vander Jaget Process. The husks are first to split into pieces. The pieces are then boiled with a weak solution of caustic-soda and squeezed. The compressed fibers are reopened, softened and cleaned. It is claimed that good quality fiber could be produced using this technique in less than two hours.
5. Caraan Process. The husk is fermented for four days at 37°C with the aid of the fungus Aspergillus sp., previously isolated from partially retted husks. This process is reported to give 37 percent fiber output.

Extraction of Fibre

After retting, the husks are taken out of the water and washed. Outer skin peeled off, placed on wooden blocks and beaten with a wooden mallet for separating the fibers from the pith. After fibers are separated from the pith, these are cleaned and then spread on the shade for drying. The fibers spread for drying are occasionally beaten and tossed up with poles to remove the remnants of pith and impurities still adhering to the fiber. For making superior types of fiber, especially for spinning, improved methods exist.

It is estimated that the annual production of coir in India nearly amounts to 1 m mt. Three classes of fiber are recognized in the trade. They are Mat, Curl (toe or mattress)and Bristle fiber. The bulk of fiber produced on the west coast of India is mat fiber. Mat fiber is sometimes used as a substitute for hemp in certain cordages. Curl fiber is obtained mostly from untreated husk and is short; it is used for mattresses or for stuffing upholstery, cushions etc. Bristle fiber, which is coarse and thick, is used for making brushes, and brooms. Bristle fiber is not produced in India but mostly imported from Sri Lanka.

Fiber Structure

• Individual fibers are 0.3-1.0 mm long and 0.01-0.0.2 mm in diameter; the ratio of length to diameter being 35. The lumen is medium to large, polygonal-rounded, or elliptic. The vascular bundle is collateral and is surrounded by a thick sclerenchymatous sheath. Lignin and hemicelluloses, which form the cementing materials of fiber cells, increase with the age of the fiber and the pectin decreases. As the lignin content increases, the fiber becomes stiffer and tougher.
• Length of the fiber determines its spinnability and commercial utility. Spinnability may be defined as the ease with which textile fibers may be twisted into continuous, uniform yarns, having commercially acceptable properties.

The chemical composition of coconut husk and coir fiber:

Properties	Percentage
Total water solubles	26.00
Pectins etc. soluble in boiling water	14.25
Hemi-celluloses	8.50
Lignin	29.23
Cellulose	23.81

Coir fiber is classified according to its length. Following lengths are commonly visible

• Long fibers (15 cms. And above)
• Medium ( 12-15 cms.)
• Short ( 6-8 cms.)
• Very short (4 cms.)

Deterioration

Coir has been found to be remarkably resistant to both fungal and bacterial decomposition.

Spinning

The spinning of coir yarn is mainly a cottage industry in India and abroad. It is produced either by wheel spinning or hand spinning or mechanized spinning. Handspun yarn is soft and the twist and thickness are even. Wheel spun yarn has a hard twist; it is stronger and more uniform in size and twist than handspun yarn.

The classification of coir yarn is based on variations of color, twist, pitch, scorage etc. and also an area of production like; Anjengo, Aratony, Alapat, Beach, Ropeyarn, Parur, Muppiri etc.

Weaving

Coir yarn is treated with a dilute solution of sulphuric acid, which improves its color and gives a certain amount of brightness for the production of mats, Coir mats, fiber mats, specialty mats, Mattings, rugs, bouzouki, carpets etc.

Dyeing and Printing

Colour and design play an important part in the marketing of coir products. Dyed yarn is exported to Australia for the manufacture of matting. The following dyestuffs are employed in coir dyeing. Chrysoidine YS, Bismarck Brown, Methyl Violet, Malachite Green, Magenta, Naphthalene orange, Naphthalene Red, Naphthalene Green etc.

Ropes & Cordages

Coir is resistant to the action of water and has the property of elongation without breaking. By virtue of these properties, coir has long been used for ropes and cordages. Very short (4 cms.)

