Fibres, Sutures and Surgical Dressings

Chapter 22

Fibres, Sutures and Surgical Dressings

INTRODUCTION

Fibres may be defined as any hair-like raw material directly obtainable from an animal, vegetable, or mineral source and convertible into nonwoven fabrics such as felt or paper or, after spinning into yarns, into woven cloth. A natural fibre may be further defined as an agglomeration of cells in which the diameter is negligible in comparison with the length. Although nature abounds in fibrous materials, especially cellulosic types such as cotton, wood, grains, and straw, only a small number can be used for textile products or other industrial purposes. Apart from economic considerations, the usefulness of a fibre for commercial purposes is determined by such properties as length, strength, pliability, elasticity, abrasion resistance, absorbency, and various surface properties. Most textile fibres are slender, flexible, and relatively strong. They are elastic in that they stretch when put under tension and then partially or completely return to their original length when the tension is removed.

HISTORY

The use of natural fibres for textile materials began before recorded history. The oldest indication of fibre use is probably the discovery of flax and wool fabrics at excavation sites of the Swiss lake dwellers (seventh and sixth centuries B.C.). Several vegetable fibres were also used by prehistoric peoples. Hemp, presumably the oldest cultivated fibre plant, originated in Southeast Asia, then spread to China, where reports of cultivation date to 4500 B.C. The art of weaving and spinning linen was already well developed in Egypt by 3400 B.C., indicating that flax was cultivated sometime before that date. Reports of the spinning of cotton in India date back to 3000 B.C. The manufacture of silk and silk products originated in the highly developed Chinese culture; the invention and development of sericulture (cultivation of silkworms for raw-silk production) and of methods to spin silk date from 2640 B.C.

With improved transportation and communication, highly localized skills and arts connected with textile manufacture spread to other countries and were adapted to local needs and capabilities. New fibre plants were also discovered and their use explored. In the 18th and 19th centuries, the Industrial Revolution encouraged the further invention of machines for use in processing various natural fibres, resulting in a tremendous upsurge in fibre production. The introduction of regenerated cellulosic fibres (fibres formed of cellulose material that has been dissolved, purified, and extruded), such as rayon, followed by the invention of completely synthetic fibres, such as nylon, challenged the monopoly of natural fibres for textile and industrial use. A variety of synthetic fibres having specific desirable properties began to penetrate and dominate markets previously monopolized by natural fibres. Recognition of the competitive threat from synthetic fibres resulted in intensive research directed towards the breeding of new and better strains of natural-fibre sources with higher yields, improved production and processing methods, and modification of fibre yarn or fabric properties. The considerable improvements achieved have permitted increased total production, although natural fibres’ actual share of the market has decreased with the influx of the cheaper, synthetic fibres requiring fewer man hours for production.

CLASSIFICATION AND PROPERTIES

Natural fibres can be classified according to their origin.

The vegetable, or cellulose-base, class includes such important fibres as cotton, flax, and jute.

The animal, or protein-base, fibres include wool, mohair, and silk.

Regenerated and synthetic fibres include Nylon, Terylene, Orlon, Viscose, Alginate fibres, etc.

An important fibre in the mineral class is asbestos.

The vegetable fibres can be divided into smaller groups, based on their origin within the plant. Cotton, kapok, and coir are examples of fibres originating as hairs borne on the seeds or inner walls of the fruit, where each fibre consists of a single, long, narrow cell. Flax, hemp, jute, and ramie are bast fibres, occurring in the inner bast tissue of certain plant stems and made up of overlapping cells. Abaca, henequen, and sisal are fibres occurring as part of the fibrovascular system of the leaves.

Chemically, all vegetable fibres consist mainly of cellulose, although they also contain varying amounts of such substances as hemicellulose, lignin, pectins, and waxes that must be removed or reduced by processing. The animal fibres consist exclusively of proteins and, with the exception of silk, constitute the fur or hair that serves as the protective epidermal covering of animals. Silk filaments are extruded by the larvae of moths and are used to spin their cocoons.

With the exception of mineral fibres, all natural fibres have an affinity for water in both liquid and vapour form. This strong affinity produces swelling of the fibres connected with the uptake of water, which facilitates dyeing in watery solutions.

Unlike most synthetic fibres, all natural fibres are nonthermoplastic—that is, they do not soften when heat is applied. At temperatures below the point at which they will decompose, they show little sensitivity to dry heat, and there is no shrinkage or high extensibility upon heating, nor do they become brittle if cooled to below freezing. Natural fibres tend to yellow upon exposure to sunlight and moisture, and extended exposure results in loss of strength.

All natural fibres are particularly susceptible to microbial decomposition, including mildew and rot. Cellulosic fibres are decomposed by aerobic bacteria (those that live only in oxygen) and fungi. Cellulose mildews and decomposes rapidly at high humidity and high temperatures, especially in the absence of light. Wool and silk are also subject to microbial decomposition by bacteria and moulds. Animal fibres are also subject to damage by moths and carpet beetles; termites and silverfish attack cellulose fibres. Protection against both microbial damage and insect attacks can be obtained by chemical modification of the fibre substrate; modern developments allow treatment of natural fibres to make them essentially immune to such damage.

