FIBRE TREATMENT

Abstract: A method of reducing the fibrillation tendency of lyocell fibre involves the step of contacting the fibre with an aqueous solution containing (1) a chemical reagent having at least two functional groups reactive with cellulose and (2) gelatin. The gelatin serves to prevent the chemical reagent crystallising out of the solution upon reduction of temperature.

Description: FIBRE TREATMENT Field of the invention This invention relates to a method of reducing the fibrillation tendency of lyocell fibre. It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable solvent into a coagulating bath. This process of extrusion and coagulation is referred to as "solvent spinning", and the cellulose fibre produced thereby is referred to as "solvent-spun" cellulose fibre. One example of such a process is described in US-A- ,246,221, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent such as an aqueous tertiary amine N-oxide, for example N-methylmorpholine N-oxide. The resulting solution is extruded through a suitable die to produce filaments, which are coagulated in an aqueous coagulating bath, washed in water to remove the solvent and dried. At some stage after coagulation the filaments are commonly cut into short lengths to form staple fibre. It is also known that cellulose fibre can be made by extrusion of a solution of a cellulose derivative into a regenerating and coagulating bath. One example of such a process is the viscose process, in which the cellulose derivative is cellulose xanthate. Both such types of process are examples of wet-spinning processes. Solvent spinning has a number of advantages over other known processes for the manufacture of cellulose fibre such as the viscose process, for example reduced environmental emissions. As used herein, the term "lyocell fibre" means a cellulose fibre obtained by an organic solvent spinning process, in which the organic solvent essentially comprises a mixture of one or more organic chemicals and water, and in which solvent spinning involves dissolution of cellulose and spinning without formation of a derivative of the cellulose. As used herein, the terms "solvent-spun cellulose fibre" and "lyocell fibre" are synonymous. As used herein, the term "lyocell fabric" means a fabric woven or knitted from a plurality of yarns, at least some of which yarns contain lyocell fibre, alone or in blend with other type(s) of fibre, and "lyocell yarn" is to be interpreted in similar fashion. Fibre may exhibit a tendency to fibrillate, particularly when subjected to mechanical stress in the wet state. Fibrillation occurs when fibre structure breaks down in the longitudinal direction so that fine fibrils become partially detached from the fibre, giving a hairy appearance to the fibre and to fabric containing it, for example woven or knitted fabric. Dyed fabric containing fibrillated fibre tends to have a "frosted" appearance, which may be aesthetically undesirable, particularly in textile applications. Such fibrillation is believed to be caused by mechanical abrasion of the fibres during treatment in a wet and swollen state. Wet treatment processes such as scouring, bleaching, dyeing and washing inevitably subject fibres to mechanical abrasion. Higher temperatures and longer times of treatment generally tend to produce greater degrees of fibrillation. Lyocell fibre appears to be particularly sensitive to such abrasion and is consequently often found to be more susceptible to fibrillation than other types of cellulose fibre. Intensive efforts have been made to reduce the fibrillation of lyocell fibres and fabrics. Background art US-A-5,310,424, the contents of which are incorporated herein by way of reference, describes a process for the manufacture of lyocell fibre with reduced fibrillation tendency wherein the lyocell fibre is treated with a chemical reagent having two to six functional groups reactive with cellulose. The fibre may be treated in the never-dried state (that is, after it has been washed free of solvent after coagulation but has not yet been dried) or as spun fibre (that is, previously-dried fibre) in the form of fibre, yarn or fabric. The chemical reagent is conveniently applied to the fibre from aqueous solution, often under weakly alkaline conditions because reaction of the reagent with cellulose is in general more rapid in alkaline conditions. WO-A-94/24343 describes a closely similar process. WO-A-94/09191 describes a process related to that described in US-A-5,310,424, wherein previously-dried lyocell fibre is treated with a chemical reagent containing two or more cellulose-reactive groups selected from the class