Uses of Coir

• Besides its main use as a floor covering and in rope making, coir fiber finds extensive use as packaging material to protect goods against shock in transport.
• Coir fiber finds its use in the production of activated carbon, artificial horse hair, paper pulp, roofing tiles, writing boards, thermal insulations, high stretch paper, manufacture of olive oil filters etc.
• In Germany, coir is rubberized for making cushion seating for automobiles and railways. The rubberization is brought about by Splashing layers of coir fiber and rubber with the help of a specialized machine.
• Coir yarn has been found to be the ideal lead for hop wines which is used in a brewery in U.S.A Coir bags are used in tea estates for collecting tea leaves and for transportation: and also for lifting coal from mines.
• Coir yarn is used for making fenders which are attached to ships and boats for preventing collision and shock.
• Coir mats are used for commercial packaging purposes and circular brush mats are used for packing.
• Coir mattings after bituminization offer possibilities of being used as a floor covering in godowns to withstand moisture adsorption by stored goods.
• Rubber backed coir mats are sol-proof, sound absorbent and do not scratch a polished floor. Heavy matting made out of thick coir rope is being used for transporting gas cylinder. It is used as a strainer in tube wells in place of wire mesh.
• Hardboards made of coconut husk shorts and coir dust is durable, smooth, insect proof, fire retarding and water-repellent. They may be sawed, nailed, glued and finished into a particular requirement.
• Coir waste has been recently used in the manufacture of Coprolite by incorporating with resins and other ingredients by the usual techniques of plastics manufacture. The powder so obtained is hotpressed to obtain articles of any shape using appropriate molds. It is a tough and hard material and possesses good strength and electrical resistance.

Carbon Fibers

 

Carbon Fibers

Carbon fiber is a super strong material that is extremely lightweight. It is five times as strong as steel, two times as stiff, yet weighs about two-thirds less. Carbon fiber is basically very thin strands of carbon (even thinner than human hair). The strands can be twisted together, like yarn and then be woven together, like cloth. To make carbon fiber take on a permanent shape, it can be laid over a mold and coated with a stiff resin or plastic. Carbon fiber can also be defined as a fiber containing at least 92 wt % carbons.

Carbon fibers are a new breed of high-strength fiber. It came into existence in 1879 when Edison took out a patent for the manufacture of carbon filaments suitable for use in electric lamps. However, in the early 1960s, when there was a need f of the aerospace industry – especially for military aircraft – for better and lightweight materials, successful commercial production started.

In recent decades, carbon fibers have found wide usage in aeronautics, athletic performance, automobiles, building structures and, of course, musical instruments. Carbon fibers are used in composites with a lightweight matrix.

Carbon fiber composites are ideally suited for applications where strength, stiffness, lower weight, and outstanding fatigue characteristics are critical. They are used in the occasion where high temperature, chemical inertness, and high damping are important. They have been extensively used in composites in the form of woven textiles, prepregs, continuous fibers/roving, and chopped fibers. The composite parts can be produced through filament winding, tape winding, protrusion, compression molding, vacuum bagging, liquid molding, and injection molding.

There are two most important precursors in the carbon fiber industry are polyacrylonitrile (PAN) and mesophase pitch (MP). The structure and composition of the precursor affect the properties of the resultant carbon fibers significantly. Although the essential processes for carbon fiber production are similar, different precursors require different processing conditions in order to achieve improved Performance.

Examples of Application

• Aerospace – flights, rockets, satellites
• Environment and Energy-related – wind power blade, tube power tank, battery charging flywheel, fuel cell, tidal power blade, the electric cable core
• Auto-mobile – hood, roof, propeller shaft, body panel for the bus, compressed natural gas tank
• Industrial use- the body of trains, x-ray top panel, pc housing, robot hand for liquid crystal panel, bridge pier reinforcement
• Sports material – fishing rod, bicycle, hockey stick, racket, golf shaft.

Benefits of Carbon fiber

The potentially low-cost carbon fiber composites will be in a position to provide enormous advantages to a number of technologies for current and future everyday life applications, including a number of advanced technologies that are not currently commercially feasible. Lightweight components for automobiles, buses, trains, aircraft, ships, and applications including lightweight panels and load-bearing structures could result in weight savings, leading to a major saving in the nation’s and world’s energy consumption.

Low-cost carbon fiber is a national goal towards accomplishing a number of manufacturing technological breakthroughs.

