The Chemical Technology of Wool Processing

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  • The Chemical Technology of Wool

    k p h C O D k p h

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    k p h C O O k p / h k p i h C O O k p I h : I2 'I 56 166 66 54 49 32

    J R McPhee" and T ShawT International Wool Secretariat

    'Wool House Carlton Gardens London SWlY 5AE

    tDevelopment Centre Valley Drive llkley West Yorkshire LS29 8PB

    I NTRO D UCTlON This paper is an attempt to review development in wool wet processing, during the last 50 years, from raw wool scouring to final fabric and garment finishing processes. As such, its scope is wide, despite the fact that only one fibre type is considered. Therefore, emphasis is given to those developments which have reached or look likely to reach commercial fruition. No attempt is made to cata- logue all the published papers and patents in a particular area; rather, the aim is to concentrate on those major developments which have made real advances possible at the industrial level.

    Although the chemical technology of wool wet pro- cessing is the main theme of the paper, relevant machin- ery developments will be discussed (though necessarily somewhat superficially), especially in cases where such developments have enabled new principles of process- ing to be adopted.

    SCOURING Raw Wool Scouring Raw wool scouring has seen many important changes during the last 50 years. Formerly, soap and soda scouring was universal and the scourer's sole motive for any form of effluent treatment was to recover the wool grease so that it might be sold. It was only in the late 1950s and early 1960s that scourers in some regions of the UK were prevented from discharging effluent directly into river systems. Again, 20 years or more ago, water and energy were relatively cheap and there was little incentive to save either commodity. All these factors have now changed and modern scouring systems are designed to be economical in the use of water and energy, and to reduce effluent contamination by the use of in-scour recycling processes for removal of grease and dirt from the effluent and for the conservation of scour liquors.

    According to Schofield & Schofield [l], wool scourers in 1935 generally used three to five flat-bottomed con- ventional bowls, although the Petrie & McNaught self- cleaning bowl was coming into more common use. Side tanks were sometimes employed to receive the heavily contaminated liquors from the mangles at the end of each bowl and to float off the bulk of the grease before returning the scour liquor to the bowl. Alternatively, mangle liquors were discharged directly into the drain.

    Perhaps the most sophisticated wool scouring system available at that time was the Duhamel 'Natural Emul- sion' system, which is described by Schofield & Schofield in the following terms:

    'The bowls are of much smaller capacity than the average English plant, and are designed with special settling troughs .... to allow regular discharge of the sediment. Liquor contaminated with grease is separated . , . . the lanoline (sic.) being recovered; the scour remain- ing is pumped to a reservoir and fed .. . . to the first bowl . . . . The process is continuous in respect of both recovery of the grease and supply of the liquor, water, etc.'

    Several features of the Duhamel system appeared in the WRONZ rationalised flow system some 40 years later [2]. A typical installation is illustrated schematically in Figure 1. The WRONZ system incorporates heat recovery and makes use of conventional bowls, but the liquor flow arrangements are very similar to those of the Duhamel system, consisting essentially of a loop taking greasy liquor from bowl 1, passing it through a heavy solids settling tank and a centrifugal separator then returning the partially degreased liquor to the first scour bowl. Some time later, WRONZ redesigned the scour bowls from first principles and produced a short, hopper-bottomed bowl. Together with improved ar- rangements for liquor recycling and a more sophisticated heat exchange system, these bowls form the basis of the WRONZ Mini-Bowl scouring process [3], illustrated in Figure 2. When used for scouring crossbred wools, it IS reported that this system can operate with very low liquor usage (about 1.5-2 I/kg greasy wool) in the main scouring sections and as much as 60% of the grease can be recovered in-scour [4].

    A second scouring system of recent development is the CSlRO Lo-Flo system [5,6]. This system uses the principle of 'concentration destabilisation' to increase centrifugal recovery of grease and dirt and to reduce water usage in scouring even further. If grease, dirt and suint salts, present in the wool, are allowed to build up to very high levels in the scour bowls, then the resulting emulsion can be easily cracked by heating to 95 C and the grease and dirt separated centrifugally. However, in order that the wool can be wet out with the highly concentrated scour liquor and then squeezed at the nip without blockage, it was necessary to redesign the scour bowls to use the wash-plate system rather than immer- sion. (See Figure 3).


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    Figure 2 ~ Schematic diagram of the WRONZ Mini- Bowl scouring system (Reproduced by courtesy of Wool Sci. Review)

    wool ironi leeti hopper - 3p-l spray,

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    punip v u n w piinip

    Figure 3 ~ CSIRO Lo-Flo scouring unit consisting of three wash-plate bowls (Reproduced b y courtesy of CSIRO, Division of Textile Industry, Belmont, Victoria, Australia)

    By allowing total solids to build up to levels of 25% or more in the Lo- Flo unit, it is claimed that 80% removal of grease from the scour liquors can be achieved by centri- fugal extraction. The Lo-Flo unit is not a complete scour in itself, but is meant to replace the first one or two bowls of a conventional scour. A prototype system has been installed by the IWS, in a Yorkshire mill, and operated under industrial conditions for several years. Known as the Mini-Flo system, the line consists of a three-bowl Lo-Flo unit followed by two self-cleaning conventional scour bowls and two conventional rinse bowls [7,8]. Liquors from the Lo-Flo unit and the conventional bowls are both recycled through interconnected loops incorpo- rating heavy solids settling and centrifugal separation. Total grease recovery achieved in practice over several years' operation has exceeded 65%.

    In an idealised Mini- Flo scouring system, proposed by Gibson, Morgan and Robinson [7,8] a two-bowl Lo-Flo unit would be followed by three WRONZ Mini-Bowls and two conventional rinse bowls. The Lo-Flo unit would act as the main agency for suint and grease removal from the wool, whilst the Mini-Bowls would be incorporated for their efficient powers of dirt-removal. The low-volume, highly contaminated flow-down from the first Lo- Flo bowl would be purified by evaporation and the only aqueous effluent from the system would come from the third of the Mini-Bowls. Projected grease recovery from the system would be in excess of 70%. The aqueous effluent would be relatively low in quantity and would contain only about 15% of the total COD present in the contaminants on the wool.

