Some Aspects of the Oxidation of Cellulose

T H E JOURNAL OF THE

Society of Dpers 6j Colourists ~ ~ ~ ~ ~

VUL. LI-NO. 10 OCTOBER 1936 bared Monfhly

Proceedings of the Society MANCHESTEX SECTION

Meeting held a t the rooms of the Manchester Literary and Philosophical Society on 15th March 1935, M i . L. G. LAWRIE in the chair.

Some Aspects of the Oxidation of Celldose H. A. TURNER, M.Sc., A.I.C.

The Lecturer first referred briefly to the two rather curious examples of the modification of cellulose, apparently brought about by oxidation, described by Bone (this J a r . , 1934, 50, 307) and Nabar (ihid., 306). The examples wero (a) the apparent oxidation of cellulose brought about by the evaporation of water from cotton fabrics, and (6 ) the profound accelerating influence exercised by certain leuco-vat dyes upon the hypochlorite oxidation of cotton cellulose. A paper dealing with the latter subject was published recently by Turner, Nabar and Scholefield (ibid., 1935, 51, 5), who found that the degradation of cotton cellulose, as measured by the rise in cuprammonium fluidity, produced by the oxidising action of dilute sodium hypochlorite solution acting in the dark a t room temperature, was very greatly accelerated if there were also present on the fibre a reduced vat dye. The increase in the rate of modification of the cotton by sodium hypochlorite solution a t pH 7 was so great that an increase in the fluidity, requiring some hours to bring about if white cotton were used, required only the same number of seconds in the presence of leuco-vat dyes. These authors were of the opinion that this acceleration was a special example of a principle which appeared to apply to many oxidising reactions of the most diverse kinds and occurring in many fields of chemistry. If there were present an oxidising agent and an oxidisable substance, the rate of oxidation of this substance could often be accelerated by the introduction of a third, more readily oxidisable substance. When this third substance W&EI oxidised, it often appeared that, contrary to what might havc been anticipated, the original oxidisable material was not protected from attack, but on the contrary it was attacked with increased vigour. Besides the action of leuco-vat dyes, two other examples which seemed to illustrate the operation of this prinoiple were

A ”

of interest. The first was the observation that in discharging Indigo dyeings on cotton with bichromate, the presence of oxalic acid so activated the bichromate that a clean discharge could be obtained. The acceleration of the oxidation was so marked that increased care had to be taken to prevent damage to the cotton.

Another interesting observation, made by Scholefield and Goodyear some years ago, appeared to be capable of explanation by this principle. These workers were attempting to find stable and distinctive derivatives of leuco-vat dyes in order to be able to determine whpther vat dyes, dyed on cotton, were reduced by light to the leuco-form. They attempted to couple the reduced dye on the fibre with a diazo-cnmpoud (the ability of certain reduced vat dyes to react with diazo-compounds had been observed by other workers, and the process was protectEd by patents), and obtained evidence of couplirg between some leuco-vat dyes and, e.g. Variamine Blue B Salt. This couplirg operation was found always to be accompanied by a marked diminution in strength of the fibre, and the tendering appeared to be unavoidable. Since diazonium compounds in general could act as oxidising agents under favourable conditions, it was thought that their oxidising action upon the fibre was accelerated by the oxidation of some of the leuco-compound present.

This principle, whereby the oxidation of a readily attacked material stimulated the attack upon a more resistant accompanybg substance, was clearly of great importance in textile chemistry. Almost invariably, when an oxidising agent was usedfor treating cotton or cellulosicmaterials, it was used with the object of acting upon and modifying an accompanying, more readily oxidisable material, and of leaving the cellulose intact. This was true whether the readily oxidisable substance was a natural impurity, e.g. in bleaching, a dye, e.g. in stripping and discharge printing, or the precursor of a dye, e.g. a reduced vat or sulphur dye, or aniline salt in dyeing Aniline Black. In many processes, therefore, i t was possible that the primary action, unless very carefully controlled, could turn the vigour of the oxidising attack towards the cellulose. These considerations appeared to afford a useful field for detailed inveetigation, since it was not

346 TURNER"S0ME ASPECTS OF THE OXIDATION O F CELLULOSFY' IOct. 1936

certain at the present time whether the presence of easily reducible material along with cellulose protected it from oxidation, or whether it caused it to be attacked more vigorously. Sometimes one of these alternative actions uecmed to take place, sometimes the other.

