US2341586A - Wet spinning of cellulose acetate - Google Patents

Description

v Patented-Feb. i5,

:su'sss will srnmmc or cmnmss scs'rs'rs 'Iraneisl Alles, Waynesboro, Va, alalgnor to lldal'ontdeNemoursacom PATE T OFFICE ton, Del, a eorll ration of Delaware No Drawing. Application August 7, 1941,

' Serial N- 4.5,88'l

'3 Claims. (cl. 18-54) a ing not more than 15% by weight or water, based This invention relates to the spinning of cellulose acetate nla'ments, and more particularly tothe wet spinning. of acetone-soluble cellulose acetate directly from the gum stag A number of methods have heretofore been 5 proposed for forming iiiam'ents of cellulose ace-- I tate'by directly extruding the gum (i. e., the acetic. acid-solution of cellulose acetate produced in the customary acetylation processes) through suitable orifices and into a coas tlng bath where y to form the filament. Certain of these proposed methodsare restricted to the spinning of pri-' mary or chloroform-soluble cellulose acetate as opposed to secondary or acetone-soluble cellulose acetate universally employed in the present dryis spinning methods -of yarn manufacture. Yarn.

made from primary cellulose acetate, however, is. interior to yarn made lrom the secondary cellulose acetate for tliereasons that it'is less stable cannot be dyed satisfactorily with existing dyes.

The product of these methods cannot therefore successfully compete with dry-spun yarn.

The proposed methods which do relate to the wet spinning of acetone-soluble cellulose acetate as likewise havenct achieved commercial success. In many instances, commercial failure may be laid to inherent deficiencies in the coa ulating bath. The deficiency may be in the lack of essential economy in material and operating .costs, or

it may be in the" coagulating action itself for not all coagulants for cellulose acetate are suit-:

able in'the of acetone-soluble cellulose acetate.- For example, iammonium-sulfate and ammonium chloride, which are known to be coagulantsfor acetone-soluble cellulose acetate, and which have actually been disclosed heretofore in the spinning of chloroform soluble cellu-' lose acetate, are wholly unsatisfactory in the. spinning of acetone-soluble cellulose acetate be- 40 cause the yarns produced therefrom are full of stuck filaments and are harsh and wiry to the feel and chalky in appearance; An object of my invention,"therefore, is to on the total weight of the solution, into an aqueous coagulating solution comprising not more than 15% by weight of acetic acid and not more than 25% by weight of an salt of an acid of the group consisting of formic, acetic, and nitric acids. The coagulating solution is maintained at a'temperature of from about 3 C. v to about 12 C. The yarn is withdrawn from the coagulating solution and is subjected to the usual steps of winding, washing, stretching, etc. The following general procedure is preferred "in carrying out my'invention: Cellulose acetate gum prepared by the esteriflcation of cotton linters and hydrolyzed to obtain the desired percentage of combined acetic acid, is treated with a salt of aceticacid, for instance sodium acetate,

to neutralize or render ineflective the sulfuric xacld catalyst and thereby arrest further hydrolyto hydrolysis. it is inherently more brittle, and it 20' sis. The gum is then filtered to remove any undissolved material and stored in suitable tanks for a suflicient length of time to allow the air enis immersed just below the suriace of the coagulating bath in such a way as to permit the fllaments to be spun horizontally. After passlng through a suitable guide, the yarn is withdrawn from the coagulating bath by means of positively driven rolls. The yarn may be collected on a bobbin, in a centrifugal bucket or dropped into a slowly revolving can, or the acid yarn may he cut into staple lengths and processed on a conveyor belt. The yarn may be washed in the form collected or withdrawn and: washed in a countercurrent system as a rope-or thread. The acidic washwater emuent is preferably sent to an extraction column for recovery.

that there is not an excessive increase in acid concentration near the face of the spinneret.

The coagulating solution is circulated through 'a heat exchanger to maintain the desired tem- .perature and is then introduced into thespinprovide a method for producing high-quality 4s yarns by the direct wet-spinning of gums of ace-. tone-soluble acetate. Afurther object is I or intermittently and sent to the in the provision of an economical coagulating 9 V bath especially suited for use in connection with W W W the wet spinning of acetone-soluble cellulose ace- 5o by Me ma These and other one: wm My invention is further illustrated by the folclmly new harmful lowing examples. Parts are by weight unless These objects are accomplished by my invenmi tion which, briefly stated, comprises spinning a Example I I Avportion of the acid-enriched coagulatlns'solution from the spinning trough is diverted con-f gumof acetone-soluble cellulose acetate contain dl Cellulose acetate gum containtng may, eellulose acetate (54.5% combined acetic acid), 78.75% acetic acid, 5.95% water, at a temperature of 295 C., was spun through a 240-hole spinneret, hole diameter 0.004 inch, into acoagulating bath of 12% acetic acid, 17% ammonium acetate in water at 8 C. After coagulation, the yarn was stretched 21.6% in air, and the yarn collected in the form of loose coils in a slowly revolving can, washed and dried.v

per denier, dry elongation 34.7%.

