US3318983A - Recycling ammonium hydroxide-treated water in the production of polyacrylonitrile fibers - Google Patents

Description

United States Patent C) RECYCLING AMMONIUM HYDROXIDE-TREATED WATER 1N THE PRODUCTION OF POLYACRY- LONKTRILE FIBERS Louis S. Hovis, Cary, N.C., Charles H. Apperson, Decatur, Ala, and William A. Blackburn, Chapel HilL, N.C., assignors to Monsanto Company, St. Louis, M0., a corporation of Delaware 7 No Drawing. Filed Aug. 27, 1963, Ser. No. 304,949 8 Claims. (Cl. 264*38) This invention relates to the preparation of acrylonitrile filaments and fibers. More particularly, this invention relates toa convenient and economical method of washing acrylonitrile fibers and filaments.

It is frequently a practice in the synthetic fiber industry to recover the process water used in spinning fibers and filaments. This process water normally contains concentrations of acidic compounds which would be detrimental to the fiber properties. It is well known that the effect of acids on synthetic fibers will lower the heat stability of the fiber and the fiber will undergo undesirable color changes when heated.

If the recovered process water used in spinning the fibers could be recycled and used again in the fiber producing process it would be very advantageous from an economic standpoint. Therefore, a neutralizing agent that could be added to the acid containing process water to neutralize the acids present and thus enable the reuse of the process water would be desirable. In order for such a neutralizing agent to be effective, the salts formed between the neutralizing agent and the acids present would have to be either washed out of the fiber by an additional step or else would have to be neutral salts.

It is an object of the invention to provide an improved economical method for the production of acrylontrile fibers.

It is a further object of this invention to produce an acrylonitrile fiber of improved properties by the use of a neutralizing agent in the wash water which will reduce the detrimental influence of acids on the fiber properties.

Other objects and advantages of the present invention will become apparent from the following detailed description thereof and the appended claims.

Generally, the objects of this invention are accomplished by spinning an acrylonitrile fiber or filament and thereafter washing the thus produced fiber or filament with an acid contaminated wash water that has been treated with ammonium hydroxide. This enables the process water used in the production of the fibers to be recycled and used again after treatment with ammonium hydroxide.

The invention is applicable not only to polyacrylonitrile, but also to copolymers, interpolymers, and blends thereof, particularly those containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile. For example, the polymer may be a copolymer of from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another copolymerizable mono-olefinic monomer.- Suitable copolymerizable mono-olefinic monomers include arcylic, alpha-chloroacrylic and methacrylic acids, the acrylates, such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, methoxymethyl methacrylate, beta-chloroe'thyl methacrylate, and the correspond- 3,318,983 Patented May 9, 1967 ing esters of acrylic and alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromine, vinylidene chloride, l-chloro-l-bromoethylene; methacrylonitrile; acrylamide and methacrylamide; alpha-chloroacrylamide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylate's, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N- vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters; itaconic acid and itaconic ester; N-vinyl carbazole; vinyl furan; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids or their anhydrides' or derivatives, such as diethylcitraconate, diethylmesaconate; styrene; vinyl naphthalene; vinyl substituted tertiary heterocyclic amines such as the vinylpyridines and alkyl-substituted vinylpyridines for example, 2-vinylpyridine, 4-vinylpyr'idine, Z-methyl-S-vinylpyridine, and the like; l-vinylim'idazole and alkyl-substituted l-vinylimidazoles, such as 2-, 4-, or S-methyl-l-vinylimidazole, vinyl pyrro'lidone, vinylpiperidone, and other inono-olefinic copolymerizable monomeric materials.

The polymer can be a ternary interpolyrner, for example, products obtained by the interpolymerization of acrylonitrile and two or more of any of the monomers, other than acrylonitrile, enumerated above. More specifically, and preferably, the ,ternary polymers contain from 80 to 98 percent of acrylonitrile, from 1 to 10 percent of a vinylpyridine or a l-vinylimidazole, and from 1 to 18 percent of another copolymerizable mono-olefinic' substance, such as methacrylonitrile, vinyl acetate, methyl methacrylate, vinyl chloride, vinylidene chloride, and the like.