VEGETABLE FIBRESCOTTON

COTTON

Synonyms

Raw cotton, purified cotton, absorbent cotton.

Biological Source

Epidermal trichomes of the seeds of cultivated species of the Gossypium herbaceum and other species of Gossypium (G. hirsutum, G. barbadense) freed from impurities, fats and sterilized, belonging to family Malvaceae.

Geographical Source

United States, Egypt, some parts of Africa, and India.

History

There are about 39 species of Gossypium worldwide which are native to the tropics and warm temperate regions. Three species are native to South Africa, of these, Gossypium hirsutum from Mexico has become the predominant species in commercial cotton production worldwide. About 90% of the world commercially produces cotton from G. hirsutum. G. barbadense contributes to 8% of the market while the remaining 2% belongs to the old world cotton grown in South and South-East Asia.

Gossypium herbaceum or the African-West Asian cotton: Gossypium herbaceum is the indigenous species in India. It is native to semidesert conditions like in sub-Saharan Africa and in Arabia. It is a perennial shrub. It is widely cultivated in Ethiopia and also in Persia, Afghanistan. Turkey, North Africa, Spain, Ukraine, Turkestan, and China (first cultivation in China reported was in about A.D. 600). It reaches a height of 2–6 feet, with palmate hairy leaves, lobes lanceolate, acute yellow petals and a purple spot in centre, capsule when ripe splits itself and exposes the loose white clump surrounding the seeds and strongly adhering to the outer coating. G. herbaceum requires warm weather to ripen its seeds.

Gossypium arboreum or the Pakistani Indian cotton: It is native to Northwest India and Pakistan. The use and production of cotton dates back to 2000 BC, by the Harappan civilization of the Indus Valley. Some of them are tall perennial while others are short annuals. People of Nubia are considered to be the first cotton weavers of Africa. This cotton variety extended into other parts of Africa (Nigeria) that became a cotton-manufacturing centre from the 9th century onwards.

Gossypium barbadense or South American cotton: G. barbadense gives the Sea Island, or long-stapled cotton. The oldest cotton textiles recorded from South America date to 3600 B.C. The first sign of domestication of cotton species comes from Peruvian coast where cotton bolls dating to 2500 B.C. were found. Cotton became a commercial slave plantation crop in the West Indies and as a result of it Barbados in 1650s became the first British West Indian colony to export cotton. Later on around 1670, planting of G. barbadense also began in the British North American colonies.

Gossypium hirsutum or Mexican cotton: G. hirsutum are found in coastal vegetation of Central and Southern North America and also in the West Indies. There are evidences of cotton remains dating back to 3500 B.C. in the Tehuacan Caves in Mexico and even the Spanish explorers have found cotton cultivation in the 1500s.

Cultivation, Collection, and Preparation

Cotton is cultivated by means of seed sowing method. The seeds are sown in rows of about 4–5 ft in distance. Proper fertilizers are provided timely. The cotton plants are shrubs or small trees that bare fruits (capsules) after flowering. The capsule consists of three to five seeds and is covered with hairs. The bolls are collected when ripe, separated from the capsule, dried, and subjected to the ginning press for processing. In ginning process, hairs and seeds are put before the roller with a small space, which separates the trichomes from the seeds. The short and long hair separated by delinter. Short hairs are known as ‘linters’, which are used in the manufacturing inferior grade cotton wool, whereas long hairs are used for preparation of cloth. The seeds remain after the removal of hair is used for the preparation of cotton seed oil and oil cake for domestic animal feed. The raw cotton so obtained is full of impurities like the colouring matter and fatty material. It is then subjected to further purification by treating it with dilute soda ash solution under pressure for about 15 hours. It is then bleached and washed properly, dried, and packed. The packed cotton is then sterilized using radiations.

Description

Chemical Constituents

It consists of 90% of cellulose, 7–8% of moisture, wax, fat and oil 0.5% and cell content about 0.5%. Purified cotton has almost cellulose and 6–7% of moisture.

Chemical Tests

On ignition, cotton burns with a flame, gives very little odour or fumes, does not produce a bead, and leaves a small white ash; distinction from acetate rayon, alginate yarn, wool, silk, and nylon.

Dried cotton is moistened with N/50 iodine and 80% w/w sulphuric acid is added. A blue colour is produced; distinction from acetate rayon, alginate yarn, jute, hemp, wool, silk, and nylon.

With ammoniacal copper oxide solution, raw cotton dissolves with ballooning, leaving a few fragments of cuticle. Absorbent cotton dissolves completely with uniform swelling, distinction from acetate rayon, jute, wool, and nylon.

In cold sulphuric acid (80% w/w) cotton dissolves; distinction from oxidized cellulose, jute, hemp, and wool.

In cold sulphuric acid (60% w/w) cotton, is insoluble; distinction from cellulose wadding and rayons.

In warm (40°C) hydrochloric acid it is inso luble; distinction from acetate rayon (also silk, nylon).

