THE JOURNAL OF THE

Society of Dyers and Colourists VOI. 67-NO. 3 MARCH 1941 Isaud Monthly

COMMUNICATIONS

The Reactivity of the Sulphur Linkage in Animal Fibres. Part V- Methods for Realising a Permanent Set at Low Temperatures, with

Observations on the Repair of Damage in Animal Fibres. ,J. B. SPEAKMAN, J. L. STOVES, A N D H. BRADRURY

Three methods of rralising a permanent set in strained animal fibres a t low temperatures hnve been described in a previous paper'. In one of these methods, the fibres are treatctl fir& with a sodium sulphite-so&um bisulphitc solution a t p H 6 and 35" ('., and then with a solution containing an oxidising agent, ii metal salt, or both. Disulphide bond breakdown and fibre relaxation are promoted by the rctiucing agent, whilst aftertreatment with the oxitlising agent or metal salt causes the necessary linkage rebuilding for permanent set. The possibility of using metal salts to re-form linkages in a relaxed structure was established with barium chloride, but the relative merits of different metals and metal salts were not, investigated. It is the first purpose of the present paper to remedy th is deficiency.

The preceding method of setting animal fibres was based on the discovery that an aqueous solution of sodium sulphite and aodiuni bisulphite is most effective in promoting clisulphide bond breakdown when the sulphites :we present in such proportions that the pH vnlue is 6. It was nfterwnrds found2 that concentrated solutions of sodium bisulphite in ;ticohol-water mixtures containing 40-45*,,, by volunie of alcohol are fnr more reactive than t8he aqueous solution of sodium sulphite and sodium bisulphite a t pH 6. Thus, in 15 min. at 35" C'. , tlisulphide bond breakdown is so severe that the fibres nre highly swollen and rubbery, ill1liost as if they had been boiled in an aqueous solution of sodium bisulphite. The setting of such highly relnxed structures with oxidising itgents or metal salts presents niiiny difficulties, which are discussed in the second section of the present paper.

lnterest in thc problem of linkage rebuilding in highly relnxed fibres is not, however, restricted to the possibility of devising ION temper. a t ure

A?.

Aetting processes. Any method suitable for this purpose would be equally successful in repairing fibre damage caused, for example, in bleaching with sulphites, or in stripping dyed materials with sodiuni hydrosulphite. In addition, the case of linkage rebuilding with metal salts possesses a peculiar significance. If, as seems probable, metal-containing linkages of the -S-Ba-S- and related types are formed, the resulting fibre should be more resistant to attnck by alkalis and alkaline reducing agents than the untreated fibre. Thus, the study of linkage rebuilding in highly relaxed fibres may point the way to the preparation of highly resistant fibres in which the disulphide bonds are replaced by metal-containing linkages.

EXPERIMENTAL (1) The Relative Merits of different Metal S a h

as Agents for Linkage Rebuilding. Human hair was selected for experiment on

account of the uniformity of the fibres along their length. The hair was purified by extraction with alcohol and ether successively in n Soxhlet apparatus, followed by waehing in distilled water. A 5-cm. length was taken from the root end of one of these fibres and mounted in the stninless steel apparatus shown in Fig. 1 . After measuring its precise taut length by means of a travelling microscope, the fibre WUP

irnniersed in distilled water a t 26" C . anti stretched 40% by means of the screw. The apparatus was then transferred to a tnll beaker containing 500 C.P. of a sodium sulphite-sodium bisulphite solution a t pH B and 35" C. Thr solution was made up by dissolving 22.06 g. Nn,SO,.7H,O and 30.88 g. Na,S,O, in water, adding 25 r.c. absolute alcohol a s nntioxidant,, and then making up to 500 c . c . with difltilled water. During the treatment, which wns carried out for 15 min., temperature control

74 SPEAKMAN, STOVES, & BRADBURY-"SULPHUR LINKAGE IN ANIMAL FIBRES." March 19-11

was n~iii~~t;~iinetl by inemis of i t wiiter thermost;~t. The fibre WSLS then trmsferred, without, washing. to 500 c.r, of ti 0~1M-sO1ution of zinc. nulphatr in 0.1 N-sUlphllric wid a t 35" C. for 15 niin. After being washed in threc chttnges of dintilled water, tht. fibre \ v w released in boiling wttter, from which i t was withdrawn after 1 hr. The nppnrtxtns nnd the film were then ttrictl, so

F IBAL

Pl

Fig. 1

thitt the dry length of the fibre could be measurett ;~nd the perc.entiige Net calculated. Similar experiments were carried out with other nietd salts, and the results are summttrisetl in Table I. Except where indicated, the nietiil salts ( 0 . 1 ~ ) were dissolved i r i t i 0.1N-solution of the corresponding arid.

