GB1590572A - Crimped high-strength rayon yarn and method for its preparation - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO CRIMPED, HIGH-STRENGTH RAYON YARN AND METHOD FOR ITS PREPARATION (71) We, AVTEX FIBERS INC., a corporation organised and existing under the laws of the State of New York, United States of America, of 580 East Swedesford Road, 9 Executive Mall, P.O. Box 880, Valley Forge, Pa. 19482, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment : - The present invention relates to crimped yarn comprising regenerated cellulose filaments, a method of preparing crimped highstrength rayon, to yarn produced therefrom and fabric comprising the yarn of the present invention.

In United States Patent Specification No.

3,277,226, a much improved regenerated cellulose yarn is disclosed having a combination of physical properties which have brought the yarn into great demand for textile uses.

It would be desirable to prepare this improved fibre as a crimped yarn or staple fibre, thereby increasing its coverage ability in textiles. Conventionally, crimped yarn is prepared by sluicing the fibre in a plasticizing medium, such as hot water. However, the high tenacity, high wet modulus yarn, as described in the above Patent Specification, does not crimp when sluiced in a relaxed condition in a plasticizing medium, such as hot water.

It is an object of the present invention to prepare a crimped, high-strength rayon yarn.

It is a further object of the present invention to provide a method of preparing crimped, high-strength rayon yarn.

According to the first aspect of the present invention there is provided a crimped yarn comprising regenerated cellulose filaments having a broken skin-core cross-sectional structure of which the skin comprises from 20 to 40%, preferably from 25 to 30%, of the cross-sectional area, the skin of the filaments being positioned at the inside of the bends and the exposed core being positioned at the outside of the bends of the crimp, the peripheral skin surface of the cross-sectional structure being substantially smooth and the core section is "blown-out" or protrudes from the structure, the yarn having a wet tenacity of at least 2.25 grams per denier, a conditioned tenacity of at least 3.5 grams per denier, and a wet extensibility of from 15 to 30 percent.

The above-described yarn was crimped to a high degree by sluicing in a relaxed state in a plasticizing medium, such as hot water.

The yarn denier per filament normally ranges from 1 to 15 for this invention, while the crimp rating or number of crimps per inch generally ranges from 10 to 30, depending on the processing of the yarn and the yarn denier.

By utilizing the disclosed combination of processing variables which we have discovered, the crimped rayon filaments, staple fibres and yarn produced from these spinning solutions have been found to further possess high wet modulus, good elongation and a high number of crimps per inch. The filaments and fibres of the present invention preferably have an initial wet modulus in the range of from 4 to 9 grams per denier, a conditioned elongation in the range of from 14 to 24 percent and from 10 to 30 crimps per inch, preferably 20 to 30 c.p.i.

The crimped yarn is preferably produced in the form of staple fibres which are readily blended and processed for textile purposes.

According to the second aspect of the present invention there is provided a method of preparing the crimped high-strength yarn of the first aspect of the present invention which method consists essentially of extruding a multiplicity of filaments of viscose prepared with from 6 to 9, preferably about 7.5, percent of cellulose; from 6 to 9, preferably about 7.5, per cent. of caustic soda and from 28 to 39, preferably about 34, per cent of carbon disulphide, based on the weight of the cellulose, the viscose containing from 1 to 8 percent, based on the weight of the cellulose, of a regeneration retardant and having a spinning ball-fall viscosity in the range of from 40 to 150, preferably from 70 to 80, and a common salt index in the range of from 6 to 11, preferably from 7.5 to 9.5, into a spinning bath containing; from 4 to 9, preferably from 5.0 to 6.0, w/v percent of sulphuric acid, from 2 to 5, preferabout about 3, w/v percent of zinc sulphate and from 15 to 24, preferably from 17 to 20, w/v percent of sodium sulphate, the spinning bath being maintained at a temperature in the range of from 30 to 550C., preferably from 45 to 500C, withdrawing coagulated and incompletely regenerated filaments from the spinning bath and passing such filaments through an aqueous stretch bath maintained at a temperature in the range of from 75 to 1000C., preferably from 90 to 950C., and stretching such filaments in the strength bath by from 90 to 140, preferably from 115 to 130, percent. The resulting yarn is crimped by exposing it, in the relaxed state, to a plasticizing medium.

In a preferred embodiment, the wet yarn is cut into staple and dropped into a hot sluice bath where crimping takes place. The crimped staple is then wet processed and dried.

