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Go to Advanced Search    Home    |    Search Patents    |    Data Services    |    Help Title:Process for reduction of lignin color Document Type and Number:United States Patent 4184845 Link to this page:http://www.freepatentsonline.com/4184845.html Abstract:Disclosed herein is a two-step process for reducing the color of sulfonated alkali lignins and lignosulfonates by at least 80% which comprises, blocking at least 90% of the free-phenolic hydroxyl groups in the lignin and then subjecting the blocked lignins to oxidative action by air, molecular oxygen or hydrogen peroxide. The thus treated lignins are useful as dispersants for disperse dyes and vat dyes.

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Inventors:Lin, Stephen Y. (Mt. Pleasant, SC) Application Number:05/569560 Filing Date:04/18/1975 Publication Date:01/22/1980

View Patent Images:Images are available in PDF form when logged in. To view PDFs, Login  or  Create Account (Free!) Referenced by:View patents that cite this patent Export Citation:Click for automatic bibliography generation Assignee:WESTVACO CORP (US) Primary Class:8/636 Other Classes:530/500, 530/504, 8/561, 8/650, 530/502 International Classes:C08H5/02; C09B67/46; D06P1/50; C08H5/00; C09B67/00; D06P1/44; C07G1/00; C09B9/00 Field of Search:8/89, 8/34, 8/83, 8/89R, 8/93, 260/124A, 260/124R, 260/124 US Patent References:3672817 June, 1972 Falkehag 8/793763139 October, 1973 Falkehag 260/124R3769272 October, 1973 Hintz 260/124R

3865803February, 1975

Falkehag 260/124A Modified lignin surfactants

4001202 January, 1977Dilling et al.

8/34Process for making sulfonated lignin surfactants

Other References:Imsgard et al., Tappi, 1971, 54 (No. 10), pp. 1680-1684. Brauns, F. E., "The Chemistry of Lignin", (Academic Press, New York-1952), pp. 303, 538, 541, 549. Brauns, F. E. and Brauns, D. A., "The Chemistry of Lignin-Supplement Volume", (Academic Press, New York, 1960), pp. 507-510, 513-591. Primary Examiner:Clingman, Lionel A. Attorney, Agent or Firm:Lipscomb III, Ernest B. Mcdaniel, Terry B. Claims:What is claimed is:

1. A two-step process for producing light colored lignin which comprises;

(a) reacting a sulfonated alkali lignin or lignosulfonate with from 1 to 20 moles of a member selected from the group consisting of alkylene oxides, halogen-containing alkyl alcohol, alkyl sulfonate and alkylene carbonate at a temperature from 0° C. to 200° C. until at least 90% of the phenolic hydroxyl groups are blocked and thereafter,

(b) treating said blocked lignin with an oxidant until the original color of said lignin is made lighter by at least 80%.

2. The process of claim 1 wherein said lignin is a member of the group consisting of sulfonated kraft lignin, sulfonated soda lignin and sulfite lignin.

3. The process of claim 1 wherein said blocking agent is a member of the group consisting of propylene oxide, dimethyl sulfate and chloroethanol.

4. The process of claim 1 wherein said oxidant is a member of the group consisting of air and molecular oxygen.

5. The process of claim 4 wherein said treating is carried out at a temperature from 50° C. to 150° C. at gas pressure of 50 to 200 p.s.i. for 5 minutes to 2 hours.

6. The process of claim 1 wherein said oxidant is hydrogen peroxide in amounts of 1 to 6 moles per 1,000 grams of blocked lignin and oxidizing is carried out at a pH from 7 to 11.

7. A dyestuff composition comprising a disperse or vat dye cake and from 1% to 75% by weight of said dye cake is the product produced by the process of claim 1.

Description:

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to reducing the color of lignin. More particularly, this invention relates to a two-step process for reducing the color of lignin by first blocking the phenolic hydroxyl and then oxidizing the blocked lignin.

Lignin in wood is almost colorless. Lignin isolation procedures and pulping processes invariably introduce a variety of chromophores into the structure and render the isolated lignins strongly colored. Industrial lignins (such as sulfonated alkali lignins from the kraft and soda pulping processes and lignosulfonates from the sulfite pulping process) are colored to different degrees depending on the pulping conditions and the type of pulping process employed for delignification. The drastic conditions of a pulping process, e.g., high temperature and strong caustic in combination with atmospheric oxygen, produce lignin so intensively darkened that their uses in many application areas become objectionable because of the color.

The problem of lignin color is quite predominate in application areas where lignin is absorbed onto a substrate. Thus, for example, if lignin is used as a dispersant for dyestuff, it is usually ball-milled with a dye cake and the mixture then used for dyeing natural or synthetic fibers. One of the major disadvantages and undesirable effects of lignosulfonates and sulfonated alkali lignins as dyestuff dispersants is the staining of fabric fibers of which the degree is greatly dependent on the color of lignin. This so-called fiber staining caused by lignin tends to distort the authentic color of dye on the fabric.

The causes for the dark brown color of industrial lignins and the mechanisms for the formation of chromophores during the pulping processes are not completely known, although numerous suggestions have been made previously. For example, Gierer in Sv. Papperstidn 73 (1970) p. 561 proposed o,p'-stilbenequinone, p,p'-stilbenequinone, 1,4-bis-(p-hydroxyphenyl)-buta-1,3-diene, o-benzoquinone and methylene quinone as possible chromophoric structures. Kringstad et al. in TAPPI 54 (1971) p. 1680 estimated the amount of o-quinonoid structures in spruce milled-wood lignin to be about 0.7% and stated that the amount of quinonoid structures can account for as much as 35-60% of the light absorption of the lignin at 457 nm. The majority of chromophoric structures in alkali lignins and lignosulfonates appear to be some sort of conjugated systems involving quinonoid and side-chain double bonds.

(2) The Prior Art

The aforementioned conjugated systems may be cleaved by some oxidative processes or saturated by reductive processes to achieve some reduction of lignin color. Reductive processes change quinones to colorless catecholic structures which, however, are not stable under the influence of oxygen (air) and sunlight.

