BOKM--“FRICTIONAL PROPERTIES 01’ WOOL FIBRES” S o i r 1945 _ _ _ ~- - ~ - __ 278

solution. Sometimes. however, the finely-divided copper supplied by laboratory furnishurs for Ullmdnn condensa- tions, eta., can be used satisfactorily after careful washing and, in some cases, surface etching wit,h nitric acid. At other times a supply of this copper is relatively inwtive and gives too slow a huild-up of the copper content ctntl too high a nitrite content. Resides low reactivit,y of the copper powder which may be attributed to the relative coarseness nnd compactness of the particles, these same proportics cans8 the particles to settle rapidly in tjhe ammonia, so that they are not sufficiently distributed through the volume by stirring nrrangeinent,s which a.re adeqiiate for finer and less dense powders.

It is R great convenience whore relatively small quan- tities of cnprammonium solution are required at infrequent intervals to he nhle to dispense with special preparation of the copper powder.

We hn.ve therefore carried out experiment,s in which the copper powder wm replaced by an A.R. grade of rod ciiproiis oxide. This can he ohtainecl in tt very fine stRte of division. and is stable if kept in a well-stoppered bottle. It is wetted hy, and disperses in, t,he ammonia solution extremely readily and settles much mom slowly than coppor powder. Exporiments showed that not only could tho desired concentration of disnolved copper be ohtainetl with w. lower equivalent excess of copper, if thie were present in the form of the cuprous oxide, but also that the rate of uptake of oxygen was greater. A more rapid air stream could therefore be used without excbeetling the specified upper limit of nitrite concentration. AR a result of the rhange, the time of preparation could he reduced from the normal 5 hr. to < 4 hr.

Using the experimental apparatus of Clibbens and Geake, the preparation is carried out, according to the following directions.

(a) Mflterid8- 175 g. brlght rrtl, Hnrly-cliviclvd A.K. ~‘uproux iixlclv, :1 1. niiiiimiln ~nl i i t i o i i (RP. gr., O,RHO), 1.2 I . diatilli~d water, ~ i n d 4.2 y . w i i o uiignr.

( 6 ) Stirriilg ia at. the ratr iif 1,800-2,OOO r , i ~ . i i i . It IH rtcon~ni~wlr~cl tlint, t ,hc driving ~ i i n t o r br Hxrd abow thP Htirrrr. tlii. iilcitor 8haft Iirlng wi-axial wit,h t,he Rt.irrrr fihnft au(l uttarhrd to it by 11 tkxibit~ roupliiiy.. This ia prr.frmhle to thc hrlt. itnd ~ i i i l l i ~ y drlw ( I r i i i imI ly drwrllwd.

( r ) .J irpoui ix inrrramd from 10 I . to 15 1 . pi51 hr. ( d ) Tenrpwfllwm iiiiint hv kept, a8 low IIH pousihli~, othrru’isv thc

iwproufi oxlde ia OXidlHrd HO rapidly t,hat ciiprlc cixldr i8 obtnlrlcrl ill a f’iiriii whirl1 will not dls~olvu rnlildly 111 thc siiiiiionln; I N V Hhou~d not 111, c~xcetYlrTl.

(P) Tinre of atirring ahoulcl hr 9 hr. nplirox., vlz. u i i t i l tlir disfioived ropprr roiit,rnt, is a b r w thc spnrifled c~nncriitration nf 115 R. per I . Then allow to 8rtt)le for 30 ni in . and Alt,rr throiigh n niliterrti glasR Buohnrr Rltw of niedimn porosit,y.

The following are comparative figures for preparations by the two methods-

___ ~. ~ ._ - ~~ ~

lfslriy Cciiqwr Ps lng C u ~ i r o u ~ 1 Powder Oxide (g. per I . ) (a. per I . )

_I____-

Exaniples of cuprarrirnonium fluidity tletorminations with cotton a t differont stages of degratlution u h g each of the above c~~priimn~onii~rn solutions tire given below-

Slightly I 5 1,045 teiidrrcrl ; 1,241 rottiin 956

I

This series of‘ results for the Ruiilitir>s (if the tiolut,ions of the same sample, preptmd from the respcct,ivcj cuprammonium solutions, and measured in the ~~1.1ne visconietor, agrees satisfactorily within the accepted limits of experimental error. The agreement is even more satisfactory when the meanti of three determinations we compared for earh snniple. Cuprammunium hydroxide Holution prepared from cwprous hydroxide in the manner described has been used alongside that prepared in the normal manner for a hrge number of ruprttmmonium fluichty determinations, and no approniahlo or consistent discrepancy has been observed.

This modification. therefore, appears to l e ~ t l to a mtisfac- tory and convenient method of prepaving cupranimoniurn hydroxide solution of the composition and properties required for carrying out fluidity detlerminat~ions by the standard method.

The authors thank Mr. F. Soholefield for his continuetl interest in this work mid for his valuable suggestions, and Mr. J. A. Cheethnm for rwrying out rnany of tho fluidity determinations. DNPARTMENT O F TEXTILE CHEMISTRY

COLLEUE O F ’rECHNOI.oCtY MANCHYSTER

(Receiriud on 1 7 t h Fehriinry, 1940)

~ ~ E N E R E N C S X YcholeHeltl mid Turner . I . ?‘nt i l r I m f . 109’t 24 1’130. Turner, Nnbar and HrholeHrld, t.hia J n h . , l b h , \ I , 5 . Fabar, S~hoJ~Hrld nn? Turnrr, ihrd., I O Y i , 53, 5 . .

