IE44494B1 - Hydrohilic fibres and filaments of synthetic polymers - Google Patents

Abstract

1532770 Hydrophilic filaments BAYER AG 21 Feb 1977 [25 Feb 1976] 07174/77 Heading B5B Porous filaments are prepared by dry spinning a solution of a polymer to which solution is added 5-50% by wt. of an additive substance which is solid under ambient conditions and which (a) has a m.p.t. or sublimation point higher than that of the spinning solvent used; (b) is readily miscible with the spinning solvent and a washing liquid; and (c) is a non- solvent for the polymer to be spun, and washing the additive out of the freshly spun filaments. Filaments have pronounced core-jacket structures and may be non-circular according to processing conditions. Suitable polymers are polyacrylic nitriles and polyamides or those which optionally contain heterocyclic rings.

Description

fill χ invent ι..-i I'el.itt'i. ¢,. tixUl ephi t iv tih.-t'f» , filaments ot synthetic polymers and lo a process for their production. for uuiiu-rous top I ί ca! i ous, tor example lor bed Uiii’ti 5 or underwear, it is desirable to use textiles of manmade fibres which resemble natural fibres, such as cotton, in their behaviour with respect to moisture. Accordingly, there has been no shortage of attempts to improve the properties of manmade fibres which are unsatisfactory in this respect.

For example, highly hydrophilic natural fibres have been blended with synthetic fibres. It is also known that polyacrylonitrile, for example can be mixed with a second acrylonitrile polymer containing from 30 to 80$ by weight of a polyethylene oxide methacrylate, and the resulting mixtures spun (German Patent Specification No. 1,645,532). Acrylic fibres of this type which contain ethoxylated acrylic acid derivatives with chemically bound polyethylene oxide have long been known for their antistatic effect althdugh their moisture absorption is not particularly high.

Attempts have also been made to improve the hydrophilic properties by copolymerizing certain monomers. For example, in German Offenlegungsschrift No. 2,061,213, especiall/ substituted acrylamide is proposed as comonomer.

Attempts have also been made to prove hydrophilic properties by crosslinking. German Auslegeschrift No 2,303,893 describes the hydrolysis with sulphuric acid of wet spun swollen acrylic fibres which contain the N-mefchylol 4 4 9 4 compound of an unsaturaied amide in copolymerisel form.

According to US Patent Specification No. 3,733,386, fibres with improved moisture absorption are also obtained by crosslinking, i.e. by treating the fibres with aldehyde compounds and acids.

German Patent Specification No. 2,124,473 describes vacuole-containing fibres which are said to have cotton-like hydrophilic properties after treatment with a hydrophilic agent. In the absence of treatment with the hydrophili, agent, however., the hydrophilic properties of the fibres are unsatisfactory despite the vacuoles present and the fibies can only be used to a limited extent for certain purposes because they become fuzzy and moult.

However, despite the number and variety of methods which have been adopted, it has not yet been possible to produce synthetic fibres with hydrophilic properties vhiih even remotely approach the favourable properties of cotton, these properties being developed purely on the basis of the structure of the fibres and/or the quality of the polymer used for their production., i.e. without any need for the addition of, or treatment with, agents which improve or even impart hydrophilic properties. Cotton has a moisture absorption of approximately 7% at 21°c/65$ relative humidity and a water retention capacity of approximately 45^.

Accordingly, wo hav<- sought to provide fibres and filaments which are improved in relation to conventional synthetic fibres in regard to their moisture absorption and water retention capacity, and also to provide a process for their production.

We have now found that this desired improvement is obtained by adding a solid substance which has certain specific properties to the solvent for the 4 4 9 J polymer in .·» dry sp uning process.

Accordingly, thr present invention provides a process far the production of hydrophilic filaments or fibres from filament-forming synthetic polymers by dry spinning, in a spinnin solvent which comprises introducing into the spinning solvent from 5 to 50% by weight, based on the total solvent and polymer solids, of a substance which is solid under normal conditions and which: a) has a higher melting or sublimation point than the spinning solvent used; b) is readily miscible with the spinning solvent and with a washing liquid; and c) is a non-solvent for the polymer to be spun, and washing this substance out of the freshly spun filaments.