Difficulties of Carbon Fiber

• Cost is the main hurdle carbon fiber will have to overcome before it can provide a viable energy solution.
• The second hurdle is waste disposal. When a typical car breaks down, its steel can be melted and used to construct another car (or building, or anything else made of steel). Carbon fiber can’t be melted down, and it’s not easy to recycle. When it is recycled, the recycled carbon fiber isn’t as strong as it was before recycling.
• Lack of high-speed composite fabrication techniques

Classification of carbon fiber

Based on modulus, strength, and final heat treatment temperature, carbon fibers can be classified into the following categories:

Based on carbon fiber properties, carbon fibers can be grouped into:

• Ultra-high-modulus, type UHM (modulus >450Gpa)
• High-modulus, type HM (modulus between 350-450Gpa)
• Intermediate-modulus, type IM (modulus between 200-350Gpa)
• Low modulus and high-tensile, type HT (modulus < 100Gpa, tensile strength > 3.0Gpa)
• Super high-tensile, type SHT (tensile strength > 4.5Gpa)

Based on precursor fiber materials, carbon fibers are classified into:

• PAN-based carbon fibers
• Pitch-based carbon fibers
• Mesophase pitch-based carbon fibers
• Isotropic pitch-based carbon fibers
• Rayon-based carbon fibers
• Gas-phase-grown carbon fibers

Based on final heat treatment temperature, carbon fibers are classified into:

• Type-I, high-heat-treatment carbon fibers (HTT), where final heat treatment temperature should be above 2000°C and can be associated with high-modulus type fiber.
• Type-II, intermediate-heat-treatment carbon fibers (IHT), where final heat treatment temperature should be around or above 1500?C and can be associated with high-strength type fiber.
• Type-III, low-heat-treatment carbon fibers, where final heat treatment temperatures not greater than 1000?C. These are low modulus and low strength materials.

Manufacturing of Carbon fibers

Carbon fiber is a super strong material that is extremely lightweight. Carbon fibers generally have excellent tensile properties, low densities, high thermal and chemical stabilities in the absence of oxidizing agents, good thermal and electrical conductivities, and excellent creep resistance. Therefore Carbon fiber is enabling advancement in aeronautics, athletic performance, automobiles, building structures and, of course, musical instruments.

Carbon fibers are manufactured by a controlled pyrolysis of stabilized precursor fibers. First Oxidization process is done wherein the stabilization of precursor fibers at about 200-400 °C in air is done. Then carbonization is done wherein these fibers which are stabilized and infusible are treated at a high temperature of about 1,000 °C in an inert atmosphere to remove hydrogen, oxygen, nitrogen, and other non-carbon elements.

Then graphitized is done on those carbonized fibers at an even higher temperature up to around 3,000 °C to achieve higher carbon content and higher Young’s modulus in the fiber direction. The properties of the resultant carbon/graphite fibers are affected by many factors such as crystallinity, crystalline distribution, molecular orientation, carbon content, and the number of defects. The resulting carbon fibers are then post-treated to improve their adhesion to composite matrices.

Manufacturing of Manmade Fibers / Synthetic Fibers

 

Manufacturing of Manmade Fibers / Synthetic Fibers

Manmade fibers are manufactured using different mechanical and chemical processes for example Synthetic fibers from thermoplastics are produced by extruding the molten plastic through extrusion dies (spinnerets) into a stream of cold air that cools and solidifies the plastic. (The operation is referred to as melt spinning.)

General Principles of Production Process

Polymerisation

The term polymerization defines the process of macromolecules formation through repetition of basic units: it, of course, applies only to synthesis fibers. In general, polymerization reactions are activated and controlled during the process by various parameters, as temperature, pressure,
catalyzers, reaction stabilizers.

The number of repetitive units is termed degree of polymerization and is a parameter of great significance for fiber properties setting. As the length of the single molecules is not constant but varies according to a statistical model, the degree of polymerization or the correspondent molecular weight has to be considered as an average value.

Depending on the various fiber typologies, the degrees of polymerization may range from some hundred units in the case of polymers obtained through condensation (PA, PES) to some thousand units in the case of polymers resulting from poly-addition (PAN, PP). Under a production and application point of view, the degree of polymerization is controlled by measuring following parameters:

• Relative viscosity rel= solution viscosity/solvent viscosity = flow time t1/flow time t2
• Intrinsic viscosity intr= rel /c ?0 (concentration vanishing)
• Melt flow index MFI = speed rate of the melted polymer at pre-established conditions

Relative viscosity is a parameter which is mostly used to identify nylon, while intrinsic viscosity (obtainable from the relative viscosity also by means of formulas) is used for polyester and the melt flow index for polypropylene.

There are basically two mechanisms of chemical reaction available for the synthesis of linear polymers:

• Poly-condensation: with this operation two molecules of the same type or of different types are joined together to form macromolecules by removing simple secondary products as water, hydrochloric acid, alcohol. The prerequisite for reactions of this type is the presence in the molecule (monomer) of two terminal reactive groups with functional properties.
• Poly-addition: this operation joins together several molecules and redistributes the valence links existing in the monomers, however without removing secondary products.

