Textile fabrics and their preparation for dyeing : with numerous engravings and diagrams

Front matter

TECHNICAL INSTRUCTION SERIES

TEXntli

TH

Preface

Textile Fabrics and Their Preparation for Dyeing contain?, in a form convenient for everyday use, a comprehensive treatise on the subject. The contents of this manual are based on the highly esteemed book written by the late Dr. J. J. Hummel, F.C.S., Professor and Director of the" Dyeing Department of the Yorkshire College, Leeds.

Without omitting any essential part of the original work the matter has been revised and brought up to date by Mr. A. R. Foster, Consulting Textile Expert, City and Guilds Honours Medallist. Needless to say many changes have taken place since the previous edition was published, and whilst the new processes and appliances have been incorporated, the older methods which are still in vogue in less progressive works, have been retained and revised. In this manner the manual has been made valuable, not only to the student but all employed in bleaching, finishing, and dyeing works.

Readers who may desire additional information respecting special details of the matters dealt with in this book, or instructions on any kindred subjects, should address a question to the Editor of Work, La Belle Sauvage, E.C., so that it may be answered in the columns of that journal.

P. N. HASLUCK.

16010

Contents

CHAPTER PAGE

I.— Cotton 9

II.— Flax, Jute, and China Grass 20

Chapter I. Cotton

The Cotton Plant.— Cotton is the white, downy, fibrous substance which envelopes the seeds of various species of the cotton-plant, Gossypium, belonging to the natural

Fig. 1.— Cotton Plant.

order Malvaceae. The seeds, to which the cotton fibres are attached, are enclosed in a 3- to 5-valved capsule, which bursts when ripe; the cotton is then collected and spread out to dry. The seeds are afterwards separated by the mechanical operation termed "ginning," and the raw cotton thus obtained is sent to the spinner. The cotton-

TEXTILE FABRICS.

plant (Fig. 1) is cultivated with success only in warm climates. There are numerous varieties, of which the following are the principal : —

(1) Gossypium barbadense. — An herbaceous plant, bearing a yellow flower, and attaining a height of 4-5 m. (13-16 ft.). A variety of this species yields the Sea Island cotton, much prized on account of the great strength, length, and lustre of its fibres. It is grown in the North American States of South Carolina, Georgia, and Florida, and on the neighbouring islands of the West Indies.

(2) Gossypium hirsutum. — A hairy, herbaceous plant, about 2 m. high, with pale yellow or almost white flowers. It is grown in the States of Alabama, Louisiana, Texas, and Mississippi.

Fig-. 2. — Appearance of Cotton under the Microscope.

(3) Gossypium herbaceum. — A small herbaceous plant, 1 m. high, and bearing yellow flowers. Varieties of this species are grown in India, China, Egypt, and America. The Madras, Surat, and short-stapled Egyptian cotton, also some American cottons, are obtained from this species.

(4) Gossypium peruvianum. — This species, a native of South America, grows to a height of 3-5 m. (10-16 ft.), and bears a yellow flower. It yields the long-stapled and much-esteemed Peruvian and Brazilian cottons.

(5) Gossypium religiosum. — This is a low annual shrub, about 1 m. high, and bearing a yellow flower. It is grown in China and India, and yields the so-called Nankin cotton, remarkable for its tawny colour.

(6) Gossypium arboreum. — This is a perennial tree, growing to a height of 6-7 m. (20-23 ft.), and bearing reddish-purple flowers. It is a native of India, and produces a good quality of cotton.

COTTON.

Physical Structure of Cotton. — If raw cotton is examined under the microscope, it is seen to consist of minute fibres. Their general appearance is that of spirallytwisted bands, having thickened borders and irregular markings on the surface (Fig. 2). In the better qualities of cotton, such as Sea Island, the spiral character is less prominent. Transverse sections of the fibres show them to be flattened tubes, having comparatively thick walls and a small central opening (Fig. 3).

