8 WILKINSON- “BLEACHING OF ANIMAL FIBRES BY MODEHN METHODS” Jon. 1048

THE WORSHIPFUL COMPANY OF FELTMAKERS RESEARCH htEDAL The Feltmakers’ Company offer annually a Gold Medal for Papers embodying the results of scientific research

or technical investigation connected with the art of feltmaking and published in the Journal of the Society. Further, in order to encourage research of a type likely to qualify for the award of the Medal, the Wltmakers’ Company offer annually, for an initial peiriod of 5ve years, a Research Grant of €50.

January 1946-June 1946. No sward.

KNECHT MEMORIAL FUND . A Fund of €100 was subscribed as a Memorial to the late Professor Edmund Knocht from the interest on which two prizes, in the form of books, are awaided annually to selected students of the Marichester College of Technology and the Royal Technical College, Salford.

MERCER LECTURES A sum of €20 per annum is being given to the Society for a limited period of years in commenioration of the

centenary of the discovery of mercerisation. LEOTURERS

1944 N. G. McClilloch and G. S. Hibbert. “Science in 1946 D. Entvistle, B.Sc., A.R.I.C. “Regenerated Fibres from Natural Polymers.”

tion-The Absorption of Light by Chemical

Suitable lecturers are invited to give a Mercer Lecture annually.

an Old Industry.”

“Colour.” Compounds.’’

1045 s. J. m i t e , B.A., and T. viCkcrstaff, pii,=. 1947 E. J . Bowen, M.A.9 F.R.S. “Colour and Constitu-

Proceedings of the Society WEST RIDING SECTION

The Bleaching of Animal Fibres by Modern Methods Meeting held at the Victoria Hotcl, Bradford, on 28th November, 1946, M i . W. C. HOLLAND in the chair. -

M. H. WILKINSON

. Unpigmented Fibres INTRO~UCTION

The object of bleaching-which covers a wider field than is generally rccognised- depends upon the material to be bleached. With cotton and other cellulosic fibres the object is to obtain as perfect a white as possible. On the other hand, wool and silk would appear unnatural if they exhibited the whiteness of blmched cotton or linen. For certain purposes, however, particularly where pastel shades or brilliant colours are to be dyed, there is a con- siderable advantage in starting from a bleached ground.

Again, the bleaching processes to be applied depend upon the properties of the fibre and tho type of impurities present. Cellulosic fibres, being less easily damaged chcrnically than animal fibres, may be subjected to kier- boiling with caustic alkali, but for wool, silk and hair the scouring and bleaching processes must be much less severe.

Animal fibres differ from one another to a greater extent than do the cellulosic fibres. Thus, silk does not contain sulphur and its molecular structure is quite different from that of wool and hair, although all three are protein fibres.

Whereas, in the fifty years between 1884 and 1934, wool blenchihg wus mainly confined to the worsted side of the industry, it now includes the woollen industry, largely owing ta tho successfd development of processes for bleaching pigmented fibres.

WOOL BLEACHING The ‘choice of a bleaching agent is govcrned by three

factors, viz. ( a ) the nature of the fibre to be treated, ( b ) the degree of bleaching required, and (c) the cost of the process. Bleaching can be carried out by meam of either reducing agents, e.g. sulphur dioxide (stoving), bisulphite and hydrosulphite; or oxidising agents, e.g. hydrogen peroxide, sodium peroxide, sodium perborate, potassium permanganate, persulphates and percarbonates.

Reducing agonts do not produce a permanent white, but they offer the advantages of low cost and ease of manipulation. whilst the lustre of the finished product is satisfactory. On the other hand, the bleached ground has a tendency to revert to its original colour, especially on washing. Furthermore, reducing agents, especially sulphur dioxide, leave an objectionable odoiir in the goods, and they are liable to cause much inconvenience in later

processes, especially where stoved yarns are mixed with dyed unstoved y a m . Sulphur stoving, however, is still largely employed in the blanket manufacturing industry, and as an aftertreatment to hydrogen peroxide bleaching. whilst bisulphite is also used in tho Midlands for the latter purpose.

Recent advances in our knowledge of the molecular structure of the wool fibre, and of the action on wool of reducing agents and oxidising agents, have greatly aasisted the bleacher of animal fibres. It is now known that both .reducing and oxidising agents attack the disulphide bond in animal fibres and can be responsible for degradation, 1088 of lustre and inferior handle.

Consideration must be given to the processes imme- diately preceding bleaching, especially scouring, which must be as thorough before bleaching aa before dyeing. Grease, min6ral oil and other foreign matter are not easily removed by means of soap and soda ash, and it should be remembered that the u ~ e of soda ash is liable to cause yellowing of the wool. Tho practice of using ammonia to “clear” pieces is to be deprecated, since i t is likely to upset the pH of the bleaching bath, and is the usual cause of the pink cast on peroxide-bleached wool, attributable to a high pH of the bleaching liquor, coupled with erratic release of oxygen.

In order to eradicate all trace8 of mineral oil, grease and other residues, it is advisable to use a chlorinated hydro- carbon solvent in conjunction with the soap. If the water supply is ‘‘hard”, the use of one of the many sulphated fatty alcohols now available will prevent precipitation of lime soap.

It is desirable to emphasise the necessity for covering all water and steam pipes within the bleaching plant area as a precaution against condensation and contact stains. Closed steam pipes in the bleaching bath aro oesontial, because any priming of the boilers will result in con- tamineted steam and so upset the y H of the bleach bath. Stainless steel dyeing machines have now superseded tho improvised wood vessels formerly used, which were the c a m of many stains. Clean plant, utensils and personnel are important factors.

