US3839520A

US3839520A - Process for producing porous acrylic fibers

Info

Publication number: US3839520A
Application number: US00330765A
Authority: US
Inventors: T Kobashi; N Abe
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1972-04-10
Filing date: 1973-02-08
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01
Also published as: ES413531A1; CA1038579A; JPS48103827A; JPS51210B2

Abstract

1. A PROCESS FOR PREPARING POROUS ACRYLIC FIBERS WHICH COMPRISES PREPARING A SPINNING SOLUTION OF A FIBER-FORMING ACRYLONTRILE POLYMER CONTAINING AT LEAST ABOUT 70 WEIGHT PERCENT ACRYLONITRILE AND THE BALANCE OF ONE OR MORE VINYL MONOMERS COPOLYMERIZABLE THEREWITH IN AN AQUEOUS INORGANIC SOLVENT THEREFOR, DISPERSING THEREIN AS BUBBLES OF AN AVERAGE DIAMETER LESS THAN ABOUT 50 MICRONS BOTH AN INERT LIQUID HAVING A BOILING POINT IN THE RANGE OF 30-100: C. AND AN INERT GAS WHICH ARE SUBSTANTIALLY INSOLUBLE IN SAID SPINNING SOLUTION AND AN AQUEOUS COAGULANT THEREFOR, SAID LIQUID AND SAID GAS BEING DISPERSED IN AMOUNTS GIVEN IN THE CO-DEPENDENT RELATIONSHIP ABCDE SHOWN IN THE ACCOMPANYING FIGURE, SPINNING THE DISPERSION THUS OBTAINED INTO SAID AQUEOUS COAGULANT UNDER CONDITIONS WHICH RETAIN THE DISPERSED BUBBLES WITHIN THE COAGULATED FIMAMENT, AND THEREAFTER PASSING THE COGULATED FILAMENT THROUGH STEAM OR WATER AT A TEMPERATURE OR ABOVE THE BOILING POINT OF SAID LIQUID WHILE THE FILAMENT IS IN A HOMOGENEOUS SWOLLEN GEL STATE SO AS TO EVAPORATE SAID LIQUID.

Description

Oct. 1, 1974 TOSHIYUKI KOBASHI ET AL 3,839,520

PROCESS FOR PRODUCING POROUS ACRYLIC FIBERS Filed Feb. 8. 1973 H c g I I /0 20 30 RATE OF /N TRODUC r/o/v 0F INERT 6A6 (//v 5) VOLUME BASED 0/\/ VOLUME 0F SPl/V/V/lVG SOLUT/ON/ RATE OF I/VTRODUCT/O/V 0F //V/?7' L/OU/D (/IV B) WE/GHT BASED ON WEIGHT 0F .SPl/V/V/NG SOLUTION) United States Patent 3,839,520 PROCESS FOR PRODUCING POROUS ACRYLIC FIBERS Toshiyuki Kobashi, Tsulrubo-gun, and Noboru Abe, Okayama, Japan, assignors to American Cyanamid Company, Stamford, Conn.

Filed Feb. 8, 1973, Ser. No. 330,765 Claims priority, application Japan, Apr. 10, 1972, 47/35,850 Int. Cl. B29l1 7/ 20; 1301f 7/00 U.S. Cl. 26450 10 Claims ABSTRACT OF THE DISCLOSURE Wet-spinning porous acrylic fibers from a spin dope containing a fine dispersion of both (a) an inert gas such as air and (b) an inert, low-boiling (b.p. 30-l00' C.) liquid which is substantially insoluble in the spin dope and coagulant by a process which includes passing the wet-gel fiber through steam or hot water at a temperature above the boiling point of said inert liquid to evaporate it.

This invention relates to a process for preparing porous acrylic fibers from a spinning solution prepared by dissolving a fiber-forming acrylonitrile polymer in an aqueous inorganic solvent therefor.

More particularly, the present invention relates to an industrially advantageous process for producing porous acrylic fibers containing numerous stable fine cavities therein and having excellent physical properties, which process comprises dispersing in a spinning solution of an acrylonitrile polymer in an aqueous inorganic solvent both an inert low-boiling liquid which is substantially in soluble therein and an inert gas, wet-spinning the thus modified spinning solution into an aqueous coagulant under conditions such that said low-boiling liquid is not evaporated or dissolved, and thereafter heating the thus coagulated filaments so as to evaporate the low-boiling li uid.

Many processes for producing porous or hollow fibers employing wet-spinning are previously known.