On the other hand, oxidative processes convert quinonoid structures to colorless aliphatic acids. The oxidative process also causes cleavage of unsaturated carbon-carbon bonds in the propanoid side chains of lignin molecules. By doing so, some extensively conjugated systems (chromophores) are destroyed, resulting in some reduction of lignin color. An advantage of the oxidative process is the fact that colorless end-products in oxidation reactions are stable and chromophores are not reformed thereof. However, uncontrolled oxidative conditions invite random destruction of lignin aromaticity and concurrently give rise to the formation of color bodies. For example, colored quinonoid moieties are produced in lignin by the following oxidative demethylation pathway: ##STR1##

It is also known that the color of lignin may be lightened to some degree by blocking the free-phenolic of hydroxyl in lignin. Several blocking methods have been set forth, such as in U.S. Pat. No. 3,672,817 wherein the lignin color was reduced as much as 44% by blocking the phenolic hydroxyl with an alkylene oxide or a halogen-containing alkyl alcohol. In U.S. Pat. No. 3,763,139, lignin color was reduced by blocking the phenolic hydroxyl with reagents, such as chloromethesulfonate, chloromethane phosphonate, 2-chloroethanol and the like. In U.S. Pat. No. 3,769,272, lignin color was reduced by blocking with 3-chloro-2-hydroxypropane-1-sulfonate. And in U.S. Pat. No. 3,865,803,

the phenolic hydroxyl was blocked with an agent of the type X(CH 2 ) n Y, wherein X is a halogen, an activated double bond, an epoxide ring or a halohydrin, Y is a sulfonate, phosphonate, hydroxyl, sulfide or a secondary or tertiary amine and n is an integer from 1 to 5.

Although each of the described methods for some reduction of the color of an alkali lignin or lignosulfonate, none have reduced the color to a sufficiently desirable extent or to the extent of the process of this invention.

It is thus the general object of this invention to provide a two-step process whereby the color of sulfonated alkali lignins and lignosulfonates are drastically reduced.

Another object of this invention is to provide light colored lignin dyestuff dispersants which are practically non-staining on fabric.

Other objects, features and advantages of this invention will be seen in the following detailed description of the invention.

SUMMARY OF THE INVENTION

It has been found that the extent of lignin color by the oxidative process may be maximized if the oxidative discoloration of lignin is minimized through first blocking of phenolic groups in lignin. Thus, the process of this invention comprises the steps of first treating lignins (sulfonated alkali lignins and lignosulfonates) with blocking agents to achieve at least a degree of blocking of 90%, and then oxidizing the blocked lignin with air, molecular oxygen or hydrogen peroxide. The color of lignin was reduced by over 80%. The light colored sulfonated alkali lignins and lignosulfonates are useful as dispersants for dyestuffs having as low as 20% of the fiber staining capacity of the prior art products.

DETAILED DESCRIPTION OF THE INVENTION

The lignins employed in the process of this invention include alkali lignins from the kraft pulping process and lignins derived from other alkaline processes, such as the soda or modified soda processes, sulfonated lignins, such as sulfite lignins from acid and neutral processes and sulfonated alkali lignins. One of the main sources of lignin is the residual pulping liquors of the pulp industry where lignocellulosic materials, such as wood, straw, corn stalks, bagasse and the like, are processed to separate the cellulose or pulp from the lignin. For example, the black liquor obtained from the kraft, soda and other alkali processes is not recovered as a sulfonated product but may easily be sulfonated, if desired, by reacting the product with a bisulfite or sulfite. In the sulfite pulping process, the lignocellulosic material is digested with a bisulfite or sulfite to obtain a sulfonated residual pulping liquor wherein the sulfonated lignin is dissolved. Likewise, lignin known as "hydrolysis lignin" obtained from the hydrolysis of lignocellulosic materials in manufacturing wood sugars, or "hydrotropic lignins" derived from hydrotropic pulping processes may be sulfonated and used.

By the term "sulfonated lignin," it is meant any lignin containing at least an effective amount of sulfonate groups to solubilize the lignin in water at neutral or acid conditions. Any of the sulfonated lignins may contain up to one-half of the other materials, such as carbohydrates, phenols and other organic and inorganic compounds. The presence of these other materials results in larger consumption of the blocking agents used to form the adduct; therefore, some purification of the lignin starting materials is often desirable. The non-sulfonated lignin materials may be removed by various known methods. Since the chemical structure of lignin varies according to its source and treatment, the following symbol containing guaiacyl or syringyl units will be used herein to represent both alkali lignin and sulfonated lignin from whatever source. The degree of sulfonation present in the lignin is not a controlling factor in making the blocked lignin but may be used to tailor the lignin to have desired characteristics.

The main technical problem in reducing lignin color by an oxidative process is how to minimize the concurrent formation of chromophores due to demethylation of lignin. It is widely acknowledged that the oxidative demethylation, such as in photochemical discoloration of lignin or in an alkaline-oxygen process, requires free-phenolic groups for the initiation of phenoxy radicals which in turn reacts with hydroxy radicals to form catecholic intermediates. The catecholic structures are then oxidized to colored quinonoid moieties as follows: ##STR2##

In the above sequence of reactions leading to the formation of colored bodies, it has been found that, in order to minimize the formation of phenoxy radicals, the free-phenolic groups in lignin have to be "blocked." Blocking reactions include those reactions which afford an adduct of phenolic anion and an electrophile, thus rendering the phenolic groups "blocked" and nonionizable in alkaline media.

Some useful blocking reactions are mentioned in U.S. Pat. Nos. 3,672,817, 3,763,139, 3,769,272 and 3,865,803. These patents specify the use of alkylene oxide, halogen-containing alkyl alcohol, halogen-containing alkyl sulfonate or alkylene carbonate and others as the blocking reagents; and these patents are incorporated herein by reference. Other phenol blocking reagents which perform equally well include, typical etherization reagents such as diazomethane, dimethyl sulfate and alkyl iodide, and esterization reagents such as benzoyl chloride and acetic anhydride. Although these blocking agents dramatically reduce the color of lignin, even the best performing blocking agent can only reduce the color about 50%.

In the first step of the process, the lignin is reacted with from about 1 to 20 moles, preferably about 2 to 10 moles, per 1,000 grams of lignin of the blocking reagent. The blocking step is made by simply dissolving the lignin in water and intermixing a given amount of blocking agent and reacting at a temperature between about 0° C. and 200° C. until at least 90% of the phenolic hydroxyl is blocked. A catalyst, such as sodium hydroxide may be used if desired but is not necessary. The preferred temperature will depend upon the particular blocking agent used. For example, with chloromethane sulfonate, the reaction takes place best at temperatures between 160° C. and 180° C. and with propylene oxide a temperature between about 90° C. and 110° C. appears best.

