US2474617A - Manufacture of artificial fibers - Google Patents

Description

Patented June 28, 1949 MANUFACTURE OF ARTIFICIAL FIBERS Edward Terry Cline, Wilmington, Del., asslgnor to E. I. du Pont de Nemours & Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application January 3, 1947,

j Serial No. 720,099

Claims.

ironabie fabrics where resistance to heat is necessary. Filaments have been prepared by the dry-spinning of aqueous solutions such asby the rapid evaporation of the aqueous solvent when a fine stream of the aqueous polymer solution is injected into a heated chamber. However, for such advantages as uniformity, ease of spinning yarns of high denienand inexpensive mechanical equipment requirements, wet spinning of aqueous solutions is preferable. This involves injecting an aqueous solution of the polymer into a coagulating bath. This method, however, has been accompanied by a serious disadvantage in that when the fibers are prepared by spinning an aqueous solution of the polymer into a saturated aqueous solution of an inorganic salt such as NaHzPOr to coagulate the fiber, considerable 'difflculty is encountered in removing the salt from the fiber. Water is the best solvent for the salt.

. However, in view of the water sensitivity of the hydroxyl-containingpolymer, an aqueous wash to remove the salt tends to dissolve the fibers and they become tacky when the salt concentration in the water becomes low. After the fibers have been allowed to dry, they are found to be stuck together and therefore unusable.-

A method for removing salts has been shown in U. S. Patent 2,388,325 in which water-organic solvent mixtures such as a 1:1 mixture of water and acetone, are used to remove salts from polyvinyl alcohol structures freshly precipitated from aqueous inorganic salt solutions without injurious effect. Such a method is expensive and the aqueous organic solution is less effective than water to extract water-soluble salts in view of the low solubility of the coagulating bath salts in organic solvents.

An object of this invention is an improved process for the removal of inorganic salts from coagulated hydroxyl-containing polymer structures which are obtained by injection of the polymer in a salt-containing coagulating bath. Otherobiects will appear hereinafter.

The above objects are accomplished by a procedure more particularly described below which comprises drawing under tension the wet spun filaments of a synthetic linear hydroxylated polymer. having at least one alcoholic hydroxyl group per 2.5 carbons and not more than one hydroxyl per two carbons of the polymeric chain, holding the filaments at a length of at least twice their original length, washing with water while the filaments are held at at least twice their original length to remove the coagulating bath salts from the filaments, and drying while so maintained.

The terms original or initial length as empolyed herein mean the length after coagulation of the filaments. -When no rollers or other tensioning devices are employed in the coagulating bath, this length is that of the yarn as it leaves the bath. When yarn driven rollers are used. in the coagulating bath, this length is that of the yarn at the time it encounters the first coagulating bath roller.

The following examples in which the parts given are by weight further illustrate this invention.

EXAMPLE I An aqueous solution containing 15% of a hydrolyzed ethylene/vinyl acetate interpolymer containing about 5% ethylenein the hydrolyzate, was extruded by means of a gear pump through a multihole viscose rayon type spinneret into a coagulating bath containing 45% monosodium dihydogen phosphate and 0.05% Retarder LA (20% octadecyltrimethylammoniurn bromide). From the coagulating bath the yarn was led to a positively driven Godet, a six inch diameter glass wheel fitted with an idler roller so that several yarn wraps could be taken around the wheel to avoid slippage. The yarn was then led through air to a positively driven wind up bobbin. By adjusting the speeds of thevarious drives, the yarn could be stretched in controllable amounts either in the coagulating bath or in air between the Godet and wind up or both. It was found preferable to pass the yarn in the coagulatin bath around one or more rollers mounted on vertical posts in the bath before the yarn was led to the Godet or directly to the wind up.

During the course of the spinning, some of the yarns were subjected to various degrees of stretch in the coagulating bath as calculated from the speed of the yarn as it left the bath and the peripheral speed of the first roller in the'bath. Others were stretched only slightly in the bath but were stretched various degrees in air between the Godet and wind up. Where yarn driven rollers were used in the coagulating bath, the total stretch appliedto the yarn 'w...

Q calculated from the peripheral speed of the first bath roller and the speed of the wind up bobbin.