It is possible by this process to obtain porous filaments and fibres, partly with a core-jacket structure, which have a moisture absorption of at least 2/ (at 21°C/65/ relative humidity)and a water retention capacity of, in general, more than 20/.

The polymers used for producing the filaments and fibres are preferably acrylonitrile polymers, of which acrylonitrile polymers consisting of at least 50/ by weight of acrylonitrile units are preferred.

Where acrylonitrile polymers are used, the hydrophilic properties of the fibres may be further improved by using copolymers which contain comonomers with hydrophilic groups such as amino, sulpho, hydroxyl-N-methylol or carboxyl groupso Particularly suitable compounds are, for example, acrylic acid, methacrylic acid, methallyl sulphonic acid, acrylamides and the N-methylol compounds of an unsaturated acid amide for example, N-methylol acrylamide and N-methylol methacrylamide. Mixtures of polymers may also be used, - 4 30 4 4b 4 Suitable spinning solvents are the solvents normally used for dry spinning, for example dimethyl acetamide, dimethyl sulphoxide anti N-meiliyl pyrrolidone, hut preferably dimethyl formamide.

The substance solid under normal conditions which is added to the spinning solvent has to satisfy the following requirements: its melting or sublimation point must be higher, preferably 5G°*' or more higher than the boiling point of the solvent; .t must be miscible, preierably in any ratio, both with the solvent and also with water or with any other liquid used as a washing liquid for ‘.ashing the freshly spun filaments, such as an alcohol for example; and it must be a non-solvent in the practical sense for the polymer used, in other words the polymer is totally insoluble or dissolves to only a limited extent in this substance both under normal conditions and also under the spinning conditions.

Substances such as these which are solid under normal conditions are, for example, monohydric or polyhydrie 2C alcohols, esters or ketones, for example, 1,6-hexane diol, £-hydroxybenzoic acid methyl ester, inorganic or organic acids and salts, for example, isophthalic acid, pyromellitic acid, zinc chloride and magnesium chloride.

In addition to a single solid substance, it is of course also possible to use mixtures of solids.

An important factor is that the substances used should be readily soluble in water or any other washing liquid so that they may be removed during the aftertreatment of the fibres.

In addition, it is advantageous to use substances which do not form any azeotropic mixtures with the spinning solvent used so that, as in the case of DMF-pyromellitic acid, it - 5 ™ i\ be almost compli.ely rceovei'i'd by fractional distillation out crystallisation.

Wiese substance's are added to the spinning solvent in quantities oi from 5 to 50# by weight and preferably in quantities of from 10 to 20# by weight, based on the total solvent and solids. The upper limit to the quantity of solid substance added is determined in practice by the spinnability of the polymer solution.

The higher the ratio by weight of the additive substance to the spinning solvent, the greater the degree of porosity in the fibre core and the better the hydrophilic properties of filaments produced from spinning solution mixtures such as these.

In order to obtain thorough admixture of the spinning Solution, the spinning solvent, for example dimethyl formamide, containing the additive substance is best· added first of all, followed by addition of the polymeric powder to the thoroughly stirred solution because precipitation is often observed in the event of direct addition to polyacrylonitrile solutions in dimethyl formamide.

In order to obtain fibres with the best possible hydrophilic properties by the process according to the invention, the conditions under which the spinning treatment is carried out are selected so that as little as possible of the additive substance evaporates during dry spinning in the spinning duct or is entrained by the evaporating spinning solvent. The lowest possible spinning duct temperatures, which are only just above the boiling point of the spinning solvent to be evaporated, short spinning ducts and high spinning take-off rates and hence short residence times in the spinning duct, have proved to be of considerable advantage. - 6 4 4 4 fl 4 For these reasons, the spinning duet temp» ratui’e should be a I most SO °C and preferably 5 to 5OcC above the boiling tempera in re nl' the spinning solvent used.

