Bleaching of substrates

ES 2 394 847 T3

DESCRIPTION

Substrate bleaching

Field of the invention

The present invention relates to catalytic bleaching of substrates.

Background of the invention

The bleaching of raw cotton and wood pulp are massive industries.

Raw cotton originating from cottonseed contains mainly colorless cellulose, but has a yellow-brownish color due to the natural pigment in the plant. Many impurities adhere especially to the surface. They consist mainly of protein, pectin, and wax.

The cotton and textile industries recognize a need to bleach cotton prior to use in fabrics and other areas. Cotton fibers are bleached to remove incidental and natural impurities with the simultaneous production of a substantially whiter material.

There have been two main types of bleach used in the cotton industry. One type is a dilute solution of alkali or alkaline earth metal hypochlorite. The most common types of such hypochlorite solutions are sodium hypochlorite and calcium hypochlorite. Additionally, chlorine dioxide has been developed as a bleaching agent and shows less damage to cotton than hypochlorite. Mixtures of chlorine dioxide and hypochlorite can also be applied. The second type of bleach is a peroxide solution, for example hydrogen peroxide solutions. This bleaching procedure is typically applied at high temperatures, that is, 80 to 100 ° C. Controlling peroxide breakdown due to trace metals is key to successfully applying hydrogen peroxide. Mg silicates or sequestering agents such as EDTA or similar phosphonates can often be applied to reduce decomposition.

The above types of bleaching solutions and caustic cleaning solutions can cause degradation of the cotton fiber due to oxidation that occurs in the presence of hot alkali or the uncontrolled action of hypochlorite solutions during the bleaching process. Hydrogen peroxide is also known to give reduced strengths to cotton fiber, especially when applied without proper fixation or stabilization of transition metal ions. Degradation can also occur during acid washing due to acid attack on cotton fiber, with the formation of hydrocellulose.

Purified cellulose for rayon production typically comes from specially processed wood pulp. It is sometimes referred to as dissolution cellulose or dissolution pulp to distinguish it from inferior pulps used for papermaking and other purposes. Dissolution cellulose is characterized by a high cellulose content, that is, it is composed of long-chain molecules, relatively free of lignin and hemicelluloses, or other short-chain carbohydrates. A manufactured fiber composed of regenerated cellulose, in which the substituents have replaced no more than 15% of the hydrogens of the hydroxyl groups. The wood pulp produced for papermaking contains most of the lignin originally present and is later referred to as mechanical pulp, or has been primarily defined as chemical pulp. Different sources of wood pulp can be found, such as softwood pulp (eg, from fir trees) or hardwood pulp, such as that originating from birch or eucalyptus. Mechanical pulp is used, for example, for newsprint and is often more yellow than paper produced from chemical pulp (such as copy paper or book printing paper). Additionally, paper produced from mechanical pulp is susceptible to yellowing due to light- or temperature-induced oxidation. Although mild bleaching procedures are applied for the production of mechanical pulp, to produce chemical pulp having high whiteness, various bleaching and delignification procedures are applied. Widely applied bleaches include elemental chlorine, chlorine dioxide, hydrogen peroxide, and ozone.

Although for both fabric bleaching and wood pulp bleaching, chlorine-based bleaches are often more effective, there is a need to apply oxygen-based bleaches for environmental reasons. Hydrogen peroxide is a good bleaching agent; however, it is necessary to apply it at high temperatures and long reaction times. It is desirable for industry to be able to apply hydrogen peroxide at lower temperatures and shorter reaction times than in current processes.

Macrocyclic triazacyclic molecules have been known for several decades, and their complexation chemistry with a wide variety of metal ions has been thoroughly studied. Azacyclic molecules often lead to complexes with enhanced thermodynamic and kinetic stability with respect to metal ion dissociation, compared to their open-chain analogs.

EP 0458397 discloses the use of complexes of manganese and 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN) as bleaches and oxidation catalysts, and the use for paper / pulp and paper bleaching processes. textile bleaching. 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN) has been used in dishwashing to

ES 2 394 847 T3 automatic dishwashers, SUN ™, and has also been used in a laundry detergent composition, OMO

Power ™. The ligand (Me3-TACN) is used in the form of its complex with the manganese transition metal, the complex having a counter ion that prevents deliquescence of the complex.