It is insoluble in 5% potassium hydroxide solution; distinction from oxidized cellulose, wool, and silk.

Treat it with cold Shirla stain A for 1 min and wash out. It shows shades of blue, Tilac or purple; distinction from viscose, acetate rayons, alginate yarn, wool, silk, and nylon.

Treat it with cold Shirla stain C for 5 min and wash out; raw cotton gives a mauve to reddish-brown colour and absorbent cotton a pink one; distinction from flax, jute, hemp. The Shirla stains may be usefully applied to a small piece of the whole fabric under investigation to indicate the distribution of more than one type of yarn.

It does not give red stain with phloroglucinol and hydrochloric acid; distinction from jute, hemp, and kapok.

Uses

Cotton is used as a filtering medium and in surgical dressings. Absorbent cotton absorbs blood, pus, mucus, and prevents infections in wounds.

JUTE

Synonym

Gunny.

Biological Source

It consists of phloem fibres from the stem of various species of the Corchorus; C. capsularis Linn, C. olitorius Linn, and other species like C. cunninghamii, C. junodi etc., belonging to family Tiliaceae.

Geographical Source

West Bengal and Assam.

History

Corchorus is a genus with 40–100 species of flowering plants. It is native to tropical and subtropical regions throughoutthe world. Though various species yield fibre, the chief sources of commercial jute are two Indian species the C. capsularis and C. olitorius. These species are grown in Ganges and Brahmaputra valleys.

For past many centuries, Jute has been an integral part of Bengali culture. In the late 19th and early 20th centuries, much of the raw jute fibres were exported to the United Kingdom. In ’50s and ’60s (when nylon and polythene were rarely used), Pakistan was the world’s lead jute producer. During those periods it had earned its money through jute of East Pakistan, (now called the Bangladesh). Jute was called the ‘Golden fibre’ of Bangladesh because it brought the major portion of the foreign currency for the country. World’s largest jute trade and jute processing economy was located in Bangladesh. Adamjee Jute Mill in Narayanganj, Bangladesh was world’s largest jute mill with 1,939 looms and 25,000 employees up to 2002. Presently Sonali Aansh is one of the largest jute products manufacturers in Bangladesh.

Description

They are tall, usually annual herbs, reaching to a height of 2–4 m, unbranched and if branched it has only a few side branches. The leaves are alternate, simple, lanceolate, 5–15 cm long and a finely serrated or lobed margin. The flowers are small (1.5–3 cm in diameter) and yellow, with five petals; the fruit encloses many seeds in the capsule.

Preparation

Retting is the process for the preparation of bast fibres. This process is done by three methods, that is, microbial (or water), steam, and mechanical process. The microbial or water retting process is the oldest and the popular method employed for the breaking of lignin bond present between parenchyma and sclerenchyma. The breaking of this bond facilitates the easy procurement of skin from its core. Then the material is washed dried to release pectin bond which makes the hard skin to fine thread like fibres. The jute fibres are graded according to its colour, strength and fibre length. The fibres are of white to brown and 1–4 m. long.

Microscopy

A thin transverse section of the strand when treated with phuloroglucinol and HCl, stains the strands deep red, indicating the presence of lignin. Each strand is a collection of polygonal cells which are surrounded by lumen with various sizes. These strands can be separated by treating it with mixture of potassium chloride and nitric acid.

Chemical Constituents

Jute fibres are composed primarily of the plant materials cellulose and lignin. Jute is composed of about 50–53% cellulose, nearly 20% of hemicellulose and 10–11% of lignin along with other constituents like moisture not more than 12–13%, fats, wax, and ash contributing to 1% each.

Uses

It has a large range of use (about 1,000 uses). It is listed as the second most important vegetable fibre after cotton. Jute is used chiefly to make cloth for wrapping bales of raw cotton, in the preparation of sacks and coarse cloth. They are also woven into curtains, chair coverings, carpets, Hessian cloth very fine threads of jute can be made into imitation silk and also in the making of paper. It is even used in the manufacture of tows, padding splints, filtering, and straining medium. Jute is used for the preparation of coarse bags.

FLAX

Biological Source

It is the pericyclic fibres which are removed from, the stem of Linum usitatissimum Linn., belonging to family Linaceae.

Geographical Source

It is mainly found in United States, Russia, Ireland, Northern Europe.

History

Flax fibres are one amongst the oldest fibre crops in the world. The use of flax for the production of linen dates back to 5000 years. It was the chief source for the preparation of cloth fibre till the other fibres like jute and cotton came to market. The manufacture of cloth from flax fibre in Northern Europe dates back to the period of preRomans and it is also believed that the pilgrims were the ones to introduce flax to the United States.