By virtue of this measure, most (generally 90#) of Ί the additive substance remains in the spun sliver or in the filaments.

The additive is only removed during the ai'tertrantment by washing out with wafer or another washing l-iquid. The hydrophilic properties of the fibres thus produced stay be further influenced by the nature of the aftertrsatment and the way in which it is carried out. if, for example, acrylic fibres of a UMF/1, 6-hexane dio.< mixture, after tin- spinning process according to the invention are drawn in steam or water and then washed, dried and aftertreated, the original compact jacket surface of the fibres or filaments also becomes highly microporous as a result of 1,6-hexane diol diffusing out, so that acrylic fibres with particularly high hydrophilicity are obtained.

In the spinning of ACN-polymers from DMF-pyromellitic acid mixtures with a polyacrylonitrile solids concentration of 21# by weight and a pyromellitic acid content of 10.5# by weight, it was possible, by correspondingly aftertreating the spun filaments by the process described above, to obtain acrylic fibres with a water retention capacity of more than 90# and a moisture absorption of more than 2.5#.

However, if the core-jacket fibres are first washed and then drawn, the compact jacket structure remains intact because the additive substance is washed out before drawing and the vacuoles thus formed are closed again by the drawing process.

Acrylic fibres wita a porous core and a compact jacket surface and, accordingly, lower hydrophilicity are obtained - 7 in Ibis nay (i! f. Example 2).

The washing pi -cess with waleryi other liquids may he earred out a! tempe at.ures up 1 e the hmiin/·. point. The residence time should amount to at least 10 seconds in order '» thoroughly to wash out the added substance.

It has also been found to be advantageous in the washing process to keep the slivers or filaments under only weak tension or under minimal permitted shrinkage in order to maximise the removal of the added substance.

However, it is also possible to use substances, such as isophthalic acid for example, which are substantially insoluble or completely insoluble in water, but which can be effectively washed out with another liquid, such as methanol, for example.

The advantage of this process is that, to recover the spinning solvent, the washing waters may be directly distilled without any accumulation of the additive substance. The added substance may then be almost completely extracted in another separate washing process and may be recycled for reuse in the spinning process after working Up.

The further aftertreatment of the slivers or filaments may be carried out by the methods normally used for this purpose; preparation, crimping, drying, cutting, the conditions under which the fibres are dried having a further influence upon their hydrophilicity.

Extremely mild drying conditions of at most l60°C, preferably 110 to IbO°C, and short residence times of at most 2 to 3 minutes in the dryer, give fibres with extremely high hydrophilicity.

As already mentioned, the filaments and fibres according to the invention, often have a core-jacket structure.

In this core-jacket structure, the core is microporous, - 8 .1 4 4 d the average pore diameter amounting to at most lj*. In general, it is between 0.5 and 1 μ. The surface area oi’ the core in a cross-section through the fibre generally amounts to about 70% of the total eross-seetional area.

The jacket may be compact or also microporous, depending upon the aftertreatment conditions selected.

Whereas the cross-sectional form of conventional dry spun filaments and fibres is the known dumb-bell or bene form, the filaments and fibres according to the invention mainly have othei· eross-seetional forms.

Thus, the filaments and fibres according to the invention generally have trilobal, round or bean-shaped crosssectional forms, in some cases alongside one another.

The predominant cross-sectional form depends upon the spinning conditions selected and also upon the quantity of additive substance introduced in the spinning solvent, the last measure having the greater influence.

In addition to the hydrophilicity described, the filaments and fibres according to the invention show favourable fibre properties, such as high tensile strength, elongation at break and good dyeability.

Another very considerable advantage of the fibres according to the invention in regard to wearing comfort derives from their core-jacket structure. Whereas natural fibres, such as cotton, feel wet through in the event of high water absorption, this is not the case with the fibres according to the invention. It is assumed that this is attributable to the fact that the water absorbed diffuses into the microporous core. As a result, the fibres dc not feel wet on the outside which is associated with a dry, comfortable feel.