In one such prior art process, an inert gas is dispersed in the spinning solution and the resulting dispersion is spun into fibers. The process requires use of a special dispersing device such as a colloid mill to disperse the gas as fine bubbles Within the spinning solution. However, even with the use of the special dispersing device, it is extremely difficult to provide gas bubbles of the fine diameter necessary. Consequently, the process leads to frequent stoppages due to filament breakages in spinning and stretching steps and it has not been possible to maintain the necessary continuity of processing necessary for commercial production.

In another such process, a low-boiling liquid is dispersed in the spinning solution, the modified spinning solution is then Wet-spun and coagulated, and the liquid is evaporated. However, in this process, an insufiicient number of cavities are obtained in the filaments obtained to provide the desired degree of porosity. Increasing usage of the low-boiling liquid to increase porosity not only increases production costs immensely but also leads to unacceptable fiber properties, particularly strength and elongation.

In accordance with the present invention, there is provided a process for preparing porous acrylic fibers which comprises preparing a spinning solution of a fiber-forming acrylonitrile polymer containing at least about 70 weight percent acrylonitrile and the balance of one or more vinyl monomers copolymerizable therewith in an aqueous inorganic solvent therefor, dispersing therein as bubbles of an average diameter less than about 50 3,839,520 Patented Oct. 1, 1974 "Ice microns both an inert liquid having a boiling point in the range of 30l00 C. and an inert gas which are substantially insoluble in said spinning solution and an aqueous coagulant therefor, said liquid and said gas being dispersed in amounts given in the co-dependent relationship ABCDE shown in the accompanying Figure, spinning the dispersion thus obtained into said aqueous coagulant under conditions which retain the dispersed bubbles within the coagulated filament, and thereafter passing the coagulated filament through steam or water at a temperature at or above the boiling point of said liquid while the filament is in a homogeneous swollen gel state so as to evaporate said liquid.

In accordance with the present invention, it is entirely unexpected that the combination of low-boiling liquid and inert gas should provide much finer cavities than are obtained by use of inert gas alone, that the amount of low-boiling liquid required to provide the desired porosity should be greatly reduced from that required by use of liquid alone, and that the various problems presented by the former processes should be overcome while providing porous acrylic fiber of excellent physical properties.

Although the manner by which the improved results are obtained by the present invention are not known for certain and the present applicants do not wish to be bound by any theory, it is thought that dispersing both the low-boiling liquid and the inert gas in the spinning solution causes the liquid to pass through processes of gasification and expansion which result in coalescence with the inert gas, this in turn leads to production of bubbles containing low-boiling liquid within the spinning composition, which bubbles are then reduced in size by agitation accompanying the dispersing operation, and finally the low-boiling liquid is condensed and liquefied in conjunction with the compression exerted upon the spinning solution as it is pumped in the spinning procedure. It is this behavior of the low-boiling liquid that is presumed to be a reason for the results obtained.

The low-boiling liquid useful in the process of the present invention is an inorganic or organic compound which is substantially insoluble in the spinning composition and in the aqueous coagulant used therewith. It must have a boiling point in the range of 30 to 100 C., and preferably in the range of 60 to C. Suitable lowboiling liquids are exemplified by carbon tetrachloride, butyl chloride, propionyl chloride, propyl chloride, allyl chloride, isoamyl chloride, trichloroethylene, trichloroethane, benzene, n-hexane, cyclohexane, cyclohexadiene, cyclopentane, dimethylbutane, dimethylfuran and carbon disulfide. A preferred liquid is n-hexane.

In the event that the low-boiling liquid is soluble in the spinning composition, it will be impossible to obtain fiber having the porosity characteristics that are the object of the present invention. Furthermore, if the low-boiling liquid is soluble in the aqueous coagulant, it will also be impossible to obtain fiber having the porosity characteristics that are the object of the present invention. The term substantially insoluble as used in the present specification and claim is intended to refer to a low-boiling liquid whose solubility does not exceed about 0.5 weight percent at 20 C. in either the spinning solution or the aqueous coagulant.

Low-boiling liquids having boiling points below about 30 C. cannot be employed in the process of the present invention because the spinning solutions involving aqueous inorganic polymer solvents are generally employed in wet-spinning at temperatures that would cause premature evaporation of the low-boiling liquid and consequent loss of the desired fiber porosity. Liquids having boiling points above about C. cannot be effectively employed in the process of the present invention because they are too difiicult to expand quickly and to evaporate from the fiber under the conditions normally associated with wet processing of wet-spun acrylic fibers.

