Continuous Dyeing and Polymer Shrink-resist Processes for Wool

Proceedings Continuous Dyeing and Polymer Shrink-resist Processes for Wool D. M. LEWIS International Wool Secretariat Technical Centre Valley Drive Ilkley Yorkshire LS29 8PB Paper presented to the West Riding Region on 26 February 1976. A number of polymer shrink-resist treatinents for wool in various forms have been proposed; one of the most popular of these being the chlorine-Hercosett 57 process,applicable to both w o l tops and garments. In order to increase the versatility of such processes, polymers have been developed which can be applied together with dyes at the dyeing stage. This paper describes the application of several different water-soluble polymers to wool piece goods and tops, using pad-batch methods of application. Fabrics produced by the combined dyeing and finishing techniques are capable of meeting both machine washability and colour fastness criteria required in the Superwash specification. PLoblems in developing the method for wool tops are discussed, together with indications as to their solution. Introduction m e question of continuous dyeing of wool in top and piece form has received a great deal of attention, especially over the last five years. During this period, the I.W.S. have been active in introducing the pad-batch (cold) method, based on the use of fairly h g h concentrations of urea, [ 1,2,3] to various mills throughout the world. Pad-batch (cold) dyeing methods are classified as ‘semi-continuous’ but it is felt that truly contin- uous methods of wool dyeing, at least in the case of all wool piece involving pad-steam or pad-bake techniques, are unlikely to be feasible, mainly from economic considerations. Several processes for the continuous dyeing of tops by a pad-steam method have been proposed and some are now running commercially, but the work reported in this paper relates to top dyeing by the pad-store (cold) method [4]. As far as the pad-batch (cold) dyeing process for piece goods is concerned, only limited adoption by the trade has occurred, the widest penetration occurring in Eastern Europe. The pad-store (cold) top dyeing process has, however, proved to be more attractive to many countries. It is interesting to reflect on these two contrasting reports. In the first case, although piece dyeing of 100% wool represents approximately 20% of the total wool dyeing trade, about 40-50% of these piece goods are dyed either navy or black with chrome dyes and about half of the remaining colours represent the high fashion end of the market where 1-2 wool pieces per colour is normal; since pad dyeing at room temperature cannot utilize the cheaper chrome dyes, the blacks and navies can only be produced using relatively expensive combinations of reactive dyes. Secondly, all wool piece dyeing in Western European countries is a high fashion area, and often the average number of pieces to be dyed to a particular colour is as low as five; the conclusion drawn is that only above this figure can piece padding methods demonstrate significant economic advantage over the traditional batchwise dyeing methods. Thirdly, a significant amount of wool goes into blend fabrics, and as yet there is no suitable continuous or semi-continuous process for piece dyeing these fabrics. Fourthly, the pad-store (cold) process for wool tops offers easily discernible advantages over other top dyeing methods regarding increased productivity, low equipment costs, improved top quality and low water requirements. Since the pad-batch (cold) dyeing processes developed for wool are so suitable for the application of reactive dyes of many types, including some of those primarily used on cellulosic fibres, it remains something of a paradox to use these relatively expensive dyes capable of exhibiting very high wet fastness properties on a material which invariably cannot be machine-washed unless specially treated. The most success- ful methods of imparting a shrink-resist finish to wool that render it machine-washable are based on treatments with synthetic polymers. This paper describes the development of polymers and application methods especially suitable for imparting a machine-washable finish to wool fabric and tops during dyeing by the pad-batch method. Two approaches were considered viable in achieving the above object: (i) Application of polymer during the wash-off stage. (ii) Application of polymer together with the dye at