A single cotton fibre is an elongated, tapering, and collapsed plant cell, the thin end of which is closed, and the other (by which it was attached to the seed) irregularly torn. Sometimes broad ribbon-like fibres may be noticed, which are remarkably transparent, and possess irregular folds. Their transverse section exhibits no central opening (Fig. 4). They are unripe fibres, in which no separation of the thin cell walls has yet taken place. They refuse to be dyed like ordinary ripe fibres, and appear occasionally as white specks in indigo- and madder-dyed calicoes; hence the name of dead cotton has been given

Fig. i. — Transverse Sections of Unripe Cotton Fibre.

to them. In half-ripe cotton fibres the cell walls are still so closely pressed together that the ultimate central canal is indicated in a transverse section only by a fine line. When steeped in water, however, such fibres gradually swell up and form hollow tubes. Cotton fibres vary in length 2*5-6 cm. (1-2| in.), and in breadth 0'0l7-005 mm. (-0007--002 in.).

The spiral character of the fibre makes it possible to spin exceeding fine yarn, and also accounts for the elastic character of calico as compared with linen, the fibres

Fig. 3. — Transverse Sections of Cotton Fibre.

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of which are stiff and straight. The microscopic appearance of cotton serves to distinguish it from other vegetable and animal fibres.

Chemical Composition of Cotton. — The substance of the cotton fibre is called Cellulose. This is almost universal in vegetable cells, forming the so-called ligneous matter or woody fibre of plants, but whereas in woody fibre the cellulose is encrusted with a large proportion of foreign matter — such as dried-up sap, resin, etc. — in the cotton fibre it is in a tolerably pure condition. The impurities present amount to about 5 %, this being the loss sustained by raw cotton when submitted to the process of bleaching, the main object, indeed, of which is the total removal of these impurities. The principal bleaching operation consists in boiling the cotton with a solution of sodium carbonate or hydrate. From the dark brown solution thus obtained, acids throw down a voluminous light brown precipitate, which, when washed and dried, amounts only to about 0'5 % of the weight of cotton employed. This precipitate is found to consist of the following organic substances : Pectic acid, brown colouring matter, cotton wax, fatty acids (margaric acid)> and albuminous matter. Pectic acid exists in the largest proportion, and it is not improbable that the 4'5 % loss by bleaching still unaccounted for, represents certain pectic matters, modified and rendered soluble by the action of alkalis, but not precipitated by acids.

In addition to the above-mentioned impurities of the cell wall, the raw cotton fibre seems to be covered with an exceedingly delicate membrane, or cuticle, which is not cellulose. If cotton, when under microscopical observation, be moistened with an ammoniacal solution of cupric hydrate, the fibre swells up under its influence, whereas the cuticle is unaffected and shows itself as band-like strictures or rings of various breadths. If a drop of sulphuric acid be then added, the cellulose separates out as a gelatinous mass, which, on adding a drop of iodine solution, becomes coloured blue, whereas the cuticle is coloured yellow. By moving the cover-glass aside a little, the cuticle rings are seen to be in the form of tubes, possessing apparently a spiral structure. Some observers state that during the bleaching process this cuticle is removed,

COTTON.

while others say this is not the case. The standard of moisture in raw cotton is 8*5 %, so that, reckoning the 5 % impurities already alluded to, one may consider that raw cotton contains 86'5 % of pure dry cellulose.

When submitted to chemical analysis, cellulose is found to be composed of carbon, hydrogen, and oxygen, the formula assigned to it being C6H10O5. It is closely allied in composition to starch, dextrin, and glucose, and is classed along with them as a carbo-hydrate. It is colourless, possesses neither taste nor smell, and has a density of about 1*5. If heated above 130° C. it becomes brown, and begins to decompose. In contact with air it burns without emitting any very strong odour, a fact which may sometimes serve to distinguish it from wool and silk. It is quite insoluble in the ordinary solvents, water, alcohol, ether, etc., but, as already indicated, it dissolves in an ammoniacal solution of cupric hydrate; from this it is precipitated by acids as a gelatinous mass, which, when washed with alcohol, forms an amorphous white powder.

Action of Mildew on Cotton. — Owing to its comparative freedom from impurity, cotton may be stored for a long period without undergoing any change, more especially if it is bleached and kept dry. When, however, it is contaminated with added foreign organic matter, such as starch, gum, etc. (in " finished " calicoes), and then exposed to a moist, warm atmosphere, it is very liable gradually to become tender or rotten. This is owing to the growth of vegetable organisms of a very low order, generally called " mildew." These fungi feed upon the starchy matters present, inducing their decomposition, and after some time the cotton fibres themselves are attacked. The simultaneous production of crenic, humic, ulmic, and other organic acids may possibly assist somewhat in the tendering process.