The second step in the process of reducing lignin color involves oxidation of a blocked lignin with oxidants chosen from the group of air, oxygen and hydrogen peroxide. To achieve the best color reduction, the blocked lignin should be subjected to the oxidation at an oxygen or air pressure of 50 to 200 p.s.i., oxidation temperature of 50° C. to 150° C. and duration of oxidation ranging from 5 minutes to 2 hours. The preferred oxidation parameters, however, are 100 p.s.i., 90° C. and 0.5 hours. The initial pH of blocked lignin solution should be from approximately 10 to 12.5, but preferably 11.0.

Alternatively, in the oxidation of lignin with hydrogen peroxide, the lignin solution should be adjusted to pH 7.0 to 11.0, but the best results are obtained at pH 9.0. The amount of hydrogen peroxide used ranges from 1 to 6 moles per 1,000 grams of blocked lignin.

In all cases of oxidations, whether by air, molecular oxygen or by hydrogen peroxide, a good mixing of the blocked-lignin solution is essential to achieving the best results. Localization of the oxidants in the blocked-lignin solution, particularly important in the case of reactive hydrogen peroxide, should be avoided or only a portion of the lignin solution is subjected to extensive oxidation (due to a large oxidant/lignin ratio); whereas, the other portion does not have the opportunity to be in contact with the oxidant. This will certainly result in non-uniform lignin products and, moreover, the color reduction is not maximized with the amount of oxidant used. By "non-uniform" it is meant that a part of the lignin sample is oxidized more extensively than the other.

Under certain optimal oxidation conditions, admittedly the color of an "unblocked" lignin sample can also be reduced by the oxidative method; but the magnitude of color reduction is quite limited (usually less than 30% when lignin is oxidized in an aqueous solution). Furthermore, "unblocked" lignins are extremely sensitive to the variation of temperature and pH of the lignin solutions during oxidation. Again, the reason for the difference (between "blocked" and "unblocked" lignins) is that "unblocked" lignin is oxidized to chromophores or colorless products; the rate of formation for either of the two types of structures varies depending on the oxidation conditions. In the case of "blocked" lignin, the formation of color bodies is prevented or minimized by blocking of phenolic groups; whereas, chromophores are still subjected to destruction by oxidants. Because of the lower oxidative potential of quinonoid or other chromophores in comparison with quaiacyl or syringyl units (lignin building units), mild oxidation conditions are capable of destroying the color bodies; but severe conditions are usually required to degrade the lignin building units.

The practice of this invention may be better understood in the following detailed examples.

EXAMPLE 1

This example illustrates the process of the invention by showing the effect of blocking and oxidation on color compared to non-blocked and oxidized lignins. One hundred grams of a sulfonated kraft lignin, REAX® 80C from Westvaco Corporation, were

dissolved in 400 grams of water and adjusted to pH 10.5 with 50% NaOH. The mixture was placed in a 2-liter autoclave with 11.6 grams of propylene oxide (or 2 moles per 1,000 g. lignin). The temperature was increased to 100° C.; and after 1 hour, the pH of the solution became 12.0. The solution was taken out of the autoclave and adjusted to pH 10.5 with conc. HCl. More propylene oxide (11.6 g.) was added and the mixture was cooked as before at 100° C. for 1 hour. This procedure was repeated until over 90% of the free-phenolic groups are blocked. A number of propylene oxide blocked lignins were made and the light absorption at 500 nm. measured.

The blocked lignins were then oxidized with oxygen in the following manner: 20 grams of blocked lignin were dissolved in approximately 400 grams of water and adjusted to pH 12.5 with 50% NaOH. The solution was placed in a 2-liter autoclave into which was then applied an oxygen pressure of 200 p.s.i. The reactor and lignin solution were heated at 140° C. for 1 hour. The blocked-oxidized product was spray dried and the light absorption again measured. The light absorption of a lignin sample was corrected for non-lignin contaminants and expressed as absorbence in liter per centimeter per gram (or D 500 ). The results are shown in Table I.

TABLE I ______________________________________ EFFECTS OF DEGREE OF BLOCKING AND OXIDATION ON COLOR Treatment of

Sample Sulfonated % Phenolic OH 1 %, No. Kraft Lignin Present D 500 D 500

______________________________________

-- Untreated 100 0.270 100

A-1 Blocked only

53 0.250 93

A-2 Oxidized and

-- 0.120 44

blocked

B-1 Blocked only

24 0.204 76

B-2 Oxidized and

-- 0.108 40

blocked

C-1 Blocked only

6 0.197 73

C-2 Oxidized and

nil 0.05 18

blocked

______________________________________

Note:- 1 % phenolic OH was determined by alkaline ionization spectrometric method, and assumed 100 for starting lignin.

These results show that when the phenolic hydroxyl is at least 90% blocked, i.e., sample C-1, upon subsequent oxidation at least 80% of the color is eliminated, i.e., sample C-2.

EXAMPLE 2

The products of Example 1 were tested for fiber staining. The test was as follows and the results are shown in Table II. The test for determining the extent of fiber staining caused by lignosulfonate dyestuff dispersants was to weigh out 20 grams of the lignin product and dissolve in 500 ml. of tap water, adjust the pH to 7.0 with 0.5 N HCl, and heat the solution to boiling temperature. Five swatches of cotton cloth were added to the boiling solution and staining begun for 10 minutes at a stirring rate of about 100 RPM. At the end of the staining period, the lignin solution was poured off and the swatches were squeezed out by hand and placed in a beaker. The swatches were rinsed with cold tap water for 5 minutes and dried in a home dryer for 30 minutes. For a blank experiment, no lignin was added in the staining cycle. The reflectance of the swatches was measured on a brightness meter and the staining index (I) of the lignin product calculated by the following formula: I(%)=(R o -R i )/R o where R o =reflectance of blank swatches; and R i =reflectance of stained swatches.