Although thus far the description has largely been - 9 confined to aci’j I i fibres ami their production, the invention is by no .'.-ins limited to uciylie fibres. 1.incur uroumlie po 1 .titiides for example, the poljaiitide of m-phenyle»c diamine and isophthatyi chloride, or those which optionally contain heterocyclic ring systems, for example polybenzimidazoles, oxazoles and thiazoles, etc., and which may he produced by a dry spinning process, are equally suitable for use in accordance with the invention.

Other suitable compounds are polymers with melting points above 300°C which, in general, cannot be spun from the melt and are produced by a solution spinning process, for example by dry spinning.

The water retention capacity of fibres is an important physical parameter in cases where they are used for clothing. The effect of a high water retention capacity is that, in the event of heavy perspiration, textiles worn close to the skin are able to keep the skin relatively dry and hence to improve wearing comfort.

Determination of water retention capacity (WR); The water retention capacity is determined in accordance with DIN 53814 (of. Melliand Textilberichte 4 1973, page 350).

The fibre samples are immersed for 2 hours in water containing 0.1 of a wetting agent. Thereafter the fibres are centrifuged for 10 minutes with an acceleration of n ,000 m/sec and the quantity of water retained in and between the fibres is gravimetrically determined. In order to determine their dry weight, the fibres are dried at 105°C until they have a constant moisture content. The water retention capacity (WR) in / by weight is; . _ - “+.r 4 -5 9 4 nij = weight of the moist fibres. m( =: weighi of (he dry fibres.

Del eimin.-U i '_oi of moisture absorptnin tiipticit) (MA); The moisture absorption of the fibres, based on iheir dry weight, is gravimetrical!y determined. To this end, the samples are exposed for 24 hours to a climate of 2l°c/ 65# relative air humidity.

To determine their dry weight, the sample» are dried at 105°C until constant in weight. The moisture absoiption (MA) in # by weight is; MA tr x 106 tr ~ moist weight of the fibres at 21°C/65# relative humidity mtr = (Iry weiSi!t of the fibres.

In the accompanying drawings: Figure 1 is a photograph taken with an optical microscope of the cross-section of fibres according to Example 1 (magnified 500 times).

Figure 2 is a photograph taken with an optical microscope of a cross-section of fibres according to Example 3 (magnified 500 times).

The invention is illustrated by the following Examples, in which the parts and percentages quoted are based on weight, unless otherwise stated.

EXAMPLE 1 13.5 hg of MfF were mixed whilst stirring in a vessel with 2,47 kg of 1,6-hexane diol, 4.73 kg of an acrylonitrile copolymer of 93,6# of acrylonitrile, 5.7# of methyl acrylate and 0.7# of sodium methallyl sulphonate were then added while stirring, followed by stirring for 1 hou; at 80°C and filtration. The spinning solution thus - 11 produced was drj spun from a isd-bore :.pinnoret in a spinning due), by mt ί hods known in the urt.

The spinning tim’l f eittpera I lire wns liit)1’·’. Γίιυ viscosity of the spinning solution, which had a solids concentration of 25$ and a hexane diol content of 12$ by weight, based on the total of DMF + polyacrylonitrile powder, amounted to 65 ball-drop seconds. For determining viseosity by the di'opped-hall method, see K.Jost, Eheologiea Acta Vol. 1, No. 2-3 (1958), page 303. The spun material with a denier of 1600 dtex was collected on bobbins and doubled into a tow with an overall denier of 96,000.

The tow was tlion drawn in a ratio of 1:3.6 in boiling water, washed for > minutes under low tension in boiling water and provided with an antistatic preparation. Xt was then dried at a maximum of 130°C in a screen drum dryer with 20$ permitted shrinkage, and cut into fibres with a staple length of 60 mm.

The individual fibres with a final denier of 3.3 dtex had a moisture absorption capacity of 3.2$ and a water retention capacity of 29$.

Tensile strength: 2.3 p/dtex; elongation at break 37$.