4 Nnbar a n d Turiicr tbzd. 1946 61 Z5H. Hr!holeAeld and l’ntd, &., 1928,’44, 266.

BC‘libbcns nnd GiwkP, J . Tertile I s s t . , IWR, 19, T77. I ’ i a e o a i t ~ of Cellulose Solutions, 1932. Clnrk, Delprminatim of Hiidragen Ions, Baltilnnrc, 1022, p. 114.

9 I M . 11. 323. In W n l d l’reatiin Scholeflfld ruid Turnw, thir Jour., 1945, 61, 245, 11 II&rioI ciwr;lirnI 1ndiint)riru ~ . t c i . , 1~ri13ntc. C‘omnrvnimtion.

The Frictional Properties of Wool Fibres in Relation to Felting L. Boam

I T L ~ ~ w Z U C ~ ~ O ? ~ - Pelting is the name of a property, characteristic of animal fibres only, which manifests itself in the tendency of the fibres, whatever their state of dis- persion, i.e., whether present as loose mass, top, yarn, woven or knitted fabric, etn., to migrate and thus close up on each ot,her when subjectod to the action of aqueous solutions, in particiilar soap or acid solutions, and of suitable meclianicnd forces. The entanglement indiiced by the fibre migration leads to an increased compoct.ness and consolidation of the material, which thus assiimes the fetttiires of the felted state. The term “milling” denotes the iictual proress by which felting is achieved.

The basic caiise of felting was discovered as early as 1 7 9 0 by Monge’, who showed that in felting the fibres nlwags migrate in the direction of their root end^, and he attributed this tentleiicy to the f w t that, owing to their imbricated surfare, the residctnce to motion of rtnimrtl fibres in that direction is lower thtin in the direction of their tip ends.

After many vicissitudes. the fundamental importance of th is property in felting has recently been strongly emphasised by Martina, whose usefnl term “The Directional Frictional Effect”, or “D.F.E.”, has been adopted in the prestrnt work, and has been given a quantitative inter- pretittion as the difference between the maximum (rubbing from tip to root) and the mininiuni (rubbing from root to tip) coefficient of friction of wool fibres. Ti1 Martin’s view. however, the peculiarities of the molocular structure of tho surface of wool fibres, and not their scaliness, axre responsible for the unusual frictional behaviour of wool.

Allhough there is now general agreement that fundii- mentally felting is due to the differential frictional property of wool, this does not suffive to acc,ouiit for varioiis important feiitiirw of the phenorne~ion, 0.g. the influence of the milling medium or the ternperaturu effect,

This situation has been prLrtially remedied by Spe‘tkmtul and collaborators3, whose theory of fibre migriition by local externion nnd contraction interprets these features

in t e r m ofthe extensibility w d the power of recovery ot' the fibres, but. unfortunately, this theory is limited l o wool in fubric form only. In spite of the greater emphilcris liiicl on the elmtir thtin on the frictional propertieti of wool by 8petLkmM'fl theory, there aro strong indicat,ioiuj, in tiddition to the evidence of Monge' i ir ic l of Martin', that, the predominant importance of the part played in felting by tho surface of the fibres must not be underestimated. Thus, Mercer4 found thnt n very superficial penetration of-the fibres by the milling solution was sufficient to pro- duco n degree of felting equal to that occurring with wool that has been ullowed to ii.ttti.in equilibrium with tho felting medium over a period of muny hours. Rimilasly, it is highly significant that al l the wti-folting treatments with such reagents a.s chlorine, sulphuryl chloride, sodium hydroxide and proteolytir eiuymes, e.uplicitly aim nt, restricting the retiction to tho surface of the fibres.

Consideration of these points led the present author to t,he belief that a rloser study of the unique frictione.1 properties of wool, which clearly aro of paramount i in- port,mce, might throw new light on the subject.

$>XPERIMENTAI,

Profirninnry Ew~~evim~enk- Tho 1 > irec t,ional Fri c t i onnl Effect of animal fibres can be easily tlemonstratotl by the following simple experiment. (i) A small lock (20-30 fibres) of parallel, oriented wool fibres, with their scales all pointing in the same direction, was placed between two microscope slides, nnd the top glass was moved backwards itnd forwards. The flhres were fnnnd to migrate only in tho direction of their root ends. no movoment whatever taking place towards their tips. The rate of t,rnvel was slow in the dry state, hut more mpid with fibres wetted with water. Tn solutions of soap and of sodit ash. as well IW in an acid solution, the movement was very rapid indeed. The effect of glycorol and lubricating oil was also deter- m i n d m d the various observations m e sunimarisetl in Tahlc I.

TAIM I \Yool Rntr of Migrntion

Fibrm In soda ash solntion Vrry rKdd Flhrrs In dilute sill~rhrlric ncid Very miid Flbrea In glvcerol ... ... Very slow Fibrea in Iubrlcnting oll ... Vrry slow

Human hair and cow hair were also tested, hut they were found to more much more slowly. (ii) A Ringle coloured wool fibre was placed on the

surface of R soft woollen felt and, when subjected to the osc-illating movements of a glass microscope elide resting on it. i t showed a distinct tendency to move in the direotion of its root end. Moreover, the latter soon entered the body of the felt and. on continued rubbing, the flbre eventually emerged on the other side of the felt, having tunnelled its way through it.

A t first an attempt wae made to adopt the principle of oxporiment (i) for direct quantitative measurements of the rate of fibre travel. Glass surfaces, however, were un- siutsble, because many types of wool showed a 100% travel, i.e. under the rubbing action of the top glass they migrated at a speed corresponding to the speed with which the rubbing snrfare wns moved. The iise of siioh surfaces would therefore limit the method t o fibres with a low trcivel ce,parity, and so rougher mrfaces were employed. e.g. sheet rubber and asbestos. A small lock of fibres was plamd on ~ n c h material immersed in the liquid. Tlie flbres were then covered with n glass plate which was moved backwards and forwards by means of a mechanical arrangement driven hy m electric motor. Unfortunately, the experiment'was unsuccessful. since no reedarity in the movement of the fibres could be obtained on either eurface, and this meant that it waa impossible, with any reliabilitv, to time the movement of the fibres over a piven distance OF to meemwe the distance travelled in a given time.