By far the most effective agent for linkage rebuilding is mercuric acetahe, and since mercuric chloride is useless, it seems probable that the salts of weak wids are to be preferred for linkage rebuilding processes, especially as the acetates of copper and chromium are more effective than the corresponding sulphates. The metal itself is not without importance, however, the best results, after mercury, being given by Lon nnd copper,

TAnm I

.- 1 -

. .. " ' I . . . . . r41lalri,l~ . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . , . . . . . . . . . . . .

:: set.

~ _ _ .... ~- .........

In ordcr to examine the stubility of the i i e ~ honds, fibres set in the above ninnner w e r ~ subjected to the following tretitrnents- (a) Boiling under reflux for 1 tir. with 0 . 1 ~ -

hydrochloric acid; (6) immersion in 0.1 M-Sodillm carbonatc

solution a t rooni ternperitture for 21 hr.. followed by release in boiling water for 1 hr.; or

( c ) immersion in H,S-wixter at, room temperature for 34 hr., followed by rele:iw in boiling water for 1 hr.

After these treatments, the fibres were dried in absence of tension and the residual set, determined for comparison with the origind set. Typical data are given in Tnble 11.

TABLE 11 ~ ~~ - _ _ .

I 1 .IpW " z ( ! 0 , 3 , 9,s Mrrriiriu iicctatr

Ferrous sulphate 0.0 0.9 I 1 1 . 0 8.7

Copiier siilpliatr , IO.!J I 7.6

1 g:; 11.i

I 1 .IpW " z ( ! 0 , 3 , 9,s Mrrriiriu iicctatr

Ferrous sulphate 0.0 0.9 I 1 1 . 0 8.7

Copiier siilpliatr , IO.!J I 7.6

1 g:; 11.i

Although mercuric. ac.ctiLte is highly effwtivc in forinirig new bonds between the pcptide chains of the relitxed fibre, the net\ linkages are by no means completely stable to itcitl, alktili mcl hydrogen sulphide. The full measure of instability is revealed by successive treatments with hydrogen sulphitie and alkali. For example, a fibre to which a set of 18.00/,, had been imparted by mercuric ncetate, rctaincd only 8.7'%, set after treatment with H,S-water, and when this was followed by trenttncwt with sodium carbonittc solution, the residual set was merely 34'%, , C'ot)i)er-containiIig linkages are likewise unstable in dkal i and H,S-water, but itre uiiaffectetl by hydrochloric. wid. Ferrous snlphate, on the other hand, gives bonds which .

M n ~ h 1941 SPEAKMAN, STOVES, & BRADBURY-"SULPHUR LTNKACiF: IN ANIMAL FIBltES." 75

are stitble to ;wid and H,S-water, and are only slightly affected by alkali I t seems probable that stability, where it exists, is conferred by cw-ordination of the metal atom with reactive side chains, e.g. basic side chains, in the fibre, and such co-ordination will, in turn, increase both the magnitude and the permanence of the set acquired by the fibre.

In the light of the preceding results, which have a direct utility in connexion with one of the processes for imparting a permanent set to animal fibres a t low temperatures, one of the better metal salts, viz. copper sulphate, was chosen for comparison with an oxidising tigent in the setting of highly relaxed fibres. (2) LinlcugP Rebuilding in Highly Relaxed

As has already been indicated, concentrated solutions of sodium bisulphite in alcohol-water mixtures containing 4045'71, by volume of alcohol cause such severe disulphide bond breakdown in 15 min. a t 35" C. that the fibres are highly swollen and rubbery, almost as if they had been boiled slack in an aqueous solution of sodium bisulphite. So rapid and effective is this method of relaxing strained fibres a t low temperatures that there is every reason to hope that it may form the basis of a successful low-temperature setting process. Considerable difficulty was, however, encountered in attenipting to set such highly- relaxed structures by the orthodox methock, using oxiclising agents or metal Balts an setting agents. A study of linkage rebuilding in highly- relaxed structures was therefore undertaken, choosing for the purpose the most difficult of a11 cases-fibres relaxed by being boiled slack in So/,, sodium bisulphite solution.

