EP0151284A2 - Process for desizing cotton and cotton-containing fabrics - Google Patents

Abstract

Cotton and cotton-containing fabrics are desized in strongly alkaline aqueous solution with an alkali metal hypochlorite by a process in which from 0.5 to 8.0 g/l of a tertiary hydroxyalkylamine which is soluble in aqueous alkaline solution, of an oxyethylated and/or oxypropylated ethylenediamine, of an oxyethylated polyethyleneimine, of malonic acid, of cyanuric acid, of a cyanuric acid derivative, of a urea derivative, of cyanoguanidine, of oxazolidone, of pyrrolidone, of N-methylpyrrolidone, of N-methylimidazole or of a mixture of these is added to the aqueous bath, as an activator for the hypochlorite. Activators for hypochlorite are used in the desizing of cotton and cotton-containing fabrics in strongly alkaline aqueous solutions.

Description

The invention relates to a process for desizing cotton or cotton-containing fabrics in strongly alkaline solutions with alkali hypochlorite in the presence of an activator for hypochlorite and the use of activators for hypochlorite for desizing in strongly alkaline aqueous solutions.

The warp threads are sized in order to be able to weave cotton fabrics and cotton-polyester blends without any problems. In practice, starch-containing sizing agents are usually used, which are also frequently used with semi-synthetic sizing agents, such as carboxymethyl cellulose and synthetic sizing agents, e.g. Polyvinyl alcohol or polyacrylates can be mixed. The tissues are desized by breaking down the starch and then washing out the breakdown products. The starch can be degraded, for example, enzymatically or oxidatively in an alkaline or soda-alkaline medium with persulfates and bromite.

The oxidative desizing of cotton and cotton-containing fabrics in the presence of hypochlorite in alkaline solutions is generally known. The disadvantage of this is that the degradation of native starch with hypochlorite solutions at normal temperature is not possible (see K. Frinken, Textilbetrieb, 1974, 92 (4), pages 47 to 49, in particular page 47, left column, 1st paragraph) and increasing fiber damage occurs at higher temperatures.

It is also known to use hypochlorite for bleaching for desized tissues. During this bleaching process, a pH of 11 to 12 is generally maintained and, in order to avoid fiber damage at these pH values, at which the hypochlorite is active depending on the pH value, the shortest possible residence times must be observed.

For this reason, there is as yet no satisfactory technical desizing process in practice with alkali hypochlorite.

We have now found a process for desizing cotton and cotton-containing fabrics in a strongly alkaline aqueous solution with alkali hypochlorite, which is characterized in that 0.5 to 8.0 g / l of a tertiary hydroxyalkylamine soluble in aqueous alkaline solution are added to the aqueous bath, of an ethoxylated and / or oxypropylated ethylene diamines, an ethoxylated polyethyleneimine or cyanuric acid, cyanoguanidine, oxazolidone, pyrrolidone, N-methylpyrrolidone or N-methylimidazole as an activator for the hypochlorite.

The desizing process according to the invention is advantageously carried out in the strongly alkaline range, corresponding to a content of 15 to 150 g, preferably 25 to 70 g of sodium hydroxide / 1 water and at room temperatures, at temperatures of 10 to 55 ° C. with an amount of alkali metal hypochlorite, in particular sodium hypochlorite, the second up to 8 g, preferably 2 to ₄ g of active chlorine.

The residence time is 2 to 24 hours and of course depends on the temperature and the amount of active chlorine used. In an advantageous manner, a bleaching effect is simultaneously produced in the desizing according to the invention

Cotton-containing fabric is to be understood as meaning fabric mixtures of at least 30% cotton, in particular cotton with polyester.

The activators which can be used according to the invention and are soluble in the strongly alkaline aqueous solution are: tertiary trishydroxyalkylamines having 2 or 3 carbon atoms in alkyl, such as triethanolamine, bis-hydroxyethyl-hydroxypropylamine, trishydroxypropylamine, oxethylated and / or oxpropylated ethylenediamines with a total of 4 to 10 ethylene oxide and / or propylene oxide units, such as N, N'-tetra-hydroxyethyl-ethylenediamine, N, N'-tetrahydroxypropyl-ethylenediamine, urea derivatives, such as N, N'-tetramethylurea, N, N'-tetrahydroxiethyl urea, N, N'-dimethylethylene urea, N, N'-bis-hydroxyethyl ethylene urea, propylene urea, N, N'-dimethyl propylene urea and N, N'-bis-hydroxy ethyl propylene urea, ethoxylated polyethyleneimines with 2 to 50 ethyleneimine units, their imino and Amino groups are alkylated with 1 to 5 ethylene oxide units, such as (pentahydroxyethyl) diethylene triamine or hexahydroxy ethyl) tetraethylene pentamine

Cyanuric acid derivatives such as trishydroxyethyl and trishydroxy propyl melamine and 2,4,6-trishydroxylamine triazine.

Cyanuric acid, oxazolidone-2, N-methylpyrrolidone-2 and N-methylimidazole are particularly preferred as activators.