Action of Frost on Cotton. — It has been supposed by some that wet calico is tendered when it is frozen. Although the evidence on this point is conflicting, it is quite conceivable that the crystallisation might act injuriously in a mechanical way, and that the atmospheric ozone might also exercise some slight destructive influence. The popular notion probably arises from the fact that in their rigid

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state the cotton fibres are readily broken. A similar friable condition is obtained by excessive stiffening with starch or gum.

Action of Acids on Cotton. — Cold dilute mineral acids have little or no action, but if allowed to dry upon the cotton they gradually become sufficiently concentrated to corrode and tender the fibre. The physical structure of the fibre is not affected, but the chemical composition of the disintegrated fibre seems to be somewhat altered : it contains more oxygen and hydrogen. The same corrosive action soon takes place if cotton impregnated with such acids is heated. The process of " extracting " or " carbonising" woollen rags containing cotton (destroying and removing the cotton), by means of sulphuric or hydrochloric acid, is founded on this fact.

The action of strong acids varies considerably according to the nature, concentration, and temperature of the acid, as well as the duration of its contact with the fibre.

Very concentrated sulphuric acid causes cotton to swell up, and form a gelatinous mass, from which, on the addition of water, a starch-like substance termed Amyloid may be precipitated. A solution of iodine colours this amyloid blue. Vegetable parchment is paper (cellulose) superficially changed into amyloid by a short steeping in strong sulphuric acid 140° Tw. (Sp. Gr. 1*7), then washing and drying. An increased affinity for basic coal-tar colouring matters is said to be imparted to cotton by this treatment, even when the acid is diluted to 84° Tw. (Sp. Gr. 1*42), although its physical aspect then remains unchanged. Cotton completely disorganised by acid, and obtained as a fine powder, seems to contain one molecule of water more than ordinary cellulose, and the substance thus produced has been termed Hydro-cellulose.

If the concentrated sulphuric acid is allowed to act for a longer time, the cotton dissolves with the formation of a different substance of a gummy nature, called Dextrin (C6H10O5) ; when the solution is diluted with water and boiled for some time, this dextrin is further changed into Glucose (C6H1206).

If cotton be heated with strong nitric acid it is entirely decomposed, producing oxalic acid and an oxidised cellulose soluble in alkalis. By the action of cold concentrated

COTTON.

nitric acid, or, better still, a mixture of strong nitric and sulphuric acids, cellulose is changed into so-called Nitro-cellulose. The physical structure of the cotton remains the same, although increased in weight by more than 5 %, but its chemical composition and properties are very much altered, certain elements of the nitric acid having replaced a greater or less proportion of the hydrogen of the cellulose. The most highly nitrated compound is Pyroxylin, or Gun-cotton (C12H14(NO2)6O10), produced by the short action of a very concentrated mixture of acids; it is very explosive, and insoluble in alcohol and ether. The less nitrated product, obtained by the longer action of more dilute acids, forms the so-called Soluble Pyroxylin. Its solution in a mixture of ether and alcohol constitutes Collodion, which on evaporation leaves the pyroxylin as a thin, transparent, horny film, insoluble in water. It was long ago noticed by Kuhlmann that gun-cotton had an increased affinity for colouring matters, but no practical use has been made of the fact.

Strong hydrochloric and phosphoric acids behave towards cotton like sulphuric acid, but their action is less energetic. The ultimate product of the action of hydrochloric acid on cotton is the same as that given by sulphuric acid, but there is r.o intermediate formation of amyloid.

Solutions of tartaric, citric, and oxalic acids have no destructive action on cotton if it is simply steeped in the liquid; but if cotton saturated with a solution containing 2 % of any of the above acids is dried and heated for an hour to 100° C, it becomes slightly tendered. With 4 % solutions the destructive action is very decided at 100° C, and perceptible even at 80° C. Oxalic acid has the most injurious effect in this respect. If the acid solutions are thickened with gum or starch, and if steaming be substituted for a dry heat, the corrosive action in each case is less marked, so that in the ordinary practice of the calico-printer, who frequently uses steam-colours containing 4 % or more of the above acids, there is little to fear. Still, it is well to bear in mind that even organic acids cannot under all circumstances be applied to cotton with impunity.

Acetic acid may be considered as having no perceptible action on cotton.

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Action of Alkalis on Cotton. — Weak solutions of caustic potash or soda, when used cold, have, under ordinary circumstances, no action on cotton, although long-continued and intermittent steeping and exposure to air tender the fibre. Cotton may even be boiled for several hours with weak caustic alkalis, if care be taken that it remains steeped below the surface of the solution during the whole operation, but otherwise it is very liable to become rotten, especially if the exposed portions are at the same time under the influence of steam. Such exposure is to be guarded against during certain of the operations in bleaching cotton fabrics. The tendering action is probably due to oxidation. It is worthy of note that the disorganised fibre (oxy-cellulose) possesses an increased attraction for basic coal-tar colouring matters.

In the case of raw cotton, the action of boiling with weak caustic alkalis is simply to remove those natural impurities already referred to, which cause it to be waterrepellent, and therefore difficult to wet by mere steeping in cold water.

The action of strong solutions of caustic potash or soda is very remarkable. If a piece of calico is steeped for a few minutes in a solution of caustic soda, marking about 50° Tw. (Sp. Gr. 1*25), it assumes quite a gelatinous and translucent appearance; when taken out and washed free from alkali, it is found to have shrunk considerably, and become much closer in texture. If a single fibre of the calico thus treated be examined under the microscope, it is seen to have lost all its original characteristic appearance ; it has no superficial markings, and is no longer flat and spirally twisted, but seems now to be thick, straight, and transparent. A transverse section shows it to be cylindrical, while the cell walls have considerably thickened, and the central opening is diminished to a mere point (Fig. 5). Many years ago a Lancashire calico-printer, John Mercer, discovered that calico treated in the above manner was not only stronger than before, but had also acquired an increased attraction for colouring matters. Hoping to apply the process with advantage preparatory to dyeing, he patented it. Cotton thus treated was at that time said to be Mercerised, but that term is now applied to cotton or cotton materials which are

COTTON.

treated with soda lye under a tension which prevents the shrinkage above mentioned, or are afterwards stretched to counteract that shrinkage. When dyed in the indigovat, mercerised calico requires only one dip to produce as deep a shade of blue as can be obtained on ordinary calico only after five or six dips. Again, if a piece of ordinary and a piece of mercerised calico be dyed alizarin red, making all other conditions (time, temperature, quantity of Alizarin, etc.) the same in both cases, the mercerised cloth will be found to have a much fuller and richer colour than the other. Similar differences in depth of shade are noticed with other colours. The process, however, was never adopted in general practice as a means of saving dyestuffs, but in more recent years has been largely adopted for giving a brilliant lustre to the cotton.

Caustic ammonia in aqueous solution, whether strong or weak, has, under all circumstances, no action on cotton.

Fig. 5. — Transverse Sections of Cotton Fibre after Treatment with Caustic Soda.

Dry cotton is said to absorb 115 times its bulk of ammonia gas. Solutions of the carbonates of potash, soda or ammonia, silicate of soda, borax, and soap, have practically no action on cotton. There is a case on record, however, in which calico impregnated with silicate of soda, and shipped from England to South Africa, was found, after having been packed in bales for two years, to have become tender. Examination showed that the silicate of soda had decomposed with formation of silicic acid and carbonate of soda, and it was concluded that the tendering was due partly to the long-continued action of the carbonate of soda on the cotton, and partly to disruption of the fibres by the expansive force of the crystallisation of the carbonate of soda formed within them. The explanation is not altogether satisfactory, since it was found impossible to produce the same effects artificially. Probably it was a case of oxidation of the fibre. Whatever may have been the real cause, it is well to bear in mind that

B

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under exceptional conditions like those mentioned, even apparently harmless salts may tender the cotton fibre.

Action of Lime on Cotton. — Milk of lime, even at a boiling heat, has little or no action upon cotton so long as the latter is steeped below the surface of the liquid, but if it is at the same time exposed to the action of air or steam, it becomes much tendered by oxidation of the fibre. Such exposure must be avoided in cotton-bleaching.