Cultivation, Collection, and Preparation

Though Eurasia is the native of flax it has been transplanted from its origin to most of the temperate zones of the world due to its favourable climatic condition (cool moist climate) for its cultivation. The most suitable soil for its growth is alluvial soil with deep friable loams, moderately fertile humus-rich soil, and it does not grow well in dry sandy and strong clays. Linum usitatissimum is an annual plant which grows to a height of 4 ft. It bares in itself flowers with blue or white colour and these flowers mature into bolls. Each boll consists of 10 seeds, which are sown by the end of March or in early April. The flowers come up in the month of June and the bolls are collected after a month time before they are ripe. Flax should be pulled as soon as the lower part of the plant begins to turn yellow and soon after it is been pulled, it should be tied in bunches and put into water for retting. Standing pools are beneficial for the purpose of retting because it provides better colour and a superior quality in all aspect. The process of retting through fermentation permits bacteria to break down the woody tissues andalso to dissolve the substances binding the fibre cells due to enzyme action. The branches when put in water it should be tied in small sheaves and immersed firmly with the help of a weight placed above, to facilitate equal and proper watering. In warm condition, watering process is sufficient for 10 days with proper and timely examination of the pools (after the seventh day), to check if the flax are rotten. It often happens that by the twelfth day the flax get rot irrespective of the climatic condition and it is advised to have less amount of water than excess quantity. After retting, the stems are washed and allowed to dry on grass and beaten using a machine scutched; to separate the fibres from other material and to crush the pith. The bark remaining after the process of beating is then subjected finally for combing (hackling) for the removal of traces of nonfibrous matter like wood and parenchyma and parallel pericyclic fibres are obtained.

Description

The length of fibre cells ranges from 1.2 to 5.0 cm and the length of fibres cell bundles ranges from 30 to 90 cm. The short and broken fibres are called ‘tow’. Flax is hygroscopic in nature. Flax fibre is soft, lustrous and flexible. It has more tensile strength than cotton fibre but less elasticity.

Microscopy

The flakes are a collection of 20 fibres, which are joined to each other through their pointed ends. The individual fibres when observed under the microscope show cells which are of polygonal.

Chemical Composition

The flax chiefly consists of pecto-cellulose.

Uses

Linen cloths can be prepared which is used as a filtering medium. The ‘tow’ is used in making coarse fabrics and cordage, while the long fibres are used for strong threads and fine linens. Flax fibre is also utilized as raw material for the high-quality paper industry for the purpose of printed currency notes and cigarette paper.

HEMP

Biological Source

Hemp is the pericyclic fibre obtained from Cannabis sativa Linn., belonging to family Cannabinaceae.

Geographical Source

Hemp is grown at any altitude from Norway to the Equator. The raw materials are imported from China, Hungary, America, Germany, Switzerland, Australia, Canada, France, and Norway.

History

The history of Cannabis sativa dates back to more than 6,000 years. The history of China has in its credit of having a Hemp textile production even before 4,500 B.C. which later spread to Asia in around 1,000 B.C. and reaching Europe by 800 B.C. In 1175 Cannabis sativa was grouped under taxable goods, and in 1535 an act came into force which compelled all land owners to sow 1/4 of an acre, or otherwise they be fined was formed by Henry VIII. During this period Hemp became a major crop and till 1920s about 80% of clothing was made from Hemp textiles. Traditionally, Hemp was processed by hand, which required huge labour and was costly. In 1917 American George W. Schlichten invented and patented a new machine for separating the fibre from the internal woody core (‘Hurds’) reducing labour costs. By 1930, due to the tough competition by the other varieties of hemp imported by Philippines and Mexico, the hemp production by United States had fell to less than 200 acres. Later on during World War II, farmers in the United States were encouraged to cultivate both cannabis hemp and flax for the purpose of war under the banner of ‘Hemp For Victory’, In 1937 the production of Cannabis sativa was restricted except for industrial use or research purpose but in 1970 its production was categorized as illegal for all purpose. In 1992/93 the first licenses were granted for growing Hemp of the low THC varieties (THC is the narcotic substance found in the leaves) under the ruling that Hemp is grown for ‘special purposes’ or ‘in the public interest’. At present, approximately 2,500 hectares are being grown.

Chemical Constituents

Hemp mainly consist of cellulose and lignin.

Uses

Hemp is mentioned historically to have more than 25,000 diverse uses. The historically mentioned uses are printing inks, paints, varnishes, paper, bibles, bank notes, food, textiles (the original Levi’s jeans were made from Hemp cloth), canvas and building materials. Due to its high tensile strength, bast fibres are ideal for such specialized paper products as: tea bags, industrial filters, currency paper, or cigarette paper.

ANIMAL FIBRES

SILK

Biological Source

Fibres obtained from the cocoons spun by the larvae Bombyx mori Linn., belonging to family Bombycidae/Moraceae.

Geographical Source

China, France, Iran, Italy, Japan, and India.