The preferred amounts of activator for the hypochlorite are 3 to 5 g / l. The additives according to the invention act in a surprising and unpredictable manner as activators for the hypochlorite, which is normally deactivated in the strongly alkaline aqueous medium. These additives only result in a relatively short residence time for the tissue under the oxidative action of hypochlorite. The risk of tissue damage is significantly reduced. At the same time, the fabric is bleached and the remains of the husk of the cotton are largely removed.

Compared to enzymatic desizing, which is usually also carried out as a dwell process at temperatures above 50 ° C, the new process can be carried out with good effect at room temperature, around 20 ° C, in an energy-saving manner. The bleaching effect and the removal of seed husks from the cotton without additional heat treatment are the particular advantages to be emphasized in comparison to the enzymatic desizing.

In the case of oxidative desizing with persulfate, a clear bleaching effect is not achieved when it is carried out as a residence process at room temperatures. The removal of the cotton seed husks is insufficient. Oxidative desizing with persulfates is therefore carried out in practice as a hot treatment.

As a further advantage, it should be pointed out that after the desizing process according to the invention, only a mild bleaching with hydrogen peroxide is required for the treated fabric in order to achieve a full whiteness, only about a third to a quarter of the otherwise usual amount of hydrogen peroxide being used needs.

Moreover, in the desizing process according to the invention, wetting agents, detergents and other customary auxiliaries, which must of course be stable to hypochlorite, can be added in a manner known per se. These additives are known to the person skilled in the art and generally serve to make the desizing process more reliable in its course. This also includes the use of sequestering and dispersing agents when washing out the tissues.

Hypobromite is not used in industry due to its low stability, the solutions can only be stored at around 0 ° C. The solutions disproportionate moderately quickly even at room temperature (Cotton / Wilkinson, Inorganic Chemistry, Verlag Chemie, Weinheim 1967, pages 531 to 534).

Examples and comparative examples

The activating effect of the additives on a strongly alkaline hypochlorite solution was determined by the decrease in the active chlorine content of the solutions over time. The respective active chlorine content was determined titrimetrically with sodium thiosulfate.

Test conditions: 20 ° C, 5 g / 1 active chlorine, 40 g / l NaOH

The table shows that as the level of activation increases, the active chlorine content decreases

The alkaline hypochlorite solutions are used to desize cotton fabrics made from polyester / cotton blended fabrics. The fabric pieces are soaked in desizing liquor, squeezed to 100% liquor absorption and left to linger. In all cases, the tissues are washed out immediately after treatment. The degree of whiteness, the desizing (according to the Tegewa scale) and also the DP value (average degree of polymerization) of the cellulose are determined from these pieces of fabric.

example 1

Fabric: polyester / cotton blend (65/35) size: modified thickness, degree of whiteness of the raw material 67.8, shells per 100 cm ² : 52, DP value: 2190

Composition of the desizing liquor: ₄₀ g / 1 NaOH, 5 g / 1 active chlorine, 3 g / 1 nonylphenyloxethilate, 2 g / 1 wetting agent (phosphoric acid ester).

Residence temperature: 45 ° C.

Tissue according to 1st A., active chlorine content of the desizing liquor reduced to 3 g / 1.

Residence time: 5 hours residence temperature: 45 ° C

The results of 1. A. and 1. B. show that without activator the cotton is clearly damaged and fabrics with such low DP values are normally no longer usable.

Example 2

• Baumwollnessel, mit Stärke geschlichtet, Weißgrad 56,8, Schalen pro 100 cm²: 158, DP-Wert: 2350

Tissue:

• Cotton nettle, sized with starch, whiteness 56.8, shells per 100 cm ² : 158, DP value: 2350

• 40 g/1 NaOH, 3,2 g/1 Aktivchlor, 3 g/1 Nonylphenoloxethylat, 1 g/1 Netzmittel (Phosphorsäureester)

Composition of the desizing fleet:

• 40 g / 1 NaOH, 3.2 g / 1 active chlorine, 3 g / 1 nonylphenol oxyethylate, 1 g / 1 wetting agent (phosphoric acid ester)

Residence time: 5 hours, residence temperature: 45 ° C.

The numerical results prove the special effectiveness of oxazolidone.

For comparison, an experiment according to Example 2 is carried out without addition of hypochlorite and without catalyst.

The numerical values show that alkali alone gives unsatisfactory results with regard to whiteness and peel removal, so that more peroxide bleaching is required.

Example 3

Fabric according to Example 2. Composition of the desizing liquor: 60 g / 1 NaOH, 4 g / 1 active chlorine, 3 g / 1 nonylphenol ethoxylate, 2 g / 1 wetting agent. Residence time: 16 hours residence temperature: 22 ° C

Example 4

Tissue and experimental conditions according to Example 3. When washing, 2 g / l sequestering agent (copolymer containing carboxyl groups) are added.

• 5 g/1 Stabilisator, 10 g/1 NaOH, 5 g/1 Netz-Waschmittel, 5 ml/1 H₂0₂ 35 %ige wäßrige Lösung,

Then the tissue pieces are bleached with hydrogen peroxide,
Bleaching recipe:

• 5 g / 1 stabilizer, 10 g / 1 NaOH, 5 g / 1 wetting detergent, 5 ml / 1 H ₂ 0 ₂ 35% aqueous solution,

Liquor absorption: 100% steaming time: 10 minutes bleaching temperature: 100 to 102 ° C

The results show that relatively little hydrogen peroxide can be used.