Apart from the study of oxidations as they affected the normal processing of cellulose materials, many problems were presented by the study of the action of atmospheric oxygen upon cellulose. AItbough, perhaps, many of the reactions were relatively slow and did not cause the modification of large quantities of the material over a limited period, they were taking place all the time, and they could be influenced profoundly by the presence of many substances.

Usually, the atmospheric oxidation of cellulose was undesirable, but it had been exploited in one important industrial textile operation, viz. the controlled degradation of the original cellulose during viscose manufacture for the preparation of viscose solutions of sufficiently low viscosity for spinning. This operation, in which cellulose was acted upon by air in the presence of alkali, required the most scrupulous control to maintain a uniform finished product and the oxidation, therefore, had been studied thoroughIy by many workers. Much of the information was not available, but Davidson IJ. Tmtile Inst., 1932, 23, T95), who measured the uptake of oxygen by alkaline cellulose under a variety of conditions, had suhtantiated the accepted view that alkali increases the rate of oxygen uptake, and that this was further accelerated by the presence of metallic compounds of which those from iron seemed to be the most effective.

A long story could be told of the influence of iron compounds in rendering oxygen of the air, or of simple oxidising agents, available for oxidation. They took this part in many reactions and were of great importance, of course, in biological oxidations. Almost invariably there was some iron present in the normally encountered forms of cellulose and i t required extraordinary precautions to remove i t from cellulose, from dyes, and from some of the reagents used.

It was interesting to inquire if traces of iron compounds in cellulose facilitated air oxidation by a similar kind of action to that exercised by the leuco-vat dyes. Unless very carefully purified, cellulose always contained a small proportion of reducing material. Was it possible that this material, especially in the presence of caustic soda, was capable of transforming some of the iron to the ferrous condition, the ferrous iron then being reoxidised in the air and simul- taneously accelerating the oxidation of the cellulose ? In such a cycle of operations, the effect of the presence of even small amounts of iron could result, given sdlicient time, in the oxidation of appreciable amounts of cellulose.

It was not possible to say that thig view of tho function of iron in the oxidation of cellulose had received explicit confirmation by experiment. Recently, however, Salley (J. Phys. Chem., 1934, 38, 449, 465) had given an account of some experipental work on carbohydrate oxidation. Instead of setting out from cellulose, he used the simple polyhydric alcohol, rnannitol. CH,OH.(CHOH), CH,OH, which had u carbon chain backbone like the molecules of c~llulosc~. and terminal primary alcohol groups (it would bt. seen later that it was supposed that cellulosc was fist attacked a t its primary alcohol groups), but had no aldehyde group to complicatc~ ti study of the course of the oxidation. Its reactions could be followed in solution. It seemed, therefore, to be an ideal compound for the first stage of an investigation of the behaviour of more com- plicated carbohydrates including cellulose and starches. It was known that the air oxidation of mannitol was accelerated by the action of light, and it had been found also that the presence of small quantities of metallic compounds, e.g. those of iron or copper, acceleratcd the uptake of oxygen. Moreover, the simultaneous presence of iron and alkali was most favourable to oxidation, and spectroscopic examination indicated that a complex iron-mannitol compound was formed onlyin alkaline solution. From the resultsof these experiments, the iron appeared to have a relatively slight influence upon the oxidation unless i t formed a complex with the mannitol. T t was possible that the leuco-vat dyes were effective from a similar cause, since the fact that they had a strong affinity for cotton must mean ~1

valency connexion more or less strong between dye and cellulose molecules, and this might be equivalent to the complex formation between iron and mannitol. The suggestion had becn made that the iron might act as accelerator by virtue of its oxidation from the fcrrous to the ferric state. This point had been invcstigtttd by Salley (Zoc. cit.) for mannitol. He found that if iron were present originally in thc. ferrous state, rapid absorption of oxygm occurred approximately equivalcnt to the amount of ferrous iron present. After this absorption and, presumably, the convcrsion of the iron to the ferric state, the mannitol oxidation appeared to proceed normally. Unfortun- ately, the solution itself was not antalysed after this initial rapid oxygen absorption, so that there was no direct evidence that the maruiitol remained unoxidised until all the iron was converted to the ferric state, but such evidence as has been given did not seem to support the suggested analogy between the behaviour of the leuco-vat dye and that of ferrous iron. An interesting part of the mannitol oxidation was concerned with the influence of hydrogen peroxide. Addition of hydrogen peroxide seemed greatly to stimulate the oxidation of the mannitol, since not only was the available oxygen of the peroxide taken up, but also an increased