Many unsaturated compounds which are characterized by the presence of a double link between
two adjacent carbon atoms as ethylene and its derivatives polymerise according to this reaction;
within this category fall e.g. acrylic and polyolefin fibers.

Spinning

The term spinning defines the extrusion process through bored devices (spinnerets) of fluid polymer masses which are able to solidify in a continuous flow. The spinning process is sometimes designated as “chemical or primary spinning” to distinguish it from the “textile or mechanical or secondary spinning”. The polymer processing from the solid to the fluid state can take place with two methods:

by melting:

this method can be applied on thermoplastic polymers which show stable performances at the processing temperatures (this method is used by 70% of the fibers)

by solution:

the polymer is solved in variable concentrations according to the kind of polymer and of solvent, anyhow such as to produce a sufficiently viscous liquid (dope) (this method is used by 30% of the fibers)

Solvent removal can take place in two ways:

Dry spinning

The solvent is removed through flows of warm gas suitably directed to the extruded filaments; gas temperature should be higher than the boiling temperature of the solvent, which will be extracted from the filaments, recovered and recycled. Filament solidification proceeds according to the extent of solvent evaporation; it takes place faster on the external yarn layers (thus creating a crust or skin), and successively slows down while proceeding towards the interior. As a consequence of the mass exchange, the original (round) cross-section of the filament undergoes a contraction, thus generating cross-sections which characterize the various kinds of fibers and spinning processes.

Wet spinning

This spinning method is based on the introduction of an extruded polymeric viscose into coagulation baths where the liquor, usually water, behaves as a solvent towards the polymer solvent and as a non-solvent towards the polymer mass.

Practically the solvent which is contained in the fiber in the amorphous state (gel) is spread towards the liquor and at the same time, the liquid of the bath is spread towards the interior of the fiber. The processing speeds are dependent on several parameters, as type and concentration of the
polymeric solvent and of the liquor, which bring about structural variations in the fiber. In particular the formation of an outer gardened and more compact cortex (skin), similarly to what happens in dry spinning, slows down the coagulation mechanism of the inner filament portion (core), thus creating unevenness with a more or less porous structure (voids formation). The fiber cross-sections result more or less modified, from the original round form to a lobated form, with a wrinkled surface.

Drawing

The polymer extruded by the spinnerets in form of filaments has not yet the properties which are typical of a textile fibre: in fact the polymer mass (solidified through cooling or solvent removal) is characterized by a mass of disorderly placed molecular chains (in amorphous state) which provides the material with poor thermal and chemical stability, low resistance to ageing, high plasticity and deformability and consequently insufficient physical/textile properties. If we take natural fibers as models, we need to orientate the molecular chains (orientation phase) in the direction of the fiber axis and at the same time or successively activate or increase the ordered arrangement of the intermolecular structure (crystallization phase).

Continuous filament yarns

Continuous filament yarns can be composed of a single filament (monofilament yarns) or of several filaments (multifilament yarns) and are described through abbreviations, the first figure of which indicates the total linear mass (expressed in dtex or, less usually, in den), the second figure indicates the filament number and a third figure if any shows the twists per length unit (turns/m) imparted to the yarn.

Monofilaments for traditional textile uses have linear masses ranging from 10 to 50 dtex approximately; monofilaments with larger linear masses find on the contrary use in technical applications and are identified with their thickness expressed by the diameter of the round cross-section (0.06?2 mm).

General principles of manmade fiber manufacturing

There is no substantial difference in the structure of natural fibers from that of man-made Fibres: both fiber categories are composed of macromolecules or by linear polymers, that is by the repetition of several simple molecules (monomers).

Man-made fibers are fibers in which either the basic chemical units have been formed by chemical synthesis followed by fiber formation or the polymers from natural sources have been dissolved and regenerated after passage through a spinneret to form fibers. Those fibers made by chemical synthesis are often called synthetic fibers, while fibers regenerated from natural polymer sources are called regenerated fibers or natural polymer fibers. In other words, all synthetic fibers and regenerated fibers are man-made fibers, since man is involved in the actual fiber formation process.

