The Dyeing of Cotton Fabrics

CHAPTER IX.

EXPERIMENTAL DYEING AND COMPARATIVE DYE TESTING 262

LIST OF ILLUSTRATIONS

FIG. PAGE 1. Cotton Fibre 5 1A. Cross-section of Cotton Fibre 5 2. Mercerised Cotton Fibre 7 2A. Cross-section of Mercerised Cotton Fibre 7 3. Silkified Cotton Fibre 9 3A. Cross-section of Silkified Cotton Fibre 9 4. Mather & Platt's Low-pressure Bleaching Kier 31 5. Mather & Platt's Yarn-bleaching Kier 49 6. Rectangular Dye-tank 54 7. Round Dye-tub 54 8. Section of Dye-vat 56 9. Delahunty's Dyeing Machine 58 10. Obermaier Dyeing Machine 59 11. Holliday's Yarn-dyeing Machine 60 12. Klauder-Weldon Dyeing Machine 62 13. Graemiger Cop-dyeing Machine 65 14. Graemiger Cop-dyeing Machine 66 15. Beaumont's Cop-dyeing Machine 67 16. Warp-dyeing Machine 70 17. Warp-dyeing Machine 71 18. Dye-jiggers 72 19. Dye-jigger 73 20. Jig Wince 75 21. Cloth-dyeing Machine 76 22. Dye Beck 77 23. Holliday's Machine for Hawking Cloth 78 24. Continuous Dyeing Machine 79 25. Padding Machine 80 26. Padding Machine 81 27. Dye-tub for Paranitroaniline Red 191 28. Padding Machine for Paranitroaniline Red 192 29. Developing Machine for Paranitroaniline Red 194 30. Indigo Dye-vat for Cloth 199 31. Squeezing Rollers 240 32. Yarn-washing Machine 243 33. Dye-house Washing Machine 244 34. Cloth-washing Machine 245 35. Cloth-washing Machine 247 36. Washing and Soaping Vats 248 37. Steaming Cottage 249 38. Steaming and Ageing Chamber 250 39. Hydro-extractor 251 40. Hydro-extractor 252 41. Automatic Yarn-dryer 253 42. Truck Yarn-dryer 254 43. Drying Cylinders 255 44. Experimental Dye-bath 263

CHAPTER I.. Structure and Chemistry of the Cotton Fibre.

STRUCTURE AND CHEMISTRY OF THE COTTON FIBRE.

There is scarcely any subject of so much importance to the bleacher, textile colourist or textile manufacturer as the structure and chemistry of the cotton fibre with which he has to deal. By the term chemistry we mean not only the composition of the fibre substance itself, but also the reactions it is capable of undergoing when brought into contact with various chemical substances--acids, alkalies, salts, etc. These reactions have a very important bearing on the operations of bleaching and dyeing of cotton fabrics.

A few words on vegetable textile fibres in general may be of interest. Fibres are met with in connection with plants in three ways.

First, as cuticle or ciliary fibres or hairs; these are of no practical use, being much too short for preparing textile fabrics from, but they play an important part in the physiology of the plant.

Second, as seed hairs; that is fibres that are attached to the seeds of many plants, such, for instance, as the common thistle and dandelion; the cotton fibre belongs to this group of seed hairs, while there are others, kapok, etc., that have been tried from time to time in spinning and weaving, but without much success. These seed hairs vary much in length, from 1/4 inch to 1-1/2 inches or even 2 inches; each fibre consists of a single unit. Whether it is serviceable as a textile fibre depends upon its structure, which differs in different plants, and also upon the quantity available.

The third class of fibre, which is by far the most numerous, consists of those found lying between the bark or outer cuticle and the true woody tissues of the plant. This portion is known as the bast, and hence these fibres are known as "bast fibres". They are noticeable on account of the great length of the fibres, in some cases upwards of 6 feet, which can be obtained; but it should be pointed out that these long fibres are not the unit fibres, but are really bundles of the ultimate fibres aggregated together to form one long fibre, as found in and obtained from the plant. Thus the ultimate fibres of jute are really very short--from 1/10 to 1/8 of an inch in length; those of flax are somewhat longer. Jute, flax, China grass and hemp are common fibres which are derived from the bast of the plants.

