RECENT ADVANCES IN THE EXPERIMENTAL STUDY OF WARP SIZING.

BY FREDERICK DENNY FARROW, M.Sc. (THE BRITISH COTTON INDUSTRY RESEARCH ASSOCIATION).

Received May 2 IS^, I 924.

In the manufacture of woven cloth the longitudinal or warp threads are subjected in long lengths and for a considerable time to the wearing action of the moving parts of the loom, whereas the transverse (weft) threads are inserted and immediately protected by being enclosed in the mesh of the cloth. In order to facilitate weaving it is found necessary to prepare the warp by dressing or sizing it with an adhesive preparation. The art of sizing is very ancient and its mechanical development has followed a normal course dependent on the advance of engineering practice. As far as machinery is concerned, sizing is at present well served and admirable results are usually obtained by those who have long experience, well-trained workmen, and who take precautions to maintain a uniform routine in their sizing department.

When, however, an attempt is made to define the best working con- ditions and to specify exactly the qualities which the ingredients of size should possess, it is found that present-day knowledge is insufficient to permit of this. Research on sizing is therefore required and should seek in the first place to provide methods of measuring the significant properties of size,. its ingredients, and of the sized yam and the resultant cloth, while an attempt must also be made to describe in exact terms the nature of the sizing process. Based on this preliminary and descriptive work, we may reasonably hope to see that selection and development of advantage- ous factors, with elimination of the unfit, which is the ultimate aim of industrial research. In this paper is given a short account of recent work which may be regarded as a first step towards a complete experimental account of the process of sizing and of the properties of the size-bearing cotton.

The Properties of Sized Yarn.

The warp threads of a loom in motion are subjected to a rapid cycle of changes of tension caused by the beating of the reed and the action of the harness as it opens a passage for the shuttle, with friction in addition between yarn and moving parts, as well as repeated bending of the warp. The destructive effect of periodically changing tension has been investi- gated by Owen,19 who suspended pieces of yarn loaded in a definite manner from crank-driven slides. The load on specimens so treated passes through a range of values which is repeated for each revolution of the crank shaft, the maximum and minimum values of the stresses being controlled by adjusting the speed of the machine and the magnitude of the

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304 RECENT ADVANCES I N T H E

loading weights. Dependent on these, breakage of the test specimens proceeds more or less rapidly, so that, for instance, 64 oscillations were sufficient to cause half the specimens of a sample of unsized yarn to fail, while 650 were required to produce a similar effect on the corresponding sized material. In another test, on yarn sized in thkee portions with maize, sago once and sago twice, the figures were 700, 600, and 1200 oscillations respectively, showing that the second treatment with sago had produced a marked change of properties of the yarn. When a series of samples of sized yarns from mills were tested, the breakage curves showed that corre- sponding counts of yarn sized with different mixtures or on different machines were approximately equally well consolidated, a result corre- sponding with the probable similarity of their treatment in the loom. Observations of extension made during the course of the breakage tests showed that unsized yarn extended rapidly at first, then more slowly, and finally with increasing speed smoothly up to its breaking point, whereas with sized yarn the extension became steadily slower and finally ceased, failure occurring always as an unpredictable snap, though some specimens remained intact and were apparently capable of permanently resisting the oscillation.

In the same paper is described another type of test in which definite lengths of yarn are loaded steadily at an arbitrary rate until they break. It is found that the maximum extension measurable before failure is decreased by the presence of size, and the author concludes that this effect of sizing is prejudicial to the chance of survival of yam in the loom. That sizing reduces extensibility is a fact noted also by New and Gregson171 l8 in two papers which should be read tegether, but these authors find, as regards weaving efficiency, that the less extensible of two dressed linen warps is less liable to breakage when woven. This observa- tion should not be treated as conclusive on the question of the value of high or low extensibility in a sized yarn, since Owen (Zuc. cit.) has pointed out that the variations between specimens of yarn unsized reputed to be identical in properties are sometimes so great as to mask any differences due to sizing.

Another paper dealing with destructive effects is that of New16 on friction. Yarn under tension is subjected to the action of an oscillating reed, and a record made of the average number of rubs needed to break the yarn-usually more for dressed yarn, though there is one exception to this. The paper contains some interesting information on the abrasive effect of new reeds on yarn, and suggestions are made for improvements in the construction and use of these parts. On the question of testing, proposals are made for alternative methods of recording the effects of a friction test, either by comparing that fraction of the total number of specimens which is broken by a standard treatment, or else by measure- ment of the loss of tensile strength of the rubbed yarn. The latter method of expression is shown to give results consistent with those got by record- ing the average number of rubs required for total destruction.