As shown by the photograph taken with an optical microscope of their cross-sections in Figure 1 (magnified 500 times), the fibres have a pronounced eore-jacket structure with bean-shaped to trilobal eross-sectional forms.

The residual solvent content of the fibres was less ' than 0.2$ by weight. The fibres can be deeply dyed throughout with a blue dye corresponding to the formula 4 9 4 c t > \ c---1 /) ! V\ // ί 9_.. / 0Ί The extinction value is 1,23 for 100 mg of fibre per 100 ml >1' dimethyl formamide (57 om/:, 1 cm cuvette), EXAMPLE 2 An acrylonitrile polymer with the same chemical composition as in Example 1 was dissolved in a 0.1://1.,6hexane diol mixture, filtered and spun under the same conditions. The spun material was collected on bobbins and doubled into a tow with an overall denier of 96,000«, The material was then washed in boiling water for 3 minutes under low tension, subsequently drawn in a ratio of 1 : 5,6, provided with antistatic preparation and aftertreated in the same way as described in Example 1.

The fibres with an individual denier of 3.3 dtex had a moisture absorption of 1,7^. Their water retention capacity amounted to 9.1^. As in Example 1, the fibres had a pronounced core-jacket structure with a bean-shaped to trilobal cross-section.

In contrast to the fibres according to Example 1, the jacket surface was more compact and virtually free from· vacuoles. This explains the relatively lower hydrophilieity of the fibres in comparison with Example 1, On account of the modified afterfcreatment, the vacuoles formed by removal of the hexane diol during washing were partly closed again by the drawing process carried out after washing. 3° EXAMPLE 3 .6 kg of dimethyl formamide were mixed while stirring in a vessel with 2,8 kg of isophthalic acid. .6 kg of an aery Ion. fcrile copolymer tilth the same composition as in R\ duple 1 were (lien added while stirring, followed 1>> slirrin?- for 1 hour at <>'»' and ft I i cat ion.

Vite spinning solution thus obtained was -spun III die same way as described in Example 1, The viscosity of the spinning solution, which had a solids concentration of 22# by weight and an isophthalic acid content of 11# by weight, based on BMP and PAN solids, amounted to 6S ball drop seconds.

The spun material with a denier of 1600 dtex was doubled into a tow, drawn in a ratio of 1 : 3.6 in boiling water, washed for 3 minutes in boiling water until a low tension was obtained and then treated for 1 minute with ethanol heated to 65 - 7O°C. As a result, the isophthalic acid was almost quantitatively removed. The tow was then treated with antistatic preparation and aftertreated in the same way as described in Example 1.

The individual fibres with a final denier of 3·3 itex had a moisture absorption capacity of 2,8# and a water retention capacity of l60#. As shown by the photograph taken ivith an optical microscope of the cross-sections in Figure 2 (magnified 509 times), the fibres had oval tiilobal cross-sectional forms without any really deep indentaiions and were porous throughout.

EXAMPLE 4 .4 kg of dimethyl formamide were mixed while stirring in a vessel with 2.05 kg of pyromellitic acil. 4,1 kg of an acrylonitrile copolymer with the same ehmical composition as in Example 1 were then added while stirring followed by stirring for 1 hour at 80°C and filtration.

The spinning solution thus obtained was spun in the same way as· described in Example 1, 4 4 9-1 The viscosity of the spinning solution, wnich had a sol ills content, of 21 '1 oy weight and a pyro.ne 11 iti e aei 1 (onfont of 1(1.5$ b” wf igllt, based on IWE uni PAN solids, ann unied to 0*» ball d:op seconds.

The spun materia with a denier of 1600 dfcex was again doubled into a tow an aitertreated in the same way as described in Example , The individual f res with a final denier of 3.2 dtex had a moisture absorption capacity of 2.6$ and a water retention capacity of ·ι7$ο The fibres had a bean-shaped to oval cross-section.