Od. 193.51 TURNER-"SOME ASPECTS OF THE OXIDATION O F CELLULOSE" 347

quantity of oxygen from the air. Hydrogen pcroxide thus appeared to accelerate oxidations by air, just as Kauffmann had shown that i t accelerated oxidations by hypochlorite. Since hydrogen peroxide in the presence of another oxidising agent acted as a reducing agent, losing one atom of oxygen which took with it an atom of oxygen from the molecule of the other agent, it seemed that the stimulation of oxidation which i t could bring about was analogous to the stimulation brought about by leuco-vat dyes and other oxidisable substances.

These air oxidations did not require high temperatures to become appreciable in extent, and i t should be realised that cellulose was readily modified under mild conditions.

Bone (loc. cit.) had described an experiment in which a strip of cloth was held vertically with one end dipping into water so that the water rose part of the way up the cloth; equilibrium was reached when the rate of capillary rise of the water was balanced by the rate of its evaporation into the surrounding air. After a time a brown line appeared in the region dividing the wet and dry areas. The formation of this brown line seemed to come from the local modification of the cellulose with the formation of a readily soluble brown substance. Great care had been taken in the preliminary purification of the cloth in order to make sure that the brown line was not the result of impurities carried up from the wet area by the water. The air used had becn freed from acids and traces of active oxidising substances, e.g. hydrcg:n peroxide, ozone or nitrous oxides. The water also had been carefully pursed. Under these conditions the brown line was still obtained, so that it appeared as if the action of atmospheric oxygen and evaporating water was sufficient to cause a radical modification of the cotton. The substance constituting the brown line, if it were derived from the cellulose, must have been obtaincd therefrom by a process which caused severe degradation since it was readily soluble in water and in ethyl alcohol. The brown line could be washed off, and the test piece sub- mitted to further treatment, so that a new line could be produced, and this operation could be repeated many times. A line could be formed high up on the cloth, and then, by altering the conditions of evaporation, another line could be formed lower down, and so on a t a number of levels.

This was strong evidence that the line was not a collection of impurities from the wet portion of the cloth. Although the material which caused the brown colour was soluble in water, the residual cellulosic material a t the position where a line had been formed appeared to be modified also, because deep staining with Methylene Blue occurred even though the brown material had been removed. In whatever position in a test piece a brown line had been formed, there appeared also this enhanced basic

dye absorption. The material giving rise to this absorption was not soluble or mobile. The visible formation of a brown line required some hours, but there was evidence of a much more rapid modification of the cellulose under the same conditions that were required to produce the line. If the end of a strip of very carefully purified cloth were dipped in pure water for tt minute or two so that part of the cloth were wetted, and was then dried below 100" C. sufEciently rapidly to prevent diffusion of the boundary between wet and dry portions, a distinct fluorescent line was obvious a t the boundary region when the cloth was cxamined in ultra-violet light. The fluorescent material could be extracted by water and alcohol, and its behaviour seemed to show that its formation could be regarded as the f i s t stage of the brown line formation. Thus, evaporating water and air seem to be capable of producing a rapid and detectable modification of cellulose under the very mildest conditions.

The properties of the insoluble, Methylene Blue-absorbing modification of the cellulose had not yet been fully studied, because of the &E- culties of obtaining i t in large quantities under conditions stringent enough to exclude possible interference by impurities in the cellulose, watcr or air. Copper number determinations had boen made, but while the modified material seemed usually to have a s1:ghtly higher value than the unmodified cotton, these differences were scarcely greater than the experimental errors of the analytical determinations. Sufficient modified cellulose for a cuprammonium fluidity drter- mination on the normal scale was not available, and micro - fluidity determinations were not satisfactory. With these reservations it could be stated that a rise in the fluidity of the modified portion had never been detected. If this evidenre could be substantiated, it would show an unusunl type of modification, viz. one in which substances of low molecular weight were broken from the ends of the cellulose molecules, leaving the residual molecule nearly as large as its original size.