consisting of electrophilic carbon-carbon double bonds and precursors thereof and electrophilic three-membered rings and precursors thereof. Fibre treated by the method of WO-A-94/09191 has the advantage that the protection against fibrillation so provided has improved resistance to repeated laundering. A preferred reagent for use in the method described in that document is triacryloylhexahydrotriazine (l,3,5-tripropenoylperhydro-l,3,5-triazine) (abbreviated as TAHT) . The fibre is preferably treated with the reagent under alkaline conditions. The solubility in cold water of chemical reagents such as TAHT useful in methods such as those described in US-A- 5,310,424 and WO-A-94/09191 is not always as great as could be desired. The reagent can be applied to the fibre from hot aqueous solution, for example at temperatures around 40 to 60'C, but this has the disadvantage that many of these chemical reagents suffer hydrolysis by water under such conditions, particularly in the presence of alkali, with consequent loss of activity. Furthermore, textile processors such as fabric processors often prefer to treat textiles with reactive agents using cold pad-mangle techniques, wherein a solution of the reactive agent is padded onto the textile at ambient temperature and the wetted textile is subsequently treated by storage at ambient temperature for sufficient time to produce the desired reaction. Application of hot solutions may accordingly necessitate the use of special equipment, because commercial finishing equipment rarely provides for a heated padding system. US-A-5,310,424 and WO-A-94/09191 propose that the solubility of the reagent can be increased by inclusion of a solubilising group in the reagent molecule, for example an ionic species such as a sulphonic acid group or a non-ionic species such as an oligomeric poly(ethylene glycol) chain. This has the disadvantage that it involves an additional chemical reaction step during preparation of the reagent. It is an object of the invention to overcome these disadvantages by providing a simple method of increasing the cold-water solubility of such reagents, thereby providing a method whereby solutions of such reagents can conveniently be applied to lyocell fibres, yarns and fabrics at ambient temperature by methods including padding. In other types of commercial finishing process, a hot concentrated solution of the chemical reagent is prepared, for example at about 80'C, and this solution, generally after dilution with water, is applied to the fibre at high temperature, for example at up to about 95 * C, under exhaustion dyeing conditions, for example using a jet-dyeing machine. Conditions can be chosen to minimise hydrolysis of the chemical reagent between dissolution and application to the fibre, in particular by making up the solution at neutral pH and minimising the time for which it is stored. Transfer of the solution from the dissolution equipment to the application equipment tends to incur heat loss, with the consequence that the chemical reagent may crystallise out of solution in the transfer pipework. It is a further object of the invention to provide a method whereby the risk of such crystallisation is reduced or eliminated. Disclosure of the invention According to the invention there is provided a method of reducing the fibrillation tendency of lyocell fibre including the step of contacting the fibre with an aqueous solution of a chemical reagent having at least two functional groups reactive with cellulose, characterised in that the aqueous solution additionally comprises dissolved gelatin. The aqueous solution used in the method of the invention may conveniently be prepared by dissolution of the chemical reagent and the gelatin at elevated temperature, for example by adding them separately or together to hot water at a temperature in the range 40 to 100'C, followed by natural or accelerated cooling. Solutions prepared in this manner are often found to be free from precipitation of the chemical reagent for several hours or days after cooling to ambient temperature. In the absence of gelatin, chemical reagents of low solubility in cold water generally precipitate immediately on cooling. The chemical reagent may conveniently be introduced in the form of a slurry, preferably an aqueous slurry, such as is disclosed in our copending British Patent Application No. 9519394.2, the contents of which are incorporated herein by way of reference. The slurry may for example contain from 30 to 60 percent by weight solids. The concentration of gelatin dissolved in the aqueous solution is often in the range 0.1 to 20.0, preferably 0.1 to 5.0, further