The general method of experiment was as follows-A 5-cm. length of human hair, taken from the root end of the fibre, was mounted in the setting imtrurnent shown in Fig. 1. After measuring its taut length by meam of a travelling microscope, the fibre was slacked by turning thc screw no as to lower the upper clamp. The apparatus was then immersed for 1 Iir. in 400 c.c. of a boiling, freshly-prepared, 57" solution of sodium metabisulphite con- taining 6% by volume of alcohol as antioxidant. During this process, disulphide bon& undergo disruption according to the equation3- R-S-S-R + NaHSO, = R-SH + R-S-S0,Na and, although some linkage rebuilding also occurs, the breakdown process is predominant.

The apparatus was then washed in three changes of 500 C.C. of tap water, for 2 min. each time, followed by distilled water. When the fibre was again drawn taut in distilled water, its length was invariably found to be about loo/, less than the original length, even though the latter was measured in air. In order to determine the effectiveness of any reagent or treatment in promoting linkage

Fibres

rebuilding, the rehxetl fibre was stretched in tlistilled water and, after measuring its n t w length, treated in the desired niitiuier. It was then washed in tlixtilled water, slacked, and boiled in water for I hr. While still slack, the fibre was allowed to dry in air, and its taut length was then determined. Any linkages formed while the fibre is in an extended state oppose subsequent contraction, and the permanent set acquired by each fibre was taken as a measure of the extent of linkage rebuilding. A series of experiments was performed with fibres a t various extensions, details of the reagents employed and the results obtained being given below.

(a) Oxidising Agents-(i) Potuvsiurtb Per- sulphate-Each fibre was boiled for 1 hr. in 5% sodium bisulphite solution, washed, stretched and then immersed in O.l~-potassium persulphate solution for 1 hr. a t 25" C. When relaxed fibres are stretched, side chain rearrangement takes place, and disulphide bonds are re-formed from cysteine side chains during treatment with potassium persulphate-

The R-S-SO,Na groups formed at the same time as the cysteine side chains may also take part in linkage rebuilding, either directly or as cysteine side chains formed during the washing which precedes treatment with the oxidising agent. An indication of the extent to which linkage rebuilding is promoted by potassium persulphate in relaxed fibres t t t different extensions is given by the (1atiL of Tablc ITI, illustrated by Fig. 2.

2 R-SH + K,S20 = R-S-S-R +K,SO,+ H,S04

TAD1.E 111 ____ -

20

10

k- t t : o .O

- 10

- 20

- 30 -10 0 10 20 30 40 50 60

",, EXTENSION HI& 2

Both the extension and the set are calculated as percentages of the initial length of the intact fibre,

The failure of the fibres to iicquire n positive set, even a t 60°,:, extension, is ii striking illustrfdion of the difficulty of rebuilding linkages in highly reltixed structures. At low r,utensions, part of t l i c difficulty nitby well be due tlo the iiiolecwlur disorientation which trccoriipaiiies clisulphide bond breakdown, ils is showti by the fiwt that the set incrc.ases (supercoiitriic.tioti tliminishes) with iiwrcasing niolecular re-orientittion a8 the fibres are stretched. In addition, the high degree of swelling of the r e l a x d fibres must oppose linkage rrbuilding by scp:ir:iting the peptide chins. Further experiments were t,hereforc, carried out with sotlum sulphate presetit, in the potassium persulpliate solution to depress swelling during the process of linkage wbuilding .

( i i ) Potassiuwr Prrsirlphnte and 8odiwtr Sirlpirate-Each fibre, after 1 hr. release in boiling 5"/:, sodium bisulphite solution, W ~ R washed and stretched hi water It was then immersed in M-sOdiUm sulphate solution for about 30 sec. before treatment a t 25" C. with 0.1 M-pOtaRsiUm persulphate solution containing sodium sulphate in M-concentration. After 1 hr., the fibre was removed, washed, and released in boiling water for 1 hr . Data for the resulting set of fibres stretched to various extents before oxidation are given in Table [V, illustrated by Fig. 2.