The changes produced by oxidation on the cellulose molecule had not received any very satisfactory explanation. On the newer ideas of the constitution of cellulose, the consequences of acid attack could be plausibly accounted for by assuming that hydrolysis accurred a t some of the glucosidic linkages in the cellulose chain. The action of oxidising agents was not at,Ppresent capable of so precise an explanation.%' Making allowances for differences in degree, the)products of acid attack and the products of oxidising attack often showed a striking resemblance. Both showed evidence of a reduction in molecular size as judged by the decrease in cuprammonium viscosity. Acid attack reduced the mechanical strength of cellulose and yielded substances of strong reducing properties. Oxidation under certain conditions produced similar effects,

348 TURNER"S0ME ASPECTS OF THE OXIDATION OF CELLULOSE" IOd. 1996 - although the numerical relations between reduction in strength, change in molecular size. and reducing power, were usually different in the two processes. The production of reducing power seemed to arise from the production or uncover- ing of aldehyde or glucoside groups. In oxidation processes, a greater or less proportion of these aldehydic groups seemed to go a stage further to carboxyl groups (cf. DorBe, Methods of Celluhe Chemiatry, 1933, Chapters VI and VII; also Hess, Chemie der Zellulose, 1928, Chapter IV).

Thc present views on the structure of native cellulose had been developed as the result of the efforts of a number of workers who had attacked the problems presented by a variety of experimental methods. Chief among those who had studied the reactions of cellulose and its hydrolysis products, and who had established the chemical constitution of its ultimate units was Prof. W. N. Haworth.

The proposed structures for fibrous celluloses in their native forms which met with most support at the present time, had been con- structed largely as a result of X-ray examinations, and the chief workers in this direction had been Herzog, Sponsler and Dore, Meyer and Mark, and Katz.

The smallest unit was the Celldose molecde built up from /?-glucose units by the elimination of water and the formation of glucosidic linkages thus-

-_ CH, OH

, L o < , ,, 4 ,'\/ '. OH H Crll.--O -- CH

\ I '\H H ' d H

4 CH,OH. CHOH. CH-CHOH CHOH. CHO

h I

Crll.

The size of these,chains in normal native cotton cellulose had not been agreed upon, but 100-20(3 might be taken as representing a value not widely removed from the estimate of a number of workers (cf. Kramer and Lansing, J. P h p . Chem., 1936,39,183, for an exhaustive eummary of the literature on the subject). The chains were supposed to be arranged side by side in bundles, probably about 50 chains in the bundle, and such bundles or micellm formed the bricks from which the cotton hair was built. Certain destructive processes could resolve the cotton hair into visible hair-like units or fibrills, and probably these fibrilla formed still another intermediate stage in the structure.

The forces which held the glucose anhydride units together in the chain were assumed to be

primary valency groups, whilst those which caused the chains to adhere IateraJly in the micellse, and the micelh to adhere laterally in the hair, were considered generally to be secondary valenoy forces exercised probably between h ydroxyl groups,

Whether cotton was modified by oxidation or by hydrolysis, the viscosity of a standard solution was always decreased. It waa held that the process of solution in cuprammonium loosened the attachments between the chain molecules so that they existed in dilute solution in the unassociated forni, and

as the length of the molecular chain npH decreased so also did the viscosity in standard solution. It appeared, there-

Acid hydrolysis caused a shortening in the fore, that both acid and oxidising trcat- chain, thus- ment causeti either breakage of the cellulose

chain molecules or such weakening that these chains came to pieces when the material ua8 dissolved.