The use of photography to give a permanent compact record of the character of the surface of yarn at any stage of its manufacture or testing, is a development worth the attention of those who rely on visual tests for classifying their materials.

Tests to destruction postulate the use of forces more intense than those usually applied to a warp, and an equally interesting line of research is that dealing with the energy exchanges in periodically stressed yarn, as well as with the slow changes of length, short of rupture, accompanying

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EXPERIMENTAL STUDY OF WARP SIZING 305

the load cycles. Shorter and Hal125 have used an autographic apparatus for recording the sequence of extension and contraction caused by the loading and unloading of textile fibres and yarns, and Shorter 24 has put forward a mechanical analogy to illustrate and explain the load-extension- time graphs he obtains. He imagines a fibre to be composed of “ a set of free elastic elements, a set of impeded elastic elements, and a set of im- peding or viscous elements,” the latter being a gelatinous constituent the viscosity of which depends on its water content and temperature. By this conception permanent extension produced by a small load will always disappear on unloading if sufficient time is allowed.

have used their own earlier type of autographic extensometer for measurements on sized and unsized linen and cotton yarns. The loading and unloading graphs (load-extension) of these materials, enclose areas which continuously decrease as the cycle is re- peated. With sized yarns the areas of the hysteresis loops are smaller than with unsized, and the permanent extensions are also smaller. The sugges- tion is made that there is a certain maximum load for any specimen, below which cyclical loading eventually leads to a steady value for the area an6 position of the hysteresis loop with a cessation of permanent extension, but above which permanent extension continues till the yam breaks. Peirce 2o has examined the torsional rigidity of yarns and for one sized specimen is able to conclude that the size is not present as a continuous matrix.

Of direct measurement of the breaking strength of yarn little need be said. The test in its crudest form is from time to time quoted in favour of this or that sizing material or process, but in common with other physical methods of investigation its full usefulness can only be developed by co- relating it with weaving qualities as measured by records of thread breakages in the loom.

The Mode of AppZicafion of Size.

New and Gregson 1 7 9

In sizing, the warp is passed through a vessel containing size and is then squeezed and dried. In slasher sizing the process is continuous, a single layer or sheet of closely packed yarn passing through the size box, under heavy rollers, and then either over steam heated drums or through an air chamber. There are two questions here much discussed but still debatable on account of the lack of concrete evidence; hot air drying is said to produce a rounder and therefore better yarn than does the use of heated cylinders; and the best temperature for the size is still uncertain. On the latter point the improvements claimed to result from the recent increasing use of temperature regulators are probably attributable more to uniform working than to the maintenance of any one temperature.

Dependent on the temperature and concentration of the size, the speed of working, and the counts of yarn, the latter may receive what is virtually only a surface coating or may be fully penetrated by the size. Some indi- cation of the range of penetration of different mixtures is given by Cathcart 2 but no exact analysis of the conditions leading to diversity of effects is provided. Viscosity of the size mixture and the surface actions between size and yarn are undoubtedly of prime importance in determining how far the size gets into the yarn, but no measurements of these factors has yet been made under mill conditions. I t is even uncertain what are the advantages to the manufacturer of coating or penetration. The common assumption is that the latter is desirable,2 though there are upholders l3 o f the opposite view. In actual fact it is found that many specimens of perfectly satisfactory slashed yarns have no starch in their interior. For

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306 RECENT ADVANCES IN THE

warps exceptionally liable to frictional damage concentrated size mixtures are recommended,14 and it is known that these lead to the retention of more size on the surface of yarn and less internal absorption than is obtained with lower concentrations. For resisting abrasiori it appears that a coating is desired but the location of size must have its effect on the feel of the cloth, as well as on the facility with which starch is removed as a preliminary to bleaching.