The yarn produced by the above method will vary in filament denier, mainly according to the size of the spinneret holes through which the viscose is extruded and the degree of stretch given the yarn. Other process variables will contribute in a minor way. In any event, the process is suitable for producing yarn having filament deniers ranging from 1 to 15, preferably from 1.5 to 8. The number of filaments in the fibre will vary only with the number of filaments simultaneously spun and brought together for processing.

The viscose is formed in a conventional manner and, either during its preparation or at some stage prior to spinning, the regeneration retardant is added. These materials, their use and effect are well-known to those skilled in this art and include, for example, polyoxyalkylene glycols, such as polyoxyethylene glycols, polyoxypropylene glycols and block copolymers of propylene and ethylene oxides; various amines including monoamines, diamines and polyamines, such as diethylamines, dimethylamine, ethylene diamine and diethylenetriamine; reaction products of alkylene oxides with fatty acids, fatty alcohols, fatty amines, aromatic acids, aromatic alcohols, aromatic amines, partial esters of fatty acids and polyhydric alcohols, such as reaction products of ethylene oxide with lauryl alcohols, such as reaction products of ethylene oxide with lauryl alcohol, phenol, lauryl amine, glycerol monostearate, etc., quaternary ammonium compounds, and the like. This type of material is more fully discussed in the prior art. For example, United States Patent Specification No. 2,879,170 lists many such compounds and terms them "coagulation modifiers". Other sources refer to these materials as "skin-forming viscose additives" or "viscose modifiers". In any event, these compounds and their effects are well-known.

The amount of modifier can vary from 1% to 8%, preferably 2% to 6%, based on the weight of the cellulose.

From the standpoint of availability, cost and performance, it is preferred to utilize a combination of modifiers, such as a monoamine and a polyoxyalkylene glycol or a polyoxyalkylene glycol ether of an aromatic alcohol or a polyhydric alcohol wherein the glycol or ether has a molecular weight in the range of from 600 to 4000 or to 6000; for example, dimethylamine and a polyoxyethylene glycol or a polyethylene glycol ether of phenol or sorbitol having a molecular weight within the stated range. In the use of the combination, the monoamine can be added in an amount of from 1.0% to 3.0%, and the glycol or ether in an amount of from 2% to 4%, both proportions being based upon the weight of the cellulose.

The viscose, for example, is aged (including the mixing and holding periods) for from 10 to 30 hours and preferably has a total sulphur content of approximately 1.7% to 2.4% and a xanthate sulphur content of from 1.1% to 1.6%. The sodium chloride salt test may be between 6 and 11 at the time of spinning and the ball-fall viscosity between 40 and 150 seconds.

During spinning, the temperature of the bath should be maintained in the range of from 30"C. to 550C. and the spinning speed may be in the range of 15 to 50, preferably from 25 to 30, metres per minute.

From the spinning bath, the filaments, which are coagulated and incompletely regenerated, are passed directly through a second bath, or stretch bath, maintained at a temperature in the range of from 75"C.

to 1000 C. and the filaments are stretched from 90% to 140% during their travel through this bath. The stretch bath may for example be a hot water bath or may contain from 1% to 5% of sulphuric acid, from 1% to 4% of zinc sulphate and from 4% to 7% of sodium sulphate. At this point, the regenerated, crimpable rayon may be wet processed, dried under tension and wound or, as is preferred, cut into staple, sluiced in hot water to obtain crimp, and then wet processed and dried.

Filaments and fibres produced from the described viscose and spun under the fore going conditions possess the properties and characteristics as described herein.

The fibres and filaments may be produced and the method of forming them may be practiced with conventional equipment, such as that shown diagrammatically in Fig.

4 of the accompanying drawing. A trough or tank 1 is provided as container for the spinning bath 2, which is generally recirculated in practice. Means for circulating the bath are not shown, such means being conventional in the art. A spinneret 3, mounted at the end of rounder 4, is positioned in the tank 2 being submerged in the spinning bath.

The viscose is delivered from a suitable source (not shown) to the rounder, and is extruded through the spinneret to form the filaments 5, which upon leaving the spinning bath, pass to positively driven godet 6 rotating at a speed to provide a minimum of jet stretch, and then on to a second positively driven godet 7. The godet 7 is driven at a speed greater than godet 6 and the relative speeds of the godets are selected so as to provide for the required stretching of the filaments between the two goods.