This breakage could be ascribed to hydrolytic action when produced by acid treatment, but i t was much harder to explain why oxidising treatment must also and of necessity cause breakage or wcakening ofthe chains. The most likely place for oxidising attack to commence was a t the primary alcohol group of the anhydro-glucosidic units and this group probably was converted fimt

M

' I

Sfaudinger and others had shown that

.1

and produced terminal glucosidio groups which had potential reducing properties-

Ocl. 19361 TURNER-“SOME ASPECTS O F THE OXIDATION O P CELLULOSE” 349

, L o \

H ‘ AH

into an aldehyde (which would account for the appearance of reducing properties) and finally in- to a carboxyl group. But why did this conversion seem, of necessity, to cause some shortening of the chain as judged by the change in viscosity ? Meyer and Mark (h. cit . p. 151) had put forward an explanation without any other reference or experimental support. The carboxyl group of an oxidised glucose unit in cellulose was in the /?-position relative to the oxygen bridge, thue-

COOH

A AH

If this bridge were to undergo hydrolysis by the uptake of water, a /?-hydroxy-carboxylic acid would result-

COOH

H 6 H

P-Hydroxy-carboxylic acids were unstable and tended to break down with the elimination of water and the formation of unsaturated acids. The transformation, therefore, of the primary alcohol groups in cellulose into carboxyl groups w;ts held to set up a condition of instability a t the bridge, causing it to be broken readily so that the full change to the more &able unsaturated acid could be completed. Besides the formation of a carboxyl group, the hydrolysis of the oxygen bridge had produced also a glucosidic groupin the same way that acid hydrolysis produced one. The formation of this group would account for the appearance of reducing properties in the oxidised cellulose.

The influence of the modification of the rellulose upon the tensile strength of the fibre was also a matter of great importance. The breaking of a fibre under a sufficiently great load could be imagined to take place in a number of ways, and probably an analogy could be drawn from the processes of yarn breakage in yarns spun from a material of relatively short fibre length. It could be supposed (a) that the lateral adhesion

of the chain molecules and of the mioella in the cellulose fibre was greater than the strength of the attachment between the glucose unita in the chain molecules (in that mse, a fracture of the fibre involved a rupture of some of the principal valencies in the chain molecules without slippege of the micellae or molecules past each other), or (b ) that the fracture of the fibre occurred by slippage of whole molecules or micellae past each other when a sufficiently great load was applied.

It had been calculated from chemical data that the alternative (a) should lead to a cellulose fibre of about twice the normally encountered tensile strength. Also, mechanical comminution ahould give rise to a rapid fall in the cuprammonium viscosity. If, therefore, the slippage mechanism were the practical alternative, i t was interesting to see how the chemical modification of the cellulose by oxidation could alter the ntrengthofthefibre. Thelatterpropertywould be diminished merely by the shortening of the chain molecules even if their specific lateral adhesion remained unaltered, because it might be assumed that the adhesion between one molecule and the next was dependent upon the area of contact between them, and the shorter the molecules, the smaller was this area. Also, it was likely that the replacement of hydroxyl groups by aldehyde or carboxyl groups led to a modification in the strength of the secondary valencies, leading to greater adhesion. The strength of these carbohydrate structures probably was greatly influenced by relatively small modifications in the chemical oonstitutionofthe units fromwhichthey were built. As a parallel example, Haworth had shown that starch waa built up of chain molecules, just as was cellulose, the main difference being that the original units were of the anhydro- a-glucose type; yet the occurrence of strong fibrous structures in naturally formed starches was very exceptional.

The relations between the strength of the fibrous cellulose, degree of ohemical modification, and the numerical value of the viscosity in standard solution also required consideration. Staudinger had put forward evidence to show that the specific viscosity of long-chain substances, if measured in suffioiently dilute solution, was proportional to the molecular length. This principle had been built up, however, from measurements upon compounds in which the molecalar size was almost uniform. All the available evidence showed that degraded cellulose3 were heterogeneous mixtures containing products of varying chain length. A lowering of the viscosity could be produced in two ways. The original long chains could be broken into products of approximately uniform size, or some of the molecules could be left appreciably unohanged, and others intensely attacked and broken into products of quite small chain length. The proposers of the micellar theory, from a study of the absorption behaviour of cellulose, had stated that it was very

360 TURNER-“SOME ASPECTS OF THE OXIDATION OF CELLULOSE” [Oct. IB.fS

much easier for reagents in dilute aqueous solution to penetrate into the surfaces between the micellae than to penetrate between the molecules in the micelle itself. These authors had assumed that intermicellar penetration took place to an appreciable extent only during the swelling of the cellulose. For dilute solutions, therefore, some reactions would take place more a t the surface of the micelle, attacking the outside molecules and breaking them up, and probably working gradually inwards towards the centre of the micelle. This would lead to the formation of a mixture of short-chain products with long- chain unmodified molecules. AU stages between a chemical attack sharply localised a t the micellar surfaces and one distributed over the whole micelle were, of course, possible.