the padding stage. Both of these approaches require that the polymer used should be either water-soluble or water-dispersible, and should show affinity for the wool fibre. Additionally, in method (ii), the polymer should be either anionic or nonionic, otherwise precipitation problems with anionic dyes would occur, and the polymer should not contain nucleophilic sites capable of reaction with reactive dyes. Generally, approach (ii) has proved to be highly successful only in the case of piece goods, poor results being achieved by method (i). In the case of tops, it is most likely that method (i) will ultimately prove to be successful. At this stage, it is useful to consider some of the properties of synthetic pre-polymers available for shrink-resisting wool. The most important commercially viable polymer treatments are: - the chlorine-Hercosett 57 [5] (Hercules Powder Co.) process - the Dylan CRB and Dylan GRC (Precision Processes) methods - the Synthappret LKF (BAY) [ 6 ] organic solvent application process - the Oligan SW (CGY) [7] process, applicable from both 100% organic solvent and from aqueous emulsions - DC 109 (Dow Corning) process (100% organic solvent) JSDC April 1977 105 PRE-TREATMENT PROCESSES The first two processes described above require that the wool be given some sort of pre-treatment to increase its surface energy. McPhee et al. [8,9] have observed that the critical surface tension (yc) of untreated wool fibres from a standard top is 45 dynes/cm, whereas that of mildly acid chlorinated wool is 72 dynes/cm. Since the critical surface tension of the Hercosett 57 resin film'is 52 dynes/cm, the resin cannot spread and adhere to untreated wool fibres, but spreads very evenly on to treated (e.g. acid-chlorinated) fibres. The condition for complete wetting and spreading of a polymer on to wool is that: yso polymer < yso wool [8], where yso is the specific surface free energy of the solid in vacuum. In ,the case of organic polymers, yc, the critical surface tension, is very close to the surface free energy value [ lo ] . From the above considerations, it is evident that the wool fibre surface should be modified, either by a chemical pre-treatment or by chemicals added to the pad liquor itself, if successful results are to be achieved by incorporating this type of polymer in the pad liquor or by aftertreating with this polymer during washing-off. Another important consideration when employing poly- mers of the Hercosett 57-type is their highly cationic nature, related to the azetidinium cation c1- %i-OH c The polymers are indeed so highly cationic that they readily precipitate with the anionic dyes commonly used in wool dyeing; thus, unless the ionic character of this type of polymer can be significantly altered without interfering with its crosslinking or curing propensity, they cannot be safely employed in the pad-batch dyeing liquor. On the other hand, they may have use for application as an aftertreatment during washing-off, following pad-batch dyeing, provided, of course, that most of the unfixed anionic dye has first been removed and assuming that pretreatment of the fibre with the pad liquor lowers the fibre surface tension sufficiently to allow the resin to spread. Earlier investigations [ l l , 121 into the possibility of chemically altering the ionic character of Hercosett 57 have shown that Bunte salt (S-thiosulphato) groups can be readily introduced into the polymer, producing an amphoteric poly- mer, which does not precipitate with anionic dyes, but which can be crosslinked to a polydisulphide. Experiments with this type of polymer have shown promise and the results will be reported in this paper. POLYMERS FOR USE ON UNMODIFIED WOOL Isocyanate terminated polymers Synthappret LKF has been readily available for application to wool garments and fabrics from organic solvent (usually perchlorethylene) media [13,14]. This polymer is a reactive isocyanate terminated prepolymer, probably derived from a polypropylene oxide triol, of molecular weight about 3000, prepared from the condensation polymerization of propylene oxide with trimethylol propane. Since the polymer in its original form is insoluble in water and also its emulsions in water have too low a stability,due to the ready reaction of the isocyanate groups with this medium, then in its present form it can be regarded as useless for incorporation in aqueous-based pad dyeing liquors. However, Guise and Jackson [15] have