US Application 2001 / 0025695A1, Patt et al, discloses the use of PF6 salts^- 1,2, -bis- (4,7, -dimethyl1,4,7, -triazacyclonon-1-yl) -ethane and Me3-TACN (Me4-DTNE).

US application 2002/010120 discloses the bleaching of substrates in an aqueous medium, the aqueous medium comprising a transition metal catalyst and hydrogen peroxide.

WO 2006/125517 discloses a process for catalytically treating a cellulose or starch substrate with a preformed Mn (III) or Mn (IV) transition metal catalyst salt and hydrogen peroxide in an aqueous solution. The preformed transition metal catalyst salt is described as having a non-coordinating counter ion and having a water solubility of at least 30 g / l at 20 ° C. The exemplified ligands of the catalysts described in WO 2006/125517 are 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-TACN) and 1,2, -bis- (4,7, -dimethyl-1 , 4.7, -triazacyclonon-1-yl) -ethane (Me4-DTNE).

Summary of the invention

The present invention provides effective bleaching of cellulose material while reducing cellulosic polymer degradation resulting in fiber damage.

In one aspect, the present invention provides a process for bleaching a cellulose material comprising the following step: treating the cellulose material with an unbuffered aqueous solution, the aqueous solution having an initial pH of 8 to 11, the aqueous solution comprising :

(i) a preformed transition metal catalyst (manganese catalyst), the transition metal catalyst being present in a concentration of 0.1 to 100 micromolar and (ii) of 5 to 1500 mM of hydrogen peroxide, maintaining the pH of the aqueous solution within an operating range such that the initial pH does not decrease by more than 1.5 pH units during the treatment of the cellulose material in the presence of the catalyst before rinsing and, The preformed transition metal catalyst is a mononuclear or dinuclear complex of a transition metal catalyst of Mn (III) or Mn (IV) in which the ligand of the transition metal catalyst is of formula (I):

<img file="ES2394847T3_D0001.tif" />

in which:

N - [CR ^ CFCRJ p is 3;

R is independently selected from: hydrogen, C1-C6 alkyl, CH2CH2OH, and CH2COOH, or one of R is linked to the N of another Q through an ethylene bond;

R1, R2, R3, and R4 are independently selected from: H, C1-C4 alkyl, and C1-C4 alkyl-hydroxy, wherein the pH of the aqueous solution is maintained within the operating range of 1.5 pH units by a procedure selected from:

a) The cellulose material is first treated with NaOH and at a pH of 11 to 12 for between 2 and 120 min at a temperature in the range of 50 to 110 ° C without the presence of the manganese catalyst, after which the pH is reduced to the pH range of 9 to 11 and further treated in the presence of the manganese catalyst for between 2 and 60 minutes at 50 to 110 ° C, hydrogen peroxide being added during the first NaOH treatment and / or when the manganese catalyst is present;

ES 2 394 847 T3

b) the cellulose material is treated at a pH in the range of 10-11 with sequestrant, H2O2, NaOH, and the manganese catalyst while allowing the pH to naturally drop as a result of bleaching; Y

c) The cellulose material is treated with sequestrant, H2O2, NaOH and the manganese catalyst while the pH is kept in the range of 8 to 11 by adding aqueous NaOH.

Of steps a), b) and c), step b) is the most preferred and step a) is the second most preferred.

Detailed description of the invention

PH maintenance

Stabilizing the pH provides better bleaching of the cellulosic material. The requirement to prevent the pH of the aqueous solution from decreasing by more than 1.5 pH units during the treatment of the cellulose material in the presence of the catalyst prior to rinsing can be provided in a number of ways. Below are three ways that are preferred.

First high pH with H2O2 and surfactant without catalyst, then drop in pH and addition of catalyst

1) Pretreatment of the cellulose material with base (eg NaOH) to about pH 11.5 and optionally with H2O2 before reducing the pH to the range of 8 to 11 after adding the manganese catalyst. If H2O2 is not used in the pretreatment phase then H2O2 must be added afterwards or as the pH is lowered. Optionally, low amounts of hydrogen peroxide can also be employed in the pretreatment phase and additional hydrogen peroxide can be added afterwards or as the pH is lowered. There is no longer a need to rinse or wash the cellulose material after the pretreatment step, although an aqueous wash is preferred, although this adds to the cost.

Single-stage procedure, starting at the appropriate pH range.

2) Start the treatment of the cellulose material at a pH in the range of 10 to 11 with sequestrant / H2O2 / NaOH / manganese catalyst and letting the pH drop naturally as a consequence of bleaching (typically pH 8.5 to 10).