    The secondary treatment of the dilute effluents pro- duced from modern wool scours is necessary before

    discharge to drain in some countries, and in other countries, where municipal effluent treatment charges are high, it might make good economic sense. Such treat- ments are beyond the scope of this article, but the interested reader may find reviews elsewhere [7,8].

    At the beginning of this section, it was stated that soap and soda scouring was the universal practice in 1935. Nowadays, that is no longer true and it is normal to scour wool with nonionic detergents. Ethoxylated nonyl phenols ( 8 to 9 EO units) are the detergents of choice, where their use is permitted. Otherwise ethoxy- lated straight-chain alcohols are used for their easier biodegradability. The advantage of scouring in alkaline conditions is now questioned and soda is no longer used in many scours, although a neutral salt, e.g. sodium sulphate will then often be used as a builder. In 1935, the only synthetic surfactants available were sulpho- nated oils and sulphonated fatty alcohols and although these compounds were good wetting agents, their powers of detergency were limited and they were not used in scouring.

    Yarn Scouring The majority of wool scoured in yarn form is destined for carpets and most is spun on the woollen system. For- merly, olein-based lubricants were used exclusively for woollen system spinning and consequently scouring was carried out by the saponification system using soda ash only and forming the necessary soap by reaction with the oleic acid content of the lubricant. In more recent times, there has been virtually a complete change to the use of water-miscible polyglycol type lubricants for carpet yarn spinning. These can readily be scoured using nonionic detergents in neutral conditions. Where carpet yarn blends contain substantial proportions of unscoured wools, mineral wool oils (mineral oil plus nonionic surfactant) are used for lubrication. In such cases, scouring is normally carried out in alkaline condi- tions (soda ash) using nonionic detergent. Yarns of this type which are to be hank dyed must be scoured before dyeing, but yarns spun in polyglycol lubricants from clean wools may be dyed without scouring, since the water-soluble lubricant is removed from the yarn into the dyebath and does not interfere with the dyeing process.

    The machinery used for yarn scouring has changed hardly at all in the last 50 years. Yarns are wound onto hank and transported through scouring sets by systems of tapes or brattices. Usually the sets have four bowls: two scour bowls, one rinse bowl and a final bowl where acidification and mothproofing may be carried out. There is, at the present time, an increasing tendency to use the yarn scour as a chemical processing machine [9]. Methods for chemical setting of carpet yarns [lo] and for antistatic treatment [9] have been described and are in daily use in industry.

    By comparison with the sophisticated processes and machines developed for raw wool scouring, it must be said that yarn scouring has developed little. Modern wool scouring is a truly continuous process. Bowls flow down continuously and are replenished with chemicals to maintain steady state condition, as the run progresses. Scours may run for days on end before it becomes necessary to dump bowls. In yarn scouring, however, it is normal to scour lots of only 1-2 tonnes of yarn before all bowls are dropped to be made up afresh for the next lot to be processed. Whilst additions of detergent and sodium carbonate or bicarbonate are often made manu- ally during a run this is normally done on an ad hoc basis, which in reality amounts to no more than guess- work. This system apparently gives acceptable results,

    REV. PROG. COLORATION VOL. 14 1984 59

  • but is probably wasteful of chemicals and there is little doubt that the residual oil content of the scoured yarn tends to rise during a run.

    Scouring of Knitwear The lubricants used for spinning woollen hosiery yarns are of two types. The first is a mixture of mineral oil, fatty acids (olein) and triglycerides, whilst the second is of the mineral wool oil type (mineral oil plus nonionic surfac- tant). Certain shrink-resist processes carried out on woollen spun knitwear are very sensitive to residual lubricant on the garments and here, the mineral wool oil type of lubricant shows decided advantages, being readily scourable to low residual levels with either non- ionic detergent or soap and soda. The mineral oil/fatty acid/triglyceride type of lubricant must be soap/soda scoured when shrink-resist processing is to follow and even then, satisfactory scouring is often exceedingly difficult to achieve if oxidation of the oil has occurred, on old stocks of yarn for example.

    Developments are now taking place which should provide hosiery yarn spinners with the fatty blend type of lubricant that most of them seem to prefer, but which is at the same time readily scourable either with soap or nonionics.

    Scouring of Woven Fabrics Here again is an area where few fundamental changes have taken place. Woollens are still mostly lubricated with olein-based products or mineral wool oils. Worsteds may be lubricated, as in former times, with natural oils of vegetable or animal origin, or with the more recent polyalkylene glycol based lubricants with or without mineral oil additions. Smaller quantities of oil are now used on worsteds since dry combing came into common use. Batchwise rope scouring in the dolly, using soap and soda, remains the most widely practised method of removing these lubricants and other contami- nants from woven fabrics. Processing in rope form has undoubted advantages in removal of reed marks and the creation of bulk and a kindly handle in wool fabrics, which open-width scouring is unable to provide. Certain delicate fabrics are scoured at open width, however, most commonly in a batchwise manner, but sometimes continuously. Continuous open-width solvent scouring has never assumed much importance in the woven wool industry, although it is believed to be especially useful in preparing wool/polyester worsteds for piece dyeing.

    Machinery for piece scouring has changed little in principle and the basic components of the scouring dolly remain the same. However, important detail advances have been made which have undoubtedly improved the quality and consistency of results from the dolly. Auto- matic control of scouring, including addition of reagents, is now common. The system introduced by Hemmer, whereby jets of scouring liquor are forced into and through the fabric ropes as they pass through a jet box immediately in front of the nip rollers enjoys deserved popularity. Another Hemmer innovation is the use of stripping rollers which takes the fabric from the nip and throw it against the back of the machine. This system has several advantages. It allows high running speeds to be used (up to 200 m/min) without the danger of the fabric wrapping around the nip rollers and without the forma- tion of rope marks in the fabric. It also allows a modest degree of milling to be achieved which may be sufficient for lightly milled worsteds.