T 4 I 1 1 R IV ~~

Extension ( X )

- 5.3 0.0

104 31.3 40.5 484 55.0 50.7

In agrt'ement with precwling iwgument, the set obtained in presence. of ti swctlliiig depressor is greiLter thm in its ttbsencc. The extent to whit+ oxitlation promotes linkage rebuilding is revedetl when the preceding data iLre Cornpared with those obtained in blimk experiments with sodium sulphttte solution. Each fibre was boiled sliwk in 5': (, socfiuni bisulphite Bolutioti for 1 hr. before being wasi id in water, ~t~retched in M-sociium sulphatr solution ~ i ~ n d then iinniersed in M-sodium sii lphth~ solution i i t

2.5'' C. for 1 Iir. The resulting dtitiL w e given in Tixble \', illustrated by Fig. 2.

'L'AIII.I> V

-23.5 - 17.8 - 14.7 - 12.6 - 13.0 - 12.0 - 1 l . G - 8.0

( 6 ) Mettcl Salts-C'orrespontlilig experinients to the preceding were carried out, with rz metal salt as the linkage rebuilding agent, instead of potassium persulphate.

Copper A"ulplrrr/~-As before, cacti fibre w a s boiled slack in 5" ,, sodiiiiii bisulphit,f solution, witshe d in threc ehangis of water, stretched in water a t 25" C., iriid then iinniwsetl in 0.1 M-copper sulphate solution t b t 25" C'. for 1 hr. A t the end of this time. thc fibre was washed and released in boiling water for I hr. The tlatir ohttrincd tire given i l l Tithltl \'T, illustriLte(1 by Fig. 3.

( i )

'I'<IlI,E 1 I

1.2 3.1 0 1 0.0 0 2 11.3 16.6 21.6 27.7 35.4 47.0 40.8 53.0 56.0

-I0 0 10 20 30 40 50 60 "0 EXTENSION

Fig 3

The extent, of linkage rebuilding is clcarly very small, even i L t N"/" extcnxiori. atid further t.xprriinents were carried out with :L solution containing copper sulphate and sodium sulphatc.

Popper Sulphnte nntl Sotlautri Srdphte- The usual procedure was followt (1, except tliiit the rebuilding agent consisted of i~ inixture of 200 c.c . 0.1 M-copper sulphate solution ant1 100 G.U. M-sodium sulphate solution. Linkage rebuilding was allowed to proceed for 1 hr. at 25" C., and data for the percentiige set, acquired by the stretchcd fibres ;Lrr givrw in Table VII, illustrated by Fig. 3.

Although copper sulphiLte is niorc, effective in presence of sodium sulphate than in its ;Lbsence, the extent of linkage rebuilding is clearly iiiiich smaller than when oxidising agents are used. In consequence, further experiments were carried out with mercuric tiert,ate, whic4i has

(ii)

JJGn'h 1041 SPEAKMAN, STOVES, & BRADBURY-

( i i i ) Nevcuric Acetate-A O.IM-solution of mercuric acetate in O.1N-acetic acid was used to promote linkage rebuilding, the stretched fibres being immersed in the solution for 1 hr. at 85" C. Data for the set retained by the fibres, after release in boiling water for I hr., are given in Table 1'111, illustrated by Fig. 4.

40

30

20

0

- 10

- 20

- 30 -20 0 20 40 60 80

:'b EXTENSION

Flg. 4

The extent of liiikage rebuilding was rrduced when a solution of O.l~-mercuric acetate, M-sodium acetate and 0.1 N-iLCetiC acid was used, probably on account of the greater swelling of the fibres in this medium. A summary of the results is given in Table IX.

-"SULPHUR LlNKAGE IN ANIMAL FIBRES." 77

TABLE Ix ~ - -

The results obtained with a solution of iiiercuric acetate in acetic acid give the first real indication that metal salts may be used successfully to re-form linkages in rrlaxed fibres. Its effectivenew may well be due to the fact that the new bonds, like other mercuric compounds, are ionised only to a small extent. This view is supported by the fact that mercury salts, unlike the salts of most, other metals, are highly successful in repairing the damage sustained by animal fibres in peroxide bleaching. Typical load-extension curves for a fibre in water a t 22.2" C., before and after treatment for 20 hr. with 10-vol. hydrogen peroxide, buffered to pH 12 with caustic soda and boric acid, are given in Fig. 5. A measure of the - UNTREATED

>-x-;: HZOZ 0-D-0 H202 -+ Hg (0OC.CHj)Z

0 I0 20 30 LOAD (I.)

Fig. 5

degree of daiiiage sustained by the peroxide- treated fibre is given by the reduction in the resistance to extension, whiclt amounts to 41.91Jb for an extension of 30')". After treatment with a solution. of 0.hi-niercuric- acetate in WlN-acetic acid for 17 hr., followed by washing in water, the resistance of the fibre to extension is 2.00, greater than that of the original, untreated fibre for 3U0, extension. Besides giving a second illustration of the effectiveness of mercuric acetate for linkage rebuilding, the preceding experiments serve to illustrate the manner in which metal salts may he utilised in repairing fibre damage, once the principles involved in linkage rebuilding have been established.