In the localised attack, the diminution in the fibre strevgth might be regarded as caused by the severe modification of the outer layers of the micelle so that slippag- between micellae occurred readily. Where the attack was more widely distributed in the micelle, the loss in strength could be rc g wded as due to a greater tendency of the molecules within the micclle to slip past each other.

A diminution in the cuprammonium viscosity of the oxidised product could be conceived as resulting from different causes according as one or the other types of dqpdat ion mechanism prevailed. In the general attack it might be supposed that many of the cellulose chain molecules were attacked, giving rise to molecular units also of smaller size than the original molecules, but each sufficiently large to contribute appreciably totheviscosityof the solution. Thetotalviscosity of the sample, therefore, would be a summation of the viscosity effects of the constituent units corresponding to the viscosity of a material of lower molecular weight than the original cellulose. It would be smaller, therefore, than the viscosity of normal cellulose. As an alternative to this, in the material in which intense localised attack had taken place, a limiting state might be imagined in which the modified material in the region of attack had been converted into molecules of such short length that they, while yet insoluble in water, did not contribute appreciably to the viscosity. In that case the viscosity would all be contributed by the scarcely diminished molecules in the core of the micelle, e.g. 340% of the total material were subjected to local attack and degraded to such an extent that it could not contribute to the total viscosity, while the remaining 60% were scarcely affected, the viscosity of the material in 0.5% solution would approximate to that of a 0.3% solution of the original cellulose. A further piece of evidence to substantiate this idea of localised oxidation might be forthcoming under special conditions of oxidation. If the fraction of the cellulose attacked were transformed into material of such low molecular weight as to become soluble in water, it should be possible to carry out an oxidation and to cause an

appreciable loss in weight of the original material without observing a vcry grcat diminution of the cuprammonium - viscosity of the residue.

It was considered to be of value to find if Turner, Nabar, and Scholefield (loc. c i t . ) had observed examples of the localised and the general type of attack respectively in their work on the hypochlorite attack of cellulose. In Fig. 1 ,

‘ 3 4 5 6 7 8 9 1 0 1 1 pH of Hypochlorite

FIG. 1

Chemical degradation of dyeing8 of Cibanone Orange H. and of white cotton after treatment with self-buffered hypochlorite solutions (3 g. available chlorine per 1.) for 10 mins. in the dark in the case of reduced and unreduced dycinga, and for 5 hm. in the dark in the case of undyed cotton.

from the paper by these authors, the curve marked “Reduced Dyeings” showed the relation between the cuprammonium fluidity of the modified cellulose, and the pH of the liypo- chlorite solution employed when the treatment with the oxidising agent was carried out for a few minutes only, the oxidation bcing accelerated by the presence of leuco-vat dye on the fibre. The curve marked Undyed Cotton showed a similar relationship in absenco of thc accelerating leuco-dye and with a treatment period of 5hrs. It would be seen that tho rclation- ship was quite different, although identical oxidising solutions were used in each set of experiments. Was it possiblo that one of these relationships referred to a mechanism by which localised oxidation was brought about, and the other to a mechanism in which more general attack had occurred 1 If this view were accepted, it was more probable that the localised attack would occur in the oxidation accelerated by thc leuco-vat dye. In the accelerated oxidation, the oxidising attack was very much more intense than when the accelerating substance was absent,

OCt. I9351 TURNER--‘*SOME ASPECTS OF THE OXIDATION O F CELLULOSE” 35 1

and the speed of oxidation relative to the rate of diffusion of hypochlorite molecules into the cellulose structure would also be much greater. It was reasonable, therefore, to msurne that the intense attack would be localised in the vicinity of the accelerating leuco-vat dye molecules. It was accepted by the exponents of the micellar theory that adsorbed dye molecules were con- centrated on the micellar surfaces of the cotton, and the intense attack, therefore, would be expected to be directed primarily towards the accessible cellulose molecules a t this region. Turner, Nabar, and Scholefield (ZOC. cit.) had shown that in tho accelerated oxidation, there seemed to be a connexion between the change in cuprammonium viscosity and the oxidation potential of the hypochlorite solution employed. It was easier to explain the existence of such a connexion by assuming a mechanism of localised oxidation similar to that suggested.