Where no rollers were used in the coagulating bath, thetotal stretch was calculatedfrom the peripheral speed 'oi the'Godet wheel and the speed of the wind up bobbin. These'calculations extent in' these regions as a resultfof friction between the yarn'and the bath or, any stationary object which the .yarn may touch suchfas a convergence guide. In practice; however, this? stretch is relati ely insignificant in view of the fact-that theorie tation of the yarn atthis stage is low as evident i'rommeasurement of its orientation number as defined in the following paragraph. A coagulating bath temperature of 60 0.. was used during part. thespinning. For each resistant to water so that they could be washed with water and dried without becoming stuck together. Likewise the yarns collected below a given wind up tension or below'a given orientation number were stuck whereas those col1ected abovethis critical wind up tension orzorientation number were not stuck qwashingand dry-i j ing of theseyarns was carried out" at constant "yarn I length; on' the -wind up bobbins; g- If 1 the 1 I yarns are removed i'rorn'the' bobbins and allowed to "relax completely "during washing .and*drying, j a v as in 'a skeinfthey will shrinirjfreely, l'ose orienta- V tion. and become 's'tuck; Itiwas: i'oundthat' the place at which the stretchis applied during-spin ,ning, i. e; in the-coagulatingfbath' or.in' air out- I side thecoa'gulating'bathj isimmaterialin regard to washability. Typical results obtained in this spinning are shown in'the following tables.

condition used. the tension on the yarn justbefore the wind up bobbin was measured in grams and later calculated in terms of g. p. d. (grams per denier). After each bobbin of yarn had been collected, it was washed in running tap water until the coagulating bath salts were substantially removed; It was then allowed to dry in air and the condition'oi the yarn, i. e., whether stuck or free, was observed. Free yarns were twisted on a conventional ring twister. Short lengths of the stuck yarns were unwound laboriously by hand during which many of the individual filaments were broken. The orientation numbers of the yarns were then determined by means of X-rays.

Orientation isdetermined by passing a collimated beam ofcopper filtered X-radiation through a bundle approximately 1mm; thick of parallel fibers onto a photographic plate during one hour with a distance of 5 cm. between the fiber specimen and the plate. The Phillips Metalix tube used is supplied with a 19 milliampere current at 35 kilovolts. The collimation is effected by two 25-mil diameter pinholes intensities at the equator of. the picture to that I at 90 degrees from the equator for the inner and outer rings. numbers. Thus an orientation number of one denotes that the specimen shows no orientation whereas ratios progressively greater. than one denote progressively higher degrees of orient-a tion. The orientation'numbers are expressed as 01 for the inner ring and O: for the outer ring of the X-ray diifraction pattern. Of these the O2 orientation number is more accurate and.

reproducible. These values "are given in the examples.

The ratios are called orientation It was found that if the yarns were arranged VT in order of increasing amount; of total stretch,

they were also in order of increasing orientationnumber and increasing wind. up tension as ex pressed in, grams per-denier. The yarns. col I lected below a totalstretchzof' about'100% of their original length were stuck whereas .those collected above this total stretch were sufiicientiy I yarns. The maximum'pos'siblestretch was aping. stretch and windiup tension, alsowere in orderof increasing orientation numbers. Thus.

'-Tablel Amount Yarn I Stretch'in- I I I Total 'Washedand Dried C Stretch Yarn Condition 0 A|r I Percent Percent Percent 29 0 29 'Badlg stuck. 57 0 57 0.

6 61 70 D0. 72 0 72 Partly stuck. 78 0 78 Do. 0 90 I Do. m4 0 104 Free.

6 101 112 Do. 115 0 115 Do. 124 0 124 Do. 6 230 I 258 D0. 422 o 422 Do.

Table II Amount Yarn Stretched Windup Washed and Orien- Tensioln, Dcrieddiarm gititgl Cong g. p. on: on o. a Bath Per- Percent. rent 6. I 28 6 61' 25 0 115 0 78 -0 222 0 104 0 6 138 The critical wind up tension'and'ba orientation number (ratio of X-ray intensity at the equator to that at the pole for the outer interference ring) for this yarn may beseen to. lie between 0.05 and 0.07 g. p. d. and between 2.4 and 2.8 respectively.