Wool may be bleached in the raw state, in dubbing, sliver or top form, as cops, cheeses or hanks, as knitted goods in endless rope form. and in the woven piece.

9 Jan. Ig48 WILKINSON- “BLEACHING 0%’ ANIMAL FLBREB BY MODERN BfETHODB”

NEUTRALISINO THE BLEAOH BATE The secret of successful peroxide bleaching is control, and

correct neutralisation of the bath is the key to the whole process. Four factors are involved, viz.-

(a) The type of neutralising agent employed, which varies with different types of fibre.

(b) The p H produced by the particular neutralising agent employed.

(0 ) The effect of the pH of tho bath on the rate of reletwe of oxygen, steady oxygen release being of para- mount importance.

(d) The question of whether to use a buffering agent in conjunction with the neutralising agent, in order to preserve a stoady pH throughout the whole operation, as well as a steady oxygen release.

It must be emphasised that the combined effect of pH volumetric strength and temperature, has a direct and important relationship to the efficiency of the bleaching operation and the degradation of the fibre. In bleaching unpigmented fibres these three factors remain fairly constant, provided that the correct neutralising agent and 8 suitable buffer are employed, but in pigmented fibre bleaching the position is quite Uerent. The following neutralising agents are used- Ammonia,

sodium ,silicate, trisodium phosphate and sodium pyro- phosphate, whilst borax is anexceptionally useful buiTering agent.

A M M O N L A - ~ the early days of peroxide bleaching ammonia was the universal neutralising agent, but i t was found to give an abnormally high p H as well as being responsible for very erratic oxygen release and for much over-bleaching. It was also observed that many of the bleached goods exhibited a characteristic pink cast.

SODIUX SILICATE-T~~S compound next came to the fore. Provided that it is thoroughly dissolved and uniformly distributed throughout the bleaching bath, it is quite an efficient neutralising agent and, in addition, it has a buffering effect on the bath. Sodium silicate is still in use, especially in silk bleaching, but, unless it is evenly distributed throughsut the bleaching liquor, it will produce hard patches of fibre, which ultimately show ver pronounced degradation.

&ISODIUM PHOSPHATE-T~~S is a fairly good neutralising agent for certain clasaes of work, but, unless it is used with care, the pH will be too high. SODIUM PYROPHOSPUTE- This neutralising agent,

which is reliable and in general use to-day, gives a pH between 8.2 and 9.2. The pH remains fairly steady throughout the operation, but the liquor can be buffered by the use of borax or Sttl,biliser “C”; use of the latter product is claimed to give a better white. Sodium pyro- phosphate is used to the extent of 2 oz. per lb. of 100 vol. hydrogen peroxide. The bath should impart a pink colour to Cresol Red test-paper, the working pH being 8.2.

The neutralising agent should be thoroughly dissolved before use, and under no circumstances should it be thrown indiscriminately into a bleach bath, especially if B dye jig is being used for bleaching the pieces.

Apart from woven pieces, which require a 0 vol. bath, the standard strength is 2-3 vol. hydrogen peroxide. The standard initial temperature in all cases should be 120”F., and the p H 8.2.

Sodium pyrophosphate is used as a neutralising agent for woollen and worsted goods; for silk it may be found that sodium silicate is better. Excessively high pH, volumetric strength or temperature gives rise to “pinks”, whilst inadequate scouring will impart a grey cast to the bleached

Modern peroxide bleaching is carried out by four methods, viz.-

(1) Steeping in a stationary liquor. (2) Bteeping in a circulating liquor. (3) Moving the goods in a stationery liquor. (4) Ageing.

,

goods.

The use of the ageing method, however, is to be deprecated because of (a) the impossibility of achieving a standard bleach; (b) the risk of over-bleaching, with resul$ing pinks; and (c) the unavoidable variation of shade and the ten- dency to barriness if the pieces are not periodically rotated, if on a batching roller, or constantly recuttled, if lying in

’ a heap; further, this process is useless with fibres of the pigmented type.

The importance of a steady temperature throughout the bleaching operation cannot be too strongly emphasised, and the installation of a thermostat is worthy of con- sideration. It is.desirable that the bath should be tested for pH, volume strength and temperature a t regular intervals during the process.

ALTERNATIVE PROCESS For many years the knitting yarn and knitted goods

section of the industry has desired to eliminate the sulphur stoving prooees. When sulphur-stoved yarns are mixed with dyed yarns which have not been sulphur stoved, sulphite faults are liable to develop, with consequent change of shade.

Whereas the normal hydrogen peroxide process pre- viomly described requires an overnight bleach, the ollowing process is complete in 4 hr. and gives a good

white, subsequent stovipg being unnecessary. The goods are treated a t 1 2 0 ” ~ . with 3 vol. hydrogen peroxide adjusted to pH 8.2 with sodium pyrophosphate, to which haa been added 1 lb. of sulphated fatty alcohol per 100 gall. of bleach liquor. The sulphated fatty alcohol assists penetration of the

bleaching agent into the flbres, and also indicates, by the foam on the surface of the liquor, that bleaching is actually taking place- the absence of foam is a timely warning of an inert bath. The average volumetric loss of the exhaust bath is about 60% of the original strength, as with the ordinary overnight process.

TEXTILBl HOSIERY WASTE NEW AND SECOND-HAND BERLINS, FLANNELS BLANKETS (AS RAGS),

KHABI. ETC. . ~- The use of peroxide bleaching in the fancy and low

woollen industries is in its infancy, but it has been established that a phoe exists for oxidation bleaching in competition with hydrosulphite and the sulphoxylate- formaldehyde compounds, which are largely used a t the present time.