Example II The same gum used in Example I was spun into a coagulating bath of 12% acetic acid, 17% ammonium acetate in water at 8 C. The yarn was collected in the form of loose coils in a slowlyrevolving can, washed and dried. Denier per filament 20, dry tenacity 0.79 gram per denier, dry elongation 54.3

Example III Cellulose acetate gum containing 14.35% (54.5% combined acetic acid) cellulose acetate, 6.85% water, 78.8% acetic acid, Was spun Denier per filament 20, dry tenacity 0.88 gram .through a 1600-hole spinneret, hole diameter 0.002 inch, into a coagulating bath of 13.5% acetic acid, 16.3% ammonium acetate in water at 9 C. After coagulation, the yarn was Example v11 1 The same gum used in Example VI was spun through a 240-hole spinneret, hole diameter 0.004 inch, into a coagulating bath of 11.9%

acetic acid, 25% ammonium acetate in water at 9 C. The final spinning speed was 1800 inches per minute. The yarn was collected as loose coils in a slowly revolving can, washed and dried under substantially no tension. Denier per filament 17.5, dry tenacity 0.95 gram per denier, dry elongation 45.6%. I

My invention is, of course, susceptible to wide 7 variation from the exact conditions set out in the foregoing examples, which are for purposes of illustration only. Thus, any cellulose acetate in the acetone-soluble range having a. combined acetic acid content of 50% to 57% may be employed, although the preferred acetate is one containing from 54.5% to 56% combined acetic acid.

A gum composition containing 12% to 15% by weight of cellulose acetate is in general preferred but a higher content is permissible if the gum is heated to reduce its viscosity. The water content of the gum should not exceed 15% based on the total weight of the solution, and ispreferably maintained within the range of 5-l0%.

The small percentage of sodium, ammonium, cal-- cium, or magnesium sulfate normally resulting from neutralization of the sulfuric acid acetylation catalyst may be retained, in the gum with- The gum used in Example 111 was spun through a 1500-hole spinneret, hole diameter 0.002 inch, intoa coagulating bath of 12.1% acetic acid, 15.1% ammonium acetate at 9 C. The final spinning speed was 1500 inches per minute. The yarn was collected asloose coils in a slowly revolving can, washed and dried under substantially no tension. Denier per filament 3.9, dry tenacity 0.88 gram per denier, dry elongation 49.7%.

. Example V Ezample VI Cellulose acetate gum containing 14% cellulose acetate (54.5% combined acetic acid), 4.6%

water, 81.4% acetic acid at a temperature of 26 C., was spun through a 240-hole spinneret,

The,acetic acidcontent of the coagulating bath should be kept under 15%, and preferably the acid content should be maintained at about 12% by weight. Acetic acid concentrations higher than 15% result in a weak gel yarn and broken filaments. The concentration of the ammonium .salt in the coagulating bath will depend to a large extent on the denier of the yarn being spun but should not exceed 25% by weight of the bath.

For example, when spinning 3 denier per filament yarn, satisfactory results are obtained if hole diameter 0.004 inch, into a coagulation bath of 12.25% acetic acid, 20.7% ammonium acetate at 12 C., at a speed of 1800 inches per minute. The yarn was collected as loose coils in a slowly revolving can, washed and dried under substantially no tension. Denier per filament 23, dry tenacity 0.77 grams per denier, dry elongation 48.4%.

the concentration of ammonium salt is maintained at 11% to 15%. If yarn of 20 denier per filament is being spun, it is desirable to increase the concentration 01' ammonium salt somewhat, for instance up to 20% or 25%.

It is desirable to maintain the temperature of the coagulating solution under 12 0., but not lower than 3 C. Temperatures lower than 3' C. result in a freezing of the gum in the spinneret. This, of course, could be eliminated by heating the gum prior to spinning. If the temperature of the co u ating solution is raised much above 12 C., the rate of coagulation is slowed down to a point where the gel yarn is weak with resultingbroken filaments. Best results are obtained when the temperature of the coagulant is maintained within the range of 6-9 C.

If desired, the yarn may be subjected to substantial stretch as it passes through the coagulating bath or it may be withdrawn from .the coagulating bath and stretched up to 25% to 30% in air. If it is desired to stretch the yarn more than 30%, the yarn may be run through a stretching bathcontaining 25% to 35% acetic acid at a temperature of 35 C. to 50 C., and then stretched. In this way, it is possible to obtain up to stretch.

I claim:

1. The method of forming filaments, yarns, and

- threads from cellulose acetate which comprises spinning a gum of acetone-soluble cellulose acetate containing between' 50% and 57% combined acetic acid, said gum containing less than 15% by weight 0! water. into an aqueous calculating solution maintained at a temp'erature of from about 8 C. to about 12 0.. said coagulating solution consisting of about 12% by weight of acetic acid, from about 11% to about 25% by weight of ammonium salt oi an acid of the group consisting of formic, acetic and nitric acid, and from about 63% to 77% by weight of water,- and with drawing the formed filaments from said bath.

2. The method which comprises spinning a gum consisting of 15.8% by weight of cellulose acetate containing 54.5% of combined acetic acid, 78.75% acetic acid andb.95% water into a coagulating bath consisting of 12% acetic acid and 17% ammonium acetate in water maintained at s FRANCIS P. nuns.