    Reference has already been made to the continuing widespread use of soap and soda ash as the medium for

    scouring wool piece goods. It is probably true to say that no one would have predicted this situation 50 years ago. At that time, sulphonated oils and fatty alcohols were achieving prominence as wetting agents and detergents, and were certainly a subject of popular debate at the time, as witnessed by no fewer than four papers on the subject intheJournalsof 1933and 1934 [ l l -141. Such products were used in some quantity for scouring wool goods and were followed at a later date by nonionic detergents of the ethoxylated nonyl phenol type. But the majority of the industry has always returned to the use of soap and soda, possibly for reasons of conservatism, but more probably because this system has certain advan- tages in promoting bulking, good handle and other desirable but difficultly definable properties. Despite these remarks, there is a slow trend towards neutral scouring using synthetic anionic or nonionic detergents and this method is particularly useful in cases where there are doubts regarding the fastness of colours to alkali.

    CARBONISING Carbonising may be carried out on loose wool, or on piece goods after scouring. During the last 50 years there has been a consistent movement towards the latter practice, which has probably accelerated recently. Now, there are only a handful of loose wool carbonisers in Europe and in many countries (e.g. West Germany and the USA) it is common practice to carbonise worsted piece goods as well as woollens.

    However, the methods used for carbonising have changed very little and it may be said that, considering the potential of carbonising as a fibre-degrading pro- cess, it is often poorly controlled and carried out on old and inefficient equipment.

    Some 20 years ago, the importance of using an efficient wetting agent in the acidising bath was recog- nised [15-181, A more level treatment is thus ensured and degradation of the wool may also be decreased, though the mechanism of the protective effect is by no means sure. Wetting agents are now used by virtually all carbonisers. 50 years ago, acid-stable wetting agents were not available, although the need for them seems to have been appreciated [14].

    The wool substance is attacked most rapidly by sul- phuric acid of intermediate concentrations. Therefore, it is important that drying prior to baking is carried out either at relatively low temperature, so that reaction of the acid with the wool is slow, or very quickly, so that the time of exposure of the wool to critical acid concen- trations is only brief [19].

    The neutralisation of the wool fabric after carbonising is an important part of the total process. Fabrics allowed to lie without neutralisation at moderate humidity may suffer considerable damage, so it is essential that neutralisation should take place soon after carbonising unless another wet process is to follow immediately. Neutralisation in the winch is slow and consumes large amounts of water. The best type of machine for neutrali- sation is probably an open-width scouring machine, working on the liquor-through-fabric principle. Neutrali- sation with ammonia or ammonia/ammonium acetate mixtures removes acid from the fabric far more rapidly than either sodium carbonate or sodium acetate and is to be preferred [20, 211.

    It is the practice in some countries to follow carbonis- ing by piece dyeing in strongly acid conditions using 1 :1 metal-complex colours. This method of processing can produce severe fibre damage unless conditions are very carefully controlled [22]. Further damage can be caused


  • by pressure decatising fabrics dyed and finished in this way and decatising at atmospheric pressure is recom- mended in these cases [22].

    FELTING AND MILLING The unique felting property of wool and other animal fibres has been exploited for many years in milled fabrics and felts. True felts (i.e. fabrics produced without a spinning process) will not be dealt with here and the discussion will be confined to felting/milling of yarns, knitwear and woven fabrics.

    Yarn Fel t ing The production of felted yarns, mainly for use in carpets, has increased in recent years and it is estimated that approximately 12 m kg of such yarns was produced worldwide during 1982 [23]. Various methods are used for yarn felting, including tumbling yarn hanks in aqueous washer/extractors or in rotary solvent machines in the presence of milling aids and a small amount of water [24]. The latter is probably the most widely used process. Some yarns are still milled in hank form in the traditional fulling stocks and also in various home-built devices of widely differing design. Milling may also be carried out simply by tumble drying of wet yarns [25]. In all these batchwise processes success is dependent upon careful selection of wools and yarn structure in order to minimise felting between yarns in the hank.

    A new continuous yarn felting process known as the Periloc system is now entering industry [23]. The pro- cess is capable of processing twistless structures such as rovings or condenser slubbings as well as yarns and this is something which the batch processes cannot do. In the Periloc machine, the yarns and felting medium are fed through flexible polyurethane tubes, which are agitated by means of a rotor around which they pass. (See Figure 4). Arms on the rotor alternately compress and release the tube and set up a peristaltic action which carries the yarn along. The Periloc machine is highly versatile and its products range from bulky yarns stabil- ised by surface fibre felting only, to dense, highly felted structures.

    In addition to their obvious uses in creating new textures, felted carpet yarns have been shown to give carpets of superior performance. Fibre shedding is re- duced and both durability and appearance retention improved when compared with carpets made from con - ventional yarns.

    Mi I I i ng of Kn i twear Milling of woollen-spun knitwear is usually carried out in rotary washer-extractors. The latest of these machines have fully programmable automatic controls, including control of chemical additions and are claimed to be more economical in their use of water, energy and labour than the older manually operated machines.

    Garments are nowadays, most often milled in nonionic detergent and sodium bicarbonate or polyphosphates. Some formulated soap-based products are also available.

    Wool knitwear may be finished entirely in batch solvent processing machines. Scouring, milling and shrink-resist treatments may all be carried out in the same machine [26] and this method is popular with many smaller processors, who have no other facilities for wet finishing. Batchwisz sol*/ent processing is also used for finishing knitted piece goods of a delicate nature.

    Milling of Woven Piece Goods Little has changed in the principles or practice of piece good

  • the chemical basis of setting. Speakman's results were quickly used by the hair cosmetic industry in the setting of permanent waves, but it was not until the 1960s that exploitation of his discoveries began in the wool finish- ing industry, although bisulphite setting had been used for pleated skirt panels since the mid-1950s [31]. Dur- ing the 196Os, setting could fairly be described as a favourite subject of wool research and development laboratories [32] and this activity led to the development of practical processes for use in the permanent f lat setting of fabrics, setting of permanent creases in trousers, or pleats in skirts [33-351.