In these industries the question of cost is of gregt importance, and in this respect hydrogen peroxide bleach- ing compares unfavourably with hydrosulphite stripping. On the other hand, the ehade and handle resulting from the use of hydrosulphite and the sulphoxylate-formaldehyde compounds leaves much to be desired, and it is in this oonnexion that hydrogen peroxide, given a suitable plant, shows an advantage. It provides a better and brighter ground shade, as well as stronger fabrics, whilst garnetted waste, rags, etc., yield longer fibres, a better handle, and there is no degradation of the material.

Bulk trials to substantiate this claim were carried out in open rag-stripping pans of the Simplex type, after the pans had been boiled out with soda ash and peroxide. The results achieved were sufficiently good to peimit the bleached material to be used for a higher class of trade than would have, been possible if the material had been stripped with hydrosulphite, thus offsetting most of the extra cost.

From the point of view of bleaching, noils, wastes, otc., may be clamified into two groups, viz.- (a) Virgin noils and clean wastes. (b) Berlins and wastes from worn fabrics and garments ,containing perspiration, dirt, etc. In the case of garnetted waste, there is also a percentage of pulling oil.

The noils of the various hair fibres, viz. alpaca, camel hair and mohair, can be bleached by t6e methods described below for pigmented fibres.

Berlins, flannels, etc., have been successfully bleached with 2 vol. bydrogen peroxide a t 130”a., using trisodium phosphate, or even soda ash, as a neutralising agent. GABERDINE WASTE-Strip by boiling for 16 min. in

1% ammonia; then bleach in 1 vol. hydrogen peroxide neutrdised with 06y0 ammonia, using a 15:l liquor-goo& ratio, exhaust the bleach bath, rinse off and hydroextract.

TEXTILE WASTE-The peroxide bleaching of virgin clips, i.e. clippings from dyed knitted wool fabric from the Midlands arm, offers great poeaibilitiae, since hydrosul- phite stripping imparts a very harsh handle, shortens the fibre lbngth, and the stripped ground shade is very drab. The goods are first given an ammonia strip for 30 min., including 10 min. a t the boil, and then bleached in 1.6 vol. hydrogen peroxide which has been neutralised with ammonia and to which has been added 0.1% Olauber’s salt on the weight of the material.

\ 10 WILKINSON- "BLEACHING O F ANIMAL FIBRES BY MODERN METHODS" Jun. 1948

RAW-A successful bulk trial was conducted on a 3,000-lb. lot of Grade 3 flannels which included old blankets in rag form. Using an open Simplex machine for each 600-lb. batch, bleaching was carried out with 1,000 gall. of 2 vol. hydrogen peroxide, neutralised with soda ash and containing 3 or 4 lb. of' soap. It is believed that a suitable modification of the process would overcome tho flotation expericncod.

SILK BLPACHINO The procedure for bleaching deymmod silk is similar

in every respect to that adopted for wool, except that the temperature of the bleach bath is appreciubly higher, viz. 180'~. Sodium silicate is better than sodium pyrophos- phate for neutralising the bath. Silk may.be degummed and bleached in one operation very successfully by using, a t 180°r., tho altornativo bleaching process outlined above.

I t should be noted that, when bleaching wool and silk mixtures which are subsequently to bo stovcd, it is essential to remove all traces of' residual peroxide by thorough washing prior to sulphur. stoving. Otherwise, degradation of the silk will occur through formation of sulphuric acid-

H,08 + SO, = H,SO, Two varioties of wild silk call for treatment as pig-

mented fibres, viz. t u w h silk and the various species of Aiaaphe silk (A. infiacta, A. moloneyi, A. vemta, etc.), but the straight hydrogen peroxide bleach is used.

TUSSAH SILK- This fibre, like cultivated silk, Consists of a double filament, but whereas the latter is devoid of air passages a.nd has a perfectly smooth homogeneous surface, tussah silk contairw air ducts and exhibits longi- tudinul striations. Its diameter is nearly double that of cultivated silk and it possesses a more vitreous lustre when degummed.

Chemically, tussah silk consists of fibroin and the cement which binds the filaments together, but it contains no true sericin. The fibroin of tussah is not the same as that of inulberry silk, and the so-called bast of tussuh silk offers greater resistance to alkalis. Soap appears to combine with the cement; the tussah silk .becomes more adhesive and no bast soap is obtained. The natural p i b e n t of tussah is quite different from that of cultivated silk; it is a tannin which has been modified by oxidation and cannot be destroyed by sulphur stoving. Its removal necessitates the use of olridising agents. Potassium permanganate may be used and hydrogen peroxide followed by hpdrosulphite hus given reasonably good results. In a modified I.C.I. process, 3 vol. hydrogen peroxide neutralised with sodium silicate is used with an addition of 1 % potassium persulphate and 1 % trisodium phosphOte on the weight of the material. It is possible to bleach and degum cultivated silk in one operation, but this is scarcely possible in the case of tussah silk. although it is possible to scour and bleach the spun yarn in one operation. Tussah. silk is uaually bleached a t 160°-180"~. with 3 vol. hydrogen peroxide adjusted to pH8 with sodium silicate and containing 0.5% of sulphated fatty alcohol.

Tussah silk is usually degummed in two stages as followg (1) Boil for 1.6 hr. with 1% soap and 1% sodium silicate on the weight of the goods, using a liquor-goods ratio of 20:l; wash off. (2) Boil for 2 or 3 hr. with 12% soap and 3% sodium silicate on the weight of the goods, using a liquor-goods ratio of 20:l. Bleaching then follows.