The polymer can also be a blend of polyacrylonitrile or a copolymer of from 80 to 99 percent acrylontrile and from 1 to 20 percent of at least one other mono-olefinic copolymerizable monomeric substance with from 2 to 50 percent of the weight of the blend of a copolymer of from 30 to 90 percent of a vinyl substituted tertiary heterocyclic amine and from 10 to percent of at least one other mono-olefinic copolymerizable monomer. Preferably, when the polymeric material comprises a blend, it will be a blend of from to 99 percent of a copolymer of 80 to 98 percent acrylonitrile and from 2 to 20 percent of another mono-olefinic monomer, such as vinyl acetate,

with from 1 to 20 percent of a copolymer of from 30 to percent of a vinyl-substituted tertiary heterocyclic amine, such as vinylpyridine, a l-vinylimidazole or a vinyl lactam, and from 10 to 70 percent of acrylonitrile to give a blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent, based on the weight of the blend.

While the preferred polymers employed in the instant invention are those containing at least 80 percent acrylonitrile, generally recognized as the fiber-forming acrylonitrile polymers, it will be understood that the invention is likewise applicable to polymers, copolymers, interpolymers and blends containing less than 80 percent of acrylonitrile and as low as 35 percent acrylonitrile. Polymers containing from about 35 to 80 percent acrylonitrile may be copolymerized, interpolyinerized and blended with any of the mono-olefinic monomers enumerated herein. For example, the process is applicable to fibers acrylonitrile and 60 percent vinyl chloride and to a tert. polymer of approximately 67 percent acrylonitrile, 21 percent vinyl chloride and 12 percent vinylidene chloride.

The invention is further applicable to other vinyl polymers containing a majority of vinyl chloride, vinylidene chloride, styrene and other well known vinyl polymers and to copolymers, interpolymers and blends thereof with the mono-olefinic monomers enumerated herein. For example, fi bers which are formed from copolymers of vinyl chloride and vinylidene chloride, copolymers of vinyl chloride and vinyl acetate and copolymers of vinyl chloride and vinyl formate may be treated according to the procedure of this invention.

In the preparation of acrylonitrile fibers and filaments, it is a necessary step after spinning the fiber, to wash the fiber in order to remove any residual polymer and solvent from the fiber. It would be advantageous and economical to use the process water which was used in spinning the fibers in order to wash the prepared fiber. However, the process water frequently accumulates acidic compounds which have a detrimental effect on the fiber properties, such as lowering the heat stability of the fiber.

In addition, if residual acid in the fiber is high, it will also cause corrosion of textile processing equipment such as carding and knitting machines. High residual acid in a fiber will cause the card teeth to corrode to such a degree during processing that much of the fiber must be discarded and the equipment must be shut down and the rust must be removed from the card teeth.

It has been found that the addition of ammonium hydroxide to the wash water is an effective way .to accomplish the neutralization of the acids in the wash water and in addition does not require an additional washing step to remove the salts that are formed. If a strong base is added to .the wash water to neutralize the acids present, then the fibers Washed with the treated wash water have to undergo an additional wash step to remove the basic salts which will greatly effect the heat sensitivity of the fiber if allowed to remain on the fiber.

A further advantage to the use of ammonium hydroxide wash water isthat excessive amounts of ammonium hydroxide, in addition to that amount required to neutralize the acids present, are surprisingly not harmful. It is believed that the excess of ammonium hydroxide is volatilized in the form of ammonia and water upon drying the fiber.

In addition, the basic dye acceptance of fibers can be increased by washing them with wash water neutralized with ammonium hydroxide rather than with city water. Calcium and magnesium ions contained in most city waters block dye sites and thereby reduce the basic dye acceptance. It has been found that fiber washed with process water treated with ammonium hydroxide resulted in gains up to 40 percent higher basic dye acceptance as compared with fiber washed with water containing calcium and magnesium ions.

The ammonia may be added to the wash Water containing the acidic materials at any time prior to the Washing of the fiber. The ammonia may be added as ammonia gas, liquid ammonia or any form of ammonia that will result in the formation of ammonium hydroxide. The concentration of ammonium hydroxide in the wash water may be varied to give a treated Water having a pH from about 7.0 to a pH of about 10.0. Where the treated water is recycled and used to wash fiber several times, the pH of the water must be readjusted after each use. Excessive amounts of the ammonium hydroxide are not harmful and additional washing steps to remove the salts formed are not required.