20.9 centipoises (4% aqueoussolution) was spun in a manner similar to that described in Example I. For most of theyarns collected, practically all of the stretching was done in air between the I Godet and wind up. In order to avoid sticking during washing and drying it was necessary to apply a total stretch of abo'ut190% to these proximately 400%. .As was the case in Example I, the yarns when" arranged in orderv ofincreas- 5 for the polyvinyl alcohol yarns, it was necessary that the total stretch be higher (correspondingly, a higher wind up tension with higher orientation number) to permit washing and drying without sticking than in the case of the hydrolyzed ethylene/vinyl acetate interpolymer yarns described in Example I. It is therefore evident that polyvinyl alcohol is more water sensitive than hydrolyzed ethylene/vinyl acetate interpolymers. Typical results obtained in this spinning are shown in the following tables.

Table III Amount Yarn Washed Stretch in- Total and Dried Stretch gg 3 Air tion Bath Per cent Per cent Per cent 15 59 83 Stuck 16 87 no Do. f 16 111 144 D0. 16 139 176 Do. 6 180 196 Free. 16 106 208 Do. 16 194 240 Do. 267 86 Do. ii 207 308 Do.

Table IV Amount Yarn strewn Wind Up Washed and Orienta- Tension, Dried Yarn, tion g. p. (1. Condition No. 0: Coag. Bath Per cm! Per cent 16 111 0.12 Stuck 3. 7 16 139 .15 ..do 4.6 16 166 .21 Free 5. 5 l6 194 .30 do 6.3 5 267 .87 do 8.1

The critical wind up tension and O2 orientation number for this yarn may be seen to lie between 0.15 and 0.21 g. p. d. and between 4.6 and 5.5 respectively.

The ethylene present in the hydrolyzed ethylens/vinyl acetate interpolymer appears to be responsible for its greater water resistance over polyvinyl alcohol. To avoid sticking in a bobbin process, the total stretch for polyvinyl alcohol is at least 190% and for a hydrolyzed vinyl acetate interpolymer containing 5% ethylene is 100%. Each per cent of ethylene introduced lowers the amount of total stretch by 18 from the 190%. correspondingly, if the upper limits of the critical ranges of wind up tension and O2 orientation number given in Examples I and II are taken as the critical points, then each percent of ethylene introduced lowers the wind up tension about 0.03 g. p. d. and the O2 orientation number by about 0.5 without encountering sticking in the washed and dried yarn. This is illustrated in the following table. 1

, Table V Exmu 111 An aqueous solution containing 7% ethanol and i 15.4% of hydrolyzed ethylene/vinyl acetate interpolymer containing 5% ethylene was spun in a' manner similar to that described in Example I. The spinning solution was delivered through a hole spinneret at a rate of 3 cc. a minute. In the coagulating bath, which was maintained at room temperature, the yarn was passed around 2 rollers such that the length of yarn travel in the bath was about sixty inches. The yarn was then led to a Godet wheel operating at a peripheral speed of 380 inches per minute. It was then led thru air to the wind up bobbin, operating at a peripheral speed of 1380 inches per minute, such that it was stretched in air 263%. (or a draw ratio of 3.63/1). The wind up tension was 0.58 g. p.. d. Following washing and drying of the yarn, the filaments were observed not to be stuck.

EXAMPLE IV An aqueous solution containing 7% ethanol and 12.5% of high viscosity, fully hydrolyzed PVA (polyvinyl alcohol) having a viscosity of 51 centipoises (4% solution in water was spun in a manner similar to that described in Example III. The spinning solution was delivered to the spinneret at a rate of 4.5 cc. per minute. Following passage around two rollers in the coagulating bath, the yarn was led to a Godet wheel operating at a peripheral speed of 285 inches per minute. From the Godet the yarn was led to the wind up bobbin operating at a peripheral speed of 1040 inches per minute such that it was stretched in air 265%. The wind up tension was 0.48 g. p. d. Following washing and drying the yarn could be unwound readily and the filaments were not stuck together.

EXAMPLE V EXAMPLE VI An aqueous solution containing 7.3% ethanolv i and 15.4% of a hydrolyzed ethylene/vinyl acetate interpolymer containing about 5% ethylene was spun in a manner similar to that described in Example I except that a. boiling aqueous bath containing 20% urea was used between the Godet and the wind up such that theyarn passed thru this solution while it was being stretched between the Godet and wind up. Most of the yarn was collected at a total stretch of520%. The maximum possible stretch was 600%. The water washed and dried yarn was not stuck.

EXAMPLE V'II the Godet wheel the yarn was led to a positively driven draw roll and thence to a wind up bobbin.