preferably 0.2 to 1.0, grams per litre, although higher concentrations may also be used. The amount of gelatin in the solution often corresponds to 1 to 5 parts by weight of gelatin per 100 parts by weight of the chemical reagen . The chemical reagent may be colourless or coloured. The chemical reagent preferably contains two to six, more preferably three functional groups reactive with cellulose. A preferred example of a chemical reagent for use in the invention is TAHT. For application at ambient temperature the concentration of TAHT in the aqueous solution is often in the range 5 to 60, preferably 5 to 50, further preferably 10 to 40, grams per litre. For application at elevated temperature, particularly in the range 70 to 100"C, the concentration of TAHT in the aqueous solution is often in the range 50 to 100 grams per litre. The reasons for the effectiveness of gelatin in the method of the invention are not understood. Indeed, chemical reagents such as TAHT are known as hardeners in photographic technology; that is to say, they are used as cross-linkers for gelatin to reduce its water swellability and to render it insoluble. Chemical reagents useful in the method of the invention often react most rapidly under alkaline conditions with the cellulose of which lyocell consists. In such cases the aqueous solution is preferably made alkaline by addition of an alkali, preferably to the cooled solution for ambient temperature application, shortly before application to the lyocell fibre. The alkaline solution may contain 5 to 25, preferably 10 to 20, parts by weight sodium hydroxide per 100 parts by weight of the chemical reagent. Other alkalis, for example sodium carbonate or sodium metasilicate, may also be used. Single or mixed alkalis may be used. The alkali may conveniently be added in the form of a strong stock solution. The pH of the aqueous solution after addition of the alkali depends to some extent on the nature of the chemical reagent but is preferably in the range from 8 to 12, often from 10 to 11. For low-temperature application, the lyocell fibre is conveniently contacted with the aqueous solution at ambient temperature or at slightly elevated temperatures (for example, at up to about 30'C). The aqueous solution may be applied to the fibre using known techniques, for example from a bath, by a spray or preferably by padding. The thus wetted fibre is generally then mangled to reduce its moisture content and stored at ambient or elevated temperature or heated, for example by steaming or by exposure to microwave or R.F. radiation, to effect reaction between the chemical reagent and the fibre (fixation). The method of the invention is particularly suited to cold pad- mangle (pad-batch) techniques in which the application and fixation steps are performed at ambient temperatures. After reaction, the fibre is washed with water and dried. The washing procedure may include a wash with dilute aqueous acid, for example 1 g/1 aqueous acetic acid, particularly if an alkaline aqueous solution has been used. Lyocell fibre may be treated by the method of the invention before conversion or after conversion into yarn or preferably fabric. The method of the invention is also applicable to never-dried lyocell fibre. Lyocell fibre treated in fibre, yarn or fabric form by the method of the invention may subsequently be further processed by conventional techniques, including dyeing. Alternatively, the aqueous solution may additionally comprise one or more detergents of known type whereby fibrillation-reducing and fabric scouring and preparation treatments take place simultaneously. Further alternatively, the aqueous solution may additionally comprise one or more conventional dyes for cellulose whereby fibrillation-reducing and dyeing treatments take place simultaneously. If the chemical reagent is coloured, it may itself serve as a dyestuff. Lyocell staple fibre is available commercially from Courtaulds Fibres (Holdings) Limited under the Trade Mark TENCEL. The degree of fibrillation of lyocell fibres may be assessed by the following Test Method: Test Method There is no universally accepted standard for assessment of fibrillation, and the following method was used to assess Fibrillation Index (F.I.). Samples of fibre were arranged into a series showing increasing degrees of fibrillation. A standard length of fibre from each sample was then measured, and the number of fibrils (fine hairy spurs extending from the main body of the fibre) along the standard length was counted. The length of each fibril was measured, and an arbitrary number, being the product of the number of fibrils multiplied by the