Procedure in a single phase at a lower pH with a constant pH maintenance.

3) Maintain the pH in the range of 8 to 11 during the treatment by addition, preferably continuous, of aqueous NaOH. This can be provided by using a pH probe in conjunction with a feedback loop that controls the addition of sodium hydroxide.

Other ways of maintaining the pH in the range of 8 to 11 during treatment can be used, such as by applying ion exchange resins.

Ideally, the pH is constant and is prevented from decreasing during treatment of the cellulose material in the presence of the manganese catalyst prior to rinsing. However, this is difficult to do in practice, although in reality the pH change can be minimized at a pH change of 0.2 in an industrial environment.

Preferably, the pH of the aqueous solution is prevented from decreasing by more than 1 pH unit during the treatment of the cellulose material in the presence of such manganese catalyst prior to rinsing, more preferably 0.7 pH, even more preferably 0.4 pH.

It will be appreciated that the closer the pH tolerances the higher the cost of treatment.

Cellulose material

This can be, for example, cotton, wood pulp, straw and hemp. Preferably, the treated cellulose material is wood pulp or cotton, more preferably cotton.

Raw cotton (produced in a cotton gin) is dark brown in color due to the natural pigment of the plant. The cotton and textile industries recognize a need to bleach cotton prior to use in fabrics and other areas. The object of bleaching such cotton fibers is to remove incidental and natural impurities with the simultaneous production of a substantially whiter material.

The wood pulp produced for papermaking contains most of the lignin originally present and is later referred to as mechanical pulp, or is primarily delignified, as in chemical pulp. Different sources of wood pulp can be found, such as soft wood pulp, for example from fir trees, hardwood pulp such as for example birch or eucalyptus. Mechanical pulp is used for newsprint and is often more yellow than paper produced from chemical pulp. Additionally, paper produced from mechanical pulp is susceptible to yellowing due to oxidation induced by light or temperature. Although mild bleaching procedures are used for the production of mechanical pulp, for

ES 2 394 847 T3 to produce chemical pulp having high whiteness, various bleaching and delignification procedures are applied.

Widely applied bleaches include elemental chlorine, hydrogen peroxide, chlorine dioxide, and ozone.

The materials mentioned above are discussed in WO 2006/125517.

The procedure is also applicable to laundry applications in both domestic and industrial environments. The process is particularly applicable to domestic or industrial washing machines that have the ability to control the pH during the washing process, as described in US2006 / 0054193, US2005-0252255 and US2005-0224339. The procedure is more particularly applicable to the bleaching of stains found on white institutional cotton fabrics, such as that found in prisons and hospitals.

Unbuffered system

The aqueous solution is not buffered. In this sense, the aqueous solution does not contain an inorganic buffer, for example carbonate, phosphate and borate. However, the organic sequestrant and hydrogen peroxide can be considered to have some buffering capacity, but this is not considered as a buffer within the context of the present invention. Most preferably, the aqueous solution is not buffered by other than organic sequestrant and hydrogen peroxide.

Transition metal catalyst

Documents EP 0458397 and EP 0458398 disclose the use of complexes of manganese and 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-TACN) as bleaches and oxidation catalysts and their use for paper / pulp bleaching processes. and textile bleaching. 1,4,7-Trimethyl-1,4,7-triazacyclononane (Me3-TACN) has been used in dishwashing for automatic dishwashers, SUN ™, and has also been used in a laundry detergent composition, OMO Power ™. The ligand (Me3-TACN) is used in the form of its complex with the manganese transition metal, the complex having a counter ion that prevents deliquescence of the complex. The counter ion for commercial products containing manganese Me3-TACN is PF6^-. Salt Me3-TACN PF6^- it has a solubility in water of 10.8 g per liter at 20 ° C. Additionally, the counter ion perchlorate (ClO4^-) is acceptable from this point of view due to its ability to provide a Me3-TACN manganese that does not appreciably absorb water. However, due to the potential explosive properties of transition metal perchlorate complexes, compounds containing perchlorate are not preferred. Reference is made to US Patent 5,256,779 and EP 458397, both of which are in the name of Unilever. An advantage of PF6 counterions^- or ClO4^- for the manganese complex Me3-TACN is that the complex can be easily purified by crystallization and recrystallization from water. In addition, non-deliquescent salts allow processing, for example, milling the crystals and storage of a product containing the manganese Me3-TACN. Additionally, these anions provide stable metal complexes on storage. To facilitate the synthesis of manganese Me3-TACN, highly water-soluble deliquescent counterions are used, but these counterions are replaced with much less water-soluble, non-deliquescent counterions at the end of the synthesis. Loss of product results during counter ion exchange and crystallization purification. A downside of using PF6^- as a counter ion it is significantly higher cost when compared to other highly soluble anions.