Interposed between the godets, there is mounted a trough 8 through which a second or stretching bath is circulated. The stretching bath is maintained at a high temperature which plasticizes, to some extent, the filaments and permits a higher degree of stretching. The stretching bath also effects a further regeneration of the cellulose in the coagulated and partially regenerated filaments formed in the spinning bath 2. From the godet 7, the filaments may be passed through suitable aftertreatment zones under tension and then collected on a cone or the like; however, in the preferred embodiment, the filaments are passed from godet 7 around godet 9 to a suitable cutting device 10 wherein the filaments are cut to form staple fibers and dropped into a sluice box 11 into which hot water is fed through nozzles 12.Conventionally, the staple fibers are then deposited as a mat on belt 13 and the mat of fibers then subjected to the required aftertreatments and drying in dryer 14.

The following Examples further illustrate the present invention.

EXAMPLE I Viscose was prepared by treatment of pulp sheets (high 98% alpha-cellulose, viscose grade pulp) with caustic soda, shredding the resulting alkali cellulose, xanthating the alkali cellulose and dissolving it in a caustic soda solution. The viscose so prepared contained 7.5% cellulose, 7.5% caustic soda and 34% carbon disulfide, based on the weight of the cellulose. Dimethylamine (1.75%) and 3.5% of polyoxyethylene glycol ether of phenol containing an average of 15 ethylene oxide units per mole of phenol, was incorporated in the viscose during the mixing operation. The viscose was then aged in the conventional manner at 180C. for 14 hours.

The viscose at the time of spinning had a sodium chloride salt test of about 8.5, and a ball-fall viscosity of 70 to 80 seconds.

Ball-fall viscosity is obtained by measuring the time in seconds required for a solid steel ball of 8 inch diameter to fall 8 inches in a column of viscose of 4 inch diameter at 18"C.

The dimethylamine and phenol ether may be added at any stage in the preparation of the viscose to serve as a regeneration retardant.

The viscose was spun to form a 1.5 denier, 12,000 filament yarn by extrusion of the viscose through orifices about 0.0025 inch in diameter into a spinning bath containing 5% sulphuric acid, 17% sodium sulphate and 3% zinc sulphate, the spinning bath being maintained at a temperature of about 48"C. The filaments were withdrawn from the bath, passed over a first godet, through a hot second bath, over a second godet, cut into staple, sluiced, aftertreated, and dried.The second bath was formed by diluting some of the spinning bath and contained about 2.5% sulphuric acid, about 1.5% zinc sulphate and about 8% sodium sulphate, and was maintained at a temperature of about 95"C. During passage of the filaments through the hot bath, they were stretched approximately 115%. The spinning speed was about 25 metres per minute. The wet yarn was cut into staple length fibres and dropped into a water sluice bath maintained at about 90"C. The staple fibres formed from 25 to 30 crimps per inch in the sluice bath. The crimped staple was then wet processed and dried.

The crimped fibre had a conditioned tenacity of about 4 grams per denier, a wet tenacity of about 2.7 grams per denier, a conditioned extensibility of about 14 percent, a wet extensibility of about 19 percent, an initial wet modulus of about 10.0, and was a substantially non-fibrillatable fibrous product. In cross-section, a representative filament had a smooth, broken skin which comprise about 25% of the cross-sectional area and encompassed about 65 % of the periphery of the cross-section. The core was "broken-out" of the filament cross-section to provide an unbalanced shape.

EXAMPLE II Viscose was prepared by treatment of pulp sheets (98 % alpha-cellulose, viscose grade pulp) as described in Example I. The viscose so prepared contained 7.55% cellu- lose, 7.5% caustic soda and 31% carbon disulfide, based on the weight of the cellu lose. Dimethylamine (1.05%) and 2% of polyoxyethylene glycol ether of phenol, containing an average of 15 ethylene oxide units per mole of phenol, was incorporated in the viscose during the mixing operation.

The viscose was then aged in the conventional manner as in Example I.

The viscose at the time of spinning had a sodium chloride salt test of about 8.7, and a ball-fall viscosity of 80 to 90 seconds.

The viscose was spun to form a 1.49 to 1.67 denier, 28,500 filament yarn by extrusion of the viscose through orifices of about 0.002 inch in diameter into a spinning bath containing 6.0 to 6.5 percent sulphuric acid, 17 percent sodium sulphate and 2.8 percent zinc sulphate, the spinning bath being maintained at a temperature of about 48"C.

The filaments were withdrawn from the bath, passed over a first godet, through a second hot bath, over a second godet, cut into staple, sluiced, aftertreated, and dried.