As a linkage-rebuilding agent, however, mercuric acetate is of purely ;wademic interest. In agreement with earlier results, the new bonds wrrc! found to be readily broken by hydrogen sulpliide , although not Aeriously affected by sodium carbonate solution. As before, the bisulphite-treated fibres were

78 SPEAKMAN, 8TOVE8, & BRADSURY-"SULPHUR LINKAGE IN ANIMAL FIBRES." Ofarrfr 1.951

__ Extan- slou (%)

- 7.0 I 0 1 18.7 28.0 4 0 8 48.1 89.4

stretched in water, set in a solution of 0 . 1 ~ - mercuric acetate in 0.1N-acetic acid, and then released in boiling water for 1 hr. They were then treated with either (a) 0.1 M-sodium carbonate solution for 17 hr. at room temperature, or ( b ) a saturated solution of hydrogen sulphide in distilled water for 3 hr. at room temperature. After being washed, the fibre8 were again released in boiling water for 1 hr. Data for the residual set, of the various fibres are givcn in Table X, illustribted by Fig. 4.

TABLE X

~

Yet (%) -204 -17.9 -167 -16'0 -14.5 -13.7 -11.2

--

FIiiuI Hct (%)

- 7 4 0 8 103 26.4 400 51.1

- 8.0 -26.5

10.6 - 5.2 2114 2.3 374 7.8 500 199 50.0 380

P B -14.8

-25.1 -18.3 -14.0 -13.0 - B.11 - 0 6

Exteiialon I (%)

Flnul Hct (%)

(c) Alkali untl Oxidising Agents-While i t is true that the effectiveness of mercuric acetate in linkage rebuilding may be referred, in purt, to the fact that the new bonds are ionised only to a limited extent, the failure of oxidising agents and other metal salts to give similar results is disconcerting. One possibility is that the R-SS0,Na side chains, formed by disulphide bond breakdown, are by no means fully utilised in linkage rebuilding, except with mercuric acetate. In the effort to promote linkage rebuilding, further work was carried out with fibres treated so as to make use of the thiosulphate side chains.

It has already been shown that the ability of oxidising agents to impart a permanent set to bisulphite-treated fibres is increased when the latter are treated with alkalis prior to oxidation4. During an investigation of this phenomenon, preliminary experiments showed that immemion in a 20% (by volume) solution, of 0.880 ammonia for 15 min. a t 50" C. gave a mtisfactory result, Treatment for longer times, e.g. 30 min., was less effective on account of fibre damage. The beneficial effect of alkali was established in the following manner. As before, each fibre was boiled slack in a 5% solution of sodium metabisulpbite for 1 hr. The fibre was then washed, stretched in distilled water, and transferred to a 2Oy, (by volume) solution of 0.880 ammonia for 16 min. at 60" C. After being washed in three changes of water,followed by M-sodium sulphate solution, the fibre was set by immersion in a solution of O*lM-potassiunl persulphate and M-sodium sulphate for 1 hr. a t 25" C. The fibre was then wished and released in boiling water for 1 hr.

Blank experiments were also carried out with fibres which, after being treated with sodium nietabisulnhitc and ammonia au above, wcrc

immersed in ~-8odium sulphntc sohition for 1 hr. at 25" C. before being releascd in boiling water for 1 hr.

AH the fibres used in thelie experinleiits were from a different mpply of human hair, earlier experiments omitting treatment with ammonia. were repeated. After being washed, tho bisulphite-t,reated fibres were stretched iind immersed in either ( a ) M-sodium d p h a t e solution, or ( b ) a Rolutioii of 0 . 1 M-potassium persulphate and M-sodium liulphate for 1 hr. at 25" C. They were then relewcd in bailing water for 1 hr.

Data for the percentage set rehined by the fibres used in the above four sets of experiments arc givcn in Table XI, illustrated by Fig. 6.