average length of each fibril, was determined for each fibre. The fibre exhibiting the highest value of this product was identified as being the most fibrillated fibre and was assigned an arbitrary- Fibrillation Index of 10. A wholly unfibrillated fibre was assigned a Fibrillation Index of zero, and the remaining fibres were evenly ranged from 0 to 10 based on the microscopically measured arbitrary numbers. The measured fibres were then used to form a standard graded scale. To determine the Fibrillation Index for any other sample of fibre, five or ten fibres were visually compared under the microscope with the standard graded fibres. The visually determined numbers for each fibre were then averaged to give a Fibrillation Index for the sample under test. It will be appreciated that visual determination and averaging is many times quicker than measurement, and it has been found that skilled fibre technologists are consistent in their rating of fibres. Fibrillation Index of fabrics can be assessed on fibres drawn from the surface of the fabric. Woven and knitted fabrics having F.I. of more than about 2.0 to 2.5 exhibit an unsightly appearance. The invention is illustrated by the following Examples, in which parts and proportions are by weight unless otherwise specified. Example 1 TAHT (1 g) was dissolved in hot tap water (50 ml, 70-80 * C) with stirring, optionally with the addition of other water-soluble additives to give solutions containing 20 g/1 TAHT. The behaviour of the solutions so obtained on natural cooling to ambient temperature was observed. The results shown in Table 1 were obtained: Table 1 Additive Concentration Behaviour g/i Precipitation (pptn. ) at 35-37 " C Urea 1 Pptn. at 35-37 " C Urea 5 Pptn. on cooling to 22 ' C Urea 12. 5 Pptn. after cooling to 22 ' C Urea 200 Stable for several days at 22 ' C Na,S0 4 1 Pptn. at 35-37 * C Sucrose 1 Pptn . at 35-37 ' C Gelatin 0. 1 Some pptn. after 1 hour at 22 ' C Gelatin 0.5 Stable for several days at 22 ' C Gelatin 1.0 Stable for several days at 22 ' C It will be observed that very low concentrations of gelatin suf ficed to maintain the chemical reagent in solution . The only other additive which gave any marked beneficial effect was urea at very high concentration . TAHT ( 25 g/1 ) was dissolved in tapwater at 80°C together with a non-ionic polyacrylamide ( Courgel AG 1111 , - Trade Mark of Courtaulds Chemicals ( Holdings ) Limited - , concentration 1-10 g/1 or Floergar AH 912 - Trade Mark of SNF Floergar - concentration 1-40 g/1 ) . Upon cooling, TAHT crystallized out at 30 °C except at the highest polyacrylamide concentrations . Such concentrations would be undesirably high in a commercial process , not least because of their high cost , and moreover such concentrated solutions are highly and disadvantageously viscous . The same procedure was used to assess the effect of varying TAHT and gelatin concentrations. The results shown in Table 2 were obtained: Table 2 TAHT Gelatin Behaviour g/1 g/1 45 1.125 Pptn. soon after cooling to 22' 45 1.5 Pptn. 1 hour after cooling to 22 'C 45 2.0 Some pptn. after several hours at 22'C 45 2.5 Some pptn. after several hours at 22"C 60 1.5 Pptn. on cooling to 40'C 60 2.5 Pptn. on cooling to 30'C 60 20.0 Pptn. on cooling to 40 * C TAHT (100 g/1) and gelatin (2.5 g/1) were dissolved in hot tap water (80"C). The resulting solution was diluted fourfold with cold water to give a solution containing TAHT (25 g/1) and gelatin (0.625 g/1). No precipitation occurred during dilution or on storage at room temperature. This procedure has the advantage of reduced cooling time. Gelatin (0.6 g/1) was dissolved in hot water (50°C) and the resulting solution cooled to room temperature. TAHT (24 g/1) was added and the mixture mixed in a high-shear mixer for 5 minutes. A dispersion was formed which did not settle out over several days. TAHT readily dissolves in certain water/solvent mixtures, for example 1:1 water/acetone and 1:1 water/ethanol, at room temperature. Use of such flammable solvent mixtures is not considered practical in industrial applications. TAHT is only sparingly soluble in 9:1 water/solvent mixtures at room temperature. Proton NMR analysis of TAHT solutions (20 g/1) containing sodium hydroxide (3.5 g/1) has shown that the average time for hydrolysis of one double bond in the TAHT molecule is about 5 hours at room temperature (gelatin- containing solution) and less than one hour at 50"C (with or without gelatin) . Example 2 A control solution of TAHT (20 g/1) was prepared by dissolution in water at 70-80'C with stirring, and the solution was stored at 50'C to avoid precipitation of the reagent. A solution