recently demonstrated that Synthappret LKF can be reacted with sodium bisulphite in alcohol/water solution to give an anionic, water-soluble derivative which shrink proofs untreated wool. This reaction can be shown schematically as: isocyanate prepolymer carbamoyl sulphonate prepolymer (where represents the polyether ,backbone) E The application of this water-soluble polymer to wool in the pad-batch dyeing process has been studied and the results are reported here. Kecently, Rippon [ 161 reported a further modification of this polymer by fEst partially reacting the isocyanate pre- polymer with concentrated sulphuric acid to give a n amino terminated polymer and then converting the unhydrolyzed isocyanate groups using the reaction described above. This amphoteric water-soluble polymer has a significant affinity for wool and has been shown to shrinkproof wool in an exhaustion application. Thiol terminated polymers Oligan SW [17,18], jointly developed by CGY and IWS, is an aqueous emulsion of a thiol terminated polyether. The polyether backbone is similar in character to that of Synthappret LKF and the structure of the polymer can be represented as: 0 I1 II T O - C - C H I S H Lil O-C-CH,SH This polymer is applied to untreated wool fabrics by padding from an alkaline, emulsified liquor, followed by oxidation to a poly disulphide during drying. Although an emulsion of this polymer is quite stable in aqueous solutions, it is unsuitable for use in pad liquors containing reactive dyes,since these react with the nucleophilic thiol group causing problems of pad liquor instability, poor yield of reactive dye after batching and variable shrink resistance. Bunte salt terminated polyethers Lewis [19] has described the preparation and possible 106 JSDC April 1977 application of Bunte salt polyether polymers to wool piece goods during pad-batch dyeing. This paper describes a simplified, commercially suitable application technique for using this type of polymer in pad dyeing liquors. The polymer can be represented as: 0 ~ o - C - C H z - - S S O , - N a + II L ? 0 - C - C H 2- S SO,- Na' L ? O-C-CHz--SSO,- Na+ represents a polyether backbone of molecular weight about 3000, prepared from the reaction of propylene oxide with glycerol. This type of polymer is available in Pilot Plant quantities as Lankrolan SR3 (Lankro Chemicals). The properties of the Bunte salt groups are such that the polymer is cross-linkable to a polydisulphide which imparts shrink resistance to wool under a variety of conditions. These conditions include dry heat curing, reaction with wool thiol groups under batching conditions, wet curing in boiling, aqueous dyebaths and curing by reaction with thiol com- pounds such as ammonium thioglycollate. Additionally, the anionic character of the Bunte salt group makes it quite compatible for simultaneous application with reactive dyes. The combination of hydrophobic backbone and hydrophilic end groups makes this product a surface active agent which is a very effective wetting agent for wool. Experimental - Materials and Methods MATERIALS Wool The wool used in this work was a 100% wool, 2/2 twill serge fabric; in the case of tops, merino 64s scoured white were employed. Polymers The bisulphite adduct of Synthappret LKF (BAY) was prepared as a 12.5% (wtlvol.) solution in propan-2-ol/water (50/50) by the method of Guise and Jackson [ 151 . The Bunte salt derivative of Hercosett 57 was prepared by adding sodium thiosulphate pentahydrate (40 g) to a solution of Hercosett 57 (400 ml), stirring until the crystals dissolved and leaving the solution overnight. During this period, several changes occurred in the solution; firstly it became cloudy, gradually separating into two layers and secondly, the pH rose from 5.0 to about 7. The lower layer was shown to be water soluble but only at pH values greater than 6.5 and lower than 4.5, indicating that the polymer was amphoteric. In addition, it was found to give typical Bunte salt reactions readily cross-linking to an insoluble polydisulphide. The Bunte salt polyether, Lankrolan SR3, was supplied by Lankro Chemicals Ltd., Eccles, as a 40% (wtlvol.) solution in a mixture of propan-2-ol/water. Dyes The dyes used in this work were mainly reactive dyes (for both wool and cotton) and 1 :2 metal-complex dyes of the Acid01 M (BASF) type. Awciliary products A number of wetting or antifrosting agents were examined, including: Lankropol KO2 (Lankro) - di-iso-octysulphosuccinate