    Chemical flat setting, by impregnating fabrics with sodium bisulphite or monoethanolamine sesquisulphite solutions followed by atmospheric-pressure decatising, was widely practised in the late 1950s and early 1960s as a process for permanent finishing of wool fabrics, but quickly fell into disuse from the late 1960s onwards when machinery manufacturers began to build machines for rational and efficient pressure decatising [36-381.

    Pressure decatising in batch machines, cleverly arranged with separate batching, steaming, cooling and de-batching stations, is now the standard method of providing wool worsted fabrics with a permanently stabilised finish. This process has many advantages over the wet chemical setting methods previously used. Most of all, it is a dry process and therefore cheaper and more convenient in use. Also, degradation of the wool fabric is less likely to occur if the process is not controlled quite so well as it should be. Its major disadvantages are that steaming at high temperatures tends to yellow the wool and there is a variation in the finish produced from the inside to the outside of a batch.

    Several types of continuous permanent decatising machine have been produced in order to overcome this latter defect and these machines have met with varying degrees of success. Undoubtedly, the most sophisticated is the Wira/Mather and Platt Ekofast [39] which is a continuous autoclave setting machine with patented Vaporloc seals [40] at the entry and the exit. Despite early problems in providing suitable endless wrappers to convey the fabric through the machine, it now operates successfully in several mills. In one mill, the machine is the basis of a continuous dry finishing line for worsteds, which comprises a three-head automatic shearing machine, a dewing and damping machine, an automatic weft straightener and the continuous pressure decatiser, which performs the functions of pressing, decatising and permanent finishing [41].

    Other approaches have been taken towards the pro- duction of continuous permanent finishing machines. Blankenburg and Breuers [42] have described a method in which wool fabric is sprayed to 20% wet pick-up with a solution containing 2 g/l sodium bisulphite and 2 ml/l benzyl alchol or a surfactant, then passed through a continuous atmospheric decatising machine. A second method of obtaining permanent effects at atmospheric pressure has been described by Riedel [43] and is used in the Kettling and Braun Contidec 61 5. First, the fabric, under constraint from wrappers providing high mechan- ical pressure, passes over a steaming cylinder, then a vacuum cylinder. This produces a high level of finish. The cloth then passes to a third cylinder, where it is steamed under reduced mechanical pressure to remove almost all the non-permanent part of the finish already given. The finish which remains is claimed to be perma- nent to steam pressing during garment manufacture. It is difficult to believe, however, that this method can give a finish with the same degree of permanence as is achieved by pressure decatising or chemical flat setting.

    Continuous decatising machines for (non-permanent) atmospheric pressure finishing have begun to find wider acceptance in the industry. Whether this is because initial prejudice against these machines has been over- come, or whether the machines themselves and the effects they produce have improved, it is difficult to say.

    Continuous processing has also found wide accep- tance in crabbing. Crabbing by traditional methods tends to be a dirty process, giving rise to the possibility of stained fabrics. The operation is slow and labour- intensive and must be carried out with care if subsequent piece dyeing is to be level, without listing or ending. The continuous crabbing machine of modern design (e.g. the Hemmer Conticrab or Minicrab) overcomes all these problems and disadvantages.

    The other traditional setting process ~ potting or boiling - was widely used 50 years ago as an essential part of the production of the so-called dress face finish on woollen fabrics. Nowadays, the process is used only by specialist manufacturers of billiard cloths and certain uniform fabrics. As an alternative means of producing the soft, full handle which potting gives, wet decatising is sometimes used, especially in continental European mills.

    SHRINK-RESIST PROCESSES It is in the field of special finishes that the chemical technology of wool processing has made the most important advances in the last 50 years. Processes for the production of flame retardant and insect resistant wool will also be dealt with in this review, but it is probably true that more effort has been put into the development of shrink-resist processes during the last 20 years than into al l other special finishes combined.

    Oxidative Processes In the 1930s the only processes in use for shrink-resist treatment of wool were based on chlorination. Sodium hypochlorite or bleaching powder were the usual sources of chlorine and both acid and alkaline condi- tions were used for application. Results from these processes were probably very variable, because the processes were poorly understood and badly controlled. Tendering, weight loss and yellowing were probably common and the levels of shrink-resistance attained were almost certainly unreliable. Early systematic investi- gations of the parameters influencing shrink-resistance and fibre damage led to the possibility of improved results [44], but still, chlorination of piece goods remained difficult to control.

    During the 1940s, several commercial chlorination processes were developed which attempted to overcome the problems of control.

    Notable amongst these were the Negafel process [45] using hypochlorite with formic acid at pH 4, rather than the then more usual hydrochloric acid and the Harriset process which employed alkaline hypochlorite for very short times in a continuous process [46].

    A second family of processes, which was developed with the idea of controlling the rate of chlorination, relied on the use of nitrogen-containing products which could form N-chloro compounds with the hypochlorite in the treatment bath, and thus act as retarders or chlorine sinks. Such processes included that of Shapiro [47] using sodium sulphamate, the Ciba Melafix processes, which used melamine-formaldehyde compounds [48] and the Chloregal G process of J R Geigy Co., which employed a triazinyl compound [49].