TABLE II ______________________________________

EFFECTS OF BLOCKING AND OXIDATION ON FIBER STAINING OF LIGNIN Staining Sample No. Index (I) from Example 1 % % I

______________________________________

18.6 100

A-1 16.1 87

A-2 8.4 45

B-1 12.0 64

B-2 6.7 36

C-1 11.4 61

C-2 3.9 21

______________________________________

These results show that the blocked and subsequently oxidized lignins have reduced fiber staining.

EXAMPLE 3

This example illustrates the effect of oxidation temperature on the color of "unblocked" lignin. A highly sulfonated kraft lignin, REAX® 85A from Westvaco Corporation, was oxidized with oxygen (200 p.s.i.) at temperatures varying from 30° C. to 170° C. for 1 hour. The pH of the lignin solution was adjusted to 10.0 before oxidation. The color was measured at 500 nm. and expressed as absorbence at a lignin concentration of one gram per liter and the results shown in Table III.

TABLE III ______________________________________

EFFECT OF OXIDATION TEMPERATURE ON COLOR OF "UNBLOCKED" LIGNIN Oxidation Color Values Color Sample No. Temperature D 500 Reduction 1 , %

______________________________________

Untreated

-- 0.364 0

Oxidized

1 30° C.

0.360 +1.1

2 50° C.

0.323 +11.2

3 70° C.

0.312 +14.3

4 90° C.

0.293 +19.5

5 110° C.

0.301 +17.3

6 140° C.

0.467 -28.4

7 170° C.

0.712 -95.6

______________________________________

Note:- 1 + = color reduction; - = color increase.

The results indicate that: (1) a color reduction is achieved by oxidation of "unblocked" lignin at temperatures below 110° C., with 90° C. being the optimal temperature, and (2) oxidation temperature above 140° C. greatly accelerates the formation of chromophores and the oxidized lignosulfonate becomes darker than before oxidation. On the contrary, the color of "blocked" lignin is not sensitive to the oxidation temperature. For example, a "blocked" lignosulfonate, after oxidation at 70° C. and 140° C. gives color values (D 500 ) of 0.120 and 0.114, respectively (before oxidation, D 500 =0.197). Moreover, no darkening effect has been experienced in the oxidation of "blocked" lignins.

EXAMPLE 4

This example illustrates blocking with another blocking agent, dimethyl sulfate, and oxidizing with air.

One hundred grams of a sulfonated kraft lignin were dissolved in 400 grams of water and adjusted to pH 11.0 with 50% NaOH in a 2-liter three-necked flask equipped with a mechanical stirrer, a thermometer and a 125 ml. dropping funnel. While the lignin solution was under stirring, 23.2 grams of dimethyl sulfate (2 moles per 1,000 g. lignin) were added dropwise and the temperatures maintained at approximately 50° C. When the addition was complete, the mixture was maintained at the temperature for 10 minutes. Then the pH of the mixture was readjusted to 11.0 with concentrated NaOH and 23.2 grams of dimethyl sulfate added as before. Stirring continued for 30 minutes. Repeat the addition of dimethyl sulfate until blocked lignins of desired phenolic content were

produced as determined by alkaline ionization spectra of the products. The end products were separated from inorganic by precipitation, and evaluated for their staining capacity and color values as in Example 1.

Oxidation of the blocked samples was carried out with air at 90° C. and a pH of 11.0 for 2 hours. The results of evaluation of the blocked and subsequently oxidized samples for color and fiber staining are shown in Table IV.

TABLE IV ________________________________________________________ __________________

EFFECTS OF BLOCKING AND OXIDATION ON COLOR AND FIBER STAINING OF LIGNIN Staining Sample Highly Sulfonated Index (I) No. Kraft Lignin % Phenolic

OH 1 D 500 % D 500 % % I ________________________________________________________ __________________

Untreated 100 0.270

100 18.6 100

A-1 Blocked 64 0.261

97 17.5 94

A-2 Oxidized and

-- 0.135

50 9.4 50

blocked

B-1 Blocked 28 0.212

78 14.0 75

B-2 Oxidized and

-- 0.109

40 7.6 41

blocked

C-1 Blocked 4 0.200

74 13.7 74

C-2 Oxidized and

-- 0.035

13 3.2 17

Blocked

________________________________________________________ __________________

Note:- 1 % phenolic OH was determined by alkaline ionization spectrometric method, and assumed 100 for starting lignin.

The results show that various blocking reagents and oxidants may be used.

EXAMPLE 5

The kraft sulfonated lignin prepared according to Example 1 [C-2] was evaluated as a dye dispersant using other tests.

Foaming Properties.--One gram of the dispersant was weighed out and dissolved in 100 ml. of tap water, adjusted to pH 9.5 or 7 with acetic acid and poured into a 250 ml. graduated cylinder; rapidly inverted 5 times and measured the height of the foam in ml. immediately after completing the inversion and measured again after 1 minute and 2 minutes had elapsed. If the foam disappeared within 1 minute, note the time at which all the foam vanished.

Diazo Dye Reduction.--Two Hundred Fifty milligrams of Disperse Brown 1 dye were dispersed in 200 ml. of distilled water. Ten grams of a modified sulfonated lignin dispersant were added. The mixture was thoroughly stirred and the pH adjusted to 6.0 with acetic acid. Five 4"×6" polyester-cotton blend (65/35) swatches were placed with the dye mixture in a 2-liter sealed Parr bomb and heated at 130° C. for 1.5 hours, including time-to-temperature of 25 minutes. At the end of heating, the bomb was cooled to room temperature, the contents poured off and the swatches were squeezed out by hand and placed in a beaker. The swatches were rinsed with cold running tap water for 5 minutes and dried in a home dryer for 30 minutes.

For a blank experiment, no lignin was added to the dyeing bath. The reflectance (R) of the swatches was measured on a brightness meter at 457 mm. The average reflectance of five swatches was accepted as the value for a lignin product, and used in calculation of the Kubelka-Munk number (k/s) by the following equation: k/s=(1-R) 2 /2R

where K=light absorption coefficient; and s=light scattering coefficient. The value, k/s, was used to estimate the percent diazo dye reduction according to the following formula: ##EQU1## where (k/s) i , (k/s) b and (k/s) o are the Kubelka-Munk numbers for fabric swatches after heating in a dye solution with lignin dispersants (i), without lignin (b) and undyed swatches, respectively. The results of foaming and diazo dye reduction experiments are presented in Table V.