Some experimental evidence advanced by Rius y Miro (R. R. Acad. Madrid, 1931,24,142) seemed, on first examination, to bear out the suggestion that it was possible to have a localised attack 80 intense that part of the cellulose was reduced to soluble material.

This author measured the potentials of hypochlorite solutions a t different hydrogen ion concentrations and found them to be proportional to the log of the velocity constant of the destruction of a dye by these solutions. He allowed the same solutions to act upon cotton material for a fairly long period and measured the loss in weight of the cotton; he foiind that the rehtionship-

potential = constant x log of loss in weight was approximately true. Considering the possi- bilities of complication during the reaction, Huch a relationship was surprisingly simple.

DIscnssIolv The Chairman (Mr. L. G. Lawrie) said that it

was a curious fact that most of the reactions of cellulose resulted in disagreeable products. Moreover, in many instances, it was necessary to form soda cellulose by treatment with a strong caustic soda before certain reactions would take place. This fact appeared to fit in with some of the Lecturer’s speculations on the opening up of tJhe miceIlar structure of cellulose. The tendering of cotton containing a leuco-vat dye during coupling with Variamine Blue Salt was of interest. Incidentally, he had always regarded Variamine Blue Salt as one of the most difficult coupling agents. The oxidation reaations of mannitol seemed to be very similar t o analogoue reactions applied to cellulose.

Dr. D. Ward thought that the Lecturer had done much towards making clear the mechanism of degradation in cellulose chains. Would i t not be better to try and synthesise a di-mannitol compound in which 2 mols. were linked by an ether group, in order to study what happened

a t the ether group during oxidation reactions ? If it were not possible to synthesise a substance with -CHOH groups between the end groups, such a study might be attempted with saturated chain compounds whioh did not contain hydroxyl groups. The Lecturer had referred to the possibility of cellulose molecules being held together in the micelles by means of secondary valencies. It might be imagirted that ruicellnr formation took place by virtue of the hydroxyl groups in adjacent molecules forming co-ordinate links.

The Lecturer mid that he could not say whether an ether linkage between two mannitol groups was equivalent to the oxygen-bridgd linkage in cellulose, because the latter was not a true ether linkage. If it were assumed that in the celIdose chain itself the primary alcohol groups were the first groups to be oxidised, mannitol was an ideal substance to use for studying oxidation effects of the type under discussion; it had a primary alcohol group at each end of the chain. He would like Dr. Ward’s opinion as to whether the change of the primary alcohol groups of cellulose into aldehyde or carboxyl groups would lead to a greater or lesser attraction between parallel cellulose chain molecules ‘2 If i t led to a lesser one, it would explain, in part, why oxidation caused weakening, if it were assumed that the weakening occurred because of the change in lateral adhesion between the chains, and their relatively greater ability to slip past each other.

Dr. D. Ward said that an explanation on such lines was possible if the lateral adhesion of the cellulose chains was supposed to be due to the existence of co-ordinate links between the primary alcohol groups of one chain and hydroxyl groups of an adjacent chain. The co-ordinate link might either be direct or through the intervention of water mols. In both cases it was plain that any change fundamentally affecting the primary alcohol grouping would break such links, e.g. on oxidation, -CH,-OH would become -CHO, and a co-ordinate link

of the type -CH,.OH +OCH\, = / which might

be assumed to exist in normal cellulose chains, would be eliminated.

Dr. S. M. Neale said that probably the Atructure of the cellulose fibre was not of a uniform brick-like formation; in some parts of the fibre there might be a parallel array, and in others crossing chains which had a poor arrangement reverting to a good arrangement.

The Lecturer said that he thought that Dr. Neale’s suggestion was very useful in developing the idea of localised progressive attack by reagents in dilute solution.

Mr. G. M. Williams said that he remembered a case in which cotton cloth contaminated acci- dentally with acetic acid, was wound on to a copper drum where it came into contact with

362 BREWIN-‘‘TEE WORSHIPFUL COMPANY OF DYERS” [Od. t 9 a

a recently soldered rivet. As a result, traces of copper were deposited on the cotton. The cloth was then treated with linseed oil, which was oxidised overnight in a stream of hot air. Next morning, holes were observed in the cloth.