Triton GR5 (Rohm & Haas) - alkyl sulphosuccinate Matexil PN-VP (ICI) - nonionic aliphatic ethanolamide Silicon L77 (Union-Carbide) - an ethoxylated silicone METHODS Padding A two-bow1,horizontal Peter pad ($5 metre) was employed and the pressure setting adjusted so as to give 100% pick-up on woven fabric and 130% pick-up on tops. Most of the experiments involved resin dosage levels of the order of 4% polymer 0.w.f. Batching Fabric was batched simply by rolling up round a plastic tube and covering with polythene film. Tops were batched by storing them in a sealed polythene bag. Steaming A laboratory steamer described previously was employed P O I . Washing-o ff After batching or steaming the wool was washed-off firstly in a solution of aqueous ammonia (pH 8.5) for 10 minutes at room temperature, secondly in a similar ammonia solution for 10 minutes at 50°C and finally, thoroughly rinsed with warm water. In some cases it was necessary to make the washing-off conditions more severe and these will be described as they occur. I5-I Cttbex machine testing The International Cubex machine was employed at 4OoC using a liquor ratio of 15: 1 in pH 7 buffer (Load 1 kg). Results and Discussions A consideration of the various polymer treatments described in the introduction, indicates that a successful process for combined dyeing and finishing requires the use of polymers which are water soluble, anionic and which do not interact with reactive dyes. Three water soluble polymers which meet the above criteria were studied as possible additions to the pad liquors normally used in the pad-batch dyeing process: - Synthappret bisulphite adduct - Hercosett 57 Bunte salt adduct - Lankrolan SR3 (Bunte salt terminated polyether) It is useful to consider the results obtained with these polymers separately. SYNTHMPRET BISULPHITE ADDUCT The following pad liquor was prepared: 20 g/l Urea 300 g l l Procion Red MG (1CI) (C.I. Reactive Red 5 ) JSDC April 1977 107 Synthappret bisulphite (1 2.5%) 320 g/l Solvitose OFA (thickener) (Scholten) 8 g/l Sodium metabisulphite 20 gll Wool serge was padded through the above liquor to 100% pick-up and batched for 24 hours at room temperature. After batching, the fabric was divided into three parts and each part washed-off in a different solution, viz. (i) Usual ammonia method (ii) Sodium carbonate solution (1% wtlvol.) for 15 minutes at 20°C, followed by thorough rinsing in warm and cold water. @)Thorough rinsing, firstly in warm water (5OoC) and then in cold water. Each of these fabrics was then dried and tested for washability, using the 15-1 Cubex test (1 and 3 hours wash). The results obtained are shown in Table 1. TABLE 1 Comparison of the Effect of the Three Aftertreatments on Washability of Wool Serge Fabric* Aftertreatment Area- shrinkage (%) 1 -h 3-h 4 14 0 0 ( 9 (4 (iii) 12 33 'These three tests have been carried out on a number of different fabrics (both woven and knitted) and the same pattern emerges, i.e. aftertreatment (ii) is generally necessary to achieve machine wash- ability. For comparison, a sample of the serge fabric was dyed by the cold pad-batch technique, but the Synthappret bisulphite adduct was omitted. After testing (using the 15-1 Cubex test), the fabric gave an area shrinkage of 22% after the 1-hour wash and 46% after the 3-hour wash. From a study of Table 1 it is evident that a fairly strong alkaline treatment is essential to complete the crosslinking of the polymer and to produce a machine washable fabric. However, even aftertreatment (iii) gives an improvement in the washability effect, indicating that some crosslinking occurs during batching. If the above experiments are repeated on a woo1,which has received more damage during processing, such as a bleached Doctor Flannel, all three aftertreatments give a machine washable effect, indicating that in this case sufficient crosslinking can occur during the batching period. The role of urea and bisulphite Using the above pad liquor with the important exception of urea being eliminated, wool serge was dyed, batched and washed-off in the sodium carbonate solution. After testing for 3-h in the 15-1 Cubex machine, an area shrinkage of 25% was obtained, indicating that in the absence of urea, inadequate reaction and crosslinking of the polymer had occurred. When a similar experiment was repeated with the original pad liquor, but in this case leaving out the sodium bisulphite and retaining