of TAHT (20 g/1) and gelatin (0.5 g/1) was prepared in similar manner and allowed to cool to room temperature. The solutions were then made alkaline by addition of sodium hydroxide (17.5 g/1 stock solution, to give 3.5 g/1) and stored for various times (0-30 minutes) before use. Separate samples of 100% Tencel woven twill fabric (ca. 17 g) were immersed in the solutions (600 ml) for several seconds, mangled to give 80% wet pick-up, and steamed for 5 minutes at 100°C/745 mm Hg absolute humidity. (Wet pick-up is the proportion by which the weight of the wet sample exceeds the weight of the original dry sample.) The samples were washed with dilute acetic acid, rinsed under running water and dried. The samples were then assessed for nitrogen content by the Kjeldahl technique, and the amount of TAHT fixed on the sample assessed therefrom and recorded as a percentage by weight based on the weight of the untreated fabric. The efficiency of the treatment was calculated as the amount of TAHT fixed on the fabric as a percentage of that contained in the treatment bath. The results shown in Table 3 were obtained: Table 3 Storage time No gelatin Gelatin nun TAHT % Efficiency TAHT % Efficiency 0 1.29 83 1 . 43 84 5 1.21 76 1 . 38 81 10 1.15 74 1 . 33 80 30 1 . 29 79 It will be observed that the amount of fixed TAHT and the reaction efficiency were greater when gelatin-containing solutions were used. It is believed that this is the consequence of a reduced rate of hydrolysis of TAHT in the cooler solution. Example 3 A length of 100% Tencel woven fabric (12.6 m) was padded through an application bath (1.6 1, containing 32 g TAHT (20 g/1), 0.8 g gelatin (0.5 g/1) and 5.6 g sodium hydroxide (3.5 g/1), at 22 * C). The fabric was mangled at 2.5 m/min to give a wet pick-up of 81.7%. The sample was wound onto a core, sealed in polyethylene film, and stored (batched) at ambient temperature for 18 hours. The fabric was then washed in dilute acetic acid (1 g/1), rinsed with water, and dried. Samples from the beginning and end of the roll were then analysed for nitrogen content as described in Example 2. The results reported in Table 4 were obtained: Table 4 TAHT Efficiency % Beginning of roll 1.51 88 End of roll 1.29 75 The sample was dyed with a reactive dye by conventional techniques, and pieces from the beginning and end of the roll were subjected to conventional domestic laundering (wash/tumble, w/t) cycles. The F.I. of fibres removed from these samples is shown in Table 5: Table 5 Unlaundered 3 w/t 5 w/t Beginning of 0.7 0.4 0.0 roll End of roll 0.8 0.0 0.0 Example 4 TAHT (10 g) and gelatin (0.25 g) were dissolved in tap water (400 ml) at 80'C, and the solution was allowed to cool to ambient temperature. Sodium hydroxide (1.75 g) and Zetex HP-LFN (2.5 g) (a non-ionic low-foaming detergent available from ICI Surfactants) were dissolved in tap water (100 ml) at room temperature. The two solutions were mixed to give an application bath containing 20 g/1 TAHT, 0.5 g/1 gelatin, 3.5 g/1 sodium hydroxide and 5 g/1 Zetex HP-LFN. A sample of 100% lyocell twill fabric which had been sized with polyvinyl alcohol (PVA) was padded through the application bath, mangled and stored (batched) at ambient temperature for ca. 20 hours. The fabric was rinsed off in open width on a jig using a solution of acetic acid (1 g/1) at 60 * C, followed by one rinse with hot water (60 * C) and four rinses with cold water, and then dried. The amount of TAHT fixed was estimated by Kjeldahl analysis to be 1.75% owf (i.e. by weight on fabric). The fabric was next dyed with Procion Green H-E4BD (a reactive dye available from Zeneca Ltd) under exhaust conditions, soaped off, rinsed and dried. The F.I. of fibres removed from this fabric and from an untreated control before and after laundering are shown in Table 6: Table 6 Unlaundered 3 w/t 5 w/t Treated 0.0 0.0 0.0 Control 0.0 4.9 6.5 Example 5 TAHT (4 g) , Zetex WA-HS (0.5 g) (an anionic wetting agent available from ICI Surfactants), Remazol Red RB (10 g) (a reactive dye available from Hoechst AG) and urea were dissolved in tap water (160 ml) at 80'C, and the resulting solution was allowed to cool to room temperature. Sodium silicate (24 g) and sodium hydroxide (2.96 g) were dissolved in tap water (10 ml) at room temperature, and the resulting solution was diluted to 40 ml. The two solutions were mixed together to give an application bath. A sample of 100% lyocell twill fabric was padded through the application bath, mangled, and batched at ambient temperature for ca. 20 hours. The sample was then rinsed under running water, soaped off using an aqueous solution of Sandopur SR (2 g/1) (a