    Concurrently, there were processes in use which employed oxidising agents other than chlorine - or in

    62 REV. PROG. COLORATION VOL. 14 1984

  • addition to chlorine. Thus, a peracetic acid/hypochlorite process was reported to produce wool of good white colour with little weight loss [51]. The Dylan Z process employed potassium permanganate and sodium hypo- chlorite [52] and gave a shrink-resist wool of good colour and very soft handle. Dylan later dispensed with chlorine altogether in the Dylan X processes, which used permonosulphuric acid [53]. Workers at CSIRO in Australia also developed processes using neither chlorine or chlorine-generating reagents in their perman- ganate/salt and bromate/salt processes [ 54,551

    Finally, a series of oxidative processes based on sodium dichloroisocyanuric acid (NaDCC) was devel- oped. NaDCC may be regarded as the ultimate of the chlorine retarders or chlorine sinks in the respect that it is sufficiently stable to exist as a solid compound. Several chemical companies manufacture NaDCC, which is widely used as a convenient source of chlorine, chiefly for disinfectant purposes. Several shrink- resist processes based on DCCA have been developed [50] and there are also the hybrid processes using DCCAipermonosul- phuric acid (Dylan X2) [56] and DCCAipermanganate (Orced process) [57]

    All of these various oxidative processes may be used in several ways, and most of them have both batch and continuous versions. The former are most often employed for the treatment of knitted garments in side-paddle or rotary dyeing machines, but are also used to treat woven or knitted piece goods in winches. The continu- ous processes are carried out on tops or card sliver in backwashers, with or without modification. Pad store versions of some of the processes are also available for slivers or woven fabrics and use pad mangles for appli- cation of the oxidising bath, followed by a J-box or storage scray.

    An antichlorination and neutralisation step invariably follows the oxidative process and sodium metabisulphite or sodium sulphite, perhaps with addition of alkali is usual I y employed.

    Aside from the mainstream of wet oxidative processes, dry chlorination processes were developed and commer- cially used from time to time. In 1934, Wira patented a process for gaseous chlorination [58] and their method was used to treat considerable quantities of loose wool and tops for use in hosiery during the Second World War. At a later date, CSlRO proposed a method of dry chlorination and developed an all-plastics machine for its application to blankets on a commercial scale in Australia [59]

    The most recent of oxidative methods is the Kroy Deepim process [60]. This is a continuous process for slivers, using the principle of vertical deep immersion to displace air from the slivers, thus ensuring that all fibres are contacted by the chlorinating solution, which is made simply by dissolving chlorine gas in water at 10 C. A schematic diagram of the Kroy machine appears in Figure 5. After chlorination, the wool is passed to a conventional backwasher where subsequent antichlor treatment can take place, followed perhaps by polymer treatment and application of a softener. It is claimed that the Kroy Deepim process produces a far more level treatment than other continuous chlorination processes and therefore a lower level of treatment can be used for a given effect.

    Non-Chlor inat ion Polymer Processes Although the first processes using polymers alone to give shrink-resist wool were proposed in the 1940s [61], it was not until the early 1960s that processes were developed which later enjoyed industrial use on a sig-

    WOOL IN-

    chlorine solution spray

    react ion vessel


    fume extractor water rinse

    squeeze rollers

    mesh belt

    fume extractors drip tray

    Figure 5 Schematic diagram of the Kroy Deepim continuous top chlorinating machine

    nificant scale. During the following decade, the founda- tions were laid for almost al l the processes in use today.

    Historically speaking, the first of these processes to enter industry was the interfacial polymerisation process (IFP), developed at the Western Regional Laboratory of USDA [62]. Versions of this process for continuous treatment of piece goods [63] and tops [64] have been described. The basis of the process is the in siru forma- tion of polymers on the wool surface by interfacial polycondensation. First, the wool was run through an aqueous bath containing a diamine, then through a bath containing a diacid chloride in an organic solvent, which resulted in the formation of a polyamide film on the fibre surfaces. It was then necessary to scour the fabric to restore its handle, or to rinse the top in nonionic deter- gent and formic acid before drying and gilling. The extent to which these processes were used is not known, but this method for treatment of tops was the basis of the Bancora process used by the Jos. Bancroft Company.

    Later, the same group of workers developed a related series of processes in which preformed solvent soluble polymers were crosslinked on the wool surface by small bifunctional water-soluble molecules. Alternatively, water-soluble polymers might be crosslinked with sol- vent soluble bifunctional compounds [65-67]. This method of treatment, known as phase boundary limited crosslinking (PBLC), allowed a variety of polymers to be formed on the wool surface, including polyureas, cross- linked polyolefins, polysiloxanes or polyfluoroacrylates, thus giving the possibility of oil-and water-repellent treatments as well as shrink resistance.

    Before long, the inconvenience of using organic sol- vents in textile finishing, and the advent of newer processes told against the IFP and PBLC methods and they fell into disuse.

    Almost contemporary with the USDA processes described above were processes using self-crosslinking polymers applied from solvent only. These polymers found their greatest use for the treatment of knitwear in batch solvent machines. Zeset TP (DUP) was a polyole- fin with pendant acid chloride groups, which cured by reaction with atmospheric moisture [68]. Unfortunately, the polymer was rather too reactive in this respect, and

    REV PROG. COLORATION VOL. 14 1984 63

  • its shelf life, and the life of made-up treatment baths was rather too short in industrial use.

    Synthappret LKF (BAY) [69] is still in use today. It has a branched -chai n pol yet her backbone capped with an aliphatic isocyanate. This polymer also cures by reaction with atmospheric moisture, but nevertheless has acceptable shelf life and gives a stable treatment bath. At a later date, a thiol-capped polyether, Oligan 500 (CGY), was introduced [70]. This polymer cured by reaction with atmospheric oxygen and was indefinitely stable until after application to the wool. Although the thiol- based polymer was used industrially for solvent applica- tion, it is no longer manufactured today.

    Some harshening and stiffening of handle resulted from the application of all these systems, but this was overcome by the introduction of the silicone-based Dow Corning DClO9 polymer system for batch solvent appli- cation [71-731. The DC109 system is believed to consist of a dihydroxy-polydimethylsiloxane crosslinked by a polyfunctional amino alkoxy silane.

    Although the thiol-based polymers had relatively short lives as commercial procucts, they did iead the way to a new kind of process. Their stability towards water, which was not shared by any other of the reactive self- crosslinking polymers available at the time, enabled their application to woven and knitted piece goods from aqueous emulsion in a pad mangle [74]. The polymer formulation used was Oligan 3904, a 40% aqueous emulsion of Oligan 500. At a later date, an improved polythiol, Oligan 3964 (CGY) was introduced [75,76].