The Projerties of Size. The most important ingredient of size is the starchy constituent, either

wheat flour or a pure starch. The latter has until lately been treated as being one chemical substance though the researches of Maquenne and his

l2 of Samec,22 and of Ling lo render this view untenable. Starch recovered from vegetable tissues is now known to consist of two materials, a more or less polymerised water soluble carbohydrate which yields non- viscous solutions, and is electrically neutral, and a phosphoric ester of a very similar body. The latter gives viscous suspensions in water and is precipitated from these by bases, being a negatively charged colloid. I t is called by Maquenne amylopectin, while the neutral carbohydrate, held by Ling to be a condensation product of Pringsheim's amyloses, may con- veniently be called amylose. In the starches of commerce there occur traces of proteins and possibly some hemicelluloses, but the variations of properties of specifically different starches are possibly traceable to differ- ences in their amylose/amylopectin ratio (Samec 23), though Ling lo states that this is constant for all starches.

If starch is treated with co!d acid, the bases are removed but not the phosphorus, and the washed product gives solutions much less viscous than are obtained from ordinary ~ t a r c h . ~ When a normal starch paste is pre- served under aseptic conditions for a considerable time its viscosity de- creases and its conductivity and acidity increase while free (dialysable) phosphoric acid is produced. These phenomena are manifestations of the complicated effects of the ionisation and hydrolysis of the starch phosphoric acid and of its salts, and to a certain extent of the degree of aggregation of the colloidal ester anion. None of these reactions has received fully quantitative examination, and they are mentioned here as an indication of the difficulty under commercial conditions of preparing starch of uniform properties. In future experimental work on starch, account will have to be taken of its composition as a mixture of amylose and amylopectin and of the separate reactions of each, but in what follows the material has been treated as a homogenous substance.

The properties of starch of interest to the cotton manufacturer are its adhesive qualities as a solid and the fluidity of its aqueous solutions. For an examination of the former, starch pastes have been evaporated and the resultant sheet of semi-transparent material taken as representing the deposit on pure-sized yarn. The water absorbtive capacity of these films has been determined at 20' C. when the ordinary sigmoid isotherm charac- teristic of colloidal substances is obtained, and there are indications of lag in the loss of water on drying.4 Prolonged heating of the starch appears to reduce its power of taking up water, and this may have some application in connection with the drying of sized yarn. The mechanical properties in- vestigated l5 are modulus of elasticity, breaking load, and ultimate extension at the breaking-point. In a humid atmosphere the elasticity and breaking load are lower than under dry conditions, the extension at break being little affected by humidity. Over-treatment with acids or with enzymes, or the

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EXPERIMENTAL STUDY OF WARP SIZING 307

inclusion in the paste of an excess of a hard fat such as japan wax, have the same effects as low humidity in increasing the brittleness of the starch, results to be compared with the statement that excessive acidity or fat in a size render it liable to disintegrate during weaving. Krais and Biltz Q have dried starch on strips of filter paper, and from measurements of the breaking strength of these conclude that conversion of starch to soluble starch must be conducted with care since too far-reaching hydrolysis re- duces the strengthening power of the starch.

Th Viscosi& of Stnrch Pastes.

The viscosity of a size mixture plays its part in determining the extent of flow into the interstices of the yarn, or in resisting the dispersing action of the squeezing rollers which remove excess of size from the warp, and it is desirable that some information on the conditions in the size box should be obtained. As an approach to this Farrow and Lowe set out to investi- gate the viscosity of starch pastes. They found that preparations of many kinds of starch,' if stored at goo C., decreased in viscosity at a rapid rate, but with other samples the effect was less marked. Potato starch is notorious in the industry for its instability and this was easily confirmed, but with one maize starch solutions were obtained which were satisfactorily stable and whose viscosity was not affected by passage through a capillary tube. As a result of this work it was shown that the viscosity of a starch paste apparently varies with the pressure employed to force it through a tube, in the sense that the apparent viscosity is lower the higher the driving pressure. Over the range of pressure and tube dimensions used, the results could be expressed by the equation,

[q] = PN&t/8ZV,

where [.I] is termed the coefficient of flow, and N is an empirical exponent of the value of the driving pressure expressed in dynes per square centimetre, -the other symbols having their usual significance.