TABLE XI - I I

- 8.3 -10.0 - 8.6 11.2 -152 10.5 244 -12.5 19.5 51.3 -10.2 32.0 37.3 - 9.8 40.1 51.8 - 4.2 151.2 68.7 - 2.4 50.3

I , I I I

b ~ - - o NazSOn ;:-;+): NHqOH -+ NazSO4 , , , NazS04 + KzSeOs .,.__ I.-...

20

10

- 10

- 20

-30 -I0 0 10 20 30 40 50 60

'% EXTENSION

Ng. 6

Although treatment with ammonia has a damaging effect on the fibres, as ie indicated by the lower value of set obtained with ammonia-treated fibres a t the lowest extensions in corresponding caseu, comparison of the data obtained with sodium sulphate on fibres which have and have not been treated with amnionia, leaves no doubt that treatment with aninioilia alone promotes linkage rebuilding. The linkages are, in all probability, disulphide bonds, because niercapto-compounds and thiosulphates ilrc known to react in alkaline solutioii as follow6-

Since side chain rearrangemrnt takes p1ac.e when bisiilphite-t8rcated fibres i i w Htrctched, tho oy&iiie itnd thiosulphatc side chains are

RSNH,+ R-SSOS-NH,=RS-S.R+ (NH,)ASO,.

Morch 1041 BPEAKMAN, STOVES, & BRADBURY--"SULPHUR LlNKAGE IN ANIMAL FIBRES." ?'a

not always favourably placed for the occurrence of the above reaction. Aftertreatment of the itmmonie-treated fibres with oxidising agents will, therefore, enhance the set by re-forming disulphide bonds from neighbouring cysteine side chains, as is indicated by the fact that the maximum set is imparted to bisulphite- treated fibres by treatment with ammoilia, followed by potassium persulphate in presence of sodium sulphate. The last process is, of course, superior to the treatment of relaxed fibres with potassium persulphate and sodium sulphate alone.

If, however, the relaxed fibres are treated with a 20% (by volume) solution of 0.880 ammonia a t 50" C. before being stretched, the disulphide bonds which are formed render the supercontracted state permanent, even though the fibres are subsequently stretched and treated with oxidising agents. Data for the set acquired by relaxed fibres as a result of being treated slack with 200/, ammonia a t 50" C. for 15 min., followed by extension and treatment with it solution of M-sodium sulphate and O*lM-potassium persulphate for 1 hr. a t 25" C., are given in Table XII.

TABLE XI1

lnstead of treating relaxed fibres at different extensions with ammonia and potassium per- sulphate separately, i t should be possible to combine the two treatments, if preceding argument is correct. This possibility was examined by treating relaxed fibres a t 50" C. and different extensions with solutions containing either ( a ) 20% by volume of 0,880 amnionia and O*lM-pOtassium persulphate, or ( b ) 20yu by volume of 0.880 ammonia, 0.1~- potassium persulphate and M-sodium sulphate. Data for the percentage set retained by the various fibres after release in boiling water for 1 hr. are given in Table XIII, illustrated by Fig. 7.

TABLE XI11 ~

NH40H+K28208 NH40H+KzSzOsi KnzY04 ~- ~ _ _ _ -

- 4.2 - 2 8 1 ' -6.4 -26.0 - 14.8

294 - 14.6 24.8 - 5.1 2 0 4 -17.1 1 20.1 - 7.8

Comparison of the two sets of data indicates that potassium persulphate is incapable of performing the dual function of oxidising agent and swelling depressor, but the combined

-10 0 10 20 30 40 50 60 % EXTENSION

Pig. 7

treatment with ammonia, potassium prrsulphitte and sodium sulphate is just as efficient as treatment with ammonia, followed by potawiunl persulphate and sodium sulphatc (Table XI). To use alkaline oxidising agents for linkage rcbuilding is, however, anomalous, because they are capable of destructive attack on the disulphide bonds they are intended t o re-form. If the combined treatment is adopted, either in setting processes or to repair fibre damtige, the concentration of alkali must be carefully chosen so as to conserve the bonds formed and avoid bleaching, in cases where this would be undesirable.

(d ) Alkali and Metal Saltu-In the light of the preceding results, it seemed probable that improved linkage rebuilding and set might also be realised with metal salts if the bisulphite- treated fibres were made alkaline with ammonia. As before, the fibres were boiled in 5% sodium bisulphite solution for 1 hr., washed, stretched to the required extent, treated with ammonia (20"/, by volume of 0.880) for 15 min. a t 50" C., and then immersed in a solution of 0.h-copper sulphate and M-sodium sulphate for 1 hr. a t 25" C. Data for the percentage set retained by the various fibres after 1 hr. release in boiling water are given in Table YIV, which includes corresponding results for fibres Het in a solution of 0.lM-copper sulphate and M-SOdiUln sulphate without previous treatment with ammonia.