    Two other polymer systems had, by that time, been developed for application to piece goods by aqueous padding. The first of these, Synthappret BAP (BAY) was the bisulphite adduct of Synthappret LKF [77]. It is applied in conjunction with a polyacrylate or a polyure- thane dispersion in the Sirolan BAP process [78-801. Lankrolan SHR3 (Diamond Shamrock) is a thiosulphate (Bunte salt) derivative of a polyether and may be applied in a pad-dry-cure process [81] or a pad-batch (wet cure) process [82]. The latter is claimed to give im- proved handle. Aqueous silicone-based polymer sys- tems are also produced - e.g. Ultratex ESB/ESC (CGY) - but little information on this system or its application is available in the public domain.

    The latest developments in polymer application tech- nology are long liquor exhaust processes which may be used for treating knitwear or piece goods. No oxidative pretreatment is necessary. The first of these processes were developed for Oligan 3964 and the Synthappret BAP/polyurethane dispersion system [83,84]. By addition of divalent metal salts (e.g. magnesium chlor- ide) to the treatment bath the polymers are caused to exhaust onto the wool and may be cured in the bath by addition of soda ash or ammonia. A similar process has been described for application of Lankrolan SHR3 [85] and it is also possible to apply the Ultratex ESB/ESC system by exhaustion, though no details are published.

    Chlorination-polymer Processes Parallel with the development of polymer-only shrink- resist processes came a series of processes in which the wool is first pretreated by an oxidative process and then treated with a polymer. These ideas originated in CSIRO, Australia in the 1950s and early 1960s [86-901. The theory which emerged involved a consideration of the physical chemistry of surfaces and adhesion, and stated that if the critical surface energy of the wool fibre could be raised by the pretreatment to a higher value than the surface tension of the liquid prepolymer which was applied, then the polymer would spread on the fibre and,

    provided other criteria were met, it would adhere [go]. Acid chlorination was found to be the most effective practicable means of raising the critical surface energy of wool to the required levels.

    As a result of this work, the CSIRO chlorination-resin process for continuous shrink-resist treatment of tops was evolved [91]. The polymer chosen for the process was Hercosett 57 (Hercules) a polyamide-epichlorhy- drin resin. Since its introduction in 1967, use of this process has grown until it now accounts for almost three-quarters of the world's production of machine washable wool. (Total about 26 mkg in 1982) [92]. The original process employed a specially constructed G RP bowl for chlorination and for a time, chlorine water was used in this bowl before it was replaced with acid hypochlorite. Later versions used a horizontal pad mangle for chlorination [93] and then a suction-drum backwasher bowl [94]. Finally, the Kroy chlorinator [60] has been used and it is claimed that full machine washability can now be obtained using lower applica- tion levels of both chlorine and resin [95]. Figure 6 [96] shows a series of typical plant arrangements used indus- trially for the chlorination-Hercosett process. In each case, the chlorination bowl could be replaced by a Kroy Deepim chlorinator.

    Precision Processes (Textiles) Ltd has also developed a similar continuous chlorination-resin process, using conventional backwashing plant [97]. Details of this process, known as Dylan GRC, are available only to licensees.

    Chlorination-resin treatments are widely used on knitwear [98]. The processes are mostly carried out in side paddle dyeing machines, but programmed low liquor machines (e.g. Neil & Spencer Dytex or the Dreher-Milnor machine) are coming into more frequent use and offer savings in water, energy and labour costs.

    The use of chlorination-resin treatment on knitted garments was first proposed in 1970 [99]. Initially, the Melafix II chlorination process was used, followed by Hercosett resin treatment, but more recently treatment with NaDCC at 20 C and pH 3.5-4.0 has become more common. In the Dylan GRB process, chlorination is followed by treatment with Polymer G (PPT Ltd), but as usual with Dylan processes, precise details are confiden- tial to licensees.

    .. .. . , ~. . . .

    I... .. .. , . .. . .

    / . , . I . . .. , ,, .. ... 1 .


    ,. . .. . .. .. ,. I.. ,x.. .. " , . . . .

    Figure 6 - Plant layouts used for the chlorination- Hercosett process. Top to bottom: 5-bowl plant using suction drum and conventional back washing bowls, 5-bowl plant using suction drum bowls only, 6-bowl plant using suction drum bowls only, 8-bowl plant using suction drum bowls and double drying (Reproduced by courtesy of Wool Sci. Review)

    64 REV. PROG. COLORATION VOL. 14 1984

  • Industrial Use of Shrink-resist Processes Although all the processes described in this section have been used industrially at some time, it seems worthwhile to attempt to give the reader some idea of present day industrial usage. The use of processes giving full machine washability is closely monitored by the IWS, although the same is not true of processes giving lower standards of washability and it is difficult to provide statistics in this area.

    It is estimated that in 1982, 26 m kg of wool was treated to fully machine washable standards. Of this, 75% was treated in top form, mostly by the chlorina- tion-Hercosett process. 23% was treated as knitted garments mostly by aqueous chlorination-resin process (Dylan GRB or chlorination-Hercosett). Polymer-only exhaust processes using Synthappret BAP or Lankrolan SHR3 were not widely used. Likewise solvent treatment of garments was on a relatively small scale, mostly using silicone systems, such as DC109, although some Synthappret LKF was still used. Only 2% of the total of machine washable wool was treated in knitted or woven fabric form, most of this using the Synthappret BAP (Sirolan BAP) pad-dry process.

    Oxidative processes are still in wide use, especially on knitted garments. Perhaps the most popular, in terms of production volume being processes based on NaDCC and permanosulphuric acid.