the urea, a red dyeing was produced which, after washing-off in the sodium carbonate solution, was found to give 10% area shrinkage after washing for 3-h in the 15-1 Cubex machine. From both these results it is evident that both urea and bisulphite are required to promote efficient reaction and curing of the carbamoyl sulphonate polymer, when applied by this method. Effect of batching time on the anti-felting effect Using the full pad liquor described previously, wool serge was padded and then batched for various periods of time, extending up to 24 hours. Each sample was washed-off by the sodium carbonate method and washed for 3 hours in the 15-1 Cubex machine.The results obtained are illustrated in Figure where it can be seen that at least 16 hours batchirig necessary to achieve a completely machine-washable effect. 1 , is 4 Batching time, h *After 3-h in 15-1 Cubex machine Figure 1 - Effect of batching time on fabric washability. Curing mechanism Since the machine washability achieved with the carbamoyl sulphonate polymer (Synthappret bisulphite adduc,t) is dependent on the presence of urea and on the presence of bisulphite, the reactions occurring during crosslinking must be quite complex. It is possible that carbamoyl sulphonates can undergo nucleophilic substitution reactions in the following manner: R X H + R'-NH--CO--SO,-Na' (nucleophile) (4 II R-X-C-NH-R' + NaH SO3 If nucleophilic groups in the wool (e.g. amine or thiol) react with the polymer in the above manner, it can be gathered that the improvement in shrink resistance obtained in the presence of urea and bisulphite can be related to their known effect in increasing these reactions (c.f. with reactive dyes). These reactions, however, do not lead to curing or crosslinking of the polymer itself and it is known that crosslinking to a high molecular weight polymer is essential to achieve shrink resistance [21, 221 . The only conceivable crosslinking route for this polymer would be re-conversion to the parent isocyanate, reaction with water and the formation 108 JSDC April1977 of urea links [21] - this scheme does not totally rule out some grafting reactions such as those described previously and indeed such reactions may be absolutely essential to achieve shrink resistance by the pad-batch method. Conversion to the parent isocyanate followed by crosslinking by reaction with water is illustrated in the following scheme: N=C=O NH-CO-SO;Na+ N=C=O + 3NaHS0, NH-CO-SO;Na+ E N H-CO - SO; N a+ N=C=O 'parent' isocyanate E where represents the polyether backbone. NH, f CO, 1' E N=C=O N=C=O IF N=C=O -NH-CO-HN cross-linked polyurethane HERCOSETT 57 BUNTE SALT ADDUCT Because of previous experience with Hercosett 57, it was decided to use worsted serge, all wool single jersey and the same single jersey given a mild pre-chlorination. These fabrics were padded to a pick-up of 100% through a pad liquor containing: Procion Red MG (C.I. Reactive Red 5) 20 g/l M a t e d PN-VP 10 g/l Sodium metabisulphite 10 g/l Solvitose OFA 8 gll Hercosett Bunte salt adduct (30% wt/vol) 100 g/l Urea 300 g/l After batching for 24 hours, the fabrics were given the following aftertreatments: (a) Normal pad-batch dilute ammonia wash-off (b) Washing with THPC (1% vol./vol.) solution for 15 (c) Washing with dilute H2S04 (1% vol./vol.) for 15 (d) Washing with dilute thioglycollic acid (1% vol./vol.) for minutes at 20°C minutes at 5OoC 15 minutes at 20°C After these treatments the fabrics were rinsed thoroughly in water and dried. Washing test results are shown in Table 2. From a study of Table 2, it is evident that unless the fabric is given some sort of pre-treatment, which increases its surface energy, shrink-resistance cannot be produced; in addition, even on fabrics which have been pre-chlorinated, it is necessary to include an aftertreatment step especially designed to convert TABLE 2 Effect of Aftertreatments a, b, c and d on Shrink resistance Fabric Serge Serge Serge Serge Untreated single jersey (originally shrinks 62% after 1-h in Cubex machine) Pre-chlorinated single jersey (originally shrinks 50% after 1 -h in Cubex machine) Aftertreatment d a b C d Area shrinkage (%) 43 28 31 27 50 48 51 50 54 2 6 1 Washing time (h) 3 3 3 3 1 1 1 3 the Bunte salt groups to disulphides. These limitations restrict the use of this polymer in combined dyeing and finishing processes. LANKROLAN SR3 Using the following pad liquor, wool serge was dyed by the pad-batch (cold) method: 