US3383350A - Process for producing acrylonitrile polymer fiber of predetermined fiber color - Google Patents

Description

United States Patent 3,383,350 PROCESS FOR PRODUCING ACRYLONITRILE POLYMER FIBER OF PREDETERMINED FI- BER COLOR Bobby M. Pettyjohn, Camden, S.C., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 261,871, Feb. 28, 1963. This application Dec. 9, 1965, Ser. No. 512,812

4 Claims. (Cl. 26032.6)

This is a continuation-in-part of Ser. No. 261,871, filed Feb. 28, 1963, now abandoned.

This invention relates to production of acrylic fibers of improved color uniformity, and more particularly to the control of fiber yellowness within narrow limits.

It is well-recognized that acrylic fibers tend to discolor on exposure to high temperature or alkali to give a somewhat yellowish product. While it would be desirable to provide a fiber which has no off-white shading and excellent reflectance, particularly in the interest of flexibility in end uses and good clarity of dyeings, this ideal has not yet been attained. As a reasonable compromise, fiber proc essors are willing to accept maintenance of a relatively uniform degree of whiteness so that lot-to-lot variations in whiteness do not present problems in duplication of dye shades or in variable response to bleaching and other finishing steps. In endeavoring to get uniform coloration, it it has been necessary to use combinations of additives in the spinning solutions as well as various polymer and fiber after-treatments. Using previously known processes and additives, the determination and acceptable control of fiber coloration, particularly during continuous process production, has not been attainable. Moreover, certain treatments which initially reduce coloration actually promote the development of color during subsequent processing such as scouring, washing etc.

It is, therefore, an object of the present invention to provide a process for preparing acrylic fibers having uniform coloration. It is another object of this invention to provide a process for continuously controlling coloration during the spinning process. It is a further object to provide a process for improving the whiteness of acrylic fibers which does not adversely affect other fiber properties and does not promote formation of color during subsequent processing.

It has now been discovered, and it is on this discovery that the invention is in large part predicated, that predetermined and uniform coloration of acrylic fibers can be attained with a procedure involving monitoring of the color of the spinning solution from which the fibers are spun and treating the solvent to be used to make additional spinning solution in response to the monitoring information obtained. More particularly, the objects of this invention are accomplished by dissolving an acrylonitrile polymer in N,N-dimethylformamide (DMF) to form a spinning solution, monitoring the resulting solution to determine its coloration, and thereafter adding to the N,N- dimethylformamide prior to dissolution of polymer therein a controlled amount of citric acid (CA) or diethylenetriarninepentaacetic acid (DTPA) to reduce the coloration of solution prepared to a predetermined level. The addition to N,N-dimethylformamide of very small amounts of either of the foregoing acids, i.e., from about 25 to about 800 parts per million based on the weight of polymer to be dissolved therein, is effective in reducing coloration potential With an almost immediate gain in the whiteness of the spinning solution being produced in a continuous process and of the fibers formed therefrom. In view of the rapid and efiicient action of these acids used in accordance with the foregoing discovery, it is now possible rapidly to attain a good coloration level in the continuous production of acrylic fiber. Where there is an extended lapse of time between the preparation and the spinning of the solution, additional protection may be obtained by addition of CA or DTPA to the solution, but this procedure is less desirable since yellowness already developed prior to this later addition is not eliminated. Monitoring of the solution just prior to spinning is preferred to monitoring of fiber whiteness, due to the early indication of trends afforded thereby. For example, commonly 48 hours separate the period in which polymer is first dissolved to initiate the process and the time when product therefrom is obtained and its color determined. With such lags great variation in product would result from changes based on the product color alone.

In carrying out the process of this invention, the determination of coloration can be made by using a differential colorimeter. The spinning solution may be monitored at selected time intervals or monitored continuously using apparatus of the type described in McKinney et al. US. 3,020,795. However monitored, the information obtained is used to indicate an initial addition of acid, a continued addition or a diminishng of acid added, all within the acid range given hereinbefore. Generally amounts of ether CA or DTPA greater than 800 parts per million are not required to maintain the predetermined color level. The particular amount required will vary depending on such factors as the solution temperatures employed, composition of the spinning solution, and the rate of extrusion and denier of the acrylonitrile polymer fibers formed.