The wind up bobbin was operated at a lower at'the first coagulating bath roller in spltefof 1 'the ffollowinggtable.

several different conditionsof stretch areflshown scribed in u. s. Patent 2,386,347. These polythe fact that the yarn was actually stretched mo're.

' than this prior toits relaxationbetweenthedraw i mu and the wind up bobbin. Following'winding the yarn was washed with wa'ter, allowed to dry in I air and; twisted. The results on yarns spun under pirical formula: I

- (crnoagcirnomy.(oimoa z where R is an acyl radical of an organic monocarboxylic acid, preferably acetyl and the ratio of 1/ to z is at least4-to 1 (i. e., 80%hydrolyzed) and preferably substantially completely hydrolyzed, For polyvinyl alcohol, at is zero while for the ethylene inter-polymers, the ratio of y+z to a:

is usually within the range of 6:1 to 50:1 and is preferably 6 :1 to :1 since the fibers from the latter polymers have better properties.

i.:.e., "by' stretching them and'then relaxing them controlled amounts before windin must be given a somewhat higher total stretch than yarns spun by the bobbinprocess without relaxation'as 'de- I scribedin'previous examples. Thus the total net stretch required to avoid sticking of the polyvinyl alcohol fibers described in this example is about 220% whereas only about 190% total stretch was required for the process described in Example II.

It is necessary however that the polyvinyl alcohol filaments be drawn at least 2.9 times their original length and maintained during the time they are in. contact with water (e. g., during washing) at a length of at least 2.9 times their I original undrawn .length. 'I f'the'filaments are drawn more than 2.9 times their original length,

they must'be maintained during the time they are in contact with water at their drawn length or at least 3.2 times their originallength.

The macromolecular synthetic polymers that v can be used in the process of this invention are those which haveat least one alcoholic hydroxyl group per,2.5 carbon atoms but not more than one hydroxylyfor' two'carbon atoms of 'thechain. ;By

macromolecular ismeant an organic compound :1

" having a" degree of polymerization or anumber.

ofgrecurring units of .at 'least.100 (Staudinger,

Die Hochmolecularen Organischen Verblndungen,

1932)} Such hydroxyl-containing polymers in I clude polyvinylalcohol and hydrolyzed polyvinyl ester'polymersfland copolymers whlch have the, ratioof hydr oxyl to chain carbon previously mention'ed. {In additionto the hydrolyzed polyvinyl esters such as polyvinyl'acetate, hydrolyzed copolymers of vinyl esters with ethylene, vinyl chlo- V ride, vinyl fluoride, vinylidene fluoride, vinylidene chloride, and other fiber-forming polymeric material can be employed. In such copolymers, the molar ratio of vinyl ester (hydrolyzed to vinyl alcohol) to the other polymerizable compounds is preferably between 6:1 and 50:1. Ofthe hydroxylated polymers those particularlypreferred are polyinyl alcohol and hydrolyzed ethylene/- vinyl ester interpolymers, containing from 0.12%

a to 10.0% ethylene in the hydrolyzate. The preparation of the latter interpolymers been: de-

. ,j s nmigg Speeds, Inches/Minute Tensions, nd; k v I i. rem Conditioner .Coa Godt Draw Wind At Draw At Wind "F f Bat ,7 Roll :up R ll H P'.

"i Roller i i t I Percent" 332 340 1,140 1,030 .40 .04 2101 Partly stuck. 350 311,1,384 1,103 .76 ".02. 216 -*Do. a5o .311 I 1,380 1,153 -.58 .04 220 Free. .350 new 1,334, 1,210 .s4 .08 246 Do. 350 377 soo- 1,280 .06 266 Do.

- g.,p. d.-granis 'per denier. 1

-It is apparent that yarns spun in this manner. The above polymers are dissolved in hot aqueous solution to an extent of between 5-and 30% .al-