Conaequentlg. i t was decided to determine the rate of fibre travel indimtly by evmluafing the difference between the two coefBcienta of friction of wool, for it was thought that the tQsldency of the A h t o travel in the direction of lemt &&anco, i.0. bowsrclrt their root exi&, inCreRseR in A4

direct, propirtion with Lho Iiirtgiiit.urle of the tlifforonco hetwcon tlio iiiaxiininii i u i d t,lic: Iiiinimum coefficient. Subseqiwnt rwults tiiivu pro\wI t,tiis (wntstrnt,ion t,ti be c-orrec-t. 11s is incliwited Liter.

t ' r inc ip lc of f h r Mc/ / tw/ - Most. of t,hc work 011 the fiictiontil propcrtics of textiles hits Lceu cwnc:erned with yarns and fabrics ttiid, since the D.F.E. c~in bo measurotl only on individusl wool fibres or 10okn of fibres, the mothods employed in those investig,r,ttions are of little interest for the presont purpose. 'I'here mo, howover, also some references in tho litertituro to frict.ion of fibrw, tmtl they inrlude memurements of frirtion of fibre against. fibrefi, fihre s p i n s t ti. hard snrfnca", iind fihre against cloth cornposod of tho same materid3. As none of these terhniqiies was considcred quite sui ttihle for tho purposo of the present inveiitigation, i t new method was tievelopecl.

The coeffiriont of friction is defined us tho ratio hotwemi the force rcquired to produce sliding of one surface on motJier (the tangentinl forre) and the force holding tlie Lwo snrfnccs together ( tho normal forco). \Vith pairs of lirirtl solid suhstances this ratio is nearly oonstmt, heing indopendent of the pressure, the arm of contact and t,ho rate of relative motion of the mirfacos. For nccurnte measurements of friction the surfaces under tent should ho highly polished, otlierwise the property that. is estimated will he the resultant of the moleonlar friction, the resistunve to tearing. t,he imperfection of elrtrrticity and tho extent. of irregularity of the two surfaces.

These difficulties render measnrements of fibre-fihro frirtion particularly complex, hut R nearer approach to the ideal conditions for doterminntion of friction can be mndo hy confining the measurements to friction of fibres against R hard eurface, e.g. glass. This advnntage is pairtly off& hv the fact that fibre-fibre, and not fibre-glttss friction, i R operative infelting, but it waa thought tliat at the present stage the data for the latter form of friction would 1x1 nlmost equally important,.

Briefly, the experimental method (full details of which nre given below) wm to moimt the oriented fibres on u glaes slide in the form of a small bridge which WIM placed upside down nn a horizontal glass plate immersed in the liquid. The slide was then connected h v n thread to H

contwiner, and the men,Riwements consistwl of loading tho latter bv means of tl fine water ,jet from a burette until tlie slide had just moved. The burette reading cave the vdur of the load, and, eince the weight of the slide waa known, the coefflcient of friction was calculated from the expmssion-

(:oeffldent of Fri,.t,ion I h t d rewired to o a u ~ sliding

The arithmetical difference between the maximum and the minimum coefflcient gives a numerical expression to the D.F.E. of the particular flbres in a given medium.

Weight of t h c sllde

BIG. 1

BO~--“FRICTIONAL PROPERTIEB OF WOOL FIBRES” Nw. I S 4 __ ---_ _-___ 280

wlth llauld to ensure constancv of the llnuld levcl. When t.he sllde 16 place-d on the glass platr the Abres mdtlius rompletely Imnieraed In the liquid.

The vessel18 placed In another but conslderably larger, tray, 10 I n . x 14 in., and the bracket with thipiilley arrangement I s flrmly Axed on to one of the side walls of the latter vessel. A bracket holdlng a small rrecadle-polnted axle In needle-polnted bearings serves as n pulley. The two vessele are arranged securely on standfl wlth soft felts underneath to mlnimise vihratlon.

The slide la rovlded with two small rlngs one a t each end t o ange e e g W Rook attached to one end of a’ Ane Vlnyoir flladent, whlcf connects the slide over the In t o a Hght rellulold container sunpended a t the other dnd of the thhiesd.

A burette is arranged t o deliver B fine jet of distilled water into thr container a t a constant rate of about 20-23 C.C. er mln. A lac e black-stalned knot on the filament, near the condner end colticlfc; with the level of a horimntal Hne marked on an Indicator aftached to the outer vemel.

plepatatbn of wb SMds (FL 8. 2 and 3)- The varlous stages In t,hr comtruetlon of the sllde are%lustrat.ed by Flg. 2, whllst Flp. 3 Is R photograph of the complete sllde.

Preaentdion of Renu1t.e- The usual number of read ings t a k e n for each direct ion wm 10. From the mem value of these lao/, i s ctducted as a correction for the fr ic t ion loss i n load ing due to the pin, which waa determined separately by means of a fine spring. The value thus obtained ia then divided by the weight of the slide, and this gives the roeffirient of friction. The D.F.E. is calculated by sub- t r w t i n g the value of the m i n i m u m coefficient from that of the m a x i m u m coefficient.

A typ ioa l series of measurements is given in Table I1 ( t h e weipht of the d i d e has n o t been corrected for buoyancy).

TARLR 11 - - ____- __ - _ - ~

Mnximuni Mlnlmum Rradlng , Frlctlou Frlctlon

(R.) ___-

I! . . . . . . . . . . . . ~ 10.4 I Q.2 ._ . . . . . . . . . 7 . . . I 10.4 0.0 8 . . . . . . . . . . . . 8 . . . . . . . . . . . . ~ 10.1 8.2

10 I 10.2 8.3 . . . . . . . . . . . .

Final Load Value . . . . . . 8.12 Welght of 811da . . . . . . 22.16g.

0.047 Uoet8olent of Fdctlou 11.F.E. . . . . . . . . . ... 0.414 I 0.367

In subsequen t Tables the results are presented concisely by stating only the maximum and m i n i m u m coefficients of fkiction and the D.F.E.

Rapradueibdity of Result+ The reproducibi l i ty of the results w-aa checked at an early stage in the work by ca r ry ing out two meaeurements of the D.F.E. of the same wool under ident ioal conditions, but using two different f ibre sheets. The reaults, which are given in Table 111, show that in this particular instance a difference of about 6% waa observed in the D.F.E. values.

TABLPJ IIT I , --I-

D.F.E. I Maxlmum Minimum Measurement, CoafRclent Coemclent

No. I of Frlctlon of Frictlon

mu. 8

A perfectly orlented lock OP wool coritalnlng between 400 and 000 tlbres Is arranged to form n onlforni shert, 3 cm. long and 2 cm. wldo between two glass rods. the cnrrfully coitibcd and nrnllcl kbres hrlnd held rlgidly by the two ry~clnlly drLslgned rllps. Wyth some cuperlencu R aatlsfactory sllde cnu br prrpnred In n matter 01 inlnutcs.

Ewpatimsntal Pmcedum- In the arlcctlon of l o c h of wool flrst cou- slderatlon wns that they should be prrfectly orlented, 1.e. the root or t lp ends of all Abres shoiild point In the aninr direction. Repeated dogrewing in three or four unutltles of benzene wm consldered adequate for purltlcatlon after% had bren found that more elaborate pnrlflcatlon by prolonged Hoxhltt extractlon wlth nlcohol, ether, ctc , dld not aRect the resnltfl. I n wuahlng care was taken t o retaln the orlentatlon of the flhres. After drylng’ a sultuhle portlon of the lock was used for preparing th r Rllde, whlch’ wns wclghcd arid then laced for 30 mln. In tlia llquid to ha used for the D.F.P. measnrenion%. In the nienntlmr the Rppnratus was adjusted. Thus, the horizontal

posltlon of the glass plate wm checked wlth a splrlt level, the plntv Itself thoroughlv freed front dirt nnd grlt the vessel Alled with tliv llquld the bearin 8 of th r In lubrlcnted with flue 011, and tho buretti. rleanid and fllle! wlth dgtllled water

The slide was next placed on the plntr and engaged with a hook at- tached to the Vlnyon rord carrylng the cclhilold rontalner a t Its other md. The posltlon of the slldc was adjiintrd so that the knot on the cord correaponded to tlir Irvrl of th r to Hne of thc lndlcator and thc gath of the slide WHH at an angle of 00’ t% the pin. Loadln &as then

r w n by openlng the btirette tap, the nosltlon of the blark knot belng constsntlv watchrd untll It reached tlir lowrr line on the lndlcator when the‘ tap was closed rnpldly arid the burettr rendlng recorded’ Usunlly, three mcasurenrents In t h e Rnnic dlrectlon wcre carried out consrcutlv~~ly, then th r sllde WIE rcvcmcd and the snme proredurr repeated for tho opposlte dlrectlon, after whlcli t h r alldi. wav turned round ngnin for n npw set of mrRnurrm6nt8.

~~-~ 0380 0.088 0.464 0.082

1 0.476 0.636 -_____-- - - -_

Vtwioua factors were thought t o be capable o f influencing the measurements, but on investigation were found to have little, if any, effect on the reproducibi l i ty of results. T h u s , the number of fibree forming the sheet wax found to be p r m t i o a l l y immaterial w i t h i n fair ly wide limits (200-800 flbres).

In order to emure m a x i m u m standardiaation, the middle portion of the lock wm always chosen to form the f lbre sheet, since the D.F.E. may vary along the fibre length. For the same reason, constant t i m e of wetting of the fibres and constant rate of load ing were main ta ined . All measurements were carr ied out at room temperature of 20%. approx.

RELATION BFJTWEI~ THH~ FELTDW Po- OF Vaarous WOOLS m THETR D.F.E.

“he aim of the first series of experiments waa to establish whether there existed any relatiomhip hetween the fel t ing power of various wools and t h e i r D.F.E.

A similar attempt wan made enrl ier by Speakman and rollaboretors* when they memured the “Rcaliness” of twenty-two widely different wools by’ the violin-bow method. Only a broad parallelism was founi between the milling efflcienoy of the wools and their soaliness” as mewred in ordinary air; in certain instances, however. the order of milling efflcienoy was e x a c t l y the reveree of the order of “soaliness”. ( I n order to a v o i d any possible confusion, it mu& be pointed out that the interpretation of soaliness j+ven by Speakman and collaboratoraa i s based on measurements of the different ia l f r ic t ion of the Abres and not on other surface properties s u c h as the angle of projeot ion of the sortlea or the number of ecctles per unit

Noo. 1#46

Hydrochloric ncld ... Soap ... ... Borax ... Sodlum carbonate ... Water ... .. .

281

-____-- 049 0.449 0.866 0087 0.87 0368 0.801 0066 0.20 0.448 0.807 0.052 8.80 0.681 0.682 0.040 8.40 0.600 0466 0.046

BOBX-"FRICTIONAL PROPERWES OF WOOL FIBRES" -

length.) When some of these determinations mre re- peated in water instead of air, the order in which the wools were arran ed in respect of " S C I L ~ ~ ~ A E E " waa found to be different for &e two sets of measurements.

The very considerable significance of this dependence of the D.F.E. on the medium, and of the variations among different wools with regard to the changes in their D.F.E. or ' scaliness" under the influence of various media, appears to have been underestimated by these workers. Conceivably, the D.F.E. might have dtered again in acid or alhline solution, i.e. in the conventional milling media to which the recognised felting power of those wools obviously relate. Thus, there is a powibility that a muoh closer relationehip exists between the D.F.E. and the felting power of wool, provided both are assessed in the same medium.

In the preaent series of experiments six types of wool were selected so aa to represent a gradation of felting power ranging from a very high degree of feltability, through B medium to a very low feltabilit The wools chosen were (in order of their decreasing miging efflciency aa judged by their employment in the manufacture of felts)- 70s Cape Merino, 70s Australian Merino Skin, 50s New Zealand Pieces, 50s New Zealand Matchings, 48s L u s h Weather Skirts, and 48s shopshire Matchings.

The D.F.E. of these woole waa determined in 6% 6oda a h solution, and the results obtained are given in Table IV.

TABLB IV - _ _ I I I

Wool

70s Cape Merino 70s Australlan Merinb' SWh" 60s New Zealand Pieces ... GOa Nrw Zealaud MBtchlngs 4 L Lustre Weather SLirta t8e Shropshtre Matchings ...

0.276 0.267 0984 0.917 0.928 0.278

0.206 0.208 0.328 0.260 0.202 0.282

0.070 0.064 0.066 0.048 0.096 0.016

It is evident, therefore, that in the caw of these six wools there is a complete comes ondence between their recogniaed milling eBciency and tIeir D.F.E. as measured in 6% soda ash solution.

Although the number of wools examined waa insufaoient to justify a definite conclusion that the felting power of a wool is invariably determined by its D.F.E., the above evidence muet be considered as strong support for this view.

EBFEOT OB pH ON THE^ D.F.E. The effect of pH of the milling liquor on the rate of

felting is w e l l - k n o ~ n ~ ~ ~ . Milling efflciency is highest in acid media, rather lower in alkaline solutions and loweat at pH corresponding to the isoelectric range of wool, which, in conjunction with the existence of an optimum tempera- ture of about 36°-4S"~. in the milling of certctin woven fabrica, was explained by fipeakman and collaborators9 in t e r n of extensibility and power of recovery of the fibres.

This explanation of the pH effect depends largely on the existence of an optimum temperature in the alkali milling of certain woven fabrics, but the work of Mercer', and more recently of Carter and Grieve', has shown that in the alkali felting of yarn and certain knitted hosiery fabrics there is no maximum temperature lip to 00"o. and 70°0., regptively, a fact which olearly renders it im- possible to apply Speakmads theory, including the interpretation of the pH effect, to the felting of wool in these states of dispersion.

As a result, there is at resent no explanation available of the b c t i o n of pH in t f e felting of wool in them forms. It was thought, therefore, that an examination of the effect of pH on the D.F.E. might lead to a clarification of t h i n very important aapect of the phenomenon.

The D.F.E. of 7 b New Zealand Merino wool waa deter- mined over the rmga pR 1 to pH 11 in steps of ap roxi- matel one p~ unit. ~haflrst two meeamments &I I and p% 2) were carried out in sulphuric aoid. whilst the remainder were determined in B.D.H. Univemd BufTer Bolution oonsieting of a mixture of potseeiwn dihydrogen phosphate, b r i o acid, henylacetic acid and cinnamic w i d , Between each cfknge of the medium the fibres were very thororlghly wmhed in tap water, followed by

__.__ ~- ___ __

distilled water, and then placed in the next solution for 30 min. before the measurement. The data obtained are given in Table V, illustrated by

Fig. 4.

TABLE V

mxImum Coefacient I of Friotlon

0.075

0.065

P 2 0.055

B

f 0.045

1 0.035 L a

Minlmum Ooefflclent of Frlotlon

0.347 0.336 0.344 0.971 0.910 0982 0.982 0.862 0.966 0.912 0.293 0.224

D.F.E.

0.072 0.066 0.066 0.048 0.045 0.087 0.086 0.036 0.044 0.066 0.061 0.047

I I 3 5 7 9 I I

PH FIQ. 4-EfIect of pH on D.F.E. 8nd on Bate of Felting of

Yarn and Cloth

It is evident that there exists a very close relationship between the effect of pH on the milling efflcienoy and on the D.F.E., and this important observation waa borne out by the next series of measurements in unbuffered aolutione.

The wool used wrw again 70s New Zealand Merino and the media employed were hydrochloric acid, tap water, and solutions of borax, map, and sodium carbonate. The reaidts, piven in Table VI, show that the D.F.E. inoreaaes in the order water < sodium carbonate < borax < map < hydrochloric acid, and they agree remarkably with the figures in Table V.

TAEIL~D VI

Examhation of Fig. 4 shows a striking similarity between the curves representing the effect of pH on the milling of a woven cloth in unbuffered solutions~ and of a 3-pIy yarn in buffered media' on the one hand, and the curve showing the changes in the D.F.E. over the same p H range on the other hand. Although the cornpond- ence is not perfect, i t E€M3mE sufficient to support the very important conclusion that, with regard to pH, the rate of felting of both cloth and yarn is largely determined by

I30HM--"FRICTlONAL PROPERTI168 O F WOOL FIBRES" Nou. 1945 _~________ 282

the Jnngiiitnde of the effoct of p B on the IL,~'.E, In other words, i t woiil(1 iippciir t)liiit the siipctrior felting power of wool i r i anid8 ~ a i i i alkalis i H dne to tlio ttbilit,,y of thew inciliii, i in( l w i & i i i Ixirt,icitlii,i.. t.o ;ic*i.ont.iuit,c* tlm I).V.16.