In the hydrosulphite treatment which follows the hydrogen peroxide bleach it is advisable to make the water alkaline with a little sodium silicate, and a further advan- tage is gained by adding about 10 lb. soap per 100 gall.

Anuphe SILK- Whilst Amphe silk is easier to bleach than tussah silk, the degumming of this type of silk demands a special process.

Amphe silk in yarn form can be bleached with 3 vol. hydrogen peroxide in a Hussong machine, using downward flow and a temperature of 175"-180"~. The bath is neutrulised with sodium silicate and should contain 0.1% of sulphatcd fatty alcohol. The bleach is sufficiently good to permit the dyeing of pastel shades, but, if a white is desired, an aftertreatment with 1 yo hydrosulphite solution is neceesary, followed by a sour.

SUhU&4RY The following recommendations suinmarise the pro-

cedure to adopt when bleaching unpigmented animal fibres- (a) Control the pH, the volumotric strength of the bath,

the temperature and time of bleaching. Test the bath before commencing and during bloaching, in order to detect any abnormal loss in volumetric strength or varia- tion in pH. Check the strength of the bath at the end of the operation. Keep records.

(b) Remember that an inert bath indicates that bleachmg is not taking place, whereas too high a pH leads to rapid release of oxygen and to degradation of the fibre and loss of handle.

(c) Use a buffering agent, e.g. borax, if the pH of the bath indicates the need for addition of alkali.

( d ) Remember that a pink cast is the sign of over- bleaching and calls for an examination of pH and volu- metric strength. A grey cast points to inefficient scouring and tjie need for an addition of sulphated fatty alcohol to the bleach bath.

(e) On foggy days, cover all goods proceeding to and from the bleach plant, as well as when they are in tho hydroextractor. Use clean carts and clean utensils. The workmen's han& must be clean and they must not use indelible pencils.

(f) Wash off immediately after bleaching. Goods, whether bleached or unbleached, must not lio about in a damp state for any length of time, e.g. overnight, especially in the summer months, owing to the danger of mildew developing on thorn.

( 8 ) Bleach before carbonising; do not oxidise cur- boniser's stains and faults.

(h) In piece bleaching add all the ingredients before bleaching commences. If it is necessary to add a neutralising agent during the process, it must not be thrown in indiscriminately, but added when the piece is at one end and covered with the wrupper. Any additions must be thoroughly dissolved and dispersed throughout the bath before bleaching is recommenced.

Pigmented Fibres BLEACHING OF PIGMENTED FIBRES WITHOUT

MOltDANT In the years immediately precoding the last war, the

attention of the woollen and worsted industries was directed to the possibility of bleaching the pigmented animal fibres, viz. alpaca, camel hair, cashmere, mohair, cow hair, etc. Experimental bleaching of theso fibres had achieved a considerable measure of success by 1939. Interest was mainly centred on this new project for two reaso-(u) Out of the total amount of those imported fibres, about 90% are dark, with only 10% of white hairs. and the price margin was sufficient to justify the extra cost of bleaching. (b) More important, however, was the fact that these fibres were not rationed by the Wool Control.

It is not surprising, therefore, that enterprising firms forged ahead with this project, using the standard hydrogen peroxide bleach, before the technical aspect of the process could be investigutod.

As far as piece bleaching is concerned, the normul hydrogen peroxide bleach is in general use. Alpaca, camel hair and cashmere pieces are being bleached on the dye jig with outstanding succoss, perfect levelness being obtained without stains or bars of any description.

In the normal straight hydrogen peroxide bleach thoro is a sharp fallin the volumetric strength, together with a pH awing from 8.6 to 5.6 in the fixst 20-30 min. of processing. Moreover, very little reduction in colour takes placc. This rapid pH swing is not due t o acidity in the fibres, since fibres that had been pretreated with alkali caused the same rapid fall in pH. As sodium pyrophosphato was being used as the neutralising agent, it was thought that the alkali produced was being absorbed by the fibros, the phosphoric acid thus liberated necessitating further addition of alkali to preserve the pH of the bath at the optimum value.

Tables I and I1 show the fluctuations of p H and tho volumetric strength. When the bath is acid the oxygen release is nil and the bathis inert. It will be noted (Table I) that after 30 min. the pH has fallen from 8.2 t o 6.5.

Jan. 1948 WILKINSON- “BLEACHING O F ANIMAL FIBRES BY MODERN METHODS” 11

TABLM I Fluctuating pH and Volumetrlc Loss (Oxygen Rel-)

in Bleaching Bath Hussong machine, 750 all. capacity. 625 Ib. appmx. cow hpir in process; neutrafislng agent, h o d i u m phosphate

Hydrogen

(vol.)

Tim0 Peroxide Temperature (min.) pH Strength (‘8.)

0 8.2 3.1 130 30 6.5 2.6 136 ao 7.0 2.3 140 00 7.0 2.1 146 120 7.1 1.06 148 160 0.8 1.8 160 180 7.0 1.6 160

TABLE 11 Longclose, 8 can top dyelng machine; 80 Ib. alpaca in process;

9 vol. hydrogen peroxide; neutrallslng agent, sodium pwophosphate

Addltions of Sodium Pyrophosphate a t the H ydrouen

Time Beginning of ench p H Peroxide Temperature (min.) Periodt Concentratlon (‘3.)