Table V ________________________________________________________ __________________ FOAMING AND DIAZO DYE REDUCTION Foam Test, ml. of Foam 1 % Diazo Dye pH

7.0 pH 9.5 Lignin Product Reduction Init. 1 Min. 2 Min. Init. 1 Min. 2 Min. ________________________________________________________ __________________

Blank 0 -- -- -- -- --

Example 1 [C-2]

13 15(5)

0 0 8(5)

0 0

REAX 90 2

32 42 5 5 33 8 4

REAX 85A 2

91 60 30 12 28(10)

0 0

REAX 80C 2

87 80 12 8 33(8)

0 0

________________________________________________________ __________________

Notes:- 1 Numbers in parenthesis represent time in seconds required for the foam to disappear completely. 2 Westvaco lignosulfonate dispersants.

It can be seen from the data, the lignin product prepared according to Example 1 has the lowest fiber staining, diazo dye reduction and foaming tendencies compared with the existing commercial lignin dye dispersants.

EXAMPLE 6

To demonstrate the effect of color reduction on the fiber staining tendency of a sulfonated kraft lignin, REAX® 80C was blocked with propylene oxide to a degree of blocking of over 95%, then oxidized, according to Example 1, with various amounts of alkali in the lignin solution. After oxidation, the light absorption of the solution was measured at 500 nm. and the oxidized lignin evaluated for its fiber staining ability in the same manner as described previously. Again, the Kubelka-Munk number (k/s) was calculated from the reflectance value of stained fabric swatches and plotted against absorbence at 500 nm. (or D 500 ). Table VI shows the linear relationship between (k/s) and D 500 , indicating the sole dependence of degree of fiber staining on the color of oxidized blocked lignins.

TABLE VI ______________________________________

k/s D 500

______________________________________

0.018

0.021 0.05

0.028 0.08

0.028 0.08

0.030 0.11

0.045 0.2

0.046 0.2

______________________________________

While the invention has been described and illustrated herein by reference to various specific materials, procedures and examples, it is understood that the invention is not restricted to the particular materials, combinations of materials, and procedures selected for that purpose. Numerous variations of such details can be employed, as will be appreciated by those skilled in the art.

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Go to Advanced Search    Home    |    Search Patents    |    Data Services    |    Help Title:Amine modified sulfonated lignin for disperse dye Document Type and Number:United States Patent 5972047 Link to this page:http://www.freepatentsonline.com/5972047.html Abstract:Dyestuff compositions are provided which incorporate amine modified sulfonated lignins. The disclosed dyestuff compositions exhibit improved heat stability and, as a result of the higher activity of the amine modified sulfonated lignin, less dispersant is present in the exhaust liquor and waste treatment demands are thereby reduced. The presence of tertiary amine groups in sulfonated kraft, sulfomethylated kraft, and sulfite lignins provide dispersants with package dyeing heat stabilities significantly better than those of the unmodified lignins. The improved package dyeing grinding aid/dispersant of the invention is prepared by reacting sulfonate lignin with a secondary amine using formaldehyde and alkaline conditions.

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Inventors:Dilling, Peter (Mt. Pleasant, SC) Samaranayake, Gamini S. (Mt. Pleasant, SC) Waldrop, Staci L. (Charleston, SC) Application Number:09/037353 Filing Date:03/10/1998 Publication Date:10/26/1999 View Patent Images:Images are available in PDF form when logged in. To view PDFs, Login  or  Create Account (Free!) Referenced by:View patents that cite this patent Export Citation:Click for automatic bibliography generation Assignee:WESTVACO CORP (US) Primary Class:8/552 Other Classes:8/905, 8/557, 8/913, 8/662, 8/561, 8/912, 8/915 International Classes:C09B67/46; C09B67/00; D06P1/50 Field of Search:8/524, 8/552, 8/554, 8/905, 8/912, 8/557, 8/913, 8/662, 8/561 US Patent References:

2709696 May, 1955Weish et al.

260/124Reaction of unsulfonated lignin, formaldehyde and secondary amines and product

2863780December, 1958

Ball, Jr. 106/14 Inhibition of corrosion of iron in acids

4732572 March, 1988 Dilling 8/557 Amine salts of sulfomethylated lignin4764597 August, 1988 Dilling 530/501 Method for methylolation of lignin materials

Primary Examiner:Einsmann, Margaret Attorney, Agent or Firm:Mcdaniel, Terry B. Reece IV, Daniel B. Schmalz, Richard L. Claims:What is claimed is:

1. A dyestuff composition comprising a dyecake comprising a disperse dye and aminomethylated sulfonated lignin dispersant.

2. The dyestuff composition of claim 1 wherein the disperse dye is a member of the group consisting of azo dyes and anthraquinone dyes.

3. The dyestuff composition of claim 2 wherein the azo dyes are selected from the group consisting of C.I. Disperse Orange 30, C.I. Disperse Blue 79, and C.I. Disperse Red 167.

4. The dyestuff composition of claim 2 wherein the anthraquinone dyes are selected from the group consisting of C.I. Disperse Red 60 and C.I. Disperse Blue 60.

5. The dyestuff composition of claim 1 wherein the amine modified sulfonated lignin is the product of combining an amine and a sulfonated lignin, in the presence of an aldehyde.

6. The dyestuff composition of claim 5 wherein the sulfonated lignin is selected from the group of lignins from the alkali pulping processes which have been subsequently sulfonated and lignosulfonates from the sulfite pulping process.

7. The dyestuff composition of claim 6 wherein the sulfonated alkali lignins are selected from sulfonated and sulfomethylated kraft lignins.

8. The dyestuff composition of claim 5 wherein the amine is a secondary amine.

9. The dyestuff composition of claim 8 wherein the amine is selected from the group consisting of dimethylamine, morpholine, imidazole, sarcosine, pyrrolidine, diethylamine, dibutylamine, diethanolamine, diisopropanolamine, and 2-methylimidazole.

10. The dyestuff composition of claim 5 wherein the aldehyde is formaldehyde.

11. The dyestuff composition of claim 1 wherein the amino methylated sulfonated lignin dispersant exhibits an improved activity over the sulfonated lignin not aminomethylated permitting a reduced dosage to achieve the same level of activity as the dosage required of unmodified sulfonated lignin.