The term acrylonitrile polymer as used herein is meant to include a homopolymer of acrylonitrile as well as such copolymers as those containing at least of acrylonitrile and up to 15% of one or more monoethylenically unsaturated monomers copolymerizable with acrylonitrile. Preparation of these polymers is well known, such processes being disclosed in US. Patents 2,486,241, 2,456,238, 2,837,500, and 2,837,501 as well as others.

In the examples which follow, the color value b is determined using the method described in the Journal of the Optical Society of America, vol. 42, No. 9 (1952), pages 652 to 666, by L. G. Glasser and D. J. Troy. The b values reported are proportional to the sample yellowness and are determined by reflectance of filtered light from the sample. In measuring the solution color, samples are taken at timed intervals and poured into a flat-bottom dish which is placed over one window of the differential colorimeter, the standard reference plate being placed over the other window. In making continuous measurements of the solution color, the window of the apparatus described in McKinney et al. may serve as one window of the differential colorimeter. Fiber samples are prepared for color value measurement by chopping to about 0.06 inch (0.16 cm.) or shorter lengths, slurrying in water, filtering the slurry to form a pad and drying at room temperature until dry to the touch. The pad is then placed on one window of the differential colorimeter with the standard reference plate being placed on the other window. Readings are taken with the pad oriented in each of two directions, the one direction being at 90 relative to the other.

The following examples in which parts and percentages are by weight unless otherwise specified further illustrate the invention.

EXAMPLE 1 A. Spinning solution is prepared to contain 30% by weight of a terpolymer consisting essentially of 93.6% acrylonitrile, 6% methyl acrylate, and 0.4% sodium styrenesulfonate in N,N-dimethylformamide (DMF), and 0.4% TiO based on polymer, is added as a delusterant. The solution is continuously dry-spun to a multifilament yarn which, after simultaneous drawing 4.54X (to 454% of its spun length) and extraction in a water bath maintained near its boiling point, has a denier-per-filament of 4.5.

BE. Subsequent solutions are prepared in accordance with Part A except that DTPA in increasing amounts is added, as a 17.5% dispersion in DMF, to the DMF prior to addition of the polymer. The successive solutions are spun continuously and the product fiber representative of each is analyzed for yellowness. Results are summarized in Table l.

This example illustrates yellowness regulation by the process of this invention as applied to the continuous production of 6.0 d.p.f. acrylic tow. Diethylenetriaminepentaacetic acid in amounts specified, based on polymer to be added, is added to the DMF as a 17.5% dispersion in DMF prior to addition of the polymer.

In this example, product yellowness changes are used as the basis for change in the amount of DTPA added. A substantial periol of time elapses between changes in solution and the recognition of the result in the product fiber. This lagtime is taken into account to avoid over-correction." The following directives are adopted:

(1) When one 3-point running average value of solution yellowness deviates more than 1.1 b from the aim, change DTPA by 100 ppm.

(2) When three consecutive 3-point running average values of solution yellowness deviate from 0.6 to 1.0 b from the aim, change DTPA by 50 ppm.

(3) When eight consecutive 3-point running average values of solution yellowness are on one side of but deviate from the aim by less than 0.6 b, change DTPA by 50 ppm.

In all cases, high yellowness calls for an increase in DTPA, and low yellowness calls for a decrease in DTPA. It is further directed for this exampe that a maximum of ppm. of DTPA may be used. By 3-point running average is meant that each value recorded is the average of three successive determinations, the latest result being averaged with the two values just preceding it.

It has been found that solution color correlates well with final product color if all process aspects other than solution color are precisely maintained constant. While for any short period of time such precise control may be maintained, it has been found that provision must be made for compensating adventitious variations in other conditions which will affect this correlation. The following empirically derived relationship provides for a running adjustment in solution yellowness aim:

This equation states that the aim solution yellowness (SY) for the ensuing period is calculated as that experienced for the previous period less twice the difierence between the product yellowness (PY) observed during the previous eriod and the product yellowness aim.

Tables 2 and 3 are records of two periods of continuous spinning of 6.0 d.p.f. acrylic tow using the present discovery and will illustrate the utility of the novel process of this invention. The product yellowness aim in these cases is 2.0.

The method of yellowness regulation employed in this example is better understood by considering the times when data become available. Reference is made to the first 5 days of test, summarized in Table 2, as an illustration.