The Lecturer said that tendering of cellulose materials when impregnated with oils which had to be oxidised was a common experience.

Oxidation of ethylenic bonds often gave rise to recognisable peroxide-like substances, so that there might be this distinct step between the oxidation of the drying oil and the oxidation of the cellulose.

Mr. L. Thompson asked the Lecturer if he could suggest any way of estimating the influence of mercerisation upon the strength and viscosity of cotton ?

The Lecturer said that he could not. If tenderirg took place during mercerisation, it would appear that, accordirg to the micellar theory, a fibre structure different from that of the or’ghal cellulose in which there was a more ready access of oxygen was involved.

Dr. Neale said that in the acceleration of oxidation by leuco-vat dyes, i t had been suS;sted that local effects m’ght occur on the outsides ofthe micelles, and it was to be expected that material oxidised in such a way would show high solubility in caustic soda.

The Lecturer said that he had not any information which supported the suggestion. The products of modification of accelerated oxidations of cellulose should be investigated for other properties as well as fluidity. One line which should be taken was the fractionation of the oxidation products in order to ascertain whether there was any relationship between the intensity of modification and the distribu- tion of products of different molecular size in the modified material.

Mr. G. F. Davidson said that work had been done in regard to the relationship of fluidity in mixtures of cotton and rayon. There had to be a large proportion of rayon before there was much effect. Probably half the cotton would have to be reduced to small chains before there was an appreciable efEect on the fluidity.

The Lecturer said that he doubted whether the comparison between rayon and cotton mjxtures and the system he had suggested was a fair one. The molecular size in the rayon was still fairly large. Approximately the same fluidity could be obtained with a 2% viscose solution as with 0.5% solution of scoured and carefully bleached cotton. Consequently, molecules of the viscose rayon were still acting as appreciably effective units in contributing to the viscosity of the solutions.

Mr. Davidson said that rayon did not follow the simple mixture law.

LONDON SECTION

Meeting held a t Dyers’ Hall on 4th March 1935, M i . F. W. WALKEB in the chair.

The Worshipful Company of Dyers ARTHUR H. BREWIN

In an article on the History of the Wor- shipful Company of Dyers (Jubilee Issue of this Journal, 1934), the present author wrote-

“It is customary to preface a consideration of the History of the Worshipful Company of Dyers with a lamentation upon the scanty material available . , . . that a person having an abundance of time and energy would be able to modify this lack of knowledge to some extent, but he (the present author) cannot claim to have brought new facts t o light himself, nor to have improved upon that which has been written already. His aim has been to assemble the labour of others into a composite whole, taking from each whatever seemed pertinent or worthy of preservation.”

Since the foregoing article was written it has not been possible to obtain much fresh light on the subject, either a t home or during the present author’s recent travels abroad. Indeed, the citizens of the New World classed the Worshipful Company in the same category as their own Rotary Clubs, Kiwanis, Buffaloes, etc. But without any disparagement to these excellent societies, it will be agreed that the adjective “Worshipful” sits a little awkwardly upon them; for evcn when Columbus set sail, our City Guilds were ancient institutions.

There is evidence of their existence even prior to the Norman Conquest of England. On the whole, they consisted of certain individuals who appreciated the advantages to be gained by co-operation. These Guilds were very similar to institutions which existed under the Roman Empire and aimed a t uniting men by common worship and social intercourse; they also protected trades against unjust taxes and had an eye to their internal regulation. Moreover, their benefits did not come to an end with a member’s life, for in some cases the expenses of a funeral, complete with sacrificial ceremony, were dis- charged by the Guild.

The English Guilds have been described as “fraternities by voluntary compact, to relieve each other in poverty and to protect each other from injury. Two essential characteristics be- longed to them-the common banquet and the common purse. They had also in many instcanoes a religious, sometimes a secret, ceremonial to knit more Gmly the bond of fidelity. They readily became connected with the exercise of trades, with the training of apprentices, and with the traditional rules of art.”

Thus, the Guilds were of two kinds-social or religious, and Craft Guilds. Now the trades of London, which had their recognised quarters in the city, began to be regulated by these Guilds.

Documents

Some Aspects of the Oxidation of Cellulose