History

It is native to northern China and Persia presently known as Iran. Bombyx mori is a member of a small family of about 300 moth species. The credit for the discovery of silkworm’s silk goes to an ancient empress in China, who while walking around accidentally, noticed the worms. When she touched it with her fingers, the silk came out and surrounded her finger. When the full silk had come out, she saw the small cocoon inside it; which was responsible for the formation of silk. It is even said that the Chinese princess smuggled eggs to Japan by hiding them in her hair and thus they began their love affair with silk. Due to its captivity for thousands of years, Bombyx mori is fully domesticated and cannot survive without the support of mankind. The silkworm is the larva of a moth. Larvae are monophagous which takes only mulberry leaves as its diet. The cocoon is made of a single continuous thread of raw silk from 300 to 900 metre long. The fibres are very fine and lustrous, about l/2500th of an inch in diameter. One pound of silt can be made from about 2,000 to 3,000 cocoons, and it is estimated that almost 70 million pound of raw silk are produced each year. It requires about 1 billion pounds of mulberry leaves to produced 7 million pounds of raw silk and one pound of silk is almost equivalent to 1,000 miles of filament.

Preparation

One gram of silk-worm egg consists of around 15,000 eggs which are kept at 0°C to overcome the immature development. The silkworms eat mulberry leaves day and night and they grow very fast. When the colour of their heads changes darker, it indicates that the time for them to moult has come. It require almost a month time for its development into full size. During this period it takes four moulds and their body turns slightly yellow reaching a size of 4 cm long. The silk-worm finally eats a meal which is about twenty to twenty five times its weight of leaves and attains a size of 9 cm length and 10 mm thick. The skin becomes tight and all these symptoms indicate that it is going to cover itself with a silky cocoon. The process of spinning cocoon continues for almost three days. After 7–8 days, the larvae changes into chrysalides, and the cocoons are collected by throwing them into boiling water, this kills the silkworms and also makes the cocoons easier to unravel. If the caterpillar is left to eat its way out of the cocoon naturally, the threads will be cut short and the silk will be useless. The cocoons are kept in hike warm water to remove the gum. Since all the eggs hatch almostthe same time, the cocoons also be collected together and treated at the same period. Some amount of cocoons are retained and allowed to come out for fertilization. The females lay nearly 500 eggs and these eggs are stored till further requirement is wanted.

Description

Chemical Constituents

Silk mainly consists of protein known as fibrion. Fibrion is soluble in warm water and on hydrolysis yields two main amino acids, glycine and alanine.

Uses

Silk is used pharmaceutically in the preparation of sutures, sieves, and ligatures. The ‘stiff silkworm’ (dried body in the four to fifth stage of larva, which dies due to infection of the fungus Beauveria bassiana) is used in the traditional Chinese medicine.

WOOL

Biological Source

Wool consist of hairs from the fleece of sheep Ovis aries Linn., belonging to family Bovidae.

Geographical Source

The worlds leading producers of wool are Australia (25%), China, and New Zealand (11%), while Turkey, Iran, India, and the United States (Texas, New Mexico) contribute to 2%.

History

The use of wool for clothing and other fabrics dates back to earliest civilizations. The wool trade was a serious business during medieval times and English wool export had contributed significantly as a source of income to the crown. Smuggling of wool was considered a serious offence and was punished with cutting off the hand. Wool trade had also helped Medicis of Florence in Renaissance in building up their wealth and banking. Spain with royal permission exported Merino lambs. By the end of 19th century German wool (from sheep of Spanish origin) overtookBritish wool but later by 1845 the Australian wool trade eventually overtook the German wool.

Preparation

Wool is the fibre derived from the hair of animals of the Caprinae family, mainly sheep and goats. It is produced as the outer coat of sheep. The fibre obtained from domestic sheep has two qualities which differentiate it from hair or fur. The fibres have scales which overlap like shingles on a roof and it is crimped. The amount of crimp is directly proportional with the fineness of the wool fibres and the fine wool (like merino) have up to a 100 crimps per inch, whereas coarser wools (like karakul) have one or two crimps per inch. The hairs from sheep are removed during the shearing time. After shearing, the wool is separated into five main categories: namely fleece, pieces, bellies, crutchings, and locks. It is then cleaned from dirt and high level of grease (thus ‘greasy wool’) which contains valuable lanolin is present on the hair. The grease is generally removed for processing by scouring with detergent and alkali. The wool is then treated with hydrogen peroxide for bleaching, it is then washed properly and spreaded on wire nettings and dried under hot air.

Description

Wool is generally a creamy white colour but some of the breeds of sheep naturally produce black, brown (also called moorit) and grey coloured wool. The wool is smooth, elastic, slippery to touch and slightly curly. Diameter of wool varies from 15 μm (superfine merino) to 30 or 40 μm. The finer the diameters the greater its value is. Wool is soluble in warm alkaline solutions, but not in dilute or strong acids.

Chemical Constituents

Wool mainly consists of a sulphur containing protein called keratin. Keratin is composed of amino acid like cystine.

Chemical Tests

Solubility test: It is easily soluble in warm alkali.

Wool when treated with Con. Hydrochloric acid, it does not produce any effect but dissolves silk.

When treated with cuoxam solution, it does not dissolve but swells the wool and produces blue colour. 4. Solution of wool treated with lead acetate produces black precipitate due to high sulphur content.

Uses

It is used as a filtering aid and straining medium and in the manufacture of clothing, carpeting, felt and it is alsoused to absorb odours and noise in heavy machinery and stereo speakers.