'I'lrcrc in no i ~ o r i ~ t ~ s ~ ~ o i i ~ l c i i ~ ~ ~ ~ Iwtwnen Gotttr iind liling's~ i l i i i t i t o i n ftdt iiig of IOI)SC. wool ni vtwinits ~ J H vcili~cs (wliic.)i N I I O W A ~ I t h i . t.he rii.tt3 of felt,ing Ilcc-rrnscvI witli intwutsing p H over tho wliole rimge) l~nd the nhovo I).l<',lC. c i t rv~ ( I'IK. 4). However, siich rt cornparison is nctirvely juutifi- tible, for C:ott,r and Tiling's experiments were ettrried orit, ti.t ii.hoiit> lOO"(-. , whereas the present I).Ii'.R. dti.ta ~wfer to i'ooin t,emperiit,ure; inoreover. i t is qiiestioniihle whet,lier the rewiilts of Gotte and Kling refer tm felting t L t all. Tlieir experiments bear al l the feat,urea nf t8ho no-c!allod hnrtleninp wliicali is a preliminary proue~s in tlir product,ion of naturd, tts distlinct from woven, felts: in hardening, the propelties uf wool which ttppear t,n he predominantly important iwo r:ompreasibility and plasticity, and not, the ability of wool to migrtite which is tho chnrncteristic irsaaciatetl wit.1~ felting.

It seems clonr, t,herefore, that, the lack of corrrq~ondence tmtween t,he present, results and those of Gatt,e t i n t 1 Rling vtinnot invalidat,e tlie nhove arguinont, nccnrtling to whicli the influence of pH in the felting o f wool in all form8 of dispersion is attributctl to its offect on the D.li'.E. of tlie Rbres. The significance of this conclusion froin the point, of view of the genernl thenry of felting is disiotinsetl Inter.

ANTI-FELTINII 'hFIA'I'MENT'S A N D THE: 1j.17.N. It ia generally recognisei1 that in t,reutmerrtn with

chlorine, sulphuryl chloride, ~ o d i u n ~ hydroxide, proteolytic enzymes, etc., which uru einployetl to rediice the felt,ing power or the shrinkability of wool. the reart ion nhoiiltl tllways be confined tan t,he siirface of the fibres. Under auch conditions the frictiourd properties of wool iirti itlinost certdn to bo ttffected. HS shown recently hy Mtirtiii: i m t l by Whewell, Rigelhaupt and Seliinlo.

Tho evidence of them workers, t,ogether witli the present author's own evaluation of the effect of sulphurvl chloride treatrnent described helow, leavos lit,tJft doubt that t8he success of the above reagents depentls on their ability to reduce the D.F.E. of wool. Recently, however, Barr atnil Speakman" have nuggosted that, benzoquinoiie nuid mercuric acetate reduce the felting power of wool solely hy modifying i t 6 elastic properties. Similarly, it had been claimed eltrlier by Liu, SpeakmItn ttnd Kingi2 tthnt thin done ranasd the diminidiod slirinkahility of woollrn fitbrics dyed with heavy concentration8 of rert,nin tlye!n.

In view of the theoretical significance of these ohserva- t ions, they were rhecked by mennuring the D.F.E. of itlentically treated fibres using thc present, niethotl. a,s tlivtinct from the violin-bow or the ~o-cii.llfld Iepidometer sinployed by the above workers.

The results obtained are given in l'rible VII, hnt i t must. he noted that tho figures for eiich treatment refer to (Iifferent sheets of wool fibres. In addition. the sulphuryl rhloritle dnta relate t,o wnter an the medium, those for Solwny Green 0 8 (1.C.T.) tro lyO sonp solution. whiht thP hwnzoyuinone and the mercuric, acetate dnta were obtained in n.2594, soap solution. These differences in the experi- mental conditions do not. however, tiffect the iiwfiilness of them men.siirernents, for in each case the effect of the t,rea.tment on the U.F.I3. ran he observed by cornparing the D.F.E. of tho Hame sheet of fihres before and after treatment, hoth vdnen referring t.0 mcttssiiremcnts of the 1j.F.E. in the same solntion. The wtunl treatments given t,o the fihres corresponded nt,rict,ly wit,li t,liose dest.ril)ettl in the original p a p ~ r s " * ~ * ~ ' ~ .

TABLE \'I1 .~ ~- -~

It is evident that the l).If'.E. of wool IIRN been reduced wry c!ormi(lernblg by oacli of t,liese t>reat,mento. These tlntil., t,upctht~r with the obscrvcttions of the ot,lier workers c1iiotr.d ~ h o v o , diow tliut, in i i l l ~ n s e s the tinti-felting treat- nient, is ac.an~nprrnietl by IL lnrge rctlii(:tjiori in the D.F.E., iintl it, seeins. therefore, that the diniinution of the D.F.E. is, in gonerd, the essential feature of felting prevention.

J>.P.lZ. OF WOOL IN NON-AQ[JEOUS MEDIA Wool fibres felt only to an insignificant extent in the

nbnence of aqueous medin. and the po~sibility that this fact may also be connected with the frictional propertieR of wool was next exttmined.

In this series of experiments. the friction on g l m ~ of air-dry fibre8 (70n New Zealand Merino) wan determined in the U R U ~ manner. Arst in the ttbsenro of any liquid, i.e. in air, and then in a fine Iiibrictiting oil. Tho results are siven in Tnble VII I . which also includes for comparison t,he D.F.E. value of the sanie wool in water.