Description:

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to disperse dye compositions incorporating modified sulfonated lignins (lignosulfonates). More particularly, this invention relates to dispersed dye compositions prepared with amine modified sulfonated lignins as dispersants or as grinding aids. Most particularly, this invention is related to dispersed dye compositions of improved heat stability for use primarily in package dyeing.

2. Description of Related Art (Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98)

Dyestuff compositions generally comprise a dye cake, itself comprising a dye and a dispersant and/or diluent. These dyestuff compositions are widely used to color both natural and synthetic fibers. In the dyestuff composition, the dispersant serves three basic functions: (1) it assists in reducing the dye particle to a fine size; (2) it maintains a dispersing medium; and (3) it is used as a diluent.

Dye dispersants are generally one of two major types: (1) sulfonated lignins from the wood pulping industry (via either the sulfite pulping process or the kraft pulping process) where lignocellulosic materials, such as wood, straw, corn stalks, bagasse, and the like, are processed to separate the cellulose or pulp from the lignin or (2) naphthalene sulfonates from the petroleum industry. The present invention relates to sulfonated lignin dye dispersants. More particularly, the instant invention relates to amine modified sulfonated lignin in combination with disperse dyes. Disperse dye compositions employing sulfonated lignins as dispersants is well known.

Sulfite (or bisulfite) wood pulping process lignin is recovered from the spent pulping liquor, known as "black liquor," as lignosulfonates; whereas, kraft (or sulfate) wood pulping process lignin is recovered from the black liquor as the sodium salt of lignin (products marketed under the Indulin® mark by Westvaco Corporation). This recovered sulfate lignin is subjected to sulfonation or sulfomethylation for use as dye dispersants, such as products marketed under the Polyfon®, Kraftsperse®, and Reax® marks by Westvaco Corporation. As used herein, the term "sulfonated lignins" may be used generally to refer to lignosulfonates, sulfonated lignins, or sulfomethylated lignins as before described.

The advantages of employing sulfonated lignins as dispersants in dyestuff compositions are (1) availability and (2) unique physical properties, which include good compatibility to many dye systems and outstanding dispersant characteristics at ambient and elevated temperatures. There are, however, a number of disadvantages in employing lignins as

dispersants, whether they are sulfite lignosulfonates or kraft-derived sulfonated lignins. These negative factors include fiber staining (as lignin in dry powder form is brown in color) and heat stability (as the dyeing process is conducted at elevated temperatures) of the lignins employed. These adverse properties are troublesome to dyers and many attempts have been made to overcome these disadvantages.

A number of technological developments have resulted in new methods and processes to modify sulfonated lignins to reduce the negative aspects of employing such materials as dye dispersants without simultaneously causing any major adverse effects upon those properties which render sulfonated lignins desirable as dyestuff dispersants. U.S. Pat. No. 4,001,202 describes a process for preparing a sulfonated lignin with improved fiber staining properties useful as a dye dispersant by reacting lignin with an epihalohydrin. Also, U.S. Pat. No. 4,338,091 teaches reacting a modified lignin with sodium sulfite and an aldehyde; the lignin having been modified by a pretreatment with sodium dithionate.

Additional examples of reacting or modifying lignins to make them more suitable as dye dispersants include U.S. Pat. Nos. 4,184,845, 4,131,564, 3,156,520, 3,094,515, 3,726,850, 2,680,113, and 3,769,272. The art cited is meant to show the state of the art and is not intended to be all inclusive of lignin modifications.

Although the methods for treating and preparing sulfonated lignins described above offer some advantage during dyeing, none has produced a product possessing the improvements obtained by the improved products made according to the claimed process.

During the dyeing process, only the dye exhausts itself onto the fiber where it becomes an intimate part of the fiber. The lignin and other dyeing adjuvants, which are left in the exhaust liquor, need to be subsequently treated in primary and secondary waste treatment facilities. Although lignin is a natural material, lignosulfonates are considered relatively poorly biodegradable (albeit more biodegradable than synthetic dispersants from the petroleum industry), and they are often viewed as environmentally unfriendly as they often exceed the capacity of dye houses or municipality waste water treatment facilities.

One solution to this problem would be to increase the dye dispersant activity of lignin dispersants. (The term "activity" refers to the relative amount of dispersant required to function effectively. The less dispersant required to perform, the higher its activity; whereas the more dispersant required to perform, the lower is its activity.) Such enhanced activity would permit reduced dosages required for dyeing and thereby lessen the existing waste water treatment problems.

Therefore, it is the general object of this invention to provide sulfonated lignins of improved properties to enhance their usefulness as dye dispersants.

A particular object of this invention is to increase the activity of sulfonated lignin dispersants.

Another object of this invention is to provide a process for improving the heat stability of dye formulations including sulfonated lignins.

Other objects, features and advantages of this invention will be seen in the following detailed description of the invention.

SUMMARY OF THE INVENTION

The above stated objects of the invention are achieved in the provision of dyestuff compositions incorporating amine modified sulfonated lignins. The invention dyestuff compositions exhibit improved heat stability and, as a result of the higher activity of the amine modified sulfonated lignin, less dispersant is present in the exhaust liquor and waste treatment demands are thereby reduced. The presence of tertiary amine moieties in sulfonated kraft, sulfomethylated kraft, and sulfite lignins provides dispersants with package dyeing heat stabilities significantly better than those of the unmodified sulfonated lignins.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Sulfonated lignins are highly negatively charged polyelectrolytes, due to the presence of fully ionizable sulfonate groups that are pH-independent as to its ionization. During grinding of dispersed dyes, a charged dispersant can prevent the re-agglomeration of finely ground particles, and also, like-charge repulsion prevents the cohesive interaction of dispersant molecules and keeps the viscosity of the solution low, aiding grinding. On the other hand, dyeing of polyester requires low pH conditions of approximately pH 4.5, where sulfonated lignins still exist as a highly negatively charged species, which in some instances does not provide adequate protection for dye particles under high temperature and high shear conditions in package dyeing. The situation requires an enhanced surface coverage on dye particles by the dispersant.

It is envisioned that an auxiliary group consisting of a tertiary amine attached to the sulfonated lignin that can exist in cationic form under dyeing conditions (i.e., acidic pH), could provide a neutralization mechanism for neighboring sulfonated lignin molecules on the dye surface, thereby increasing the surface coverage. The presence of tertiary amine groups would not affect the negative charge at grinding pH (i.e., alkaline), because the amines exist in the uncharged form. This, would provide a single dispersant for both formulation and dyeing. Such would greatly simplify the whole dyeing process.