The inert gas useful in the process of the present invention is non-reactive with and substantially insoluble in the spinning solution and coagulant. Suitable gases include, for example, air, nitrogen, argon, helium, and

neon.

The sole Figure of the present specification is an orthogonal coordinate diagram resulting from plotting the etfective usage levels of low-boiling liquid and inert gas and connecting the points so as to provide an enclosed effective area that represents the codependent relationship between usage of low-boiling liquid and usage of inert gas that is effective in the process of the present invention. The etfective coordinates connected are represented as A (1, 5), B (1, 0.01), C (30, .01). D (30, 0.5) and E (5, 5). The area represented by the smaller diagram results from connecting coordinates F (2, 2), G (2, 0.05), H (10, 0.05), I (10, 0.5) and J (5, 2) and indicates a preferred codependent relationship between usage of low-boiling liquid and usage of inert gas. The values of low-boiling liquid plotted are weight percentages based on the weight of the spinning solution. The values of inert gas are volume percentages based on the volume of spinning solution. Usages of low-boiling liquid and inert gas within the area defined by connecting the coordinates, as shown in the figure, lead to the desirable results of the present invention. Usages outside the area enclosed by connecting the coordinates result in loss of the desirable properties achieved by the present invention.

The inert gas and low-boiling liquid may be introduced into the spinning solution by any convenient method for dispersion therein. The low-boiling liquid may be intro duced and dispersed in the spinning solution first, fol lowed by introduction and dispersion of the inert gas. Alternatively, the inert gas may first be introduced and dispersed in the spinning solution followed by introduction and dispersion of the low-boiling liquid. A particularly preferred method of introduction is to prepare first a gaseous mixture by dispersing the low-boiling liquid in the form of a gas or mist into the inert gas and then introducing and dispersing this gaseous mixture into the spinning solution. This preferred procedure of introduction and dispersion of low-boiling liquid and inert gas enables extremely fine bubble sizes to be obtained in the spinning solution.

In effecting dispersion of the low-boiling liquid and inert gas in the spinning solution, mechanical agitation is employed. A particularly effective mechanical device is a planetary gear type liquid disintegrator or an in-line homomixer used in conjunction with transport of the solution. It is generally preferred to carry out dispersing until the average bubble diameter in the spinning solution is not more than about 50 microns, preferably not more than about microns, as measured from photomicrograph determinations, as later described. When the average bubble diameter exceeds about microns, problems with respect to spinnability, filament breakage at the time of spinning and stretching, and non-uniform pores may result. Therefore, it is desirable to maintain bubble diameter below about 50 microns to avoid such potential problems.

The spinning solution with its dispersed content of low-boiling liquid and inert gas is then spun into an aqueous coagulating bath in accordance with conventional wet-spinning procedures. conventionally, the aqueous coagulating bath is maintained at a temperature below about 20 C. and preferablybelow about 10 C. and coagulation is effectively accomplished. Use of aqueous coagulating bath temperatures in excess of about 20 C. results in devitrification of acrylic fibers obtained from aqueous inorganic solvent solutions of fiber-forming acrylonitrile polymers and is to be avoided. The bubbles introduced into the spinning solution by the combination of lowboiling liquid and inert gas are present in the fiber coagulated as specified. The coagulated fiber is water-washed, which may be accompanied by partial stretching, in accordance with conventional procedures. Such water-washing does not involve temperatures in excess of about 20 C. The washed fiber is then treated in hot water or steam at temperatures at or above the boiling point of the lowboiling liquid while the fiber is still in a homogeneous swollen gel state. By such treatment, the low-boiling liquid present in the liquid state in the swollen gel fiber is quickly evaporated so as to leave fine cavities Within the fiber. The cavities result from evaporation of the low-boiling liquid alone, such liquid in conjunction with inert gas, or from coalescence of cavities resulting from evaporation of lowboiling liquid and escape of inert gas entrapped in the initially coagulated fiber, i.e. prior to use of hot water or steam. The cavity-containing fiber is then stretched in hot water at a temperature above about C. Such stretching causes elongation of the cavities in the direction of stretching and the fiber thus obtains uniform elongated cavities over its entire length. Hot-stretching may be in a single step or in staged amounts in multiple steps. Some stretching may also accompany water-washing prior to cavity formation by taking advantage of the limited cold stretchability of the spun filament. Stretching may also be carried out by use of steam. The stretching contemplated is that conventionally employed for fiber orientation purposes.