TABLE V l l l ~~ -~ ~- .~

I I I

1'1 10 tli ff nt,ence hetwccrn tl 16 n 1 t i p i t i i t le of the, U. F. 13;.

( n ) in wtitor, tmd (h) in tiir t int i in liihrirnt,ilig oil. is r r n i d ; . ~ h l e , t,lie former vnllie Imiiig 1ifJlii'"siinAtBIS' twice i.ho l11,tter vnluos.

It seem:< c l ~ i i i . . t,liert$uore. t , l i h t t . t,his tiiiist be tlio inorit iinportnnt ( ' i t i i ~ of' tho low felt.ing power of wool i i ~ non- iiqueoun medin,. which iqprent ly inhibit folt,ing through their innbilit,y to onlittnro tho D.F.E. .41lI)thB~ coiitributory t'liu8e may be the inahility of tho non-ciqimoua: media. owing t,o their lack of swelling puwer. t,rl n.ffect other uievhimical proprrt,ies of t,lw fihrns. o.p. rigidity.

DISOUSSION Consitloration of felting in ti10 light, of tlie evitleni:e of

other workers mid tho present author'n own obsorviitions Iradn to thG cwwhision t>htLt the feltsd state of woo1 is iu*hieved by fibre travel. In fact, felting and fibre niigrrtbion renulting in the entanglemerit, n f tho fibres rnn ho considered nlinost synonymous.

Thnre in also genernl iigroement that tlie 1)roperty of wool fiincinmentnlly responsible for this mi-directionad fihre-triivel is its Directional or T)ifferont,iril Erictioiiiil El?fect, i.e. the posmssinn hy wool of two iuiequal ro- ttfFic-ients of friction, brit no interpretit.tion of tho r61e pliiyctl in felting by such exsent,ial factors a s the milling metliitin, temperat,ure. and the mechunirnl forces involved I m n yet been found generally acreptiible. In addition, tlie inode of oporntion of some of the viirinufi ant,i-folting agents is still not, completely elucitlatotl.

In industrial practice the felting properties of wool iiro iit,ilised in two major directiotw- ( 1 ) in t,lie nitmiifartnre of the so-caIIe(l natiirnl fnltn which two m n d e hy felting mitsnes of loose. unqxin nntl unwoven, fibrori. nntl (2) in the more fmnilinr milling of fiihricn. The method of iwhieving felting is nssontitdly the name in I)ot>ti crises; i t consist8 of rjiibjecting the fibres siiniilt.uneottdy t o tho ctction of certain liquitls, 0.g. Rolutionn of acid or ROILP, and to mechanical forces which are iisiially intermit,t,ent, and romprotwive.

Them industrial examples, however, do not represent felting in its simplest form. Thus, it, was diarovered during the present investigation that, when n. few gmms of carded, good-felting wool are pltr,io~d in a smnll jar con- taining B little dilute acid or soap solution nnct siibjected for a few minntes to rapid oscillatory movement in R shskmg machine, a solid hard hall results. Clnarly. in t,his instance, a remarkahly high degree of felting in achieved wit,hout the applioation o f the iwmpressivo fnrrw normally em loyed in milling. I! is therefore evident t,hat felting ran be produced by

forcse of diverse typypen. provided that they prnmot,o fibre- travel by initiating and maintaining, probnhly inter. mit,tently, that unidirectional migration which leads to

fibre interlocking, entangleiusnt, interlacing, etc., i.e. to the felted atate. Since the mecliauism of fibru-travel depends on tho

fuot that tlie friction of the wool fibre is less when rubbed from root to tip thun from tip to root, a suitable meohanical stimulus will cause the fibre to migrate m the direction of the root elid, i.e. in the direotion of the least frictional whtance, and, when the resistance to motion in that direction becoinea progressively Iew than in the other, this tendency for movement should increme to a corresponding degroe. In other words, tlie felting power should be influenced by the difference between the mani- iuurn and the minimum coeficient of friction of the fibres, and, since the felting cupauity of the same fibres varim according to milling conditiom, the D.F.E. should be a variable quantity.

The present results;, which ure suiluiiarised below, have fdly confirmed this .fundamental eontention, for t,hey show clearly that the degree of felting power is principelly determined by the magnitude of the D.F.E.

( I ) ?lie U.F.E. values (in alkali) of >I rimye of wools possemng widely thfferent felting properties htivu been fbtind to correspond strictly to their recognised felting powcrs. This has indicated that, in general, the felting power of wool probably depenh principally on tho tnagnitutb of its D.F.E., uv meastired in the milling medium.

(2 ) The dependence of the degree of felting power on tlie p H of the inilling liquor has been established to be due to the latter's influence on the magnitude of the D.F.E. 'l'hs, the superior felting efficiency of wool in acids and tclkalis i8 due to the ability of these media, and acids in pnrticiilar, to accentuate the D.F.E.

(3) It har, beeu discovered that iii non-aqueoun media the D.F.R. of wool is very low cornpared with the D.F.E. in aqueous solutions, m d the low felting power of wool in the dry state w d in lubric,at,ing oil is at)trihitted to thia

(4) Apparently, all anti-felting ttyeiit;.J cauw diminut>ioii in the D.F.E., dtliough i t is possible th8.t. the ability of' some of these reagent8 to increase tho resist,ance to doforination of the fibres ooutributes to bheir efficiency by rendeiing fibre eiitmiglement inore ciifficnlt.

'l'lle preaerit evidmce thuci iiuii(utm8 t h t felting power iu primarily a function of t.lie magnitude of the D . F . K . and. therefore, of the ratc of fibre-travel, whioh, iii accordmce with the mechanism suggested above, is cleasly achieved by free inigrstion, irrespective of the S t U t e of aggrqation of the wool.