There is an important point of difference between seed fibres and bast fibres, that is in the degree of purity. While the seed fibres are fairly free from impurities--cotton rarely containing more than 5 per cent.--the bast fibres contain a large proportion of impurity, from 25 to 30 per cent. as they are first obtained from the plant, and this large quantity has much influence on the extent and character of the treatments to which they are subjected.

As regards the structure of the fibres, it will be sufficient to say that while seed hairs are cylindrical and tubular and have thin walls, bast fibres are more or less polygonal in form and are not essentially tubular, having thick walls and small central canals.

=The Cotton Fibre.=--The seed hairs of the cotton plant are separated from the seeds by the process of ginning, and they then pass into commerce as raw cotton. In this condition the fibre is found to consist of the actual fibrous substance itself, containing, however, about 8 per cent. of hygroscopic or natural moisture, and 5 per cent. of impurities of various kinds, which vary in amount and in kind in various descriptions of cotton. In the process of manufacture into cotton cloths, and as the material passes through the operations of bleaching, dyeing or printing, the impurities are eliminated.

=Impurities of the Cotton Fibre.=--Dr. E. Schunck made an investigation many years ago into the character of the impurities, and found them to consist of the following substances:--

=Cotton Wax.=--This substance bears a close resemblance to carnauba wax. It is lighter than water, has a waxy lustre, is somewhat translucent, is easily powdered, and melts below the boiling point of water. It is insoluble in water, but dissolves in alcohol and in ether. When boiled with weak caustic soda it melts but is not dissolved by the alkali; it can, however, be dissolved by boiling with alcoholic caustic potash. This wax is found fairly uniformly distributed over the surface of the cotton fibre, and it is due to this fact that raw cotton is wetted by water only with difficulty.

=Fatty Acids.=--A solid, fatty acid, melting at 55 deg. C. is also present in cotton. Probably stearic acid is the main constituent of this fatty acid.

=Colouring Matter.=--Two brown colouring matters, both containing nitrogen, can be obtained from raw cotton. One of these is readily soluble in alcohol, the other only sparingly so. The presence in relatively large quantities of these bodies accounts for the brown colour of Egyptian and some other dark-coloured varieties of cotton.

=Pectic Acid.=--This is the chief impurity found in raw cotton. It can be obtained in the form of an amorphous substance of a light yellow colour, not unlike gum in appearance. It is soluble in boiling water, and the solution has a faint acid reaction. Acids and many metallic salts, such as mercury, chloride and lead acetate, precipitate pectic acid from its solutions. Alkalies combine with it, and these compounds form brown substances, are but sparingly soluble in water, and many of them can be precipitated out by addition of neutral salts, like sodium and ammonium chlorides.

=Albumens.=--A small quantity of albuminous matter is found among the impurities of cotton.

=Structure of the Cotton Fibre.=--The cotton fibre varies in length from 1 to 2 inches, not only in fibres of the same class but also in fibres from different localities--Indian fibres varying from 0.8 in the shortest to 1.4 in the longest stapled varieties; Egyptian cotton fibres range from 1.1 to 1.6 inches long; American cotton ranges from 0.8 in the shortest to 2 inches in the longest fibres. The diameter is about 1/1260 of an inch. When seen under the microscope fully ripe cotton presents the appearance of irregularly twisted ribbons, with thick rounded edges. The thickest part is the root end, or point of attachment to the seed. The free end terminates in a point. The diameter is fairly uniform through 3/4 to 7/8 of its length, the rest is taper. In Fig. 1 is given some illustrations of the cotton fibre, showing this twisted and ribbon-like structure, while in Fig. 1A is given some transverse sections of the fibre. These show that it is a collapsed cylinder, the walls being of considerable thickness when compared with the internal bore or canal.

Perfectly developed, well-formed cotton fibres always present this appearance. But all commercial cottons contain more or less of fibres which are not perfectly developed or are unripe. These are known as "dead fibres"; they do not spin well and they do not dye well. On examination under the microscope it is seen that these fibres have not the flattened, twisted appearance of the ripe fibres, but are flatter, and the central canal is almost obliterated and the fibres are but little twisted. Dead fibres are thin, brittle and weak.

=Composition of the Cotton Fibres.=--Of all the vegetable textile fibres cotton is found to have the simplest chemical composition and to be, as it were, the type substance of all such fibres, the others differing from it in several respects. When stripped of the comparatively small quantities of impurities, cotton is found to consist of a substance to which the name of cellulose has been given.

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