The six 3-point running average values of solution b listed opposite Day of Test 1 are available for averaging by about 6 a.m. of that day. Due to the lagtime, however, these values are pertinent to product yellowness values appearing on the third day of test. The product color average for that day is calculated about noon, and the two values, solution color 5.7 and product yellowness 1.9, are employed to calculate a new solution color aim (5.9) according to the preceding formula. It will be noted that this aim is higher than at least eight 3-point running average solution [1 values reading backwards from the latest value available at that time (4.8 obtained at 12 n. on Day of Test 3). No DTPA was being used at that time, however, so no change is possible under the operating directives established.

On the fourth day of test, a new solution color aim, 5.0, is available based on the product color available about noon and the average solution colors of the second day of test. It will be noted that the four latest solution color b values at that time are above the aim. By approximately 6 a.m. that day, four additional values have been accumulated which also are above the aim. Proper adherence to procedure would have led to a change (to add 50 ppm. DTPA) at 8 a.m. on the fifth day of test. The addition was not begun, however, until about 4 pm. That was late, but otherwise in accordance with the operating instructions. In this general manner the data for the remaining 26 days of operation (Tables 2 and 3) were obtained and employed in accordance with the present discovery.

Despite the variations from proper procedure as noted under Remarks in Table 2 and 3, study of the product color data show satisfactory control. These results are particularly significant if it is realized that the changes made to bring about a product color of a particular value, are made in point of time about two days in advance of the existence of the product in form suitable to determine its color. Hence the method of the invention is of effective control in continuous operations.

As noted above citric acid can be used in place of the DTPA in like manner with similar results and this is shown in the following example.

EXAMPLE 3 TABLE 4 Additive None 50 p.p.m. DTPA 50 ppm. citric acid 4.8 4.2 4.2 1.8 1.5 1.8 2.76 2.88 2. 66 Elongation, perce 30.9 31.6 32. 5

B. In a further test of the effectiveness of citric acid in reduction of rate of yellowness development several solutions are prepared in the laboratory to contain 10% by weight of a polymer similar to that employed in Example 1. The DMF employed as solvent in each case is representative of one of four lots known to have differing propensities for yellowing polymer dissolved and heated therein. Before addition of the polymer, the amount of citric acid indicated in Table 5 is added to the solvent. The citric acid added to the solvent is based on the weight of polymer to be added. No delusterant is added.

The solutions prepared are stored for three hours at 65 C., which heat treatment has been found to approximate the amount of thermal discoloration reached in a commercial spinning process. The solutions are poured into a spectrophotometer cell which provides a 1-cm. thickness of solution in the path of the beam and the absorbance is measure at 345 my using pure solvent as a standard. The results are tabulated in Table 5. It will be noted that a leveling effect is attained, the larger reductions generally occurring with those lots of solvent which have the greater tendency to promote yellowness in the polymer.

TABLE 5 DMF Lot N o. Citric Acid, Absorbance, Approx. Final p.p.m. 345 m Product [1" It will be readily apparent from the foregoing examples that the broadest utility of the present invention is realized by determining the final product-color in advance of spinning. By utilizing the process of this invention, corrections are made based on the yellowness of the spinning solution, and thus the yellowness of the resulting fiber is maintained at a predetermined, more-uniform level. As previously indicated, a useful prediction of final product color can be made by determining the whiteness of the solution removed from the delivery system in advance of, but adjacent to, the spinning head. The statistical data thus obtained are utilized in determining routine operating procedures to be applied to specific operating conditions. While direct monitoring of the supply of solution passing through the delivery system is preferred, it will be apparent that the advantages of this invention may be obtained by utilizing similar conditions and equipment in laboratory apparatus to estimate the color of the solution as samples from the delivery system. Thus, a change which affects the level of whiteness can be predicted and compensated for before it is seriously apparent in the final product.