The swollen gel fiber containing cavities and oriented by hot-stretching is then compacted as to fiber structure by drying and may be subjected to such additional conventional processing steps as may be desired. Such additional steps include, for example, heat-relaxation, finishing agent treatment, and post-drying, as are conventionally employed.

It is not necessary to elfect cavity formation by use solely of an added heat-treating step with hot-water or steam, but the formation of cavities may accompany a. suitable conventional step performed on the fiber while it is still in a homogeneous swollen gel state before compacting. A preferred operation during which cavity formation is carried out is in conjunction with hot-stretching for orientation purposes. It is also possible to carry out cavity formation in conjunction with water-washing by elevating the temperature thereof in stages.

The acrylic fiber obtained by the process of the present invention has elongated fine cavities uniformly distributed over the entire fiber length. These cavities are not collapsed by any subsequent processing steps such as stretching, compacting, or crimping steps. The resulting fiber also has high strength and elongation properties and is eminently suitable for such uses as clothing, bedding, and stuffing by virtue of its light weight and elastic and insulating properties, which are important requirements for many industrial uses.

The acrylonitrile polymer useful as the fiber-forming polymer may be a homopolymer of acrylonitrile or a co polymer containing at least about 70 weight percent acrylonitrile and the balance of one or more vinyl monomers copolymerizable therewith. A mixture of polymers may also be employed.

As the polymer solvent used to form the spinning solution, an aqueous inorganic solvent is required. Suitable inorganic solvents include concentrated aqueous solutions of thiocyanate salts, such as sodium, potassium, ammonium, and calcium thiocyanates, zinc chloride, and perchloric, nitric, and sulfuric acids. Organic solvents, such as dimethylformamide, dimethylacetamide, or dimethyl sulfoxide, cannot be used in the process of the present invention since they dissolve the low-boiling liquid and do not enable the required dispersed state thereof to be achieved.

The concentration of acrylonitrile polymer in the spinning solution is generally in the range of about 5 to 25 weight percent, based on the weight of the spinning solution, and is influenced by the molecular weight of the polymer, as'is known.

The aqueous coagulant employed is that normally associated with the particular aqueous inorganic polymer solvent employed. No special requirements as to aqueous ratio of 5 in boiling water. The boiling water treatment also caused the low-boiling liquid to gasify and evaporate from the fiber with the entrapped air to provide cavities in the fiber. The fiber was then dried in air at 120 C. to compact the structure and finally heat-relaxed in saturated 5 coagulant are imposed by the process of the present insteam at 125 C. The various modifications and detalls vention. are given in Table I.

The invention is illustrated by the examples which follow COMPARATIVE EXAMPLES wherem all parts and percentages are by we1ght unless otherwise Specifically designated The procedure followed was as 1n Examples 1-11 above Theporosity value of the fiber is evaluated by deter- Q P thiflt h spinmng Solutlons, modlfied mining the specific gravity of the fiber. It has been deboiling hquld l? Y Wlth gas termined that a fiber pmpamd Without Provision f arately. The mod1ficat1ons and deta1ls are also g1ven 1n cavities therein has a specific gravity of 1.18. It has also Table been determined that satisfactory porosity is not achieved Processmg h fibers of Examples 1 11 no problems until a specific gravity below about 1.15 is achieved. w1 th respect to SPmPmg F": 'lihe fibers The average bubble diameter D of the Spinning Solw tamed had low specific grav1t1es, thus 1nd1cat1ng numerous tion with its dispersed content of low-boiling liquid and cavftfest and had excellent strength In Vlew of the many inert gas is obtained by obtaining a photomicrograph of Cavltlesthe dispersion and measuring the diameter D, of 200 Processmg the fibers of comparatlve ExamPlS bubbles therein. The average diameter is then calculated spmnmg Problems were encountered In Comparatlve from the relationship amples AC, the filaments broke frequently both upon spinning and upon stretching, thus stopping continuity of 200 the spinning process. The stoppages increased with ing i creasing usage of air. The fiber obtained where processing D: was practical was poor in porosity, containing few cavities of non-uniform size. In Comparative Examples D and E, EXAMPLES 11 few cavities were obtained. Use of higher amounts of lowboiling liquid beyond that reported caused such frequent A copolymer conslstfng of 90% acfylomfnle and 10% filament breakage as to provide a fiber of no practical methyl acrylate was d1ssolved at 70 C. 1n an aqueous value. solution o 4 Sodlum thlocyanal to Prowle a Polymer In order to determine the nature of the fibers produced concentratlon of 11 The solut1on was deaerated and by the process of the Present invention and of the cPoled to 25 T1118 9 9 was dlvldfid 1 parative process, photomicrographs of cross-sections of s xteen port1ons for further mod1ficat1on and use 1n sp 1nthe fibers of Example 3 and Comparative Example C g Eleven P F were employed In P P were made. These photomicrographs revealed that the fibers 111 a w q Wlth the Process P lnven' fiber of Example 3 contained numerous fine and uni- 10 a d five Portlons Wem p y In P P g formly distributed cavities while the fiber of Example by comparative prior art procedures. Each portion, su1t- C contained a few large cavities non-uniformly ably modified was individually processed into fiber. distributed,