    INSECT-RESISTANT FINISHES Insect proofing is probably the least glamorous of all the special finishes applied to wool, yet in terms of volume of wool treated, it is by far the most important. About 200 m kg of wool are given an insect-proof finish each year and most goes into carpets; other less import- ant end uses for insect proofing being upholstery fabrics, blankets, uniform fabrics, knitwear and hand knitting yarns.

    Mothproofing Agents Synthetic- mothproofing agents have been available for more than 50 years. The first of these were Eulan New and Eulan CN Extra, marketed by I G Farbenindustrie in the 1930s [100,101]. These were sulphonated triphe- nylmethane derivatives (I and II, Figure 7) with insectici- dal propenies. They were applied to wool by exhaustion from acid baths at the boil and could be applied simulta- neously with dyes. A few years later, J R Geigy Co. introduced Mitin FF (Ill, Figure 7). again a mothproofing agent of the colourless acid dye type [102]. In a more concentrated form - Mitin FF high conc. - is a moth- proofing agent still in use today, mostly for the treatment of uniform fabrics, where its superior fastness is most advantageous.

    These early mothproofing agents were expensive and required high application rates, typically 2-3% on weight of wool. As a consequence they never enjoyed the scale of use of their later counterparts.

    In the late 1950s the first of the highly effective and relatively inexpensive modern mothproofing agents were introduced. Eulan U33 (BAY) (IV, Figure 7) followed the chlorinated colourless dye tradition. Eulan WA New, which was first marketed in the early 1960s contained the same active ingredient, but was a more dilute prod- uct. The introduction of dieldrin-based mothproofing agents (V, Figure 7) in 1958 [ lo31 followed a discovery at CSIRO that hydrophobic insecticides, having no inherent affinity for wool, could successfully be applied by exhaustion from acid dyebaths if the insecticide was emulsified in the bath [104].

    The introduction of these inexpensive mothproofing

    C I k + , A A J C I OH cp OH

    I CYNa $: II


    V CI V I

    CH3 FH3

    V I I V l l l

    Figure 7 - The active ingredient of some mothproofing agents used commercially during the last 50 years: I.Eulan New, II. Eulan CN Extra, 111. Mitin FF, IV. Eulan U33, V. Dieldrin, Vl. Mitin LA, VII. Mitin LP (second active ingredient), VIII. Permethrin

    agents led to a huge expansion of industrial mothproof- ing in the 1960s and this was effective in reducing the incidence of insect attack on wool goods to very low levels. Unfortunately, there is evidence that, 20 years later, both the textile industry and consumers have become complacent about mothproofing, and the IWS has found it necessary to expand its technical and quality control activities in this area in order to ensure that Woolmark products susceptible to insect attack are satisfactorily protected [ 1051.

    Development of mothproofing agents continued dur- ing the 1960s and 1970s. Ciba-Geigy introduced Mitin LA conc. (VI, Figure 7) in the early 1970s [106]. This product was more recently replaced by Mitin LP, which probably contains the synergistic mixture of compounds IV and VII in Figure 7 [107].

    Very many general purpose insecticides have been examined for use as mothproofing agents [108,109 and references therein] and as a result of this activity, new mothproofing agents based on synthetic pyrethroid insecticides have recently entered the market. Several of these - Perigen (Wellcome/Stephenson Bros.), Moth- proofing Agent 79 (Shell), SMA-V (Vickers), Mitin BC (CGY) and Antitarma NTC (Dalton) - have permethrin (VIII, Figure 7) as their active ingredient. Eulan SP (BAY) contains a pyrethroid of undisclosed structure, whilst Mitin AL (CGY) is a mixture of permethrin and a hexahydropyrimidine derivative [l l o ] . The work which went into the development of these new mothproofing agents is well documented [ log-1 171. The pyrethroid- based agents are cheap and highly effective; they have very low mammalian toxicity and although their toxicity


  • to aquatic life is high, this should be no problem provided mill effluents are passed through a sewage treatment works before entering surface waters [ I 171. Possibly the greatest advantage of the pyrethroid-based mothproofing agents is that they are the only products capable of protecting wool from the larvae of the brown house moth (Hofmannophila pseudospretella) at eco- nomic application levels [I 18,1191, This species is now the most common cause of insect damage to wool goods in the moist temperate climates of North West Europe and New Zealand

    Mothproofing Met hods The first synthetic-mothproofing agents were intended for application in dyebaths at the boil and this is still overwhelmingly the method of choice. However, changes in fashion in the carpet industry have led to an increase in the amount of undyed wool used and now it is common to apply mothproofing agents in raw wool scouring or during the scouring of carpet yarn hanks, by metering mothproofing agent and acid into the final rinse bowl. Although, when using this method, the wool is exposed to the mothproofing liquors for only a short time at relatively low temperature, exhaustion of the bath onto the wool takes place. Like all continuous exhaust processes, careful control must be exercised if successful results are to be achieved [9]. Dry-spun yarns are often proofed by addition of mothproofing agent to the spin- ning lubricant, but this method gives only a superficial treatment of relatively poor fastness and treatment of the wool during scouring is to be preferred.

    Scouring and milling of yarns in batch solvent- processing machines is growing in importance and Eulan BLS (BAY), a mothproofing agent made es- pecially for solvent application, may be used on solvent- scoured yarns.

    FLAME RETARDANT FINISHES Wool is regarded as a naturally flame-resistant fibre. It has a high ignition temperature, a high limiting oxygen index and a low heat of combustion. If wool is ignited by a strong heat source it does not melt or drip and burns for only a short time when the heat source is removed. Untreated wool will pass many flammability test methods, especially those where the test sample is horizontally inclined [ I 20,1211.

    In the early 1970s, regulations were issued in the USA which made it necessary for carpets to pass the so-called US tablet test [122], in which a burning methenamine pill is placed on the test sample, and for aircraft up- holstery fabrics to pass a framed vertical flammability test [123]. Untreated wool, in moderately dense carpet constructions passed the methenamine pill test, but in the open shag pile constructions which were then popular in the USA, untreated wool could not meet the specification. The test for aircraft interior fabrics also was so severe that untreated wool could not comply.