A second bath was formed by diluting some of the spinning bath and contained about 2.5 percent sulphuric acid, about 1.5 percent zinc sulphate and about 8 percent sodium sulphate, and was maintained at a temperature of about 95"C. During passage of the filaments through the hot bath, they were stretched approximately 105 percent.

The spinning speed was about 29 metres per minute. The wet yarn was cut into staple length fibres and dropped into a water sluice bath maintained at about 95"C. The staple fibres formed from 21 to 25 crimps per inch in the sluice bath. The crimped staple was then wet processed and dried.

The crimped fibre had a conditioned tenacity ranging from 3.45 to 3.60 grams per denier, a conditioned elongation of from 20.2 to 21.0 percent, and was a substantially non-fibrillatable fibrous product.

In cross-section, a representative filament had a smooth broken skin which comprised from 20 to 25 percent of the cross-sectional area and encompassed about 75 percent of the periphery of the cross-section. The core was "broken-out" of the filament crosssection to provide an unbalanced shape.

Similarly, fibres having filaments ranging in denier up to about 15 and having like physical characteristics, may be spun and processed with crimp ratings in most instances dropping to about 10 with the high denier filament yarns.

It will be noted that the above-described process steps, with certain critical exceptions, conform to those of the above-mentioned United States Patent Specification No.

3,277,226. The process of that patent pro- duces a yarn wherein the individual filaments have a cross-sectional structure as representatively shown in Figure 1 of the accompanying drawing. This type of structure may be defined as a smooth, unbroken skin-core cross-section wherein the skin comprises from about 20 to about 40% of the total cross-section. Yarns of these filaments, as described in the aforementioned Patent Specification, have extremely desirable physical characteristics, but they do not crimp when placed relaxed in a plasticizing medium. To obtain a crimpable yarn approaching the high physical and structural qualities of this prior high-stretch yarn, it was found that the spinning conditions must be modified to a small, but critical degree.Outside of these critical limitations, for the viscose composition employed, one either would not obtain the desired crimp rating or, in the other extreme, the loss of physical properties would be too great.

The critical spinning conditions for this invention were found to be, in combination: 1) A specified higher range for the sodium sulphate concentration in the spinning bath; 2) A generally higher temperature maintenance for the spinning bath; and 3) A generally lower range for the sulphuric acid concentration in the spin bath.

It should be observed that all of the spinning conditions, including the viscose specifications, are considered critical for the preparation of the crimpable yarn of this invention. Should viscose of a different specification than described be employed, the yarn quality would be changed. However, with the viscose employed herein, the above critical spinning conditions produce a yarn having individual filament crosssectional shapes, as representatively shown in Figure 22 of the accompanying drawing.

It is seen that the cross-section shown in Figure 2 differs from that of Figure 1 in the presence of a broken skin portion which has shrunk back somewhat to permit the "blowing-out" or protrusion of some of the core material. This is in contrast to fibres of uneven cross-section which are substantially circular, that is, have a conjugate spin -ning type of cross structure without a "blown-out" or protruding core section such as shown in Japanese Patent Publication No.

41-17699. Ideally, the broken skin remains smooth and covers at least 50 and up to about 75% of the periphery of the crosssectional shape. This permits retention of much of the high strength characteristics and quality of the filament type shown in Figure 1. Should different spinning conditions be employed, the yarn properties and filament cross-section would be modified to the point of defeating the objects of this invention.

For example, the filament skin could remain unbroken with a resulting non-crimpable yarn; the broken filament skin could retract to a degree causing considerable loss of yarn strength; or the filament skin surface could become crenulated, such as seen in Figure 3 of the accompanying drawing, a representative cross-section of a filament of conventional crimped rayon yam, causing loss of yarn strength and increasing soil retention properties.

As will be evident from Figure 2 the skin there is like that of Figure 1 (and unlike that of Figure 3) in that it is substantially smooth; it is like that of Figures 1 and 3 in that it is substantially uniform in thickness throughout, with its thickness at any one point being much less than the thickness of the core.

It is seen then, that the spinning conditions for this invention are critical in order to obtain a yarn which will crimp satisfactorily without excessive loss of high-strength characteristics and quality.

The wed moduli of the yarns of this invention, as defined in United States Patent Specification No. 3,277,266, can be brought up to as high as about 12, depending on the degree of stretch and bath temperature within the given ranges. The higher wet moduli are obtained by higher stretch and lower bath temperatures.

For the purposes of this invention, the term "skin" is employed to designate that portion of the regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more filaments mounted in a wax block is taken and mounted on a glass slide with Meyer's albumin fixative.