TABLE I Fiber properties Average Low boiling hquld bubble Arr Specific diameter Ex usage Name Usage gravity Strength (microns) 4 1. 0 n-Hexane 2. 0 1. 15 3. 76 12 6.0 do. 0.1 1.06 3. 0s 14.

6. 0 Carbon tetrachlon'de-. 0. 1 1. 10 3. 10 24 28 n-Hexane 0.25 0.90 1.76 26 d 1.25 0. 90 1.82 23 0 1.18 3.75 32 o 1.18 3. 35 34 0 1.13 2.55 40 3.5 1.17 3.65 0.0 do 9.0 1.15 2.76

1 Volume percent on volume of spinning solution. 2 We1ght percent on weight of spinning solution.

Grams per denier.

4 Based on photomicrograph of spinning solution.

Each portion of the spinning solution processed in accordance with the present invention was modified with both low-boiling liquid and inert gas (air) as indicated in Table I. The spinning solutions thus modified by incorporation of low boiling liquid and air were agitated by means of a planetary gear type liquid disintegrator so as to provide the average bubble diameter given in Table I. The low-boiling liquid and air were introduced into the spinning solution separately, the liquid being added first.

The modified spinning solution, in each instance, was spun into an aqueous coagulation bath at 0 C. consisting of a 12% aqueous solution of sodium thiocyanate. The spinnerette contained orifices, each of 0.1 millimeter diameter. The coagulated fiber was water-washed at 20 C. and stretched at a stretch ratio of 2 in conjunction therewith. The washed fiber was then stretched at a stretch We claim:

1. A process for preparing porous acrylic fibers which comprises preparing a spinning solution of a fiber-forming acrylonitrile polymer containing at least about 70 weight percent acrylonitrile and the balance of one or more vinyl monomers copolymerizable therewith in an aqueous inorganic solvent therefor, dispersing therein as bubbles of an average diameter less than about 50 microns both an inert liquid having a boiling point in the range of 30100 C. and an inert gas which are substantially insoluble in said spinning solution and an aqueous coagulant therefor, said liquid and said gas being dispersed in amounts given in the co-dependent relationship ABCDE shown in the accompanying Figure, spinning the dispersion thus obtained into said aqueous coagulant under conditions which retain the dispersed bubbles within the coagulated filament, and thereafter passing the coagulated filament through steam or Water at a temperature at or above the boiling point of said liquid while the filament is in a homogeneous swollen gel state so as to evaporate said liquid.

2. The process of Claim 1 wherein the average bubble diameter is less than about 30 microns.

3. The process of Claim 1 wherein said liquid and said gas are dispersed in amounts given in the codependent relationship FGI-HJ shown in the accompanying Figure.

4. The process of Claim 1 wherein said liquid is nhexane.

5. The process of Claim 1 wherein said liquid is carbon tetrachloride.

6. The process of Claim 1 wherein said gas is air.

7. The process of Claim 1 wherein said acrylonitrile polymer contains 90 weight percent acrylonitrile and 10 weight percent methyl acrylate.

8. The process of Claim 1 wherein said aqueous inorganic solvent is 44% aqueous sodium thiocyanate.

9. The process of Claim 1 wherein said aqueous coagulant is 12% aqueous sodium thiocyanate.

10. The process of Claim 7 wherein said spinning solution contains 11 weight percent polymer.

References Cited UNITED STATES PATENTS OTHER REFERENCES Abstract of German Often. 2100700 (7/22/1971) published in Chem. Abstracts, Vol. 75, p. 55, 1971 (152874Z).

JAY H. WOO, Primary Examiner US. Cl. X.R.

161-178; 260-25 E, 29.6 AB, AQ; 264-53, 182