20 g/l Procion Red MG (C.I. Reactive Red 5) Urea 300 g/l Lankrolan SR3 (40% wt/vol.) 80 g/l 20 g/l Sodium metabisulphite Solvitose OFA 8 g/l The batched fabric was washed-off after 24 hours by the usual dilute ammonia technique and tested for machine washability: after washing for 3-h in the 15-1 Cubex machine, zero area shrinkage was recorded. Although the above system appeared to Zive adequate wetting at the nip, the quality of the resulting dyeing was very frosty. In order to attempt to improve this situation, additions of other auxiliary products were made to the following navy blue pad liquor: Drimalan Blue F-2RL (C.I. Reactive Blue 103) Drimalan Orange F-GL (C.I. Reactive Orange 53) Urea Lankrolan SR3 (40% wt/vol.) Sodium metabisulphite Solvitose OFA Addition (I)* Matexil PN-VP (ICI) Addition ([I)? Lankropol KO2 (Lankro) 20 g/l The results are shown in Figure 2, where it can be seen that without any additions the dyeing is extremely frosty, with Matexil PN-VP slightly better and with Lankropol KO2 'Product (i) is the diethanolamide o f a fatty acid ?Product (ii) is di-iso-octyl sulpho succinate. JSDC April 1977 109 Pad liquor: 3OOgl-' Urea 9Ogl-' Lankrolan SR3 8gl-I Solvitose OFA 2Ogl-I Bisulphite 4Ogl-' C.I. Reactive Blue 103 1Ogl-' C.I. Reactive Orange 5 3 Figure 2 - Effect of auxiliary products on frosty dyeing extremely level, non-frosty dyeings are achieved. These observations correspond to those of Angliss et aL [23], who have studied the role of sulpho succinates in preventing frosty pad dyeing on wool tops. All the above samples were found to give 0% area shrinkage following washing for 3-h using the 15-1 Cubex test. Effect of urea on the degree of shrinkproofing Using the following pad liquor: Procion Red MG (C.I. Reactive Red 5) 20 g/l Sodium metabisulphite 20 g/l Lankrolan SR3 (40% wtlvol.) 90 g/l Solvitose OFA 8 g/l wool serge was padded to 100% wet pick-up and batched 24 hours. After washing-off in the normal manner, the samples were tested for washability; area shrinkage values of 22% and 48% were recorded after Cubex washing for 1 hour and 3 hours, respectively. It is therefore evident that urea performs a most important function in promoting crosslinking of the Bunte salt polymer. The role of sodium metabisulphite In order to clarify the role of sodium metabisulphite, the following pad liquors were prepared: (i) Urea Lankrolan SR3 (40% w/v) Sodium metabisulphite Solvitose OFA Lankropol KO2 (ii) As (i), but plus: C.I. Reactive Red 5 (Procion Red MG) 10 g/l (iii) As (ii) but plus: C.I. Reactive Red 5 (iv) As (i) but plus: C.I. Reactive Red 29 (Procion Red H-3BN) 10 g/l (v) As (iv) but plus: C.I. Reactive Red 29 The two Procion dyes were selected since they represent extremes of reactivity (the dichloro-s-triazinyl Procion M dye being highly reactive, whereas the monochloro-s-triazinyl Procion H dye possesses low reactivity). Wool serge was padded through the above five pad liquors to 100% pick-up and the samples batched for 24 and 48 hours. Following batching they were washed-off by the usual dilute ammonia method and tested for shrink resistance. The results obtained are shown in Figure 3. 24-h Batch 48-h Batch 40, Bisulphite, gl-' Bisulphite, gP' X No dye 0 1 OgT1 C.I. Reactive Red 5 o 1 Ogl-' C.I. Reactive Red 29 A 3OgT' C.I. Reactive Red 5 3Ogl-' C.I. Reactive Red 29 Figure 3 - Effect of bisulphite concentmtion on shrink resistance A study of this figure reveals that sodium metabisulphite is a very important factor in achieving machine-washability; if it is omitted from the pad liquor only a minor effect on prevention of felting shrinkage is achieved. In the case of pad liquors containing no dye, a machine-washable level of shrink resistance is achieved using only 7 g/l of metabisulphite and batching for 24 hours; if the batching period is extended to 48 hours this concentration can be reduced to 5 g/l. At lower levels of metabisulphite concentrations, the most important effect observed in this figure is the major interference in the shrink resist effect by the dye of higher reactivity. Technically this is important since, if moderately deep colours of highly reactive dyes are to be dyed, and, if a batching time of 24 hours is required, the metabisulphite concentration must be increased to 30 g/l, the alternative being to increase the batching time to 48 hours and use the preferred 20 g/l metabisulphite concentration. A similar inteference effect was observed with