    The only flame-retardant (FR) finishes available for wool at that time were non-durable treatments based on inorganic borates or phosphates, so in order to protect two of wool's important markets, it was necessary to develop new improved treatments.

    The first of these new finishes used tetrakishydroxy- methylphosphonium chloride (THPC) along with urea and a melamine-formaldehyde concentrate in a pad dry-cure~wash-dry process [I 241, The process was expensive and inconvenient in use and adversely affected fabric handle, but it was used industrially for a time to treat substantial quantities of aircraft upholstery fabrics. Fortunately, this process was soon superseded

    by the IWS Zirpro treatments, developed by Benisek [I 25,1261, in which negatively charged titanium or zirconium complexes are exhausted onto wool in acid conditions either during or after dyeing. Treatment of piece goods from a long liquor bath at 60 C for 30 min is the method most commonly used, but a number of variants of the process are available to suit most condi- tions and substrates.

    Modifications of the Zirpro process have been devel- oped to comply with special requirements. For example, a low-smoke Zirpro treatment [I 271 is used to satisfy the smoke and toxic gas emission specifications of aircraft manufacturers. Where very short after-flaming times are specified, a process is available which makes use of the synergistic effect given by simultaneous application of the Zirpro complexes with tetrabromophthalic acid [128].

    The Zirpro treatments are relatively inexpensive and do not affect the handle of the treated wool. The titanium complexes yellow the wool and this yellowness in- creases on exposure to light. There are many industrial end-uses for FR wool where this discoloration is unim- portant, but nevertheless, it is usual to employ the slightly more expensive zirconium complexes, which do not cause yellowing.

    Zirpro treatments are widely used throughout the world and it is estimated that 35 mkg of wool has been treated since 1972, mostly for carpets, protective cloth ing and contract upholstery.

    Fabrics for protective clothing may be required to possess special attributes other than flame retardancy, and several multipurpose finishes, combining the Zirpro process with shrink-resist and/or water- and oil-repellent treatments have been developed [I 26.1 29 -1 31 1.

    Other flame-retardant processes for wool have appeared, using sulphamic acid [I 321, chlorendic acid [I331 or tetrabromophthalic acid [134], but none of these has been so widely used as the Zirpro process. A process based on a water-soluble oligomeric vinyl phos phonate (Fyrol 76) was used briefly on wool and wool blend fabrics [I 35,1361, but the product is now with- drawn.

    CONCLUSIONS AND FUTURE PROSPECTS It is convenient to consider the wet processing of wool as falling into two categories. On the one hand are the old-established 'conventional' processes such as scour- ing, milling, crabbing and carbonising and on the other hand are the newer special finishes, including shrink^ resist treatments, mothproofing, setting with chemicals or high pressure steam and flame-retardant finishes.

    In the first category, simple chemistry and simple machinery is used. These processes have evolved to their present state largely by trial and error and even 50 years ago they had reached a degree of maturity that made further significant changes seem unlikely. Generally speaking, this has been the case and any improvements which have taken place have been slow and evolution- ary in nature. There is one exception, however, and that is the case of raw wool scouring. Here, change has been forced on the industry by legislation regulating or even forbidding the discharge of heavily contaminated efflu- ent. The major developments in wool scouring technol- ogy which have taken place as a result have also brought about major savings in the use of labour, water and energy; but these savings would not in themselves have been sufficient to persuade industry to adopt the new technology. In developed countries especially, the costs of labour, water and energy will probably continue to rise steeply and traditional finishing processes will need


  • to become more efficient in all respects. In that case, the next 50 years may see more new developments in the conventional wet processing area than have occurred during the previous 50.

    In the field of special finishes, change has been more rapid and more dramatic. In the 1930s. the only special finishes applied to wool were crude and badly controlled shrink-resist processes and some insectproofing, the latter little-used because of its high cost. These pro- cesses were applied in response to two very obvious deficiencies of wool as a textile fibre. However, there was little incentive for manufacturers to apply these processes, because wool's traditional markets appeared safe in the absence of competition from synthetic fibres. Without a doubt, the arrival of synthetics in the 1950s and 60s provided a spur to the development of special finishes for wool. Improved shrink-resist processes, cheaper insect-proofing chemicals and permanent set- ting processes all received extra impetus from the competition brought by synthetic fibres, which were inherently shrinkproof and mothproof and were readily settable by heat alone. Ten years later, new legislation governing the flammability of textiles for certain end- uses provided the incentive for the development and industrial adoption of flame-retardant processes.

    Thus, it must be said that the wool textile industry has usually accepted major changes in methods of wet processing only when forced to do so, either by legisla- tion in the case of raw wool scouring and flame- retardant processes, or by competition from synthetic fibres, in the case of several of the special finishes.

    Minor improvements in processing methods and machinery have found acceptance more readily, but even in some instances where new machinery has employed old principles, there has been resistance to change. Examples are the initial reluctance of the industry to accept continuous crabbing, continuous decatising and even combined scouring and milling machines, on the grounds that these new techniques were somehow inferior to traditional methods and were incapable of producing a cloth possessing certain indefinable but desirable features. Nevertheless, it is possibly true to say that a series of minor evolutionary developments is capable of bringing about change in the wool industry more rapidly than a revolutionary development which is likely to find acceptance only slowly, if at all.

    The authors wish to acknowledge the valuable contribu tions to this paper, in the form of discussions, sugges- tions and criticisms made by colleagues in the IWS Development Centre, Ilkley, and by friends in the wool textile and textile chemical industries In particular, we would like to thank the following Dr L Benisek, Mr J H Mills, Mr B Robinson and Dr M A Rushforth, all of IWS, Mr G Redman of Benjamin R Vickers & Sons Ltd, Mr P Ryley of Hield Bros Ltd and Mr A Lockwood of Gledhill Bros & Co Ltd

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    (1971) 1183.

    68 REV. PROG. COLORATION VOL. 14 1984


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