EXAMPLE 5. ,7 kg of dimethyl foraatnide were mixed while stirring in a vessel with 2.0 kg of £-hydroxy benzoic acid ester, 4,0 kg of an acrylonitrile copolymer with the saiae chemical composition as in Example 1 were then added whiIs stirring, followed by stirring for 1 hour at 80°G and filtration.

The spinning solution thus obtained was spun in the same way as described in Example 1 and the spun material subsequently aitertreated. The ester content, based on DMP-PAN mixtures, amounted to 12$ by weight.

The viscosity of the spinning solution, which had a solids content of 24$ by weight, amounted to 61 ball drop seconds.

The individual fibres with a final denier of 3.3 dtex had a moisture absorption of 2.7$ and a water retention capacity of 42$.

The fibres had an oval to bean-shaped, highly porous cross-sectional form.

EXAMPLE 6 0.3 kg of dime> hyl iormamide wore mixed while stiiring in a vessel with I.,' kg of zinc chloride. 4.0 kg of aj. acrylonitrile copolymer according to Example 1 were then added with stirring. After stirring for 1 hour at 80°C, the fiLtered solution, which had a zinc chloride content of 12$ by weight. based on DMF and PAN solids, was dry spun and aftertreatod in the same way as described in Example 1.

The viscosity of the spinning solution amounted to ball drop seconds.

The fibres with a final denier of 3.3 dtex had an oval to bean-shaped cross-sectional form.

The moisture absorption amounted to 2.9$ and the water retention capacity to 28$.

Claims (12)

1. Λ Μΐιΐ,’ι’ s for : In ;·ι .ulllc I ί ·>·ί >11' ii} li Ιιφ!ι 1 i I 11 lit.Hi Ils ί· fibres 11 mu fi lameiii -forming synllieiic polymers by i ly spinning in a spinning solvent·, which comprises introdte5 ing into the solvent from 5 to :>’*$ by weight, based on the total solvent and solids, of an additive substance which is solid unde:- noxmial conditions and which: a) has a higher melting or sublimation point than tinspinning solvent used; , 0 b) is readily miscible with the spinning solvent and with a washing liquid; and £) is a non-solvent ftr the polymer to be spun, and washing the additive substance out of the freshly spun filaments. ,-

2. A process as claimed in Claim 1, wherein the polymer is an acrylonitrile polymer.

3. A process as claimed in Claim 2, wherein at least 30$ by weight of the acrylonitrile polymer consists of acrylonitrile units, 20 A. A process as claimed in any of Claims 1 to 3, wherein the additive substance is introduced in a quantity of from 10 to 20$ by weight, based on the total solvent and solids.

4. 5. A process as claimed in any of Claims 1 to 4 wherein the additive substance is a monohydric or polyhydrie 25 alcohol, ester or ketone, an inorganic or organic acid or a salt thereof.

5. 6. A process as claimed in any of Claims 1 to 5, wherein the spinning solvent is dimethyl formamide. 17

6. 7, A process as el ’imed in an. of Claims i to (>, wherein i he spuming duct (eiparatisre i .·, at ιιιοκι wl’f ah.ivi> the boiling temperature of the spinning solvent used.,

7. 8, A process as claimed in Claim 7 S wherein the 5 temperature is at most 5°C to 30°C above the boiling temperature of the spinning solvent used.

8. 9, A process as claimed in any of Claims 1 to S, wherein the resulting filaments and fibres are subsequently dried at a temperature of at most I6O°C for a period of up to

9. 10 3 minutes. 10, A process as claimed in Claim 9, wherein the drying temperature is from 110°C to 140*0,

10. 11, A process for the production of hydrophilic filaments or fibres substantially as herein described with reference. .- to any of the specific -Examples.

11. 12, Hydrophilic fibres or filaments when produced by a process as claimed in any of Claims 1 to II,

12. 13o Dry spun filaments or fibres with porous structures of filament-forming synthetic polymers with a moisture 20 absorption.of at least 2/ at 65/ relative humidity andat 21°C and with a water retention capacity of at least 20/. 14, Dry spun filaments or fibres as claimed in Claim 15 substantially as heroin described with reference to any of the specific Examples,