(%) (%) 0.26 8.2 0.842 102 - 8.0 0.554 110’

0

46 0.126 6.6 0.527 112 30

66 0.25 5.0 0.476 - 65 0.25 5.0 0,468

120 0.25 6.0 0.340 130 136 0.60 8.6 0.330 160 0.0 8.0 0,316

- 80 0.26 5.0 0.408 120’

- - Temperature raised by introduction of steam.

t In each cam Ute addition of sodium pyroyhos hate raised the pH value from that shown in column (3p to 8.2.

In view of the rapid fall in pH from 8.2 to 5.6 in nearly every case where pigmented fibres were being bleached with hydrogen peroxide, a series of laboratory tests were carried out to determine the alkali absorption of the various fibres.

Ten-g. samples of five dif€erent animal fibres were each soaked a t room temperature for G hr. in 400 C.C. of a 0.1% sodium carbonate solution. A t intervals, a 5 C.C. sample was withdrawn from each solution and titrated with 0.0462~-hydrochloric acid. From the titration made a t the end of 0 hr., the percuntage absorption of sodium carbonate, on the weight of the material, was calculated.

TABLE I11 Alkali Absorptlon Tests on Varlous Fibres

The results are given in Table 111.

Titration with O.O452~-HydrorhlorIc Acid (0.0.) Scourcd

Time Raw Rabbit Rabbit Camel (hr.) Wool Fur Fur Hair Alpaca

(a) (a)

9.6 1.0 0.0 0.4 1.3 1.0

loarc in weight occuw during the bleaching process. Although m y expensive pretreatment is out of the ques- tion, some pretreatment is necessary, as the excessive dust, etc., causes erratic oxygen release and there is the usual p H fluctuation.

It wm therefore decided, after bulk trials, to give the unscoured hair a cold treatment G t h 2% hydrochloric acid for 30 min. This treatment reduced the content of vegetable matter and the amount of flotation, as well as lightening the shade.

The goods were thoroughly washed off in the machine (bussong or Obermaier) after the acid treatment and then bleached in 2-3 vol. hydrogen peroxide adjusted with trisodium phosphate to p H 9.2, the temperature v n g gradually raised from 120’F. to 180”~. during 3 hr. l!he material WM not scoured before bleaching.

A trial with oxalic acid in place of hydrochloric acid gave a lighter result, but degradation of the fibre waa greater than with hydrochloric acid.

UOLD MORDANT PROOESS The idea of employing a metallic salt was by no means

a new one. Before 1939, I.G. Farbenindustrie A,-G. gave a recipe using ferrous sulphate, tartar emetic and sodium chloride as a mordant, followed by a bleaching with hydrogen peroxide, and a third treatment using Decrolin and hydrochloric acid.

This I.G. process had no2 been developed commercially, possibly owing to the need for three separate treatments. Moreover, on investigating this process i t was quickly discovered that control was impossible and that i t showed the same pH fluctuation and volumetric loss that had already been experienced.

In ordinary circumstances the presence of iron in hydrogen peroxide bleaching baths should be avoided, owing to its catalytic action on the decomposition of the peroxide and the consequent wastage of oxygen. By limiting the amount of iron, however, advantage may be taken of this catalytic action to secure a higher degree of bleach than’ is otherwise obtainable. Fibres impregnated with a solution of an iron salt under strictly controlled conditions appear to retain some of the iron within the fibre structure, SO that, on subsequent treatment with hydrogen peroxide, catalytic decomposition takes place within the fibre itself, whereby nascent oxygen is released in contact with the pigmented matter, thus giving an exceptionally high degree of bleach.

In contrast to the I.G. process, it was realiscd that tho use of a reducing agent was an essential feature of the process. Sodium hydrosulphite or sodium bisulphite was used in conjunction with the ferrous sulphate in the mordant bath. This is similar to the iron mordanting of wool for subsequent dyeing, in which ferrous sulphate (Fe,SO,,7H,O) is generally uaed, with cream of tartar or ~~ ~.

oxdic acid-as t h e assistant or reducing agent, the usual 4.0 0.9 0.9 0.3 1.2 0.9 4.5 0.0 0.0 0.3 1.2 0.Q 6.0 0.7 0.0 0.2 1.1 0.8 . percentage of each being 3-6%, both being dissolved 6.6 0 6 0.8 0.2 1.0 0.7- senaratelv. Ferrous oxide is deposited on the flbre and 6.0 0.6 0.0 0.2 0.Q 0.7

Na CO absbrbtd (%) ... 2.85 2.85 3.82 1.53 3.04

,THE TWO-STAUE MORDANT-PEROXIDE BLEACH It soon became apparent that a more effective pro-

cedure WM necessary which would give a greater reduction in colour. Increase of either the volumetric strength or temperature, or the use of a neutralising agent giving a higher pH, only resulted in destroying the soft “soapy” handle which is characteristic of alpaca and to a lesser degree of camel hair, as well as the lustre of the fibres under consideration. It W&B also necessary to deal with the “flotation” which occurs and causes difficulties when bleaching loose fibres.

Progress was quite rapid and there were quickly avail- able- (a) A modified two-stage process for cow hair, whioh includes a pretreatment in cold hydrochloric acid. (b) A two-stage process in which the fibres are deliberately impregnated with iron salts before bleaching.

PRETREATmNT WITH HYDROCHLORIC ACID The h b f i b r e to be tackled was cow hair, which waa

eventually processed by a modified two-stage process. Cow hair will withstand fairly rough treatment, e.g. a higher bleaching temperature and pH, without any sign of degradation. Owing to its dirty condition, 16-20%

th‘e presGnce of the reducing agent prevents oxidation from the ferrous to the ferric state.