though usually between 5 and 20% is'used. There may be also added smallamounts of water-soluble aliphatic alcohols, amines, or mercaptans. Fordiflicultly soluble polymers, mixtures of an ride, etc. Particularly desirable in view of the better coagulating properties (effectiveness in removing water from the polymer solution) is an 'aqueouscoagulating bath consisting .of monosodium 'dihydrogen phosphate (NaHaPOi) l1av-- Lingfa specific gravity of about 1.4 at 25 C.' The salt bath shouldhave a high concentration, e. g., it should .benearly saturated with salt or of sulficient concentration'to remove water rapidly from the aqueous polymersolution. Cationic surface active agents'suchascetyl trimethyl pyridinium bromide'in amounts of from 0.005 to 0.05% based on the wei'ght of the bath are also advantageous J in that-the filaments have improved properties and spinnerets are less likely to foul.- Cationic surface active agents are described in British Pat- ..ent. 499,334. Usually the bath is saturated with respect to the surface active agent. The bath is usually maintained'at temperatures of 5 to 80 C. The drawing onstretching of the filaments 'with resulting molecular orientation along the fiber axis is conducted under a tension which draws them to a length of at least twice their initial length and which orients the filaments to an extent that when held at fixed length they are insufficiently softened' by water to cause sticking of the dried filaments. Although in allinstances .the tensionapplied' draws them, to a length of at least twice their initial length, or is at least 0.05 gram per denier, the exact amount of orientation unecessary :will depend on the water sensitivity of the particular polymer, and theminimum tension wilLtherefore, be higher for the more water tion of fabrics, cordage, etc.

sensitive polymers. This figure can be obtained readily by trial or by the rule given below for approximating the minimum tension that should be'applied to orient the fiber so that it can be washed with water and dried. V

For a polymer represented by the empirical formula (C2H3OH)a (C2H4)b, the first member being the polyvinyl alcohol or hydrolyzed vinyl ester constituent, the percent by weight of which is indicated by the letter a, and the second member being the ethylene constituent, the per cent by weight of which is indicated by the letter I), the minimum tension to be applied is such that the increase in length in percent of the filaments is equal to 190 minus the product (18)b. The tension in grams per denier is equal to 0.21 minus the product (0.03) (1)). Thus, for polyvinyl alcoholitself, the tension should be such to produce an increase in length of at least 190% or at least 0.21 gram per denier. Less tension with correspondingly less orientation-can be applied in the case of the hydrolyzed ethylene/vinyl ester interpolymers, but in any instance the minimum tension is such that the increase in length is at least 100% or must exceed 0.05 gram per denier.

The maximum tension used naturally must be less than the breaking strength of the fiber. Although tensions near the maximum may be employed, such tensions may result in more broken filaments in the yarn than are desired. It is preferable to operate at tensions or length increases of about 75% of the maximum during the wet drawing. After drying the filaments, the fibers may be further oriented by drawing at elevated temperatures to give filaments having high tensile strength. The amount of this hot drawing is inversely proportional to the amount of wet drawing done during the spinning operation.

The fibers obtained by the process of this invention are particularly useful for the prepara- Aftertreatments with formaldehyde or other materials can be applied to the fibers to further reduce their water sensitivity. In view of the electrical insulating properties of hydrolyzed ethylene/vinyl acetate interpolymers, the fibers of such interpolymers may also be used in electrical insulation, e. g., for tape winding or braiding of electrical conductors.

As many apparently widely diflerent embodiments of this invention may be made without departing from the spirit and scope thereof, it

i is to be understood that I do not limit myself 10 to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. In the process for manufacture of filaments, fibers and like structures from a synthetic linear hydroxylated polymer wherein an aqueous solution of from 5% to 30% by weight of said polymer is coagulated in an aqueous solution of an inorganic salt, the improvement which comprises drawing the wet spun filaments at least twice their initial length under a tension which orients the filaments to an extent such that they do not stick together after washing with water aloneand drying, holding the drawn filaments under tension at least twice their original length and while the filaments are so held washing them to remove said salt with an aqueous wash which consists essentially of water and which causes swelling of the filaments in their undrawn and unoriented state, and then drying the filaments while so held, said hydroxylated polymer having at least one alcoholic hydroxyl group per 2.5 carbon and not more than one hydroxyl per two carbons of the polymeric chain.

2. The process set forth in claim 1 in which said hydroxylated polymer consists predominately of hydrolyzed polyvinyl ester.

3. The process set forth in claim 1 in which said hydroxylated polymer consists predominately of hydrolyzed polyvinyl acetate.

4. The process set forth in claim 1 in which said hydroxylated polymer is a hydrolyzed ethylene/vinyl acetate interpolymer containing from 0.12% to 10% ethylene in the hydrolyzate.

5. The process set forth in claim 1 inwhich said salt is monosodium dihydrogen phosphate.

EDWARD TERRY CLINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS