WO1996005356A1

WO1996005356A1 - Cellulosic textile materials

Info

Publication number: WO1996005356A1
Application number: PCT/GB1995/001922
Authority: WO
Inventors: Hardev Singh Bahia
Original assignee: Courtaulds Fibres (Holdings) Limited
Priority date: 1994-08-17
Filing date: 1995-08-15
Publication date: 1996-02-22
Also published as: TR199501020A2; GB9416616D0; AU3188195A

Abstract

Flame-resistant modified lyocell fibre is provided which has a limiting oxygen index (LOI) of at least 36, a phosphorus content of at least 3 % by weight and a tenacity of at least 10 cN/tex, or an LOI of at least 32, a phosphorus content of at least 2 % by weight and a tenacity of at least 20 cN/tex. A flame-resistant cellulosic textile material is produced by treating a cellulosic textile material comprising lycoell fibre with a phosphoric acid and an acidic salt or ester thereof and a nitrogen-containing basic compound such as urea. The tendency to fibrillation of a lyocell textile material is reduced by treatment of the textile material with a phosphoric acid or an acidic salt or ester thereof and a nitrogen-containing basic compound.

Description

FOR THE PURPOSES OF INFORMATION ONLY

Codes used to identify States party to the PCT on the front pages of pamphlets publishing international applications under the PCT.

AT Austria GB United Kingdom MR Mauritania

AU Australia GE Georgia MW Malawi

BB Barbados GN Guinea NE Niger

BE Belgium GR Greece NL Netherlands

BF Burkina Faso HU Hungary NO Norway

BG Bulgaria IE Ireland NZ New Zealand

BJ Benin IT Italy PL Poland

BR Brazil JP Japan PT Portugal

BY Belarus KE Kenya RO Romania

CA Canada KG Kyrgystan RU Russian Federation

CF Central African Republic KP Democratic People's Republic SD Sudan

CG Congo of Korea SE Sweden

CH Switzerland KR Republic of Korea SI Slovenia

Cl Cβte d'lvoire KZ Kazakhstan SK Slovakia

CM Cameroon LI Liechtenstein SN Senegal

CN China LK Sri Lanka TD Chad

CS Czechoslov akia LU Luxembourg TG Togo

CZ Czech Republic LV Latvia TJ Tajikistan

DE Germany C Monaco TT Tπnidad and Tobago

DK Denmark MD Republic of Moldova UA Ukraine

ES Spain MG Madagascar US United States of America

FI Finland ML Mali UZ Uzbekistan

FR France MN Mongolia VN Viet Nam

GA Gabon - 1 - CELLULOSIC TEXTILE MATERIALS-

Field of the invention

This invention relates to flame-resistant cellulosic fibre, to a process for the production of a flame-resistant cellulosic textile material, and also to a process for the treatment of cellulosic textile material to confer other advantages such as reduced fibrillation.

Background art

Flame-retardant treatments for cellulosic textile materials are reviewed in "Flame Resistant Cotton" by W.A. Reeves and G.L. Drake, published by Merrow in 1971. The treatment of cotton with phosphoric acid and a nitrogen- containing basic organic compound such as urea is described at pages 29-32 of the above-mentioned book by Reeves and Drake and also in GB-A-604197, GB-A-634690 and GB-A-638434. Such treatments have had little or no commercial use in more recent years, when flame-retardant treatments have generally been based on materials derived from tetrakis(hydroxymethyl) phosphonium chloride.

It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable organic solvent into a coagulating bath. This process is referred to as "solvent spinning", and the cellulose fibre produced thereby is referred to as "solvent-spun" cellulose fibre or as lyocell fibre. Lyocell fibre is to be distinguished from cellulose fibre made by other known processes, which rely on the formation of a soluble chemical derivative of cellulose and its subsequent decomposition to regenerate the cellulose, for example the viscose process. One example of the solvent spinning process is described in US-A-4,246,221, the contents of which are incorporated herein by way of reference. Cellulose is dissolved in a solvent such as a tertiary amine N-oxide, for example N-methylmorpholine N- oxide. The resulting solution is then extruded through a - 2 - suitable die into an aqueous bath to produce an assembly of filaments, which is washed in water to remove the solvent and is subsequently dried.

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 dissolving cellulose in the solvent 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 textile material" means lyocell fibre whether in continuous filament, sliver, roving, tow or cut fibre form, for example staple fibre form, or as a yarn or fabric, such as woven, knitted or nonwoven fabric, comprising lyocell fibre.

Disclosure of the invention

We have found, according to the invention, that the treatment of lyocell fibre and textile material comprising lyocell fibre with a phosphoric acid compound and a nitrogen-containing basic compound yields fibre and textile material having surprisingly high levels of flame resistance and other advantageous properties . This is all the more surprising since flame retardants have generally been less effective on man-made cellulosic fibres such as rayon than on cotton.

Flame-resistant cellulosic fibre according to one aspect of the invention is characterised in that the fibre is a modified lyocell fibre and has a limiting oxygen index LOI of at least 36, a phosphorus content of at least 3% by weight and a tenacity of at least 10 cN/tex. The LOI is measured as described in ASTM-D-2863.

Flame-resistant cellulosic fibre according to another aspect of the invention is characterised in that the fibre - 3 - is a modified lyocell fibre and has an LOI of at least 32, a phosphorus content of at least 2% by weight and a tenacity of at least 20 cN/tex.

The nitrogen content of the flame-resistant cellulosic fibre according to the invention is generally at least 0.3%, usually at least 0.5%, by weight.

A process according to the invention for the production of a flame-resistant cellulosic textile material comprises treating a cellulosic textile material with a phosphoric acid or an acidic salt or ester thereof and with a nitrogen-containing basic compound and is characterised in that the cellulosic textile material comprises lyocell fibre.

The cellulosic textile material which is used in the process of the present invention comprises lyocell fibre, which can be in the form of continuous filaments, for example a continuous multifilament tow, or cut fibres, for example staple fibre of a staple length which may be in the range 2 to 100 mm, o it can be a yarn, sliver, roving or fabric, including a woven, knitted or nonwoven fabric, comprising lyocell fibre. The yarn, sliver, roving or fabric preferably contains at least 50% by weight lyocell fibre, and most preferably 100% of the fibre in such a yarn, sliver, roving or fabric is lyocell fibre, but blends of lyocell fibre with other cellulosic fibre, for example cotton or viscose rayon fibre, or non-cellulosic fibre such as polyester, nylon, polyolefin or acrylic fibre can be used.

The phosphoric acid compound and nitrogen-containing basic compound are preferably applied together from aqueous solution. The phosphoric acid compound is preferably orthophosphoric acid H₃P0₄, although other phosphoric acids such as pyrophosphoric acid can be used, as can acidic phosphoric acid salts and esters having acidic protons such - 4 - as ammonium dihydrogen phosphate, sodium dihydrogen phosphate, diammonium hydrogen phosphate or a mono- or di- alkyl phosphate in which the alkyl groups have up to 12 carbon atoms such as onoethyl phosphate.

The concentration of phosphoric acid compound in the aqueous solution used to treat the lyocell textile material is generally at least 2% by weight and preferably at least 4% by weight orthophosphoric acid, or an equivalent amount of another phosphoric acid material, and can be up to 25 or 30% by weight. The most preferred concentration of phosphoric acid compound will vary according to the desired properties in the treated textile material. If a very high LOI is required, for example 36 or more, the phosphoric acid concentration is preferably in the range 6-25% by weight, producing a treated textile material with a phosphorus content of 2-8% by weight. If a somewhat lower LOI is acceptable but the textile material is required to retain more of its tenacity, a phosphoric acid concentration in the range 4-15% may be most preferred. The level of phosphorus incorporated in the lyocell textile material is also dependent on the liquor ratio (the ratio of the weight of phosphoric acid solution taken up by the textile material to the weight of material). The liquor ratio is preferably in the range 0.7:1 to 4:1, most preferably 1:1 to 2.5:1, liquor to textile material. We have found that a better combination of flame-resistant and tensile properties in the treated fibre is obtained when the phosphoric acid concentration is in the range 6 to 13% by weight and a high liquor ratio of 1.5:1 to 2.5:1 is used, rather than by using a higher phosphoric acid concentration with a lower liquor ratio.

The nitrogen-containing basic compound is preferably urea, but it can alternatively be another nitrogen- containing basic organic compound, for example cyanamide, guanidine, dicyandiamide, methylol dicyandiamide, melamine or a partially methylolated melamine or thiourea, or it can - 5 - be ammonium cyanate or thiocyanate. The nitrogen- containing basic compound is also preferably applied from aqueous solution. Urea, for example, is preferably used as a solution containing at least 5%, preferably at least 10%, by weight urea, up to 40 or 50% by weight. Other nitrogen- containing basic compounds are generally used at similar concentrations.

The phosphoric acid compound and the basic nitrogen compound can be applied separately to the lyocell textile material, in which case either the phosphoric acid compound or the basic nitrogen compound can be applied before the other, but they are preferably applied simultaneously to the textile material from a single solution. The weight ratio of phosphoric acid compound to urea or other basic nitrogen compound in such a solution is preferably between 0.25:1 and 1.25:1, most preferably 0.4:1 to 0.7:1.

The treatment solution is generally applied by a known technique appropriate for the type of textile material being treated, for example a multifilament tow or yarn can be treated by padding (passing through a bath of treatment solution followed by squeezing to control the amount of solution taken up by the textile material). A fabric or a rope of staple fibre can be treated by padding or by any of the treatments known for dyeing or applying finishing agents to fabrics.

The temperature at which the phosphoric acid compound and the basic nitrogen compound are applied to the lyocell textile material is not crucial and can for example be ambient temperature or any temperature between 0°C and 90 or 100°C, but the textile material should preferably be heated after the phosphoric acid compound and the basic nitrogen compound have both been applied to the textile material and the textile material has been removed from the reagent solution(s). Heating can be in air or any other gas which is substantially inert to the reaction, for example - 6 - nitrogen. The treated textile material should be heated at a temperature in the range 120-180°C, most preferably 140- 170°C. The time of heating is preferably 5 to 10 minutes at 170°C or longer at lower temperatures, for example 45 to 90 minutes at 120°C. During the heating step, reaction takes place between the cellulose of the lyocell fibres and the phosphoric acid compound and the basic nitrogen compound. Initially, this reaction causes the fibres to become weak and water-swellable, but when the preferred times of reaction are used the fibres become crosslinked and thus stronger and more stable to washing. Prolonged heating for more than the preferred times causes gradual degradation of the fibres. The preferred time and temperature of reaction are dependent on each other but are generally independent of the concentration of reagents applied to the lyocell textile material.

The reagent solution applied to the textile material is preferably unbuffered. If orthophosphoric acid is used as the phosphoric acid compound and urea is used as the basic nitrogen compound, the reagent solution initially has a low pH (generally below 1) but the pH approaches neutral as the treated textile material is heated and the urea and phosphoric acid react. If it is desired to avoid such a low pH, a phosphoric acid compound capable of acting as a buffer, such as potassium dihydrogen orthophosphate, can be used as all or part of the phosphoric acid compound, so that the pH of the reagent solution is for example in the range 5 to 6. A non-phosphate buffering agent can be used, but this is not preferred.

The type of lyocell textile material chosen as starting material may depend on the degree of fire- resistance required. If a highly fire-resistant fibre is required, for example for use in a fire barrier fabric, the textile material treated may be lyocell staple fibre or more preferably a tow of lyocell fibre which is cut into staple fibre after the treatment with the phosphoric acid compound - 7 - and basic nitrogen compound. The tow preferably comprises dried lyocell fibre as sold commercially, although the process of the invention can alternatively be performed on never-dried lyocell fibre. Treatment with a relatively concentrated solution of phosphoric acid and urea at a relatively high liquor to fibre ratio within the ranges stated above can form fibres having a phosphorus content of at least 3%, for example 4 to 5%, by weight, a nitrogen content of at least 1%, for example 1.2 to 1.5%, by weight and an LOI of at least 36, preferably at least 38, for example in the range 38 to 42. Fibres of such high LOI have not previously been produced from any cellulosic fibre. Moreover, the fibres of such high LOI produced according to the invention have a tenacity of at least 10 cN/tex and usually at least 15 cN/tex. The fibres can be processed into fire barrier fabrics by nonwoven technology such as air-laying followed by needling or adhesive bonding and may be processable by conventional textile processes such as yarn spinning followed by weaving or knitting. A fire barrier fabric formed of the flame-resistant fibres of the invention can for example be used in fire blankets, furnishings and upholstery, particularly seats for aircraft and trains, protective clothing and hot gas filtration. In such fire barrier fabrics, the fibres of the invention can be used in conjunction with high-temperature-resistant fibres such as aramid, glass, ceramic, metal or oxidised acrylic fibres. In general, the fibres of the invention can be used in place of polyacrylate fibres in the fire barrier fabrics described in EP-A-258513, EP-A-296027, EP-A-323765 and "Research Disclosure" No. 26175 published January 1986.