Before progress could be made i t became necessary to determine the following points- (a) The rate of decom- position of hydrogen peroxide in presence of the mordant solution (me Tables V and VI). (b) The consumption of alkali at various p H values and the effect of tempcrature on the rate of alkali absorption. (c) The effect of using the salts of other metals as mordants, e.g. salts of copper, tin and aluminium. ( d ) The amount of residual iron in the fibre after mordanting. (e) The possibility of using a hot mordant bath.

( 1 ) Ferrous sulphate is the best salt to use for the mordant, degradation being very evident with copper sulphate, whilst the bleaches obtained, using other salts, were markedly inferior to those given with ferrous sulphate .

(2) A cold mordant bath is alkaline after mordanting. The subsequent bleaching bath exhibits pH and volu- metric strength variation, as well as a temperature increase.

(3) The hot m o r h t bath is acid after mordanting, yet the bleaching bath is controllable and exhibits a steady pH and volumetric loss, and no rise in temperature.

These tests led to the following conclusiom-

12 WILKINSON- "BLEACHING OF ANIMAL FIBRES BY MODERN METHODS" Jan. 1948

It is suggested that acetic acid might be added to the mordant bath in order to assist the exhaustion of the iron salts. It would also be of advantage to remove iron from the fibrgs after processing.

After considerable experiment, a method was evolved which appeared to work well and which was, to a reason- able extent, capable of being controlled. Bulk trials were made in a Longcloee machine on batches of alpaca in top form. The data obtained in these trials are given below.

The process was as follows- The material was given a preliminary alkali scour to remove oil residues, 2"Tw. so& ash (1% solution) being circulated for 1.6 hr., after which the goods were washed off thoroughly. Mordant,ing was then carried out cold for 3 hr. with 3% ferrous ammonium mlphate, 3% sodium hydrosulphito and 1 yo sulphated fatty alcohol, all percentages being on the weight of material. (Alpaca of lighter shade would require lower percentages of mordant and reducing agent.) The ferrous ammonium sulphate and sulphated fatty alcohol were added to the liquor, using a 10 : 1 liquor-goods ratio, and circulated for a time before gradually adding the hydrosulphite in solution. (In order to reduce the cost, ferrous sulphate and ammonium sulphate may be used in the proportions of 139 : 66, using 205 parts of this mixture in place of 196 parts of ferrous ammonium sulphate.)

The bleaching procoas follows after tho goods have boon given a thorough rinsing. Anhydrous sodium pyrophos- phate (6% on weight of material) and 1% sulphated fatty alcohol are mixed and added to the machine, which has previously been filled with water and heated to 125"~ . The liquor is circulated for about 30 min. until the p H , which is 9.6 after mordanting, has fallen to 8.6. Hydrogen peroxide is then added to give a strength of 2-3 vol., according to the depth of shade of the fibres being pro- ceased. The pH must be measured regularly a t 30-min. intervals, and, if the bath becomes acid or inert, equal amounts of soda ash and sodium pyrophosphate added to maintain the pH at 8.0 (about 1 Ib. of each was found necessary for each 60 Ib. raw material to raise the pH from 0 t6 8).

A fresh difficulty arose, however; for reasons which could not then be explained, the temperature increased sharply to 16Oo-16O0~., with a risk of fibre degradation and the loss of the "~oapy" handle peculiar to alpaca. It is now thought that this increase in temperature is cawed by interaction betwoen the hydrogen peroxide and the residual hydrosulphite, as i t is significant that this tempor- ature rise does not occur when a warm mordant is used.

For camel hair, the amounts of ferrous ammonium sulphate and hydrosulphite can be reduced to l*G%, and in the bleach bath 3% sodium pyrophosphate is sufficient.

After bleaching, all goods are washed off thoroughly before hydroextraction.

The following two works trials were carried out on alpaca, using an 8 can, stainless steel, Longclose pack dyeing machine. In Trial A the alpaca tops were of varying shades and balled differently; whereas in Trial B the tops were of various blended shades and were not in ball form, but hanked.

TRIAL A- The alpaca (166 Ib. 5n bull form) was pro- cessed in 160 gall. of liquor. Scouring was done in 2"Tw. eada e h at 130"~., followed by washing off. The mordant bath contained 6 lb. ferrous ammonium sulphate (or 3 Ib. 9 oz. ferrous sulphate mixed with 1 Ib. 11 oz. ammonium sulphate may be used), 6 Ib. sodium hydro- sulphite and 1 Ib. sulphated fatty alcohol. Bleaching was then carried out with 7 lb. sodium pyrophosphate, 1 6 Ib. sulphated fatty alcohol and 4 gall. of 100 vol. hydrogen peroxide. The pH fluctuatcd and fell from 8.6 to 6.0 i n 20 min. and the volumetric strength decreased by 60%; the temperature rose gradually and was 166"~. 4t the end of the operation.

TRIAL B- The procedure wm the same as in Trial A, but the weight of alpaca top (unballcd) was 60 Ib. The initial pH of the hydrogen peroxide bath was 8.6, but i t had fallen to 8.0 after 20 min. Alkali was next added, viz. 1 lb. sodium pyrophosphate and 1 lb. Boda ash, with the result that the p H after 36 min. was still 6.0. Further alkali, viz. 2 Ib. soda ash, was then added, cctusing the pH to remain steady at 8.6 until the end of the bleaching operation.

At intervals throughout the bleaching operation in Trial A, samples of the peroxide liquor were removed and

titrated with 0-1N-potassium perinanganate in order to determine the amount of hydrogen peroxide remaining in the bath.