Levafur E dyes (BAY) at full depths but no interference was observed with Drimalan F ( S ) , or Verofur (BAY) dyes, or with non-reactive dyes. Using the following pad liquor: Urea Lankrolan SR3 (40% wtlvol.) Sodium Metabisulphite Solvitose OFA Lankropol KO2 Dye 110 JSDC April 1977 a variety of dyes were applied at various depths and the shrink resistance (3-h, 15-1 Cubex) determined after 24 hours. The results are shown in Table 3. It is of interest to consider the mechanism involved in the above effects. Since interference only occurs with dyes possessing very high reactivity at full depths, the implication is that these dyes are reacting rapidly with the wool thiol groups so vital to the crosslinking of the Bunte salt polymer. The importance of thiol groups to the system is also emphasized in Figure 3, and explains the need for metabisul- phite additions. According to Leach [24] the free thiol content in the form of cysteine in untreated wool is very low, of the order of 39 p per mole/g. Since the low temperature curing reaction under neutral pH conditions of the Bunte salt polymer to a crosslinked polymer depends on the presence of a thiol group, it is necessary to create more of these entities by the action of metabisulphite on the cystine linkages in wool, viz. I c=o I I o=c I CH-CH2-S-S-CH2-CH 1 + NaHS03 NH NH wool cystine \1 ?OHe I I I I c=o I I CH-CH2-SH + Naf-03SS-CH2-CH I NH I NH I I wool cysteine wool cysteine-Ssulphonate I o=c Ths reaction and its reversibility under alkaline conditions is very well documented [25, 26, 27, 28, 29, 301. It is of interest to note that one of the above products, wool cysteine-S-sulphonate, is itself a Bunte salt. The proposed curing reaction for the Bunte salt polymer, Lankrolan SR3, is as follows: SS0;Na' SSO;Na+ SSO; Na' I I I I c=o c=o 3 CH-CH2-SH + N H I wool cysteine I S-S-CH,-CH c = O I 1 NH I I I + 3NaHS0, C=O I CH-CH2-S-S I LS-s--CH2--CH I I I NH NH disulphide rearrangement I mixed disulphide 131, 32, 331 i 1: o=c I I I I CH-CH,-S-S-CH2-CH NH fully % S - - ~ ~ ' " * cross-linked polymer wool A H I cystine (reformed) I TABLE 3 Effect of Dye Type on Shrink Resistance Procion Brilliant Red H3B (ICI) (C.I. Reactive Red 3) Procion Navy H-4R (ICI) (C.I. Reactive Blue 40) Levafix Brilliant Red E-G (BAY) (C.I. Reactive Red 67) Levafm Brilliant Blue E-B (BAY) (C.I. Reactive Blue 29) Drimalan Red F-2GL ( S ) Verofx Red GGL (BAY) (C.I. Reactive Red 99) Drimalan Blue F-2GL ( S ) Verofix Blue GGL (BAY) (C.I. Reactive Blue 94) Procion Yellow M G 8 G (ICI) (C.I. Reactive Yellow 86) Acidol Scarlet M-L (BASF) Conc (gl-' 1 10 20 40 10 20 40 10 20 40 10 20 40 10 20 40 10 20 40 10 20 40 10 20 40 Area shrinkage (%) 0 0 0 0 0 4 0 0 13 0 0 16 0 0 0 0 0 0 0 8 24 0 0 0 In practice, not all of the Bunte salt groups in the polymer will be crosslinked to the corresponding disulphide; the degree of crosslinking (P,) can, in fact, be calculated from gel point theory : 1 Pc = 1341 ,where f is the polymer functionality. In (f- 1)" the case of Lankrolan SR3, f is approximately 3 and therefore the extent of reaction at the gel point is about 71%. At first sight, it is somewhat surprising that the Bunte salt group in the polymer is able to react so efficiently with the wool thiol group under the slightly acidic conditions in the pad liquor; in fact, the pH of the system changes as the bisulphite anion is adsorbed and reacts with the fibre, the pH of an aqueous extract after batching being 7.0 (compare with the initial pad liquor pH of 5.0). Another factor which could interfere with the curing of the Bunte salt polymer could lie in the competing reaction between cysteine-S-sulphonate (wool Bunte salt groups) and cysteine. Effect of batching time The following pad liquors were prepared: JSDC April1977 111 (i) Urea Lankrolan SR3 Sodium metabisulphite Solvitose OFA (ii) As (i) plus C.I. Reactive Red 5 30 g/l (iii)As (i) plus C.1. Reactive Red 29 30 811 Samples of wool serge were padded through these liquors and batched for various periods from 0-56 hours. After the particular batching period, the samples were washed-off in the normal manner and tested for shrink resistance. The results are illustrated in Figure 4. It can be readily seen that in the case of liquors (i) and (iii) a batching period of 17 hours is quite adequate, but in the case of liquor (ii), containing the highly reactive dye, prolonged batching (48 hours) is essential. 