The neutralizing agent in the form of ammonium hydroxide, ammonia gas, and the like, is added to the wash water at room temperature and thoroughly mixed with the wash water. The wash water may then be used to wash the prepared fiber.

The invention will be more fully described with reference to the following examples demonstrating the prep- EXAMPLE 1 Two thousand eight hundred and fifty grams of dimethylacetamide containing 2 percent by weight of acetic acid was chilled to -5 C. To this chilled composition, 950 grams of an acrylonitrile copolymer comprising 93 percent of acrylonitrile and 7 percent vinylacetate and having a specific viscosity of 0.151 was added. The materials were slurried for minutes at 350 rpm. The slurry was then transfer-red to a spinning machine and spun into a spin bath comprising 55 percent of dimethylacetamide containing 2 percent acetic acid and 45 percent water to produce fiber. The fiber was then washed with wash water recovered from the preparation of similar fiber. The wash water contained about 0.07 percent by weight of acetic acid and had a pH of 3.6. The col-or, heat stability and basic dye acceptance of the fiber Washed as described above is shown in the table below. It was found that fiber washed as described above caused undesirable corrosion on the card used in the normal processing of fibers. The test for card corrosion was conducted by running a sample into the carding machine, shutting the machine down and allowing it to stand overnight. Since the fiber contained acetic acid, the machine would not start up again the next morning.

EXAMPLE 2 a This water was analyzed and found to contain 20 ppm.

of calcium, 2 p.p.m. of magnesium, 6 ppm. of sodium and potassium, and 1.5 p.p.m. of heavy oxides. The color, heat stability and basic dye acceptance of the fiber washed as described above is shown in the table below.

EXAMPLE 3 Wash water was prepared by adding grams of glacial acetic acid to approximately 50 gallons of deionized water in a stainless steel drum. The acetic acid and the water were mixed by recirculating the mixture for approximately 5 minutes. The wash water had an acetic acid content of about 0.07 percent by weight. Ammonium hydroxide was added to the wash water in an amount sufficient to give the wash water a pH of 9.25. This wash water was used to wash fiber prepared according to the procedure of Example 1. The color and heat stability of the fiber washed as described above is shown in the table below.

EXAMPLE 4 Wash water was prepared by adding 140 grams of glacial acetic acid to approximately 50 gallons of deionized water in a stainless steel drum. The acetic acid and the water were mixed by recirculating the mixture for approximately 5 minutes. The wash water had an acetic acid content of about 0.07 percent by weight. Ammonium hydroxide was added to the Wash Water in an amount sufiicient to give the wash water a pH of 8.0. This wash water was used to wash fiber prepared according to procedure of Example 1. The color, heat stability and basic dye acceptance of the fiber washed as described above is shown in the table below.

The color results indicative of heat stability used throughout the examples consist of measurement of purity and brightness as calculated from the tristimulus values determined on a General Electric spectrophotometer by the methods recommended by the Standard O-bserver and Coordinate System of the International Commision of Illumination, as fully set forth in the Handbook of Colorimetry, published by the Technology Press, Massachusetts Institute of Technology, in 1936. All of the measurements given were made on crimped, annealed, and carded staple samples made from skeins of 200 wraps of 3.0 denier per filament fiber.

The basic dye acceptance (BDA) values given in the table below were obtained by mixing 25 ml. of a bufiercd (pH=5.2) solution of Sevron Blue 2G dye with 0.6 grams of fiber in a sealed tube at 100 C. for 2 hours. The exhausted dyebath was then analyzed spectrophotometrieally to determine the amount of dye remaining and the percentage of dye uptake on the fiber.

The following table shows a comparison of the color and heat stability of the fiber washed in the various examples set forth above.

COLOR, HEAT STABILITY AND BASIC DYE ACCEPT- ANCE TABLE.

Initial Color Heated Color (145 C. for

25 min.)

P BR

Percent;

Example 1. 0 Example 2. Example 3. 2

Example 4 BR represents brightness and P represents purity above.