TABLE XlV

-28.3 - 19.2

19.0 - 164 27.1 - 14.9

3*4 - 12.1 "9 1 -114

- 12.3 - 84

60.2 - 6.8 5 2 4 - 4.3 60.8 3.8

The two sets of results make it clear that the treatment of bisulphite-trcated fibres with

80 SPEAKMAN, STOVES, & BRADBURY-"SULPHUR LINKAGE IN ANIMAL FIBRES." Lvfurdb 1041

itmmonia causes only a slight improvement in the extent of linkage rebuilding. Further, since the treatment of relaxed fibres with ammonia promotes disulphide bond formation, the number of met,al-containing linkages in the set fibres must in any case be small. Attempts were, however, made to combine the treatments with alkali and metal salt in order to increase both the degree of set and the number of metal-containing linkages. The fibres, which had been boiled in sodium bimlphite solution in the usual way, were Htretched in water and trhen immersed for 1 hr. in one of the following media a t 50" C.-

(i)

( i i ) ( i i i )

Data

A basic chrome aluni solution, prepared by mixing 100 c.0. of 0.1666~-chrome alum with 31.43 C.C. of 1.0604~-ammonia, and ageing for 1 hr. a t 50" C. before use. O.5M-sodium tungstate solution, pH 8.55. O-5~-sodium aluminate solution, pH 11.5 approx. for the percentage set retained by the

various fibres after 1 hr. release in boiling water are given in Table XV.

TABLE XV

Basic Chronic Alum -

Extcn- I SiOll (%) 1 (%)

- 0.2 -21.3 10.9 -12.8 1 0 5 - 8.6 2 0 0 - 5.3 40.7 - 0.1 50.5 2.8

In the belief that the various salts might serve both as swelling depressors and agents for linkage rebuilding, sodium sulphate was omitted from the solutions, but some advantage might accrue from its use. Despite its high alkalinity, sodium aluminate is singularly effective in promoting linkage rebuilding in bisulphite- treated fibres, as shown in Pig. 8, where it is compared with a solution of copper sulphate slid sodium sulphate (Table XIV). - N a A Q

Y-'-X CuSO4 + NazS04

At high extensions, the set given by sodium aluminate is a8 high as that due to HucceHsivr treatments with ammonia and itn oxidising agent in presencc of (I swelling depressor.

s U M M A R Y AND C'ONCLl1SION

In i~ previous p a p d , it has been shown that a satisfactory permanent set may be imparted to strained fibres a t low teniperatures by successive treatments with a sodium sulphite- sodium bisulphite solution a t pH 6 and it solution containing either an oxidising Rgerit or a metal salt. The comparison of different metal salts as setting agents, which has now been undertaken, has shown that among the simpler compounds the best results are given by salts of weak acids, e.g. acetic mid. The metal itself is not without importance, however, mercury, iron and copper being the most successful of those examined. In the case of mercury , the met a1 - containing linkages respon - sible for set are by no means completely stable to acid, alkali and hydrogen sulphide, but iron-containing linkages ere singularly resistant to these reagents. An interesting possibility is thus revealed. Once the laws governing linkage rebuilding have been established, it should be possible to prepare highly-resistant animal fibres by converting the whole of the disulphide bonds into metal-containing linkages.

The preceding method of setting strained animal fibres at low temperatures was based on the discovery that aqueous solutions of sulphites are most effective in promoting disulphide bond breakdown and fibre relaxation when the pH value is 6. It has since been found3 that concentrated solutions of sodium bisulphite in alcohol-water mixtures containing 40-45'$& by volume of alcohol are even more reactive with the disulphide bond. In 15 niin. a t 35" C., disulphide bond breakdown is so severe that the fibres are highly swollen and rubbery, almost a,s if they had been boiled in an aqueous solution of sodium bisulphite. The setting of such highly relaxed fibres presents many difficulties, which have been studied with fibres relaxed in boiling sodium bisulphite solution. Two causeg of difficulty were found to be associated with the high swelling and molecular disorientation which accompany severe disulphide bond breakdown. As regards swelling, improved linkage rebuilding was realised with both osidising agents and metal salts when the solutions coiit,ained sodium sulphate ab: swelling depressor. The clifliculty of molecular disorientation \\as overcome by stretching the relaxed fibres to re-orient the molecules, but the sct imparted by after- treiitment with oxidising agents or mt%al salts was diseppointingly low. It seenictl likely, therefore, that t8he -S-fiO,Nii groups formed by bisulphite attack 011 cystine linkages w ere not being fully utilised in hlkagc rebuilding.