5ot I Batching time, h X No dye o 30gl-I C.I. Reactive Red 29 30gl.' C.I. Reactive Red 5 Figure 4 -- Effect of various dyes on rate of shrinkresistance using 20gll bisulphite in the pad liquor Dye selection Using the above method, wool piece can be processed to give a machine washable fabric; the concept of machine washability is not, however, only dependant on the anti-felt finish, but also depends on colour fastness specifications. I.W.S. have produced specifications to meet both of the above aspects in developing the Superwash wool project, which is mainly based on a continuous top or garment batch treatment with a low level acid chlorination followed by Hercosett 57 application 135, 51. Tests produced to specify colour fastness, include the I.W.S. TM 193 wash test [36] and a short liquor alkaline perspiration test, TM 174. Possibly because the above process, using the Bunte salt polymer, Lankrolan SR3, involves no pretreatment with chlorine, it has been found that the colour fastness properties of many non-reactive dyes meet the Superwash specifications, even at fairly full depths. Selected 1 :2 metal-complex (especially those with ionic sotubilizing groups) and 1: 1 premetallized dyes, together with ranges of reactive dyes, developed both for wool and cotton have found application. As far as reactive dyes are concerned, it should be noted that, since it is essential to include sodium metabisulphite in the pad liquor in order to achieve polymer crosslinking, those reactive dyes which are inactivated by this agent should not be employed [37]. In particular, these sensitive dyes include those which contain reactive vinyl groups, such as dyes from the Lanasol (CGY) and Remazol (BAY) classes. Effect of resin dosage In practice, it would be desirable to use the minimum amount of polymer in order to produce the softest handle possible. On woven fabrics, industrial trials have shown that 2.5% Lankrolan SR3 (0.w.f.) is perfectly adequate to impart machine-washability and on knitted fabrics a minimum dosage of 3% 0.w.f. is required. Wool Tops in Combined Dyeing and Finishing As mentioned in the introduction, the cold pad-store method has proved to be an extremely attractive method of dyeing wool tops. However, when the above combined dyeing and finishing methods were tried on untreated wool tops no success was recorded. In the case of Lankrolan SR3 the tops were found to be machine-washable only before gilling; gilling itself was a very difficult problem due to the large number of fibre-fibre bonds formed by the cured polymer. This indicates that the excellent shrinkproofing effects obtained on piece goods with this polymer are mainly due to the introduction of fibre-fibre bonds which stabilize the structure. A scanning electron microscope photograph taken of worsted serge simultaneously reactive dyed and finished with Lankrolan SR3 is reproduced in Figure 5. This clearly shows the inter-fibre bonds formed by the polymer. Figure 5 - Scanning electron microscope photograph of wool fibres from fabric treated with Lankrolan SR3 Further work is certainly required to clarify the type of polymer treatment system required to combine the pad-store top dyeing process with a polymer application to impart shrink resistance. 11 2 JSDC April 1977 Conclusions This paper has surveyed a number of possible resin systems which can be included in the cold pad-batch dyeing system for wool fabrics to impart shrink resistance. The most promising polymer system is a poly-ether solubilized by Bunte salt groups; the product is available as Lankrolan SR3 (Lankro). It has been shown that the inclusion of sodium metabisul- phite in the pad liquor is essential for the achievement of machine washability. The selection of dyes is also vital, since reactive dyes of high reactivity can, if used at full depths, interfere with the degree of shrink resistance obtainable; it is, however, possible to obviate this effect by prolonging the batching time. Non-reactive dyes can also be used in this system and many 1 : 1 and I :2 metal-complex dyes will meet Superwash colour fastness specifications when applied with this polymer system. * * * The author expresses his appreciation of the careful assistance of Miss S. Tinsley with the experimental work. References 1. Lewis and Seltzer, J.S.D.C., 84 (1968) 501. 2. Gibson, Lewis and Seltzer, J.S.D.C., 86 (1970) 298. 3. B.P. 1,003,651, assigned to I.W.S. Nominee Col Ltd. 4. 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