Although the manganese transition metal catalyst used may not be deliquescent due to the use of counterions such as PF6^- or ClO4^-, for industrial substrates it is preferred that the transition metal complex is soluble in water. It is preferred that the preformed transition metal is in the form of a salt, so that it has a water solubility of at least 50 g / l at -20 ° C. The preferred salts are those of chlorine, acetate, sulfate and nitrate. These salts are described in WO 2006/125517.

The preformed transition metal catalyst can be added all at once, in multiple additions, or as a continuous flow. The use of continuous flow is particularly applicable to continuous procedures.

Preferably, R1, R2, R3 and R4 are independently selected from: H and Me. Most preferably, the manganese catalyst is derived from a ligand selected from the group consisting of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3-TACN) and 1,2, -bis- (4,7, - dimethyl-1,4,7, -triazacyclonon-1-yl) -ethane (Me4-DTNE).

The preformed transition metal catalyst salt is preferably a dinuclear complex of Mn (III) or Mn (IV) with at least one O bond.²-.

Materials to change the pH

The pH of the aqueous environment of the cellulose material can be easily changed by the addition of acid or base. Suitable examples of acids are hydrochloric acid, sulfuric acid, and acetic acid. Suitable examples of bases are sodium hydroxide, potassium hydroxide, and sodium carbonate. The acidic and basic components are preferably added in the form of aqueous solutions, preferably dilute aqueous solutions.

ES 2 394 847 T3

Organic sequestrant

Preferably, the aqueous solution comprises from 0.01 to 10 g / l of an organic scavenger, the scavenger being selected from: an aminophosphonate scavenger and a carboxylate scavenger. This is particularly preferred where the cellulose material is cotton.

The sequestrant is either an aminophosphonate sequestrant or a carboxylate sequestrant. Preferably, the sequestrant is either an aminophosphonate sequestrant or an aminocarboxylate sequestrant.

The following are preferred examples of aminophosphonate sequestrants: nitrile trimethylene phosphonates, ethylenediamine-N, N, N ', N'-tetra (methylene phosphonates) (Dequest ™ 204) and diethylene-triamine-N, N, N', N, Npenta (methylene phosphonates) (Dequest ™ 206), more preferably diethylene-triamine-N, N, N ', N, Npenta (methylene phosphonates. One skilled in the art will be aware that different types of each Dequest ™ exist, for example, as phosphonic acid or as sodium salts or any mixture thereof.

The following are preferred examples of aminocarboxylate sequestrants: ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylenediaminetetraacetic acid (HEDTA), nitrilotriacetic acid (NTA), N-hydroxyethylaminodiacetic acid, N-hydroxyethylaminodiacetic acid, diacetic acid-glutenta- acetic acid, diethylene diacetic acid (DT-PA), diethylene diacetic acid, diethylene diacetic acid , ethylenediamine-N, N'-disuccinic acid (EDDS), methylglycinodiacetic acid (MGDA) and alanine-N, N-diacetic acid. A more preferred aminocarboxylate sequestrant is diethylenetriaminepentaacetic acid (DTPA).

The sequestrants can also be in the form of their salts, for example alkali metal, alkaline earth metal, ammonium salts, or substituted ammonium salts. Preferably, the sequestrant is in the form of the free acid, sodium or magnesium salt.

Examples of carboxylate sequestrants are polycarboxylates that contain two carboxy groups and include the water-soluble salts of succinic acid, malonic acid, (ethylenedioxy) diacetic acid, maleic acid, diglycolic acid, tartaric acid, tartronic acid, and fumaric acid, as well as ether carboxylates. Polycarboxylates containing three carboxy groups include, in particular, water-soluble citrates, aconitrates and citraconates, as well as succinate derivatives such as carboxymethylsuccinates. Carboxylates containing four carboxy groups include the oxydisuccinates disclosed in British Patent No. 1,261,829, 1,1,2,2-ethane tetracarboxylates,

1,1,3,3-propane tetracarboxylates and 1,1,2,3-propane tetracarboxylates. Polycarboxylates containing sulfo substituents include the sulfosuccinate derivatives disclosed in British Patent Nos. 1,398,421 and 1,398,422 and in United States Patent No. 3,936,448, and the sulfonated pyrolyzed citrates disclosed in British Patent No. 1,439,000.