The process of this invention is, of course, not limited to utilizing solutions prepared from the polymer specifically described in the examples, but is equally applicable to other polymers containing at least combined acrylonit-rile in the polymer chain. Copolymers containing up to 15% of monomers of monoethylenically unsaturated copolymerizable monomers such as those described in US. 2,436,926 and US. 2,743,944 are suitable. Among those monomers are methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, 2-nitro-2-methyl propyl methacrylate, methoxyethyl methacrylate, chloroethyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, dimethyl aminoethyl methacrylate, and the corresponding esters of acrylic or alpha-chloroacrylic acids; acryland methacryl-amides or monoalkyl substitution products thereof; unsaturated ketones such as methyl vinyl ketone, phenyl vinyl ketone, and methyl isopropenyl ketone, vinylidene chloride, vinyl chloride, vinyl fluoride, vinyl carboxylates such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinyl thiolacetate, and vinyl stearate, esters of fumaric maleic, citraconic, and mesaconic acids, N- alkyl maleimides; N-vinyl carbazole, N-vinyl succ-inirnide, N-vinyl phthalimide, vinyl esters, mono-olefins, or substitution products thereof such as styrene, furyl ethylene, ethylene, and isobutylene may be used. In addition, the copolymers may contain from about 0.1% to about 10% of a copolymerizable monomer having sulfonic acid or sulfonate salt groups such as allyloxyethylsulfonic acid, allylthiopropanolsulfonic acid, vinyldichlorobenzenesulfonic acid, naphthylethylene sulfonic acid, methyl styrenesulfonic acid, as well as disulfonic and amino sulfonic acids.

The concentration of the polymer in the spinning solution should be between about 25% and 40%, and the solution should have a viscosity within the range of about 15 to 750 poises at the temperature of spinning with viscosities between about 50 and about 200 poises being preferred. Spinning of the polymers to form fibers may be accomplished using known dryand wet-spinning procedures.

In preparing the polymers and spinning solutions, various additives such as flame retardants, pigments, antistatic agents and spinning adjuvants may be included. The adjuvants, such as flame retardants, may be included in amounts up to about 10% by weight of the polymer without influencing adversely the degree of whiteness regulation afforded by this invention.

It will be appreciated that changes from the details given can be made in this invention without departing from its scope.

What is claimed is:

1. In the continuous production of acrylic polymer filaments in which acrylic polymer is dissolved in a solvent to provide a spinning solution and the resulting spinning solution is extruded in a spinning zone to form acrylic filaments which are processed to produce an acrylic fiber form and the color of the filaments determined, that method of adjusting the color of the acrylic fiber being produced comprisingsa-mpling spinning solution as it is advanced to the spinning zone and analyzing its color, and adding to the solvent to make additional spinning solution prior to the addition thereof to the previously formed spinning solution, an effective amount of diethylenetriaminepentaacetic acid to reduce the coloration of spinning solution produced thereby to a level to produce fibers of satisfactory color.

2. The process of claim 1 in which the acid is added in an amount of 25 to 800 parts per million based on polymer to be added.

3. The process of claim 2 in which the polymer comprises at least 85% acrylonitrile and up to 15% of a monoethylenically unsaturated monomer copolymerizable with acrylonitrile and the solvent is N,N-dimethylformamide.

4. The process of claim 1 further comprising analyz- References Cited UNITED STATES PATENTS 2,502,030 3/1950 Scheiderbauer 26029.1 2,878,206 3/1959 Holmes et al 260-32.6 3,150,160 9/1964 Dexter 260-439 MORRIS LIEBMAN, Primary Examiner.

H. S. KAPLAN, J. A. GAZEWOOD,

Assistant Examiners.

Claims (1)

1. IN THE CONTINUOUS PRODUCTION OF ACRYLIC POLYMER FILAMENTS IN WHICH ACRYLIC POLYMER IS DOSSOLVED IN A SOLVENT TO PROVIDE A SPINNING SOLUTION AND THE RESULTING SPINNING SOLUTIO IS EXTRUDED IN A SPINNING ZONE TO FORM ACRYLIC FILAMENTS WHICH ARE PROCESSED TO PRODUCE AN ACRYLIC FIBER FORM AND THE COLOR OF THE FILAMENTS DETERMINED, THAT METHOD OF ADJUSTING THE COLOR OF THE ACRYLIC FIBER BEING PRODUCED COMPRISING SAMPLING SPINNING SOLUTION AS IT IS ADVANCED TO THE SPINNING ZONE AND ANALYZING ITS COLOR, AND ADDING TO THE SOLVENT TO MAKE ADDITIONAL SPINNING SOLUTION PRIOR TO THE ADDITION THEREOF TO THE PREVIOUSLY FORMED SPINNIG SOLUTION, AN EFFECTIVE AMOUNT OF DITHYLENETRIAMINEPENTAACETIC ACID TO REDUCE THE COLORATION OF SPINNING SOLUTION PRODUCED THEREBY TO A LEVEL TO PRODUCE FIBERS OF SATISFACTORY COLOR.