M a d r 1941 SPEAKMAN,STOVEB, & BRADRURY--“8lTLPHURLTNIL\C~E INANIMALFTRRES.” 81

This view W ~ H confirnietl by the discovery t h t ~ t trlit’ trcdment of reluxecl fibres with imiinoniir, nfter extension md prior to oxiclcrtion. nugniented the degree of srt. presumably by rc-forining cyntine linkngcs bet ween tlie pept,i(ltA cliainn according to t lie equxtion-

Equidly siLtisfwtory results were obtained by the combined use of amnioniti and an oxitlising iigt’nt, but tlie concentration of iilkali and the conditions of treatment must be rctrefully t-hosen so t o avoid oxidative tleconiposition of the disulphide bonds formed. Although pretreatment with ammonia was not pnrticularly effective in imgtuenting the set imparted to bisulphite-treated fibres by means of metal salts. the combined i i ~ e of alknli and i i metal salt, as exemplified by H U ~ I (*ompounds tts

sodium tungstate md sodium sluminate, Wits highly sucressfd in proniat,ing linkage rebuilding and set.

A new method of setting imiinltl fibres at low temperatures thus emerges from the preceding observations. In the first place, the fibres are relaxed by treatment with ii

concentrated solution of sodium bisulphite in aqueous alcohol a t 35” C. The washed fibres, if not already in the desired configuration, ran then be deformed and treatcd with either (a ) an alkaline oxidising agent, e.g. an ammoniacal solution of potassium persulphate containing a swelling depressor, or ( b ) a solution of sodium tungstate or sodium aluminate, containing a swelling depressor.

Such metho& of re-forming linkages in bisulphite-treated fibres are of importance in relation to Elsasser’s methode of setting and lustring wool. For this purpose he boiled the .yarn in sodium bisulphite solution, the material being stretched before or after treatment, and then fixed by means of such agents a8 chlorine, formaldehyde and basic alum. The process has seen little or no comlnercid appliciition,

1%-RNH, f R-S-SO,NH,=H.-S-S-R+ (NH 8)2SOJ.

probnbly becaiise the “fixing” niethodn eniployetl were designed simply to reniovtb excess bisulphittb from the yarn ~ n d not, to re-form linkages in the rchxed fibres. I t s~eii is likely that the apldiration of the iibove print*iples of linkage rebuilding to the lustring process will give. yarns of sufficiently iniproved strength to make the process practicable. I n generctl. the new niethocts of rebuilding linkages in bisulphite- treated fibres may be utilised to repair fibw damage mused, for example, in blciiching with sotliuni bisulphite or in stripping dyed miiterials with sodium hydrosulphite.

AH regards the preparation of highly-resistant fi bres by converting disulphide bond9 into metal-conttiining linkages, the funbtniental difficulty is the molecular disorienttition whirh accompanies severe disulphide bond breakdown. For this purpose, re-orientation by stretching is inadmissible. There are, however, two possible ways of preventing disorientation- the molecular structure of the fibre can be stabilised by forming other resistant linkages, e.g. by means of quinone, before proceeding to break down the disulphide bonds; or the treatments with sodium bisulphite and metal salt can be repeated alternately, the time of treatment with sodium bisulphite solution being insufficient, on any one occasion, t o cause such severe disulphide bond breakdown as to permit molecular disorientation. Both these methods, which have given promising results in preliminary experiments, wi l l he fur t l i t~ considered in a later paper. TEXTILE CHEMISTRY LABORATORY LEEDS UNIVERSITY (Received on 2nd January, 1941)

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REFERENCES Speakman, this Jour., 1936, 62, 423. Speakman, E.P. 463,700, line 1 1 1 , p. 4. Speakman, this Jour., 1936, 62, 335; Elsworth ant1

Speakman, E.P. 453,700, line 3, p. 3. Footner and Smiles, J.V.S., 192.5, 127, 2887. Elsasser. Q.P. 233,210.

Phillips, J. Tlexlzle l n s t . , 1938. 29, ‘l’219.