After dewaxing in xylene, the section is placed in successive baths of 60 percent and 30 percent alcohol for a few minutes each, and it is then stained in a 2 percent aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for one to two hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10 percent water and 90 percent dioxane for a period varying from five to thirty minutes, depending on the particular filament, the dye is entirely removed from the "core", leaving it restricted to the "skin" area.

The crimped rayon yarns and fibres are used alone or in blends with natural or synthetic fibres to produce textiles with improved coverage. The crimped staple of this invention was made into both woven and knitted fabrics which were observed to provide a significant improvement in cover when compared with fabrics prepared from the non-crimping fibre of United States Patent Specification No. 3,277,226. The crimped staple also imparted more bulk to these fabrics.

WHAT WE CLAIM IS:- 1. A crimped yarn comprising regenerated cellulose filaments having a broken skin-core cross-sectional structure of which the skin comprises from 20 percent to 40 percent of the cross-sectional area, the skin of the filaments being positioned at the inside of the bends and the core being positioned at the outside of the bends of the crimp, the peripheral skin surface of the cross-sectional structure being substantially smooth and the core section protruding from the structure, the yarn having a wet tenacity of at least about 2.25 grams per denier, a conditioned tenacity of at least about 3.5 grams per denier, and a wet extensibility ranging from 15 to 30 percent.

2. A crimped yarn according to Claim 1, wherein the individual filament denier is in the range of from 1.5 to 8.

3. A crimped yarn according to Claim 1 or 2 in the form of staple fibres.

4. A crimped yarn according to Claim 1, 2 or 3 wherein the individual filaments have a cross-sectional structure in which the skin portion is of substantially uniform thickness.

5. A crimped yarn according to any one of the preceding claims, having an initial wet modulus in the range of from 4 to 9 grams per denier.

6. A crimped yarn according to any one of the preceding claims, having from ten to thirty crimps per inch.

7. A crimped yarn according to any one of the preceding claims, having a conditioned elongation of fourteen to twentyfour percent.

8. A method of preparing crimped highstrength rayon yarn in accordance with Claim 1, which method comprises extruding a multiplicity of filaments of viscose prepared with from 6 to 9 percent of cellulose, from 6 to 9 percent of caustic soda and from 28 to 39 percent of carbon disulphide, based on the weight of the cellulose, the viscose containing from 1 to 8 percent, based on the weight of the cellulose, of a regeneration retardant and having a spinning ball-fall viscosity in the range of from 40 to 150 and a common salt index in the range of from 6 to 11, into a spinning bath containing from 4 to 9 w/v percent of sulphuric acid, from 2 to 5 w/v percent of zinc sulphate and from 15 to 24 w/v percent of sodium sulphate, the spinning bath being maintained at a temperature in the range of from 30 to 550C., withdrawing coagulated and incompletely regenerated filaments from the spinning bath and passing such filaments through an aqueous stretch bath maintained at a temperature in the range of from 75 to 100"C., stretching such filaments in the stretch bath from 90 to 140 percent and then sluicing the filaments in a relaxed state in a plasticizing medium.

9. A method according to Claim 8, wherein the denier of the crimped high

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. representative cross-section of a filament of conventional crimped rayon yam, causing loss of yarn strength and increasing soil retention properties. As will be evident from Figure 2 the skin there is like that of Figure 1 (and unlike that of Figure 3) in that it is substantially smooth; it is like that of Figures 1 and 3 in that it is substantially uniform in thickness throughout, with its thickness at any one point being much less than the thickness of the core. It is seen then, that the spinning conditions for this invention are critical in order to obtain a yarn which will crimp satisfactorily without excessive loss of high-strength characteristics and quality. The wed moduli of the yarns of this invention, as defined in United States Patent Specification No. 3,277,266, can be brought up to as high as about 12, depending on the degree of stretch and bath temperature within the given ranges. The higher wet moduli are obtained by higher stretch and lower bath temperatures. For the purposes of this invention, the term "skin" is employed to designate that portion of the regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more filaments mounted in a wax block is taken and mounted on a glass slide with Meyer's albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60 percent and 30 percent alcohol for a few minutes each, and it is then stained in a 2 percent aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for one to two hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10 percent water and 90 percent dioxane for a period varying from five to thirty minutes, depending on the particular filament, the dye is entirely removed from the "core", leaving it restricted to the "skin" area. The crimped rayon yarns and fibres are used alone or in blends with natural or synthetic fibres to produce textiles with improved coverage. The crimped staple of this invention was made into both woven and knitted fabrics which were observed to provide a significant improvement in cover when compared with fabrics prepared from the non-crimping fibre of United States Patent Specification No. 3,277,226. The crimped staple also imparted more bulk to these fabrics. WHAT WE CLAIM IS:-