Action of Chlorine and Hypochlorites on Cotton. — Cotton is quickly tendered if exposed to moist chlorine gas, especially in strong sunlight. The action may be due partly to the direct action of chlorine upon the fibre, one portion combining with and another replacing some of its hydrogen, partly to the destructive action of the hydrochloric acid thus produced, and partly to oxidation. Solutions of hypochlorites (bleaching powder, etc.) tender cotton more or less readily, according to the strength and temperature of the solutions and the duration of their action. Even a very weak solution of bleaching-powder will tender cotton if the latter be boiled with it; but when used cold, even if it be at the same time exposed to the air, the destructive action is inappreciable, and confined merely to bleaching the natural colouring matter of the cotton. If a piece of calico is moistened with a solution of bleaching-powder to 5° Tw. (Sp. Gr. .1 025), then exposed to the air for about an hour, and washed, it will be found to have acquired an attraction for basic coal-tar colouring matters similar to that possessed by the animal fibres. Cotton thus treated also decomposes directly, the normal salts of aluminium, iron, etc., attracting metallic oxide. Experiment has shown that this remarkable change is due to the action of the hypochlorous acid liberated by the carbonic acid of the air. The cotton thereby becomes chemically changed to what has been called by Witz, its discoverer, Oxy-cellulose.

Action of Metallic Salts on Cotton. — Under ordinary circumstances, solutions of neutral salts have no action on cotton ; even those of acid salts have no appreciable effect if the cotton be merely steeped in them while cold ; but if boiled with them the effect is similar to that of the free acids, though slightly less marked. If cotton is impregnated with solutions of the salts of the earths and heavy

COTTON.

metals, then dried, and heated or steamed, the salts are readily decomposed ; a basic salt is precipitated on the fibre, and the liberated acid affects the fibre according to the nature and strength of the salt solution employed.

The use of aluminium chloride, which was at one time recommended for the purpose of destroying the cotton in rags containing cotton and wool (" extracting also the application of the " topical " or " steam colours," and the " mordanting " process employed by the calico-printer, are all based upon the above facts.

Action of Colouring Matters on Cotton. — With few exceptions, colouring matters are not directly attracted from their solutions by the cotton fibre, hence it is not readily dyed, and special means of preparing it to receive the dyes have to be adopted in most cases (mordanting). The reason of this inert character of cotton is not yet satisfactorily explained; probably both its chemical and physical structure have an influence in the matter.

Chapter II. Flax, Jute, And China Grass

The Flax Plant. — The term " flax " designates the flax or linen fibre and also the plant from which it is obtained. Linen fibre consists of the bast cells of certain species of the genus Linum, more particularly Linum usitatissimum, a plant belonging to the natural order Linacece. It is an herbaceous plant, having a thin, spindle-shaped root, a stem usually branched at the top, smooth lanceolate leaves, and bright blue flowers, and is cultivated in nearly all parts of Europe.

The time of sowing varies in different countries from February to April, consequently the time of harvest also varies, and may be from June to September.

If the object of the farmer is to obtain good fibre, and not seed for re-sowing, the plant is gathered before it is fully matured — namely, when the lower portion of the stem (about two-thirds of the whole) has become yellow, and the seed capsules are just changing from green to brown. At this stage the plants are carefully pulled up. If they are left in the ground till the plant is fully ripe and the whole stem is yellow, the fibre obtained will be more stiff and coarse.

The freshly-pulled flax is at once submitted to the process of " rippling," which has for its object the removal of the seed capsules. This operation is performed by hand, by drawing successive bundles of flax-straw through the upright prongs of large, fixed iron combs, or " ripples." If the pulled flax has been dried and stored, the removal of the seeds is usually effected by the seedingmachine, which consists essentially of a pair of iron rollers, between which the flax-straw is passed.

Betting. — The most important operation in separating the fibre is that of " retting," the object of which is to decompose and render soluble by fermentation, as well as

FLAX, JUTE, AND CHINA GRASS.

to remove, certain adhesive substances which bind the bast fibres not only to each other, but also to the central woody portion of the stem, technically termed the " shrive," " shore/' or " boon."

The various moles of retting may be classified as : —

(1) Cold-water retting, which may be carried out with running or with stagnant water.

(2) Dew retting.

(3) Warm-water retting.