Example 5

• Baumwoll/Polyester Hemdenpopeline (50/50);
• Weißgrad: 65,8
• Schalen pro 100 cm² : 4₀;
• DP-Wert: 3012

Tissue:

• Cotton / polyester shirt poplin (50/50);
• Whiteness: 65.8
• Dishes per 100 cm ² : 4 ₀ ;
• DP value: 3012

• 25 g/1 NaOH; 2 g/1 Aktivchlor; 5 g/1 Netz- und Waschmittel Verweilzeit: 16 Stunden,

Composition of the desizing fleet:

• 25 g / 1 NaOH; 2 g / 1 active chlorine; 5 g / 1 wetting and detergent residence time: 16 hours,

Residence temperature: 20 ° C liquor absorption: 100%

Example 6

• Baumwollinlett, Weißgrad 55,8

Tissue:

• Cotton ticking, whiteness 55.8

DP value: 2980, trays per 200 cm ^2: 27

• 140 g/1 NaOH, 5 g/1 Aktivchlor, 3 g/1 Waschmittel, 5 g/1 Laugler-Netzmittel.

Composition of the desizing fleet:

• 140 g / 1 NaOH, 5 g / 1 active chlorine, 3 g / 1 detergent, 5 g / 1 Laugler wetting agent.

Residence time: 16 hours residence temperature: 45 ° C liquor absorption: 80%

Comparative Example I

The fabric according to Example 4 is desized enzymatically.

• 5 g/1 enzymatisches Entschlichtungsmittel
• 2 g/1 Kochsalz
• 3 g/1 _Nonylphenoloxethylat

Composition:

• 5 g / 1 enzymatic desizing agent
• 2 g / 1 table salt
• 3 g / 1 _N onylphenol oxethylate

Residence time: 3 hours residence temperature: 75 ° C

The fabric is then bleached according to example 4, but using 4 times the amount of hydrogen peroxide compared to example 4.

If one subjects the desized tissue to a boiling point (40 g / 1 NaOH, 1 g / 1 wetting agent, 10 minutes at 100 ° C) and the tissue is bleached according to the above recipe (with 20 ml / 1 H ₂ 0 ₂ 35%) ) you get the following effect:

Comparative Example II

Oxidative desizing with K ₂ S ₂ 0 ₈ .

• 40 g/1 NaOH
• 2 g/1 ^K ₂ ^S ₂ ⁰ ₈
• 5 g/1 Netz-/Waschmittel
• 2 g/1 Sequestriermittel

The fabric from Example 2 or Example 4 is treated with the following desizing liquor:

• 40 g / 1 NaOH
• 2 g / 1 ^K ₂ ^S ₂ ⁰ ₈
• 5 g / 1 wetting agent / detergent
• 2 g / 1 sequestering agent

Residence time: 10 minutes residence temperature: 100 to 102 ° C liquor absorption: 100%

After washing out, the following effects are measured:

After hydrogen peroxide bleaching according to Example I, the following values were measured on the fabric:

From the comparative examples it can be seen that in the case of enzymatic desizing for a peel-free white tissue, decoction and increased peroxide bleaching are necessary; even in the case of oxidative desizing with persulfate, increased peroxide bleaching is necessary in order to achieve the same effects.

Claims (5)

1. A process for desizing cotton and cotton-containing fabrics in strongly alkaline aqueous solution with alkali hypochlorite, characterized in that 0.5 to 8.0 g / 1 of a tertiary hydroxyalkylamine soluble in aqueous alkaline solution, an oxyethylated and / or oxpropylated ethylenediamine, an ethoxylated polyethyleneimine or malonic acid, cyanuric acid, a cyanuric acid derivative, a urea derivative, cyanoguanidine, oxazolidone, pyrrolidone, N-methylpyrrolidone or N-methylimidazole or their mixtures as activators for the hypochlorite. 2. The method according to claim 1, characterized in that the activator for the hypochlorite is cyanuric acid, oxazolidone-2, N-methylpyrrolidone-2 or N-methylimidazole. 3. The method according to claim 1 or 2, characterized in that the activator for the hypochlorite is added to the aqueous bath in an amount of 3 to 5 g / 1. 4. Use of tertiary hydroxyalkylamines soluble in strongly alkaline aqueous solutions, ethoxylated and / or oxypropylated ethylenediamines, ethoxylated polyethyleneimines, cyanuric acid, cyanoguanidine, oxazolidone, pyrrolidone, N-methylpyrrolidone or N-methylimidazole as an activator for hypochlorite and for dewaxing cotton in the dewaxing of dewaxing cotton in strongly alkaline aqueous solutions with alkali hypochlorite in an amount of 0.5 to 8.0 g / 1. 5. Use of cyanuric acid, oxazolidone-2, N-methylpyrrolidone-2 or N-methylimidazole as an activator for hypochlorite in the desizing according to claim 4.