REGENERATED AND SYNTHETIC FIBRES

VISCOSE

Synonyms

Rayon, regenerated cellulose.

Source

Viscose is a viscous orange-red aqueous solution of sodium cellulose xanthogenate obtained by dissolving wood pulp cellulose in sodium hydroxide solution and treating with carbon disulphide.

Preparation

The starting material is cellulose prepared from coniferous wood (spruce), or scoured and bleached cotton linters. The wood is delignified similar to cellulose wadding. It reaches the rayon manufacturers as boards of white pulp, containing 80–90% of cellulose and some hemicellulose (mainly pentosans). The hemicellulose being alkali-soluble, are removed in the first stage of the process by steeping in sodium hydroxide solution. The excess alkaline liquor is pressed out and alkali-cellulose (sodium cellulosate) remains. This is dissolved by treatment with carbon disulphide and sodium hydroxide solution to give a viscous solution of sodium cellulose xanthate. After ‘ripening’ and filtering, the solution is forced through a spinneret, a jet with fine nozzles, immersed in a bath of dilute sulphuric acid and sodium sulphate, when the cellulose is regenerated as continuous filaments. These are drawn together as a yarn, which is twisted for strength, desulphurized by removing free sulphur with sodium sulphide, bleached, washed, dried and conditioned to a moisture content of 10%.

Description

The rayon is a white, highly lustrous fibre. Its tensile strength varies from two-third to one-and-a-half times that of cotton. When wetted, it loses about 60% of its tensile strength. It has a proportionately greater loss than is found with cotton. The fabric is a water-repellent (e.g. cotton crepe bandage).

Chemistry

Viscose rayon is a very pure form of cellulose. Its ash contains sulphur. The cellulose molecules of the original natural material are more separated from one another inthe viscose solution than in the vegetable material and in the regenerated fibres is still less closely packed. The sideto-side aggre gation of the long-chain molecules is different from that in natural celluloses. The size of the molecules is also reduced. Wood cellulose has molecules of the order of 9,000 glucose residue units, whereas those of viscose rayon have only about 450.

Chemical Tests

The fibres give the general tests for vegetable and regenerated carbohydrate fibres.

On ignition they behave like cotton; distinction from acetate rayon and alginate yarn, wool, silk, nylon, and glass.

With N/50 iodine and sulphuric acid, 80%, they give a blue colour similar to that given by cotton; distinction from acetate rayon, alginate yarn, jute, hemp, wool, silk, and nylon.

With ammoniacal copper oxide they behave like absorbent cotton; distinction from acetate rayon, jute, wool, and nylon.

Cold sulphuric acid, 60% w/w, dissolves the fibre; distinction from cotton, oxidized cellulose, alginate yarn, flax, jute, hemp, and wool.

Warm (40°C) hydrochloric acid does not dissolve the fibre; distinction from acetate rayon, silk, and nylon.

It is insoluble in boiling potassium hydroxide solution (5%); distinction from oxidized cellulose, wool, and silk.

Shirla stain A produces a bright pink; distinction from cotton, oxidized cellulose, acetate, rayon, wool, silk, and nylon.

Phloroglucinol and hydrochloric acid produce no red stain; distinction from jute, hemp, and kapok. The fibres, like cotton, are insoluble in acetone, formic acid 90% or phenol 90%; distinction from acetate rayon and nylon.

Uses

Viscose rayon is used to manufacture fabrics, surgical dressings, absorbent wool, enzyme, and cellophane.

ALGINATE FIBRES

Alginate fibres are composed of calcium alginate.

Preparation

An aqueous solution of sodium alginate is pumped through a spinneret which is immersed in a bath containing acidic calcium chloride solution. In the bath sodium cations are substituted with calcium cations and the insoluble calcium alginate is precipitated as continuous filaments. The filaments are collected, washed, and dried for surgical purposes.The filaments are cut up to give stable form of length 1–8 inches for preparing calcium alginate wool or a fabric. Trace amounts of substances are added to the calcium alginate to inhibit mould and bacterial growth.

Description

Alginate fibres are fairly lustrous and pale cream coloured. The fibres may be processed into absorbable, haemostatic dressings. They give general tests for vegetable fibres. They are soluble in ammonical copper nitrate and 5% sodium citrate solution.

Chemistry

Alginic acid is composed of polymers of both mannuronic and glucuronic acids. The properties of the two are variable and alginates of different origin have different compositions and properties. Kalostat haemostatic dressing is derived from the seaweed Laminaria hyperborea collected off the Norwegian coast and yields an alginate with a glucuronic mannuronic ratio of 2:1. Other dressing is prepared from Laminaria and Ascophyllum species collected off the west coast of Scotland and gives an alginate with a glucuronicmannuronic acid ratio of about 1:2. On a wound surface the α-linkages of the glucuronic acid polymer are not easily broken so that fibre strength is retained and a strong gel is formed on contact with the wound exudates. A high ratio of mannuronic acid polymer (β-linkages) yields a product giving a weaker gel and less retention of fibre strength. The Kalostat dressing can be removed from the wound with forceps and Sorbsan is removed by irrigation with sodium citrate solution.