Carefully selecting an amine of a proper acidity constant (pK a ), achieves the above described desired disperse dye dispersant. Formaldehyde condensation of an amine with sulfonated lignins is an instance of the well-known Mannich reaction. The Mannich reaction process has been demonstrated in several patents: U.S. Pat. No. 4,017,475, with simple amines including dialkanol amines; Canadian Patent 1,018,520, with primary aliphatic amines; U.S. Pat. No. 4,562,236, 1985, with fatty amines; and U.S. Pat. No. 5,188,665, with polyamines.

Japanese Patent publication 07224135 describes the use of amino acid-modified lignin as a dispersant for dyeing fabrics. This preparation is not suitable for package dyeing applications because it would have a very high viscosity at formulation conditions and would tend to precipitate at polyester package dyeing conditions at pH 4.5. Laboratory testing of this approach (using 2-methylgycine, amino acid) proved to be unsuccessful in this respect.

What has been discovered, however, is that the selection of suitable amines and the desirable amount of amine modification (based on their acidity constant) allows prediction of the dispersant-viscosity behavior of the modified sulfonated lignin dispersant at basic pH and also at acidic pH. Amines of various forms are suitable to provide a tertiary amine group on the sulfonated lignin structure. Preferred amines are secondary amines, and among the most preferred secondary amines, based on their pK a

values and flash points, are those listed in Table I.

TABLE I ______________________________________ Secondary Amines Amine pK a Flash point (° C.) ______________________________________

Imidazole 145 6.95 2-methylimidazole -- 7 Morpholine 35 8.3 Sarcosine -- 10 Pyrrolidine 37 10.1 Dimethylamine (40%) 15 10.7 Diethylamine -28 11.1 Dibutylamine 41 11 Diethanolamine 149 9 Diisopropanolamine 12.65 ______________________________________

The amine modification of sulfonated lignin approach is based on amine ionization principles which are dependent on the amine pK a , which in turn dictates lignin solubility at a given pH and, thus, performance.

Once secondary amines are attached to the lignin, they are unique in that they exist at alkaline pH in their tertiary form and do not interfere with the anionic character of the negatively charged sulfonate groups. As pH is lowered, the amines assume a positive charge, which can neutralize a portion of the anionic moieties in the negatively charged lignin. The resulting reduced solubility of the lignin enhances its interaction with the dyestuff particle and results in a higher activity dispersant. Laboratory investigations have shown that to achieve similar heat stability as REAX 85A, the industry standard,

amine modified sulfonated lignins allow 50% or greater dosage reduction in "mother paste" package dyeing heat stability. (See Heat Stability Testing section below.)

The materials prepared were evaluated for their dispersion stabilities and package dyeing heat stabilities. The general trends realized in these preparations were that, with increasing amine content, amine modified sulfonated lignins showed greater package dyeing heat stability. However, by increasing the amine content, the dispersant's viscosity increases at low pH. In aminomethylation of sulfonated lignins, since the maximum level of substitution is determined by the pK a of the amine, selection of an amine with very low acidity (e.g., imidazole, pK a =7), the substitution level can be as much as about 16 wt. % and still maintain the desired viscosity and solubility. Whereas, with an amine of high pK a (e.g., dimethylamine, pK a =10), the maximum substitution level can only be about 8 wt. %.

Amine modification of sulfonated lignins for use in dyestuff compositions permits the use of higher sulfonated lignin during milling and general formulation while lowering the solubility at acidic pH for improving the dye bath stability during the high temperature, high shear package dyeing environment. The resulting lower dosage requirement has the potential to make higher strength dye liquids which should translate into added benefits for many dyestuff producers in addition to the environmental benefits resulting from the lower dispersant requirement.

Ideally, the amine needed for a standard disperse dyeing should have a pK a as low as possible, as typical dyestuff formulations occur at alkaline pH conditions of about 8.0-8.5. At this pH, the amine would not interfere with the solubility of the lignin precursor. At dyeing conditions of pH about 4.0-5.0, the amine is protonated, which neutralizes a portion, or all, of the negatively charged sulfonic and carboxylic acids in the lignin molecular portion backbone. The extent of charge neutralization is dictated by the number of negatively charged groups in the lignin and the protonated fraction of amine groups.

For the purposes of this invention, the substitution level (wt. % amine) and the pK a

values include those that result in optimum dispersed dye dispersants with various amines, including dimethylamine, imidazole, morpholine, piperazine, and aminoethylpiperazine when used in preparation of liquid and powder formulations with various azo dyes (e.g., Orange 30, Blue 79, and Red 167) and various anthraquinone dyes (e.g., Red 60 and Blue 60).

Preparation of Aminomethylated Lignosulfonates

A 20-25% aqueous solution is prepared by gradual addition of dry sulfonated lignin (lignosulfonate) powder (preferably selected from the group of commercially available sulfonated lignins/lignosulfonates consisting of POLYFON O®, REAX 85A®, POLYFON H®, Vanisperse CB®, Marasperse CBA®, Ufoxane RG®, Ultrazine NA®, and Lignosol SD60®) to water maintained at 40° C., and the solution pH is adjusted to 10.6 with 50% NaOH. The prepared solution is treated with an amine (preferably selected

from the group of amines consisting of dimethylamine, morpholine, imidazole, and 2-methylimidazole) followed by addition of an equimolar amount of formaldehyde, and the combination is then heated at 90° C. for 3-12 hr. For the purposes of the following examples, the molar amounts of amine used per 1000 g of sulfonated lignin/lignosulfonates are 0.5, 0.075, 1.0 and 2.0.

Heat Stability Testing

The primary dispersant to be evaluated is weighed (0.5 g based on solids) into a 100 mL beaker and mixed with 2.0 g of dyestuff to form a "mother paste" (prepared by grinding 15 g of a disperse dye with 5 g of a commercially available grinding agent) and 5 mL of a buffer solution (pH=5.5). For a proper (i.e., fair) comparative evaluation, the mother paste is formed by grinding the disperse dye with the grinding agent to a standard particle size. Then, aliquots are withdrawn from the formed mother paste to which the dispersant is added. This assures that all dispersants are tested under standardized conditions.