Cold-water Retting. — The best system of retting in running water is said to be practised in the neighbourhood of Courtrai, in Belgium, where the water of the sluggish river Lys is available. The bundles of flax straw are packed vertically in large wooden crates lined with straw. Straw and boards are afterwards placed on the top, and the crate thus charged is anchored in the stream and weighted with stones, so that it is submerged a few inches below the surface. In a few days fermentation begins, and as it proceeds additional weight must be added from time to time, in order to prevent the rising of the crates through the evolution of gas. As a rule, after steeping for a short period, the flax is removed from the crates, and set up in hollow sheaves to dry ; it is then repacked in the crates, and again steeped until the retting is complete. According to the temperature, quality of flax, etc., the duration of the steeping may be from 10-20 days. The end of the process must be accurately determined by occasionally examining the appearance of the stems, and applying certain tests, The flax bundles should feel soft, and the stems should be covered with a greenish, slime, easily removed by passing them between the finger and thumb ; when bent over the forefinger the central woody portion should spring up readily from the fibrous sheath. If a portion of the fibre is separated from the stem and suddenly stretched, it should draw asunder with a soft, not a sharp, sound. When the retting is complete, the flax is carefully removed from the crates and set up in sheaves to dry.

Stagnant-water retting is the method usually adopted in Ireland and Russia. The flax is steeped in ponds, preferably situated near a river, and provided with suitable arrangements for admitting and running off the water.

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This mode of retting is more expeditious than when running water is employed, because the organic matters retained in the water very materially assist the fermentation ; there is, however, always a danger of " over-retting," that is, the fermentation may become too energetic, in which case the fibre itself is attacked and more or less weakened. This danger is minimised#by occasionally changing the water during the steeping process. The quality of the water employed in retting is of considerable importance ; pure soft water is the best, calcareous water being altogether unsuitable. The waste water, being strongly impregnated with decomposing organic matter, poisons the streams into which it may run, and destroys the fish ; but it possesses considerable value as a liquid manure.

After retting in stagnant water, the flax is drained, then thinly spread on a field, where it is left for a week or more, and occasionally turned over. This process is termed " spreading " or " grassing." Its object is not merely to dry the flax, but to allow the joint action of dew, rain, air, and sunlight to complete finally the destruction and removal of the adhesive substances already alluded to. After a few days' exposure the stems begin to " bow," the fibrous sheath separates more or less from the woody centre, and the latter becomes friable.

Dew retting consists in spreading the flax on the field and exposing it to the action of the weather for 6-8 weeks, without any previous steeping. Damp weather is the most suitable for this method, since all fermentation ceases if the flax becomes dry. Dew retting is practised largely in Russia and in some parts of Germany.

Warm-water retting was a system recommended in 1847 by R. B. Schenck. It consists in steeping the closelypacked flax bundles in covered wooden vats, filled with water heated to 25°-35° C. By this means the fermentation is much accelerated, and the operation is completed in 2-3 days ; the process seems, however, to have met with only limited success.

Chemical retting, the process recommended by R. Baur, may be mentioned. It consists in first squeezing the fresh or dried flax straw between rollers, and then steeping it in water till the latter ceases to be coloured yellow.

FLAX, JUTE, AND CHINA GRASS.

It is next drained and steeped for 1-2 days in dilute hydrochloric acid (3 kg. concentrated HC1 per 100 kg. flax), until the bast fibres can be readily separated. The acid liquid is then run off, and the flax is well washed with slightly alkaline water, or such as contains a little chalk. A further treatment with dilute bleaching powder solution to dissolve away still adhering woody matter, and a final washing, complete the process. A well-retted flax is said to be thus obtained in the course of a few days only.

Chemist ry of Betting. — Experiments by Kolb indicate that the adhesive matter which cements the flax fibres together is essentially a substance called pectose. During the retting process the fermentation decomposes this insoluble pectose, and transforms it into soluble pectine, and insoluble pectic acid. The former is washed away, the latter remains attached to the fibre.

Breaking. — The next operation is to remove the woody centre from the retted and dried flax, after which the fibres must be separated from each other. It is rather beyond the scope of this manual to give more than a general account of the nature of the various mechanical operations for effecting this. They comprise " breaking/ 1 " scutching/' and " hackling."

The first operation aims at breaking up the brittle woody centre of the flax into small pieces, by threshing it with an indented wooden mallet, or by crimping it with a many-bladed " braque." The operation is now extensively done by machinery, the flax being passed through a series of fluted rollers.