It is. of course, very likely that other properties of wool, e.E. elasticity, crimp mid compressibility, play theis pwt, but the present view, which interprets the various aspcta of the feltinq principally on the basis of the frictimal

CEU88.

behrtviour of wool, seems to offer a mucli simpler and more comprehensive explanation of the phonomenon. Two importat. mYpoots of the subject have not been

discussed in tile present paper, viz. the temperature effect wid the feltability of wool in admixture with non-animal f ibm, but both form part of work now in progresw, whiuh JSO includea studies of the nature of the unique friotional properties of animal fibms.

SUJklblARY

The plieiiomenon of felting has bmn sttided in relation to the frictional properties of wool end a new experimental method of inemiring tho Directional or UifferentLal b'rictional Effect (l>.F.E,) of wool fibres is described. An interpretation of various aspects of felting, viz. the variability of felting power among various wools, the pH efiect, lack of felting power in non-aqueous niedia, mechanism of felting prevention and the function of mechtLnictt1 forces in felting. is offered in terms of tho frictional behaviour of wool fibres. The preeent evidence hw led to the oonolusion that felting power is primerily n function of the insgnitiide ot the U.F.E., and therefore of the rate of tibre-trevel. Whilst the rbles of other properties, e.g. elmticity, rrimp and rompressibility, may not be negligible, changes iu the D.h'.& seem capable of expluiniiig simply many feat,ures of the felting phermmenon without the need to invoke any other properties.

'l'he author thanks the Directors of Porritts & Spencer Ltd. for permission to publish this paper, Dr. W. S. Shaw for hi, guidance and encouragement during these investi- gationn, ctnd Mr. J. M. Preston for helpful suggestions in the preparation of this paper. REsEUOIi DEPABTllbENT

Poaarns & SFENOEB Lw. BAMEORD, NR. ROCEDALN

(Hereifxd on 4th May. 1946)

RWERENCES ' h u g e , dnic. de Clrinrtk, 1790 6, 30i .

Mnrtin thls Jvur 1944 60 $25. Speak&an and 8 t h J : Tehik Inrt., 1931, 22 TSY9; Bpeakmau

Htott and Olian &id., 1939.24, T27Y; Speakman, Menkart and Liv ,ibid 1944 '45 T41. ' &laoe'r, A&. J . bourbil Sci. I th i . Rer., 1948, 15, 285.

5 Adderley, J . l 'eztilc Inst., 1922, 13, TB4O; Morrow, ibid., 1931, 22, "426; Schmidheuser and l4to11, Kkpzys ' T&iJ,.-ZtQ., 1838, 41, 103' Umnlng Melliancl T'ezhibe?. 1937 18 t145. " UnrkG nnd M&h Wool: A StudGof tld Phre tI.M.8.O. 1929 p. 146. Bkinklc Lnd MORlECn, Antrr. Dvedtu k e p , 1036.'24, 271 Ohamfhaln and 8 e a k u n Nature 1942 &, 646.

Unrtar end Griuve #mi Indtlet~ie~ Resnr& Asmzation, Ypecrbl Publieation No. d 1044 Oct., p 17.

t'ridcaux %ad wnrd J.0.h'. 1R.24' 125 4% u'U6tta and Kltng, KbUdid-d:, lSSU', 62,"LIY. la Whswcll Itigelhnupt. wid Xoliin, Nnhtre lS44 154, 772. It Barr a d Speakmu, this Jofw., 1941, 6b, Y95.'

l i t , Y eakiiiaii and KIIIR, ibid., 1939, 55, 183. Hall, !. T ~ t i l e Inst., 1038, 30, l'Z38.

A Theoretical Discussion of Further Substitution in Homonuclear Mononitronaphthylamines

H. H. HODRSON and D. E. HATEWAY Introc2ucttot~- A considerable amount of experimeiitul

work has been devoted to the reactivity of benzene and its derivatives. a d , with the advent of the electronic theory, i t is now possible to deduce with a high degree of probability vhat position an entering substituent will take when the electronic! characters of tho substituantw already present and of the reagent are known. In the naphthalene seriee, however, the situation is much more complex, but a nurvay of existing data by Veael$ and Jakea' led to their reoognitionofthefollowing two types of substitution, which are analogow to those in benzene chemktry, although viewed from a rather diflerent and very suggestive stand- point. (1) T h e op-substitution in the benzene series, when the substituent produces high electron density at these positions. i w to be regarded aa attack by the electro- philic reagent at the possible quinonoid positions, with the proviso that of the two alternatives poseibla substitution will occur mdily at the position whi&voomerrponds to the mare st blequinone (p-benmquinone ia mucH hoke stable than it! o-isomeride*). On this hypothanis, a plausible

explanation is afforded of the precedenow which p-sub- stitution usually takes over o-substitution (e.g. in the bromination of phenols), and i t will be racalled that modern electronic theory can explain the saxnu phenomena by wsuming that activation of the p-position is moro frequent, although less intense. than a t the two o-posi- tionsa. (2) Further, m-substitution in the benzene series, where the substituent produces low elcrtrofi density at the 0- and p-positions, will correspond to attack of the electro- phlic reagent a t the non-quonoid positiona. The con- verse holds for nucleophilic reagents.

This idea of reactivity at positiom of varying cpi&oid stability is then shown to have fundamental eigniflcance in naphthalene chemistry, where six naphthaquinones e ~ g possible, viz. X:2-, 1:4-, 1:s-, 1:7-, 2:3-, and 2:6-, although d y three are actually known, and these are in the order of stability 1:4- > 1:3- > 2:6-.

of resonahce'f') has been used to explain the colour of & nitromphthyl- arnined on Che basis of the possibility of n)eon&nce into

Recently, however, the modern theo