Calcium alginate fibres of commerce contain substantial traces of substances used to inhibit mould and bacterial growth in the sodium alginate spinning solution. Spinning lubricants such as lauryl or cetyl pyridinium bromide (antibacterial) are also applied to the filaments. These substances must not be used in the case of bacteriological swabs. Before use as an absorbable haemostatic dressing some calcium alginate dressing must be immersed in sodium chloride to give a fibre of the calcium alginate covered by sodium alginate. The degree of conversion is conditioned to give the desired rate of absorption when in use; the greater the proportion of sodium alginate the faster the absorption rate. Alginate filaments are composed of salts of the long-chain molecules of alginic acid, and there is little cross-linking between the chains in the fibre.

Chemical Tests

The fibre burns in a flame and goes out when removed from flame.

With (N/50) iodine and sulphuric acid, a brownish-red colour is produced, the filaments swell and dissolve to leave a strand of insoluble alginic acid.

In ammoniacal copper nitrate solution they swell and dissolve.

The fibres are insoluble in 60% w/w sulphuric acid.

The fibres are insoluble in warm (40°C) hydrochloric acid.

The fibres are insoluble in boiling 5% KOH (swell and acquire a yellow tint).

The fibres are soluble in 5% sodium citrate solution.

Fibre, 0.1 g, boiled with 5 ml of water remains insoluble but dissolves when 1 ml 20% w/v sodium carbonate solution is added and boiled for 1 min. A white precipitate of calcium carbonate is formed, depending on the proportion of original calcium alginate present. When centrifuged and the clear supernatant acidified, a gelatinous precipitate of alginic acid is produced. The precipitate will give a purple colour after solution in NaOH and addition of an acid solution of ferric sulphate.

Shirla stain A gives a reddish-brown colour.

Alginate haemostatic fibres are invisible in polarized light with crossed Nicols.

Uses

The alginate absorbable haemostatic dressings are nontoxic and nonirritant. They have advantages over oxidized cellulose, which include selective rate of absorption, sterilization (and resterilization) by autoclaving or dry heat and compatibility with antibiotics such as penicillin. They are used internally in neurosurgery, endural and dental surgery to be subsequently absorbed. Externally, they are used (e.g. for burns or sites from which skin grafts have been taken) to arrest bleeding and form a protective dressing which may be left or later removed in a manner appropriate to the type of dressing employed. Protective films of calcium alginate may also be used by painting the injured surface with sodium alginate solution and then spraying it with calcium chloride solution. Calcium alginate wool as a swab for pathological work or bacterial examination of such things as food processing equipment and tableware permits release of all the organisms by disintegration and solution of the swab in, for example, Ringer’s solution containing sodium hexametaphosphate.

NYLON

Nylon is a synthetic thermoplastic polymer invented in 1935 by Wallace Carothers at Du Pont. It is the first commercially successful polymer and the first synthetic fibre made from inorganic ingredients like coal, water, and air. It is made of repeating units linked by peptide bonds.

History

The first product was a nylon-bristled toothbrush in 1938. Nylon replaced the Asian silk in parachutes during the World War II; it was also used in making tents, ropes and other military supplies. Nylon was also used in the production of a high-grade paper for United States currency. Due to the war 80% was accounted by cotton and the rest 20% by other manufactured and wool fibres. Later in 1945, 25 % of the market was taken by manufactured fibres and the hare of cotton fell down. It took Du Pont 12 years and $27 million United States $ to refine nylon and develop the industrial processes for bulk manufacture. Nylon mania came to an abrupt stop at the end of 1941, when America entered World War II. After the war ended, Du Pont went back to selling nylon to the public, engaging in another promotional campaign in 1946 that resulted in an even bigger craze triggering off ‘nylon riots’.

Chemistry

Nylons are condensation copolymers formed by reaction of equal parts of a diamine and a dicarboxylic acid, so that peptide bonds form at the both ends of each monomer in a process analogous to polypeptide biopolymers.

Uses

Nylon still remains an important plastic and not just for use in fabrics. In its bulk form, it is very wear-resistant and so is used to build gears, bearings, bushings, and other mechanical parts.

TERYLENE (DACRON)

Terylene is a polyester fibre produced by condensating ethylene glycol with terephthalic acid. Its chemical formula may be represented as: H[OCH2 CH2 OOCC6 H4 CO]n OH. Terylene fibres are pre pared by an identical process to that for nylon. On heating the fibres with phosphoric acid (90%) for 1 minute, it retains its form. This test is negative in case of nylon. Terylene is used in the same way as nylon.

ORLON

Orlon is obtained by polymerizing acrylonitrile. It is represented as [CH2 CH (CH)]n , It is a white fibre; sticks at 235°; ironing temperatures above 160°C may cause yellowing; sp. gr. is 1.17. Its inflammability is similar to that of rayon and cotton. Generally it has very good resistance to mineral acids; excellent resistance to common solvents, oils, greases, neutral salts, sunlight but it is degraded by strong alkalis. It resists attack by moulds, mildew and insects. The 100% polyacrylonitrile fibres are rarely used commercially due to difficulty in dyeing.