soaping-off agent for reacting vat and azoic dyes available from Sandoz AG) at 95'C for 20 minutes, rinsed with hot and cold water, and dried. The amount of TAHT fixed on the fabric was estimated by Kjeldahl analysis to be 1.07% owf. The F.I. of fibres removed from this fabric and of fibres of an untreated control before and after laundering are shown in Table 7: Table 7 Unlaundered 3 w/t 5 w/t Treated 0.0 0.0 0.0 Control 0.0 7.3 6.3 Example 6 TAHT (4 g), gelatin (0.1 g) , urea (20 g) and Drimarene Navy K-2B (6 g) (a reactive dye available from Sandoz AG) were dissolved in tap water (160 ml) at 80"C, and the solution was allowed to cool to ambient temperature. Sodium carbonate (2 g) and sodium hydroxide (0.8 g) were dissolved in tap water (40 ml) at room temperature. The two solutions were combined to produce an application bath. A sample of 100% lyocell twill fabric was padded through the application bath, mangled and batched at ambient temperature for ca. 20 hours. The sample was then rinsed with running water, soaped off using an aqueous solution of Sandopur SR (2 g/1) at 95'C for 20 minutes, rinsed with hot and cold water and dried. The amount of TAHT fixed on the fabric was estimated by Kjeldahl analysis to be 1.00% owf. The F.I. of fibres removed from this fabric and of fibres of an untreated control before and after laundering are shown in Table 8: Table 8 Unlaundered 3 w/t 5 w/t Treated 0.0 0.9 1.3 Control 0.0 4.7 7.0 Example 7 TAHT may be applied to lyocell fibre using jet dyeing equipment, wherein the TAHT is exhausted onto the fibre. In this process, TAHT is dissolved in water at 80 * C in a dye kitchen to give a solution. The solution is transferred to the jet dyeing machine through pipework, and its temperature may fall to about 60"C during the transfer. The solution is diluted to the desired concentration for application to the fibre in the jet dyeing machine and reheated to about 95 * C for application to the fibre. A solution was prepared by dissolving TAHT (90 g/1) and gelatin (2.25 g/1) in water at 80"C. A small proportion of the TAHT crystallised out when the temperature of the solution was reduced to 60 * C. The amount which crystallised out was insufficient to cause significant pipe blockage. A control solution was prepared as above, but with the omission of gelatin. A high proportion of the TAHT crystallised out when the temperature of the solution was reduced to 60"C. The amount which crystallised out would have caused severe pipe blockage problems on production jet-dyeing equipment. In both cases, all the TAHT redissolved when the respective solutions were reheated to 80'C.

Claims: CLAIMS 1. A method of reducing the fibrillation tendency of lyocell fibre, including the step of contacting the fibre with an aqueous solution of a chemical reagent having at least two functional groups reactive with cellulose, characterised in that the aqueous solution additionally comprises dissolved gelatin. 2. A method according to claim 1, characterised in that the fibre is contacted with the aqueous solution at ambient temperature. 3. A method according to claim 2, characterised in that the aqueous solution is prepared by dissolution of the chemical reagent and the gelatin in water at elevated temperature followed by cooling of the solution to ambient temperature. 4. A method according to any preceding claim, characterised in that the concentration of gelatin dissolved in the aqueous solution is in the range 0.1 to 20.0 grams per litre. 5. A method according to claim 4, characterised in that the concentration of gelatin dissolved in the aqueous solution is in the range 0.2 to 1.0 gram per litre. 6. A method according to any preceding claim, characterised in that the chemical reagent is triacryloylhexahydrotriazine. 7. A method according to claim 6, characterised in that the concentration of triacryloylhexahydrotriazine dissolved in the aqueous solution is in the range 5 to 60 grams per litre. 8. A method according to claim 7, characterised in that the concentration of triacryloylhexahydrotriazine dissolved in the aqueous solution is in the range 10 to 40 grams per litre. 9. A method according to any preceding claim, characterised in that it includes the steps of (1) padding the aqueous solution onto the lyocell fibre, and (2) thereafter treating the fibre under conditions effective to produce reaction between the chemical reagent and the lyocell.

Inventors: KRAVCHUK PAUL, KRAVCHUK, PAUL
Applicants: COURTAULDS FIBRES HOLDINGS LTD, KRAVCHUK PAUL, COURTAULDS FIBRES (HOLDINGS) LIMITED, KRAVCHUK, PAUL
Application year: 1996
Main classification: D06M15
IPC codes: D06M13, D06M15, D06M101