Textile materials having a somewhat lower LOI of 32 or more, for example 32 to 36, but a higher tenacity of at least 20 cN/tex can be produced by using a lower concentration of the phosphoric acid compound and the basic nitrogen compound and/or a lower liquor to fibre ratio. Such textile materials generally have a phosphorus content of at least 2%, for example 2-4%, by weight and usually a - 8 - nitrogen content of at least 0.6%, for example 0.6 to 1.2%, by weight. Various textile materials can be treated to form products having this LOI. Tow or staple fibre can be treated and subsequently spun into yarn and processed into woven, knitted or nonwoven fabric or formed into nonwoven fabric without spinning. Yarn, for example spun yarn or continuous multifilament yarn, can be treated and the treated yarn can be woven or knitted or formed into a nonwoven fabric. Alternatively, a fabric, which may be woven, knitted or nonwoven, can be treated with the phosphoric acid compound and the basic nitrogen compound to form the flame-resistant textile material.

The textile materials treated according to the invention have other valuable properties as well as flame resistance. In particular, they have a reduced tendency to fibrillate compared to textile materials formed of untreated lyocell fibre. Fibres 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. Such fibrillation is believed to be caused by mechanical abrasion of the fibres during treatment. Lyocell fabric has often been found to be more susceptible to fibrillation than fabric made from other types of cellulose fibre, such as cotton.

Thus, according to another aspect of the invention, a process for reducing the tendency to fibrillation of a lyocell textile material is characterised in that the lyocell textile material is treated with a phosphoric acid or an acidic salt or ester thereof and with a nitrogen- containing basic compound. - 9 -

The phosphoric acid compound and the basic nitrogen compound are preferably applied together from aqueous solution. Concentrations of the phosphoric acid compound and the basic nitrogen compound used to reduce fibrillation tendency are generally similar to or somewhat lower than those used to form a textile material of LOI 32-36, for example a concentration of phosphoric acid or acidic salt or ester thereof of 3-15% by weight and a urea concentration of

5-25% by weight. After application of the phosphoric acid compound and the basic nitrogen compound, the textile material is preferably heated at 120-180°C for 90 to 5 minutes. Any kind of lyocell textile material can be used as the starting material, for example a tow, yarn, staple fibre or woven, knitted or nonwoven fabric.

The textile materials produced according to the invention also have ion-exchange properties.

The invention is illustrated by the following Examples:-

Examples 1 to 3

Samples of lyocell fibre tow of decitex per filament about 2.5 as sold under the Trade Mark "Tencel" were immersed at ambient temperature in aqueous solutions containing urea and orthophosphoric acid and were squeezed between rollers to remove excess liquor. The concentrations of reagents and liquor ratio of the fibres after squeezing are shown in Table 1 below. The samples of tow thus treated were heated in an air-induced oven at 150°C for 45 minutes. The properties of the fibres after heat treatment are shown below; the LOI measurement was carried out on tufts of 50 mm staple fibre cut from the treated tow. - 10 -

Example Concentration Liquor Tenacity Extensibil.it Initial No. of Reagents Ratio LOI Dtex cN/tex y Modulus

7. (IN) cN/tex

Urea HjPO, Solution /Fibres

1 20 8.5 2.0 39.1 2.3 27.8 6.7 1219

2 35.3 18.7 1.2 36.1 2.6 16.5 2.8 1240

3 32.7 17.4 1.2 40.4 2.7 18.4 5.7 867.4

Example 4

The process of Example 2 was repeated with the variation that the heating step was carried out at 160°C for 15 minutes.

Example 5

The process of Example 3 was repeated with the variations that potassium dihydrogen phosphate was added to the aqueous solution of urea and orthophosphoric acid to buffer it to pH6 and that the heating step was carried out at 160°C for 13 minutes.

The products of Examples 4 and 5 were scoured with an aqueous solution of lg sodium carbonate and lg soap flakes per litre at 90°C for 30 minutes, to test their durability, before carrying out the tests on flame resistance and mechanical properties. The results obtained are shown in Table 2 below. - 11 - Table 2

Example Liquor Reagents '.'. Reaction Tenacity Ext IM

No. LOI Dtex cN/tex '• cN/tex

Urea H-PO. Temp Time

°C in

4 Water 35.3 18.7 160 15 37.2 2.5 18.5 1251

3.7

5 Buffer 32.7 17.4 160 13 40.2 2.6 16.0 5.0 814

5 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 0 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 5 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 0 fibres were graded 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, fibres were visually compared under 5 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 - 12 - averaging is many times quicker than measurement, and it has been found that skilled fibre technologists are consistent in their rating of fibres .