Polycarboxylates containing four carboxy groups include the oxydisuccinates disclosed in British Patent No. 1,261,829, 1,1,2,2-ethane tetracarboxylates, 1,1,3,3-propane tetracarboxylates, and 1,1,2,3 -propane tetracarboxylates.

Other suitable water-soluble organic salts are homo- or co-polymeric polycarboxylic acids or their salts, the polycarboxylic acid comprising at least two carboxyl radicals separated from each other by not more than two carbon atoms. Polymers of the latter type are disclosed in GB-A-1,596,756. Examples of such salts are polyacrylates of molecular weight 2000 to 5000 and their copolymers with maleic anhydride, such copolymers having a molecular weight of 20,000 to 70,000, especially about 40,000.

Also copolymeric polycarboxylate polymers that, formally at least, are formed from an unsaturated polycarboxylic acid, such as maleic acid, citraconic acid, itaconic acid, and mesaconic acid as the first monomer, and an unsaturated monocarboxylic acid, such as acrylic acid. or an alpha-C1-C4 alkyl acrylic acid as the second monomer. Such polymers are available from BASF under the trade name Sokalan® CP5 (neutralized form), Sokalan® CP7 and Sokalan® CP45 (acid form).

The most preferred sequestrants are Dequest ™ 2066 or DTPA.

Surfactant

It is preferred that the bleaching procedure is carried out in the presence of a surfactant. The use of surfactants, for example, helps remove waxy materials found in cotton. For substrates originating from cotton pulp, no hydrophobic substrates are found and therefore the need for surfactants in the treatment process is not as preferred. In this regard, it is preferred that a surfactant is present in the range of 0.1 to 20 g / l, preferably 0.5 to 10 g / l. It is preferred that the surfactant is a nonionic surfactant and more preferably biodegradable.

Experimental part

Experiment 1: pH control by continuous addition of a NaOH solution during the bleaching procedure.

ES 2 394 847 T3

Raw cotton with a Berger Whiteness value of 5.5 +/- 1.0 was treated as follows: 6 grams of the cotton were dipped in temperature controlled glass beakers in a 60 ml solution (cloth / liquor ratio 1/10) containing 20 microM of [Mn2O3 (Me3-TACN) 2] (PF6) 2.H2O, 2.3% H2O2 (equal to 6.66 ml (35%) / l; w / w cotton wrt), 0.4 g / l H5-DTPA (ex Akzo-Nobel; trade name Dissolvine D50; 50% purity), the pH value was adjusted to the desired level (after correction for temperature differences), 2 g / l Sandoclean ™ PCJ (ex Clariant).

A few drops of NaOH (1 M) were added to maintain the pH (within 0.2 pH units) for 30 minutes of solutions stirred at 75 to 80 ° C. The pH was controlled with a peachmeter. Subsequently, the cotton samples were rinsed with 2 to 3 liters of hot demineralized water (80 ° C), then washed with large amounts of demineralized water, centrifuged in a centrifugal dryer for 3 minutes and dried overnight under conditions ambient. The optical properties of the fabrics were then measured using a Minolta CM-3700d spectrophotometer, using L, a, b values ​​which were converted to Berger Whiteness values.

Whiteness values ​​are expressed in Berger units. The Berger whiteness formula is given below:

Bberger = Y + aZ - bX, where a = 3.448 and b = 3.904.

The X, Y, Z values ​​are the coordinates of the achromatic point.

The results of the experiments are given in Table 1.

Table 1: Whiteness results (Berger) obtained using 20 microM of [Mn2O₃ (I₃-TACN) 2] (PF6) 2.H2O in an unbuffered solution with 0.2 g / l DTPA at 80 ° C for 30 minutes.