TABLE IV

The results are given in Table IV

P m e Pennanganate Hydrogen Peroxide Hydrogen Perolddo (inin.) Titration (c.c.) Strength (%) YtGllgtll (vol.)

0 64.3 20 51.6 36 39.2 50 84.2

1 4 9 5 0,877

0.411 omx

70 18.1 n m n

3.65 2.92 2 2 2 1.37 1.118 -~ - . ._. - ._

90 10.9 0.186 0.62 110 8.6 0.146 0.49

The amounts of chemicals used, exprcssed as a percentage on the woight of alpaca, woro as follows- Mordartt : 3.3% ferrous ammonium sulphate, 3.3% sodium hydrosulphite and 0.66% sulphated fatty alcohol. Bleach: 132% sodium pyrophosphate (total), 4.96y0 soda ash and 33.3% hydrogen peroxide.

The conclusions derived from these trials are that the process is very suitable for alpaca, camel hair, etc., pro- vided that it can be adjusted to permit of systematic control. Loose matorial, sliver. tops, cops and cheeses can be treated in a Longclose circulating liquor machine provided that (a) circulation is continuous; (b) the tops are not tightly wound, otherwise ponetration of mordant and bleach is uneven; and ( c ) precautions are taken to avoid channelling. The process in its present form is not suitable for piece goods owing to the difficulty of obtaining even impregnation with the iron salt.

In view of the difficulties encountered in the bulk trials, experimontal work was necessary to ascertain (a) the reason for the fall in pH, (b) how to prevent the high initial loss of volumetric strength, and ( c ) the causc of the sharp rise in temperature.

The following trial showed the effect of the comtituentt3 of the mordant bath on the decomposition of hydrogon peroxide stabilised with sodium pyrophosphate. Two baths were prepared containing 3 vol. hydrogen peroxide and 0.6% sodium pyrophosphate (on the weight of liquor), with addition of ( i ) 0.2 Ib. ferrous ammonium sulphate and 0.2 Ib. sodium hydrosulphite per 100 gall., and (ii) 0.4 Ib. ferrous ammonium sulphate and 0.4 .lb. hydro- sulphite. I n each case the temperature was 130"~ . The results are given in Tublo V.

TABLE V Hydrogen Peroxide Concentration (%)

Time (min.) (i) (ii) 15 0~0B9 0.980 30 0,775 0.677 46 0,704 0,610 60 0.6154 0.401 .. 90 0.662 0.32s

210 0.337 0.238

Tests were also carried out to determine the degree of decomposition of hydrogon peroxido in presonce of iron mordant solutions. They diowed that, in presence of soluble iron, decomposition is ra.pid, but that a precipitate of ferric hydroxide does not cause rapid decomposition. The solutions consisted of 3 vol. hydrogen peroxide with the following additions per 100 gall.- (1) 0.26 Ib. ferrous ammonium sulphate and 0.25 Ib. sodium hydrosulphite; (2) 0.5 Ib. each of ferrous ammoniym sulphate and hydro- sulphite; (3) 1.0 Ib. each of ferrous ammonium sulphato and hydrosulphite; (4) 0.5 Ib. ferrous ammonium sulphate only; (5) 0.6 lb. ferric hydroxide, and (6) no addition. The results are given in Table VI.

TABLE VI Hydrogen Pcroxldc Concentration ( %)

Time (ruin.) ( 1 ) (2) .(3) (4) ( 6 ) (0)

0 0.986 0,980 0,986 0.986 0.980 0,086 15 0.119 0.612 0.0 0.156 04367 0469 60 0.0 0.0 0.0 0.087 0.0 0.828

HOT MOBDANT PROCESS So far the mordanting had only been carricd aut in tho

cold, in order to avoid impairing the handle, luatre und strongth of tho pigmented fibres. It was next docidod to use a warm mordant bath in place of the cold one.

Eighteen bulk trials were successfully carried cut using the following procedure. Mordanting was commencod cold, the temperature of the bath being gradually raised to 130"~. over a period of 3 hr.; the final pH was 4.8.

Jan. 1948 WILKINSON-"BLEACHING OF ANN

Temperature was purposely raised, in order to promote dissociation of the ammonium salt and volatilieation of the ammonia thus liberated, as well as to allow the hydro- sulphite to assist in the destruction of the fibre pigment. The suhscquent hydrogen peroxide bleaching was also commenced cold and the temperature raised gradually to 130"~., but bleaching proceeded for only 1.5 hr. Twelve Ib. sodium pyrophosphate and 2 pints of 0.880 ammonia were added to the peroxide bath, the purpose of the latter addition being to rcplace that lost through decomposition of the ammonium sulphnte in the mordant bath. The volumetric strength fcll in 30 min. from 1.8 vol to 0.93 vol., so the bath was made up to 1.8 vol. again and neutrdieed with ammonia, bleaching being concluded after 1.6 hr. There was little ar no pH variation, the volumetric loss was steady, and there was no rise in temperature due to the chemical reaction.

It is therefore apparent that mordanting should be carried out a t 130"~. instead of cold, and that the final acid state of the bath (pH 4*8), together with thevolatilisa- tion of the ammonia and the utilisation of the hydro- sulphite, has stabilised the bath and given a process which is reliable and controllable. Moreover, the flotation dim- culties experienced in the cold mordant process are less ovident .