The total weight is adjusted to 50 g with deionized (DI) water. The well-stirred mixture's pH is adjusted to between 4.5-5.0 using a 25% solution of acetic acid. The package dyeing process begins by pouring the dye sample into the dye chamber of a laboratory package dyer. The dyeing cycle consists of heating the dye bath from 70° C. to 130° C. at 2 degrees per minute while recording the pressure at a constant flow rate. Temperature versus the differential pressure is recorded during the dyeing cycle. If instability occurs, the pressure increases until the dyestuff solubilizes, after which the pressure decreases to its original level. This represents what is referred to as the "dyeing curve." The area under the curve then is recorded as package dyeing heat stability (bar ° C.). Ideally, the area under the curve should be zero (0). All experimental samples were tested with disperse Orange 30 dye as the primary screening test.

EXAMPLE 1

Dosage studies of aminomethylated REAX 85A, POLYFON O, and POLYFON H were conducted and compared with the dosage requirements of unmodified REAX 85A, considered the industry standard dyestuff dispersant for package dyeing. Results are presented in Table II.

TABLE II ________________________________________________________ __________________ Dosage Response of Aminomethylated REAX 85A, POLYFON O and POLYFON H HS

(bar ° C.) HS (bar ° C.) Reduced Lignin Type Acid Point (g) 100% Dosage Reduced Dosage Dosage (%)

________________________________________________________ __________________

REAX 85A (05026) 2.1 20.6 -- --

REAX 85A (05026) + 0.4 20 0.75 Mole DMA REAX 85A (05026) + 0.4 15 1.0 Mole DMA REAX 85A (05026) + 0.4 10 2.0 Moles DMA POLYFON H --2.3 -- (05136) POLYFON H 15 25.4 (05136) + 1 Mole DMA POLYFON O(03306) 3.6 --4.3 -- POLYFON O(03306) + 0.4 20 1 Mole DMA POLYFON O(03306) + 17 1 Mole DMA POLYFON O 0.4 5.1 23.6 15 (03306) + 1 Mole DMA ________________________________________________________ __________________

The preparations generated from POLYFON O and REAX 85A showed improvements were formulated in liquid and powder form. The optimum amine substitution levels and suitable amines were determined by evaluation of these samples according to their dispersion stability and package dyeing heat stability.

EXAMPLE 2

A 20-25% aqueous solution of POLYFON O was prepared by the gradual addition of dry POLYFON O powder to water maintained at 40° C., and the solution pH was adjusted to 10.6 with 50% NaOH. The solution was treated with the amine, followed by formaldehyde, and was heated at 90° C. for 3-12 hours under atmospheric pressure.

The following tests were performed according to standard laboratory procedures: package dyeing at pH 4.5 on a Zeltex Colorstar PC 1000 (Werner Mathis); AATCC heat stability test (No. 167); and acid point based on the weight of 10N sulfuric acid required to precipitate a dispersant from a 6% aqueous solution. The package dyeing heat stability results are shown in Table 3.

TABLE 3 ______________________________________ Package Dyeing Heat Stability of Amine Modified Sulfonated Lignins Wt % of HS (bar °

C.) Acid Amine Sample/REAX 85A Sample substitution Point Blue 79 Orange 30 ______________________________________

REAX 85A 1.8 11.2/11.2 19/19 POLYFON O 3.6 23.7/11.2 24/19 PolyO + 1.0 mol 0.6 6.7/11.2 7.9/19 imidazole PolyO + 2.0 mol 0.07 9.6/16.7 7.6/19 imidazole PolyO + 1.0 mol 8 1.0 10.2/11.2 7.42/19 2-methylimidazole PolyO + 2.0 mol 16 0.08 8.7/16.4 5.2/21.6 2-methylimidazole PolyO + 1.0 mol 0.1 11.8/17.1 7.23/19 morpholine PolyO + 2.0 mol 16 0.09 5.1/16.4

0/19 morpholine ______________________________________

Morpholine modified POLYFON O showed improved Orange 30 package dyeing heat stability reaching perfect heat stability with a degree of modification at 2.0 mole of amine. Imidazole and 2-methylimidazole modified POLYFON O did not improve appreciably beyond the 1.0 mole level. For Blue 79, the 2.0 mole modifications performed better than the 1.0 mole modifications for all the derivatives, as well as unmodified REAX 85A; the morpholine modification performed best overall.

The examples herein are intended to be representative only and not all inclusive of the scope of the subject matter of the disclosed invention. The invention is further set forth and defined in the claims which follow.

That which the inventors consider as the subject matter of the invention include:

(1) A dyestuff composition comprising a dyecake comprising a disperse dye and an amine modified sulfonated lignin dispersant;

(2) The dyestuff composition of (1) wherein the disperse dye is a member of the group consisting of azo dyes and anthraquinone dyes;

(3) The dyestuff composition of (2) wherein the azo dyes are selected from the group consisting of Orange 30, Blue 79, and Red 167;

(4) The dyestuff composition of (2) wherein the anthraquinone dyes are selected from the group consisting of Red 60 and Blue 60;

(5) The dyestuff composition of (1) wherein the amine modified sulfonated lignin is the product of combining an amine and a sulfonated lignin, in the presence of an aldehyde;

(6) The dyestuff composition of (5) wherein the sulfonated lignin is selected from the group of lignins from the alkali pulping processes which have been subsequently sulfonated and lignosulfonates from the sulfite pulping process;

(7) The dyestuff composition of (6) wherein the sulfonated alkali lignins are selected from sulfonated and sulfomethylated kraft lignins;

(8) The dyestuff composition of (5) wherein the amine is a tertiary amine;

(9) The dyestuff composition of (8) wherein the amine is selected from the group consisting of dimethylamine, morpholine, imidazole, sarcosine, pyrrolidine, diethylamine, dibutylamine, diethanolamine, diisopropanolamine, and 2-methylimidazole;

(10) The dyestuff composition of (5) wherein the aldehyde is formaldehyde; and

(11) The dyestuff composition of (1) wherein the amine modified sulfonated lignin dispersant exhibits an improved activity over the sulfonated lignin not modified with amine permitting a reduced dosage of at least 20% to achieve the same level of activity as the dosage required of unmodified sulfonated lignin.

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