The constants [q] and N fully define the fluid properties of the pastes as far as flow through a tube is concerned, but the limitation is necessary since it is now known that for shear between concentric cylinders other constants are obtained which are analogous to [.I] and N, but differ from them in rnagnitude.1' Of [q] it may be said that it resembles viscosity in that its logarithm is a continuous and nearly linear hnction of the starch concentration. Its value lies between 2 and I, approaching the latter limit for dilute solutions and being for water obviously unity when [q] is replaced by 7 the ordinary viscosity. The relation between concentration and N is non-linear and is less regular than that for the coefficient of flow. The whole anomalous behaviour is probably an expression of the structure of starch paste containing a con- tinuous, purely viscous phase, and a disperse, deformable constituent. The practical result is that in any attempt to measure the apparent viscosity of starch two constants will have to be determined, unless a decision is reached to make all measurements in an instrument of standard dimensions.

No attempt will be made here to discuss the work of those who follow Bingham,' and give their results in terms of yield value and mobility. This mode of treatment completely failed for the starch results, but it is probable that there is more than one kind of plastic substance, and more than one law of flow is possible. Porst and Moskowitz,21 considered the possibility of expressing their data for starch by means of an exponent of

The significance of N is not clear.

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308 RECENT ADVANCES IN THE STUDY OF WARP SIZING

the pressure, but their work was done at low temperature and throws little light on actual sizing conditions. De Waele 26 has given a full discussion of Bingham’s work in a paper which preceded that of Farrow and Lowe, and showed there that for vaseline the flow was represented by an equation containing a power of the pressure, but the dimensions of the capillaries used were not introduced into his expression.

The subject is dealt with at length on account of its interest to the textile industry, which uses starch preparations for sizing, finishing, and calico printing, as well as in the hope that its discussion may lead to a more academic study of the problem and possibly to a better elucidation of the structure of sols of emulsoid colloids.

Summary.

Size is applied to cotton warps in order that they may be woven with a minimum of breakage. When cloth is to be bleached the size is removed immediately after weaving, but many materials are sold and used with the size still present. The changes of physical properties of yarn or cloth as a result of sizing are at present ill defined, but continued development of recently described methods of examining textiles should enable their essential characteristics to be ascertained with exactitude.

When the requirements of the weaver as well as of the merchant and user are known, it will be possible to demand that the sizer shall produce definite effects on the warps he treats. The successful fulfilment of these demands will only be realised as a result of a study of the process of sizing and of the materials used therein.

BIBLIOGRAPHY.

1 Bingham, ‘Cathcart, Cotfon, 1921, 85, 481. 3Farrow and Lowe, J. Text Inst., 1923, 14, T. 414. 4 Farrow and Swan, J. Text . Inst., 1923,: 14, T . 465.

6 Gatin, Gruzewska Mme., Compt. rend., 1908, 146, 540. 7 Hadfield, Text. Manufacturer, 1g23,49, 123. 8Hinchley, r. Text. Inst., 1919, 10, 198, 277. 9 Krais and Biltz, Lkpzig. Monats. Text. Ind., 1923, 38, 207. l o Ling and Nanji, Trans. Chem. Soc., 1923, 123, 2666. 11 Lowe, Unpublished work (The British Cotton fndustry Raeurch Associutiott). l2 Maquenne and ROUX, Ann. Chim. Phys., I904 [VIII.], 2, 109; 1906, 9, 179. l 3 Moore, Text. Manufacturer, 1915, 41, 189. 14 Nanson, Cotton, 1922,86, 243. Is Neale, Forthcoming publication (The British Cotton Indtrstry Research Associa-

16 New, J. Text. Inst., 1924, 15, T. 230. 17918 New and Gregson, J. Text . Inst., 1922, 13, T. 25 ; 1923, 14, T. 447. 190wen, J . Text. Inst., 1923, 14, T. 375.

21 Porst and Moskowitz, J. Ind. Eng-. Chem., 1923, 15, 166. BSamec, Koll. Beihefte, 1911 to 1920, 3 to 12. 23 Samec, Koll . Beihefte, 1920, 12, 281. %Shorter, J. Text. Inst., 1924, 15, T. 207. 26Shorter and Hall, J. Text. Inst., 1923, 14, T. 493. 96 de Waele, J. Oil and Colorir Clremtsts Assn., 1923, 6, 33.

Fluidity and Plasticity,” 1922, McGraw Hill Book Company.

Fouard, 6‘ L’Etat colloidal de l’amidon ; Laval, Paris, 1911.

t w r r ) .

Peirce, J. Text . Inst., 1923, 14, T . 390.

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