<td>pH (initial)</td><td>pH (final)</td><td>Bw</td><td>DT</td>

<td> 9,75</td><td> 7,3</td><td> 51,0</td><td> 0,4</td>

<td> 10,0</td><td> 9,5</td><td> 63,1</td><td> 0,8</td>

The results shown in Table 1 indicate that when the pH is controlled (input 2), the bleaching effect is much greater than when the pH is allowed to drop below 8.0. As a limit, the bleaching performance in the absence of the manganese catalyst shows 41.0 BW (at pH 10) under these conditions. Without added DTPA, in the presence of catalyst, the whiteness is about 10 BW lower than in the DTPA system.

Experiment 2: pH control by pretreatment of the cotton with NaOH / H2O2 without catalyst and then reduction of the pH to an optimum level and addition of the catalyst.

Raw cotton with a Berger Whiteness value of 5.5 +/- 1.0 was treated as follows: 6 grams of the cotton was dipped in temperature controlled glass beakers in a 60 ml solution (cloth / liquor ratio 1/10) containing 0.5 g / l DTPA, 2 g / l Sandoclean PCJ, 2.3% H2O2 (equal to 6.66 ml (35%) / l; wrt cotton w / w) , for 15 minutes at 75 ° C. Subsequently, sulfuric acid (1 M) was added until the desired pH was reached followed by 20 microM of [Mn2O₃(I₃-TACN) 2] (PF6) 2.H2O and the mixture was left for 15 minutes with continuous stirring. No NaOH solution was added during the bleaching procedure in the presence of the catalyst. After the allotted time, the fabrics were washed and dried as exemplified above. Whiteness values ​​are expressed in Berger units, as defined above.

The results are given in Table 2.

Table 2: Whiteness results (Berger) obtained using 20 microM of [Mn2O₃ (I₃-TACN) 2] (PF6) 2.H2O in an unbuffered solution with 0.2 g / l DTPA at 75 ° C for 15 minutes, after allowing the fabrics to be pretreated with NaOH / H2O2 for 15 minutes at 75 ° C (input 1) versus the addition of catalyst at the beginning of the bleaching experiment at pH 9.75.

Table 2

<td>pH (stage 1)</td><td>pH (stage 2)</td><td>pH (final)</td><td>Bw</td><td>DT</td>

<td> 11</td><td> 10</td><td> 9,4</td><td> 60,0</td><td> 0,0</td>

<td> 9,75</td><td></td><td> 7,6</td><td> 51,0</td><td> 0,4</td>

ES 2 394 847 T3

The results in Table 2 indicate that the pretreatment step offers a great advantage in bleaching results, compared to the comparative experiment in which the catalyst was allowed to bleach the substrate starting from pH 10 without a pretreatment step. (entry 2). As a comparative example, bleaching fabrics at pH 11 without catalyst, produced a final pH of 9.9 and 51.0 BW points (0.9 dT).

Experiment 3: starting at pH 10.9 and letting the pH drop during the bleaching reaction.

A batch of raw cotton with a Berger Whiteness value of 0 was treated as follows: 6 grams of the cotton were dipped in temperature controlled glass beakers in a 60 ml solution (cloth / liquor ratio 1/10) containing 10 microM of [Mn2O3 (Me3-TACN) 2] (PF6) 2.H2O, 2.3% H2O2 (equal to 6.66 ml (35%) / l; wrt cotton w / w), 0, 4 g / l of H5-DTPA (ex Akzo-Nobel; trade name Dissolvine D50; purity 50%) and 2 g / l of Sandoclean ™ PCJ (ex Clariant). The temperature of the experiment was 77 ° C.

The pH of the water containing Sandoclean, Na5DTPA, cotton and an appropriate amount of NaOH was determined at room temperature, heated to 77 ° C, the pH value was controlled and then hydrogen peroxide was added. Then, a correction was made for the addition of hydrogen peroxide by adding some extra NaOH. The catalyst was then added and left stirring for 30 minutes. The fabrics were then rinsed and washed as described above. The pH of the solution after the bleaching phase was determined after allowing the solution to cool to room temperature. As a comparative experiment to determine the effect of the manganese-triazacyclononane compound, no catalyst was added. The results are given in the table below. Whiteness values ​​are expressed in Berger units, as defined above.

<td></td><td>pH (initial)</td><td>pH (final)</td><td>Bw</td><td>DT</td>

<td>No catalyst</td><td> 10,7</td><td> 9,6</td><td> 51,5</td><td> 0,6</td>

<td>With catalyst</td><td> 10,7</td><td> 9,7</td><td> 57,6</td><td> 0,7</td>

The results shown in the table indicate that at this pH the effect of the catalyst is significant, compared to the reference experiment.