Natural fibers are essentially composed of atoms of various elements, such as carbon, hydrogen, oxygen, sometimes of nitrogen and other elements (sulphur) in lower quantities; during their biological growth, these elements form the rings of long molecular chains. The development of man-made fibres was based on the knowledge acquired with natural fibers which structure was taken as a model; the difference between the two fiber categories is that natural fibres form macromolecules through biological growth, while the growth process of man-made fibres is driven by technical equipment (artificial fibers use instead of natural polymers).

Nylon Fiber

 

Nylon Fiber

Nylon does not absorb water – this is great for some uses, but also means that nylon fabric and movement combine to create static electricity.

Nylons, or polyamides (PA), are high-performance semi-crystalline thermoplastics with attractive physical and mechanical properties that provide a wide range of end-use performances important in many industrial applications.

While nylon takes many forms, it made its name as a textile fiber and revolutionized the textile industry. According to Fortune magazine in 1940, nylon was the fifth basic textile development in 4,000 years; the others were mercerized cotton, mechanical mass production, synthetic dyes, and rayon. In turn, nylon led to a host of other fibers and plastics that are integral to an advanced industrial society.

Manufacturing

About 8 billion pounds of nylon are produced each year in the U.S. Nylon is an artificial fiber. It is durable, strong and resists abrasion.

In 1939, the DuPont company first manufactured NYLON – it was the first synthetic fiber made in the United States. It was used in nylon stockings during wartime, but even after the war became preferred over silk, and quickly replaced silk in most hosiery.

Nylon is made of polymers known as polyamides which contain carbon, oxygen, nitrogen, and hydrogen. Solid chips of these polyamides are melted and forced through a heated spinneret. The spinneret has from one to hundreds of holes. Their size and shape change the characteristics of the resulting fiber. The fiber solidifies as it cools, and can then be spun or woven.

Properties and Uses Nylon

Nylon does not absorb water – this is great for some uses, but also means that nylon fabric and movement combine to create static electricity.

Nylon has some of the look and feel of silk. It is used in sheer hosiery, sails, parachutes, blouses, gowns and veils, swimsuits, lingerie, and even car tires. Nylon has also replaced wool as the fiber most used in carpets. A process called air-texturing adds bulk to the nylon to make it useful as a floor covering.

Characteristics of Polyester Fibers and Products

• Resists abrasion (but can “pill”)
• Very resilient (springs back into shape)
• Resist wrinkling
• Very high heat can “melt” the fabric
• The right amount of heat can be used to permanently “heat set” a crease or pleat
• Easy to wash and wear
• Does not absorb water (can be uncomfortable when worn next to the skin in warm weather unless loosely woven)
• Dries quickly
• Attracts static electricity which also attracts dirt and lint
• Although they do NOT absorb water, they DO absorb oil and grease. This means synthetics
• resist soiling, but once an oil-based stain soaks in, it can be difficult to clean.
• Strong fiber (but nylon is stronger)
• Often blended with cotton or even wool to add crease resistance
• Polyester does not absorb water, but it can be produced in such a way (as in polypropylene and microfibers) as to “wick” water away from the skin

Summary

• Nylon was the first synthetic fiber manufactured in the US.
• It is made from polymers consisting of carbon, oxygen, nitrogen, and hydrogen.
• Nylon is a versatile fiber used in clothing, carpet, and tires.

Characteristics and usage of Manmade Fibers

 