Orlon fibre is suitable for furnishing (awnings, tents and furniture), anode bags in electroplating, knitwear, rugs, and dressings.

SURGICAL DRESSINGS

A material used to protect a wound and to heal is called a surgical dressing. They serve various functions for the injured site. They remove wound exudates from the site, prevent infection, and give physical protection to the healing wound and mechanical support to the supporting tissues. A good quality of dressing should be durable, easy to handle, sterilized, formed from loose threads and fibres, and it should not adhere to the granulating surface. Surgical dressings are classified as:

Primary Wound Dressings

Primary wound dressings are applied over the wound surface to absorb pus, mucus and blood. They minimize maceration. Some dressings adhere to the wound surface and cause pain on removing them. Now nonadherent dressings are available such as petrolatum-impregnated gauge, viscose gauze impregnated with a bland, hydrophilic oil-in-water emulsion or an absorbent pad faced with a soft plastic film having openings.

Absorbents

Absorbent cotton is widely used to absorb wound secretions. Other absorbent materials are rayon wool, cotton wool, gauze pads, laparotomy sponges, sanitary napkins, disposable cleaners, eye pads, nursing pads, and cotton tip applications. They are used in the shape of balls or pads.

Bandages

A bandage is a material which holds dressing at the required site, applies pressure, or supports an injured part or checks haemorrhage. The bandages may be elastic or nonelastic in nature. Common gauze roller bandage and muslin bandage rolls are employed most frequently. Elastic bandages may be woven to form elastic bandage, crepe bandage and conforming bandage.

Adhesive Tapes

Surgical adhesive tapes may be a rubber-based adhesive or an acrylate adhesive. Rubber adhesive tapes are cheap, superior and provide strength of backing. In case of operation or postoperation acrylate, adhesive tapes are used to reduce skin trauma.

Protectives

Protectives are employed to cover wet dressings, poultices, and for retention of heat. They prevent the escape of moisture from the dressing. Some protectives are plastic sheeting, rubber sheeting, waxed or oil-coated papers, and plastic-coated papers.

SUTURES AND LIGATURES

A surgical suture is a thread or sting used for sewing or stitching together tissues, muscles, and tendons with the help of a needle. If these threads or fibres are used to tie a blood vessel to stop bleeding without the use of a needle, then they are digested in animal tissues,for example, catgut, kangaroo tendon, and synthetic polyesters. If the sutures are not absorbed in the body, they are called nonabsorbable sutures, for example, silk, cotton, nylon, synthetic polyester fibres and stainless steel wire. A good quality of suture should be well-sterilized, nonirritant; having wellmechanical strength, fine gauze and with minimum time of absorption.

Absorbable Sutures

Surgical catgut

Catgut is a sterilized fibre or strand prepared from collagen of connective tissues obtained from healthy animals like sheep and cattle.

Preparation

The submucosal layer of small intestine of a freshly killed animal is used for the preparation of catgut. About 7.5 m long intestine is cleaned and split longitudinally into ribbons. The inner most mucosa and two outer layers of submucosa, muscularis, and serosal layers, are removed with the help of a machine leaving behind the submucosa. Up to six such ribbons are stretched, spun and dried to form a uniform strand. These fibres are polished to get smooth strings, gauzed for their diameter, cut into suitable lengths and sterilized by placing the catgut in glass tubes filled with anhydrous high-boiling liquids like toluene or xylene and then heating in an autoclave. Sterilization may be done by irradiating the suture by electron particles or by gamma rays from cobalt-60. Kangaroo tendons, used in hernia and bone repairs, are prepared from the tails of kangaroo by the identical method adopted for the preparation of catgut, Chromicized surgical catguts are prepared by soaking the ribbons in solutions of chromium salts for tanning the tissues. These fibres are not affected by proteolytic enzymes in the body and they are not absorbed rapidly in the body.

Synthetic polyesters

The polymers obtained by condensation of cyclic derivatives of glycolic acid (glycolide) with cyclic derivatives of lactic acid (lacticide) are used to prepare synthetic absorbable sutures. These sutures have high tensile strength and are degraded by hydrolysis and absorbed in the tissue.

Nonabsorbable Sutures

Nonabsorbable sutures are not affected by the body fluid and remained unchanged for a long period. They are removed after healing of the wounds. Silk, cotton, nylon, and metallic sutures are classified as nonabsorbable sutures.

Silk sutures

Silk sutures are prepared by spinning or twisting silk fibres into a single strand of varying diameters. The sutures are smooth and strong and braided by combining severaltwisted yarns into a compact mass. The strands are sterilized and boiled with water to soften them.

Cotton sutures

Cotton sutures have uniform size and recommended in critical parts where strength of the sutures is required for long time.

Nylon sutures

The microfilaments of nylon are braided into strands of required diameter. These sutures are strong, water resistant, and used in skin and plastic surgery.