1. A crimped yarn comprising regenerated cellulose filaments having a broken skin-core cross-sectional structure of which the skin comprises from 20 percent to 40 percent of the cross-sectional area, the skin of the filaments being positioned at the inside of the bends and the core being positioned at the outside of the bends of the crimp, the peripheral skin surface of the cross-sectional structure being substantially smooth and the core section protruding from the structure, the yarn having a wet tenacity of at least about 2.25 grams per denier, a conditioned tenacity of at least about 3.5 grams per denier, and a wet extensibility ranging from 15 to 30 percent.

2. A crimped yarn according to Claim 1, wherein the individual filament denier is in the range of from 1.5 to 8.

3. A crimped yarn according to Claim 1 or 2 in the form of staple fibres.

4. A crimped yarn according to Claim 1, 2 or 3 wherein the individual filaments have a cross-sectional structure in which the skin portion is of substantially uniform thickness.

5. A crimped yarn according to any one of the preceding claims, having an initial wet modulus in the range of from 4 to 9 grams per denier.

6. A crimped yarn according to any one of the preceding claims, having from ten to thirty crimps per inch.

7. A crimped yarn according to any one of the preceding claims, having a conditioned elongation of fourteen to twentyfour percent.

8. A method of preparing crimped highstrength rayon yarn in accordance with Claim 1, which method comprises extruding a multiplicity of filaments of viscose prepared with from 6 to 9 percent of cellulose, from 6 to 9 percent of caustic soda and from 28 to 39 percent of carbon disulphide, based on the weight of the cellulose, the viscose containing from 1 to 8 percent, based on the weight of the cellulose, of a regeneration retardant and having a spinning ball-fall viscosity in the range of from 40 to 150 and a common salt index in the range of from 6 to 11, into a spinning bath containing from 4 to 9 w/v percent of sulphuric acid, from 2 to 5 w/v percent of zinc sulphate and from 15 to 24 w/v percent of sodium sulphate, the spinning bath being maintained at a temperature in the range of from 30 to 550C., withdrawing coagulated and incompletely regenerated filaments from the spinning bath and passing such filaments through an aqueous stretch bath maintained at a temperature in the range of from 75 to 100"C., stretching such filaments in the stretch bath from 90 to 140 percent and then sluicing the filaments in a relaxed state in a plasticizing medium.

9. A method according to Claim 8, wherein the denier of the crimped high

strength rayon filaments produced is in the range of from 1.5 to 8.

10. A method according to Claim 8 or 9, wherein the stretched filaments are cut into staple fibres and the staple fibres sluiced in an aqueous bath maintained at a temperature in the range of from 75 to 1000C.

11. A method according to Claim 8, 9 or 10, wherein the viscose is prepared with about 7.5 percent of cellulose, about 7.5 percent of caustic soda and about 34 percent of carbon disulphide, the viscose containing as a regeneration retardant, about 1.75 percent of dimethylamine and about 3.5 percent of a polyoxyethylene glycol ether of phenol, the viscose having a spinning ball-fall viscosity in the range of from 70 to 80 and a common salt index in the range of from 7.5 to 9.5.

12. A method according to Claim 8, 9 or 10, wherein the spinning bath contains from 5 to 6 percent of sulphuric acid, about 3 percent of zinc sulphate, from 17 to 20 percent of sodium sulphate and is maintained at a temperature of about 48"C, the aqueous stretch bath containing about 2.5 percent of sulphuric acid.

13. A method according to Claim 8.

wherein the denier of the crimped highstrength rayon filaments produced is in the range of from 1.5 to 8 and the stretched filaments are cut into staple fibres and sluiced in a water bath maintained at a temperature in the range of from 75 to 1000 C.

14. A yarn in accordance with Claim 1, substantially as described in foregoing Example I.

15. A yarn in accordance with Claim 1, substantially as described in foregoing Example 2.

16. A method according to Claim 8, substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

17. A method according to Claim 8, substantially as described in foregoing Example 1.

18. A method according to Claim 8, substantially as described in foregoing Example 2.

19. The product of any one of Claims 8 to 13 and 16 to 18.

20. A fabric comprising the yarn of any one of Claims 1 to 7, 14 and 15.