As many variations of this invention may be made without departing from the spirit and scope thereof, it is intended that the invention be limited solely by the scope of the appended claims.

We claim:

1. In a process for the preparation of fibers from vinyl polymers wherein a vinyl polymer is dissolved in a solvent therefor which may contain an acid contaminant, the resulting homogeneous solution is extruded into a coagulating medium which may contain an acid contaminant to produce fibers, and said fibers are subsequently Washed with an aqueous solution, the improvement which comprises treating said aqueous solution used in the preparation of said fibers with ammonium hydroxide when said aqueous solution is contaminated with acid and then using the thus treated aqueous solution in washing additional fibers.

2. In a process for the preparation of fibers from vinyl polymers wherein a vinyl polymer is dissolved in a solvent therefor which may contain an acid contaminant, the resulting homogeneous solution is extruded into a coagulating medium which may contain an acid contaminant to produce fibers, and said fibers are subsequently washed with an aqueous solution, the improvement which comprises treating said aqueous solution used in the prepara tion of said fibers with ammonium hydroxide when sait aqueous solution is contaminated with acid to give 2 solution having a pH of from about 7.0 to about 10.0 anc then using the thus treated aqueous solution in washing additional fibers.

3. The process as defined in claim 2 wherein the viny polymer is an acrylonitrile polymer.

4. The process as defined in claim 3 wherein the acrylonitrile polymer is a copolymer of at least percen acrylonitrile and up to 20 percent of vinyl acetate.

5. In a process for the preparation of fibers from vinyi polymers wherein said polymer is dissolved in a solvent therefor which may contain acetic acid, the resulting homogeneous solution is extruded into a coagulating medium which may contain acetic acid to produce fibers, and said fibers are subsequently washed With an aqueous solution, the improvement which comprises treating said aqueous solution used in the preparation of said fibers with ammonium hydroxide when said aqueous solution contains acetic acid and then recycling the thus treated aqueous solution for use in washing additional fibers.

6. In a process for the preparation of fibers from vinyl polymers wherein said polymer is dissolved in a solvent therefor which may contain acetic acid, the resulting homogeneous solution is extruded into a coagulating medium to produce fibers, and said fibers are subsequently washed with an aqueous solution, the improvement which comprises treating said aqueous solution used in the preparation of said fibers with ammonium hydroxide when said aqueous solution contains from about 0.01 to about 0.10 percent by Weight of acid to provide a solution having a pH of about 7.0 to about 10.0 and then recycling the thus treated aqueous solution for use in washing additional fibers.

7. The process as defined in claim 6 wherein the vinyl polymer is an acrylonitrile polymer.

8. The process as defined in claim 7 wherein the acrylonitrile polymer is a copolymer of at least 80 percent acrylonitrile and up to 20 percent of vinyl acetate.

References Cited by the Examiner UNITED STATES PATENTS 2,553,483 5/1951 Sowter 264-38 2,723,900 11/1955 Hooper 264182 2,916,348 12/ 1959 Cresswell 2641 82 ALEXANDER H. BRODMEARKEL, Primary Examiner.

F. S. WHISENHUNT, D. J. ARNOLD,

Assistant Examiners.

Claims (1)

1. IN A PROCESS FOR THE PREPARATION OF FIBERS FROM VINYL POLYMERS WHEREIN A VINYL POLYMER IS DISSOLVED IN A SOLVENT THEREFOR WHICH MAY CONTAIN AN ACID CONTAMINANT, THE RESULTING HOMOGENEOUS SOLUTION IS EXTRUDED INTO A COAGULATING MEDIUM WHICH MAY CONTAIN AN ACID CONTAMINAT TO PRODUCE FIBERS, AND SAID FIBERS ARE SUBSEQUENTLY WASHED WITH AN AQUEOUS SOLUTION, THE IMPROVEMENT WHICH COMPRISES TREATING SAID AQUEOUS SOLUTION USED IN THE PREPARATION OF SAID FIBERS WITH AMMONIUM HYDROXIDE WHEN SAID AQUEOUS SOLUTION IS CONTAMINATED WITH ACID AND THEN USING THE THUS TREATED AQUEOUS SOLUTION IN WASHING ADDITIONAL FIBERS.