Characteristics and usage of Manmade Fibers

Type	Characteristic	Major Uses
ACETATE	Luxurious feel and appearance A wide range of colors and lusters Excellent drapability and softness Relatively fast-drying Shrink-, moth-, and mildew-resistant	Apparel: Blouses, dresses, and foundation garments. Lingerie, linings, shirts, slacks, sportswear. Fabrics: Brocade, crepe, double knits, faille, knitted jerseys, lace, satin, taffeta, tricot. Home Furnishings: Draperies, upholstery. Other: Cigarette filters, fiberfill for pillows, quilted products
ACRYLIC	Soft and warm Wool-like Retains shape Resilient Quick-drying Resistant to moths, sunlight, oil, and chemicals	Apparel: Dresses, infant wear, knitted garments, ski wear, socks, sportswear, sweaters. Fabrics: Fleece and pile fabrics, face fabrics in bonded fabrics, simulated furs, jerseys. Home Furnishings: Blankets, carpets, draperies, upholstery. Other: Auto tops, awnings, hand-knitting and craft yarns, industrial and geotextile fabrics.
ARAMID	Does not melt Highly flame-resistant High strength High resistance to stretch Maintains its shape and form at high temperatures	Hot-gas filtration fabrics, protective clothing, military helmets, protective vests, structural composites for aircraft and boats, sailcloth, tires, ropes and cables, mechanical rubber goods, marine and sporting goods.
BICOMPONENT	Thermal bonding Self-bulking Very fine fibers Unique cross sections The functionality of special polymers or additives at reduced cost	Uniform distribution of adhesive, Fiber remains a part of the structure and adds integrity, Customized sheath materials to bond various materials, Wide range of bonding temperatures, Cleaner, environmentally friendly (no effluent), Recyclable, Lamination/ molding / densification of composites.
LYOCELL	Soft, strong, absorbent Good dyeability Fibrillates during wet processing to produce special textures	Dresses, slacks, and coats.
MELAMINE	White and dyeable Flame resistance and low thermal conductivity High heat dimensional stability Processable on standard textile equipment	Fire Blocking Fabrics: Aircraft seating, fire blockers for upholstered furniture in high-risk occupancies (e.g., to meet California TB 133 requirements) Protective Clothing: Firefighters’ turnout gear, insulating thermal liners, knit hoods, molten metal splash apparel, heat resistant gloves. Filter Media: High capacity, high efficiency, high-temperature baghouse air filters.
MODACRYLIC	Soft Resilient Abrasion- and flame-resistant Quick-drying Resists acids and alkalies Retains shape	Apparel: Deep pile coats, trims, linings, simulated fur, wigs, and hairpieces. Fabrics: Fleece fabrics, industrial fabrics, knit-pile fabric backings, non-woven fabrics. Home Furnishings: Awnings, blankets. Carpets, flame-resistant draperies and curtains, scatter rugs. Other: Filters, paint rollers, stuffed toys.
NYLON	Exceptionally strong Supple Abrasion-resistant Lustrous Easy to wash Resists damage from oil and many chemicals Resilient Low in moisture absorbency	Apparel: Blouses, dresses, foundation garments, hosiery, lingerie and underwear, raincoats, ski and snow apparel, suits, windbreakers. Home Furnishings: Bedspreads, carpets, draperies, curtains, upholstery. Other: Air hoses, conveyor and seat belts, parachutes, racket strings, ropes and nets, sleeping bags, tarpaulins, tents, thread, tire cord, geotextiles.
OLEFIN	Unique wicking properties that make it very comfortable Abrasion-resistant Quick-drying Resistant to deterioration from chemicals, mildew, perspiration, rot, and weather Sensitive to heat Soil resistant Strong; very lightweight Excellent colorfastness	Apparel: Pantyhose, underwear, knitted sports shirts, men’s half hose, men’s knitted sportswear, sweaters. Home Furnishings: Carpet and carpet backing, slipcovers, upholstery. Other: Dye nets, filter fabrics, laundry and sandbags, geotextiles, automotive interiors, cordage, doll hair, industrial sewing thread.
POLYESTER	Strong Resistant to stretching and shrinking Resistant to most chemicals Quick-drying Crisp and resilient when wet or dry Wrinkle- and abrasion-resistant Retains heat-set pleats and creases Easy to wash	Apparel: Blouses, shirts, career apparel, children’s wear, dresses, half hose, insulated garments, ties, lingerie and underwear, permanent press garments, slacks, suits. Home Furnishings: Carpets, curtains, draperies, sheets and pillowcases. Other: Fiberfil for various products, fire hose, power belting, ropes and nets, tire cord, sail, V-belts.
PBI	Highly flame resistant Outstanding comfort factor combined with thermal and chemical stability properties Will not burn or melt Low shrinkage, when exposed to flame.	Suitable for high-performance protective apparel such as firemen’s turnout coats, astronaut space suits, and applications where fire resistance is important.
RAYON	Highly absorbent Soft and comfortable Easy to dye Versatile Good drapability	Apparel: Blouses, coats, dresses, jackets, lingerie, linings, millinery. Rainwear, slacks, sports shirts, sportswear, suits, ties, work clothes. Home Furnishings: Bedspreads, blankets, carpets, curtains, draperies, sheets, slipcovers, tablecloths, upholstery. Other: Industrial products, medical, surgical products, non-woven products, tire cord.
SPANDEX	Can be stretched 500 percent without breaking Can be stretched repeatedly and recover original length Light-weight Stronger and more durable than rubber Resistant to body oils	Articles (where stretch is desired): Athletic apparel, bathing suits, delicate laces, foundation garments, golf jackets, ski pants, slacks, support and surgical hose.