The following details illustrate the use of the process on the large scale- For 200 Ib. alpaca use 500 gall. liquor containing 3 Ib. ferrous sulphate, 1.6 Ib. ammonium sulphate and 0 Ib. hydrosulphite. Start. the bath oold and gradually raise the temperature to 130"~. to volatilise ammonia and promote the action of the hydro- sul hite. Next, bleach in 1.8 vol. hyxrogcn peroxide, to which has been atidcd 12 Ib. sodium pyrophosphate and 2 pints of 0.880 ummonia to bring the pH to 8.6. Ble~chirig is commenced cold and the tem- perature raised to 130'~. in 1.8 hr. After SO min. the volumetric strength will have fallen to 0.81 vol. The strength is restored to 1.8 vol. and a further 2 pints of 0.880 ammonia are added. After a furthcr 30 min. the strength will be slightly less than 1 vol., but a t the end of 1.6 hr. a satisfactory bleach will have bcen obtained.

Recently, the question of the "brassy" shade which is obtained with some types of alpaca was raised, and the following tests were cnrried out with a view to deadening this shade. Tho usual peroxide bath was used and common salt was added in amounts varying from 1% to 7.5% on the weight of material. The results showed that the addition of 2.6% salt to the bleach bath is effective in deadening this brassy shadc.

Analyaes were made to determine tho iron content of alpaca after mordanting. With a cold mordant, 0~086% iron was found to be present, and with a warm mordant, 0.07570. Although better bleaches are obtained with fibres which show a high content of iron, fibres from the best bleach baths have not the highest iron content. I t is possible that factors which result in penetration of the Abres by the mordant mlution also facilitate the removal of the iron during bleaching. As an alternntive process, consideration might be given

to the possibility of using acetic acid in conjunction with the ferrous sulphate, with H view to assisting the exhaustion of the mordant bath.

The following recipe is suggcsted- 16 g. ferrous sul- phate, 2 C.C. acetic acid (80%), 10 g. ammonium chloride, and 2-3 g. sulphated fatty alcohol per I . , with a liquor- goods ratio of 26-6O:l. Enter a t 40"c. and stoep over- night. The bleach bath might contain, per 1.. 46 C.C. of 100 vol. hydrogen peroxide, 8-10 g. borax, 2 g. sodium pyrophosphatc, and 2-3 g. of u water.soncnhg agent, e.g. Trilon B (IC), a t 40%.

Rcmoval of the iron from the fibren by means of a souring treatment after bleaching is also worthy Of con- sideration, although tlw extra troatment would prolong the process.

The final pH is 4.8.

:AL FIBRE8 BY MODERN METHODS" 13

The author thanks Mr. H. Wilkinson for advice and aasistance in preparing this paper for publication, and Mr. J. D. Kitohing for helpful criticism.

Discussion Mr. A. CRosBY said that fie had tried different methods

of mordanting with. various shades of alpaca. He had started with black and had reduced i t to a dark brown, and had obtained a reddish-fawn from a dark brown, but beyond that stage he obtained a brassy yellow. Could the Lecturer say why the brassiness appeared?

The Lecturer said that there were certain brown shades of alpaca with which this brassiness was experienced and i t could only be deadened by the use of common salt in the bleaching liquor. I f any attempt wm made to improve the colour by m- of increased volumetric strength, pH or temperature, the lustre, handle and tensile strength were bound to d e r .

Mr. H. FOSTER asked whether other metal salts would give results equal to or better than ferrous sulphate, and whether there was any reason why ferrous sulphate was preferred.

The Lecturer replied that laboratory and bulk tests had shown that ferrous sulphate was undoubtedly the best salt for the mordant proems. Copper salts caused degrada- tion and the bleach bath could not be controlled, whilst tin and aluminium mordants yielded greatly inferior bleached grounds.

Mr. SUTOLIP~E asked whether iron would be present in the fibre or in the liquor.

The Lecturer replied that the goods were washed off thoroughly after mordanting and there waa little likelihood of any appreciable amount of iron being resent in the liquor, but it was reasonable to suppose &at the fibres were impregnated with iron.

Mr. HOLDEN suggested that the conditions in a bleaching bath would hinder the determination of volumetric strength and of pH measurements with the glass electrode.

The Lecturer said that, in the average factory, in- sufficient care was taken when determining the pH and volumetric strength of hydrogen peroxide bleaching liquors. Firma refused to incur the expense of purchasing electrical pH meters, or even B.D.H. universal indicator sets. factory because the peroxide bleached the indicator. Titrations with potassium permanganate solution gave only an approximate indication of the volumetric strength.

Mr. THOMPSON aaked whether peroxide bleaching would remove urine stains from heavy woollens, e.g. blankets.

The Lecturer replied that i t waa doubtful whether urine stains could be removed with relatively dilute peroxide. They were partiallyremoved _.- by a cold solution of hydro-

Mr. J. M. GOODALL mid that the Lecturer had emphagised the need to use primary fatty alcohol sul- phates in the bleach bath. Was there any danger in scouring with a seoondary fatty alcohol eulphate?

The Lecturer said that secondary fatty alcohol sulphates caused some yellowing of the bleached material if used in a bleach bath, but in scouring this question did not arise.

In reply to a question concerning the use of downward flow in a Huasong machine, the Lecturer said that if upward flow w8s used. especially with y a m and dubbing, there was a risk of felting.

Mr. F. WILKINSON asked the Lecturer whether he advised mordanting prior to bleaching in piece form.

The Lecturer replied that he did not recommend the mordant pretreatment for any goods in piece form, owing to the difflculty of obtaining even impregnation with the iron salt, which was essential if bleaching was to be even. The normal hydrogen peroxide process gave excellent results with alpaca, cashmere, mohair and camel hair pieces.

The w e of indicators, however, was not very satis-,

eulphite.

A4