The treated fibres of Examples 1 to 4 were assessed for their tendency to fibrillate by placing a small tuft of about 30 fibres cut to 6 mm in 8 ml water with 4g glass microspheres in a sample tube and shaking the tube for 20 mins before examining the fibres visually as described above.

The fibres of both Example 1 and Example 4 had a Fibrillation Index of 0 (wholly unfibrillated) . By comparison, the lyocell fibre tow used as starting material had a Fibrillation Index of 5 according to this assessment method.

Example 6

Lyocell fibre tow as used in Examples 1 to 3 was padded with an aqueous solution of 20% by weight urea and

12% by weight orthophosphoric acid at a liquor to fibre ratio 1.5:1. The padded fibre was heated at 150°C for 20 minutes to produce a flame-resistant fibre.

The flame-resistant fibre was washed with soapy water at 90°C. The fibre was then chemically analysed for phosphorus and nitrogen content with the following results:-

Phosphorus content 4.22% by weight Nitrogen content 1.37% by weight

Claims

- 13 - CLAIMS

1. Flame-resistant cellulosic fibre, characterised that the fibre is a modified lyocell fibre and has a limiting oxygen index of at least 36, a phosphorus content of at least 3% by weight and a tenacity of at least 10 cN/tex.

2. Flame-resistant cellulosic fibre according to claim 1, characterised in that the fibre has a nitrogen content of at least 1% by weight.

3. Flame-resistant cellulosic fibre according to claim 1 or claim 2, characterised in that the fibre has a limiting oxygen index of at least 38 and a phosphorus content of 4 to 5% by weight.

4. Flame-resistant cellulosic fibre, characterised in that the fibre is a modified lyocell fibre and has a limiting oxygen index of at least 32, a phosphorus content of at least 2% by weight and a tenacity of at least 20 cN/tex.

5. Flame-resistant cellulosic fibre according to claim 4, characterised in that the fibre has a nitrogen content of at least 0.6% by weight.

6. A process for the production of a flame-resistant cellulosic textile material comprising treating a cellulosic textile material with a phosphoric acid or an acidic salt or ester thereof and with a nitrogen-containing basic compound, characterised in that the cellulosic textile material comprises lyocell fibre.

7. A process according to claim 6, characterised in that the flame-resistant textile material has a limiting oxygen index of at least 36 and a phosphorus content of at least 3% by weight. - 14 -

8. A process according to claim 6 or claim 7, characterised in that the nitrogen-containing basic compound is urea.

9. A process according to any of claims 6 to 8, characterised in that the cellulosic textile material is treated with an aqueous solution containing 4 to 25% by weight orthophosphoric acid.

10. A process according to any of claims 6 to 9, characterised in that the cellulosic textile material is treated with an aqueous solution containing both the phosphoric acid or acidic ester or salt thereof and the nitrogen-containing basic compound in a ratio of between 0.25:1 and 1.25:1 by weight.

11. A process according to claim 10, characterised in that the cellulosic textile material is treated with an aqueous solution containing 6 to 13% by weight phosphoric acid at a liquor ratio (the ratio of the weight of phosphoric acid solution taken up by the textile material to the weight of the material) in the range 1.5:1 to 2.5:1.

12. A process according to any of claims 6 to 11, characterised in that after treatment with the phosphoric acid or acidic salt or ester thereof and the nitrogen- containing basic compound the textile material is heated at a temperature in the range 120 to 180°C.

13. A process for reducing the tendency to fibrillation of a lyocell textile material, characterised in that the lyocell textile material is treated with a phosphoric acid or an acidic salt or ester thereof and with a nitrogen- containing basic compound.

14. A process according to claim 13, characterised in that the phosphoric acid or acidic salt or ester thereof and the nitrogen-containing basic compound are applied together - 15 - from aqueous solution.

15. A process according to claim 14, characterised in that the concentration of phosphoric acid or acidic salt or ester thereof in the aqueous solution is 3 to 15% by weight.

16. A process according to claim 14 or claim 15, characterised in that the nitrogen-containing basic compound is urea present at a concentration of 5 to 25% by weight in the aqueous solution.

17. A process according to any of claims 13 to 16, characterised in that, after application of the phosphoric acid and the nitrogen-containing basic compound to the lyocell textile material, the textile material is heated at a temperature in the range 120 to 180°C.