WO2011012471A2

WO2011012471A2 - Natural dyes

Info

Publication number: WO2011012471A2
Application number: PCT/EP2010/060339
Authority: WO
Inventors: Thomas Bechtold; Christa Fitz-Binder; Amalid Mahmud-Ali
Original assignee: Universität Innsbruck
Priority date: 2009-07-28
Filing date: 2010-07-16
Publication date: 2011-02-03
Also published as: AT508000B1; EP2478060A2; WO2011012471A3; AT508000A4

Abstract

The invention relates to a method for producing a solution containing a dye and to a method for dyeing a substrate, characterised by the following steps: a. transferring the dye from biological material into an aqueous medium, b. precipitating the dye from the aqueous medium by the addition of a suitable precipitant, wherein at least a part of the precipitant forms a part of the dye precipitate, c. separating the dye precipitate from the aqueous medium and d. transferring the dye from the dye precipitate into an aqueous medium by adding a release agent and dyeing the substrate with an aqueous solution by releasing the dye from the dye precipitate by adding a release agent to the aqueous solution, characterised in that the release agent is a complexing agent, selected from the group of polycarboxylates, polycarboxylic acids, amino polycarboxylic acids, such as NTA or EDTA, oxalate, gluconate, citrate, phosphate, polyphosphate or combinations thereof.

Description

natural dyes

The invention relates to a method for producing a solution containing a dye of biological material. Furthermore, the invention relates to a method for dyeing a substrate, preferably textile, by means of a dye of biological material.

In the case of colored substrates, a distinction must be made between dyes colored with pigments and with pigments (including the historical dyes). Dyes are in dissolved form for the dyeing process and show affinity / substantivity to the substrate, the material to be dyed. Pigments e.g. Ingredients in artist paints and varnishes are in insoluble form and have no affinity for the material to be dyed. It is therefore an appropriate matrix to provide a binder system whereby the pigment is bound to the carrier. With the exception of pigment dyeing, where binder systems must be used in a targeted manner, when dyeing textiles and leather dyes are applied from their, usually in water, dissolved form and fixed by various processes on the substrate.

Natural dyes are substances that are obtained from biological material, such as from vegetable and to a small extent from animal sources of raw materials, by extraction and serve to color a substrate. The extraction can be carried out in aqueous solution or by addition of chemicals. For example, the literature recommends the addition of alkalis such as soda or caustic soda, of acids or of solvents. The aim of these concepts is to produce as concentrated an extract as possible of extracted plant / animal origin.

When using natural dyes from vegetable raw materials, a central problem is the fact that the content of coloring matter in the plant is relatively low (usually <5% by weight), therefore, the achievable levels of natural dye in the aqueous extraction are limited.

Extracting the dyes with a solvent or with the addition of chemicals dramatically degrades the resource balance of the dye recovery and removes an ecologically unmanageable amount of chemicals from the process with the extracted material. It comes therefore for a lasting extraction of the Natural dyes only water as extractant in question. For the production of concentrated products a substantial removal of the water used in the extraction is necessary. However, water has a very high specific heat of vaporization.

The production of concentrated products is therefore only possible with high energy input (evaporation) or expensive processes (ultrafiltration / reverse osmosis), which severely worsens the ecological profile of the dyes.

From the point of view of resource consumption even more disadvantageous is the procedure in which the natural dye is precipitated as pure substance by the addition of ethanol from the solution, then further concentrated by evaporation and dried.

The dye concentrates provided according to the prior art therefore do not meet the requirements for ecological and resource-conserving products and are therefore more likely to be regarded as marketing products. A critical examination of the aspects of sustainability, energy consumption and resource consumption shows that the concentration step always leads to a deterioration in the overall balance. According to the state of the art, a resource-saving extraction by aqueous extraction and the immediate use of the extracts for dyeing purposes takes place locally in the textile dyeing. The relatively dilute aqueous extracts are used directly in the dyeing plants. As a result, a concentration can be avoided, but the achievable color depths are limited and the process is limited to techniques with "long liquor", ie with a high ratio of volume dyebath to commodity eg 20: 1. This results in a solvent-free and chemical-free extraction of natural color fabrics From plant materials and energy-saving use, the direct extraction on site, however, is logistically almost impossible for the dyeing companies, since the handling of extremely large amounts of plant material is required.

In the extraction of color lakes and pigments, the extracted dye is deliberately converted by the addition of precipitants such as metal salts in an insoluble form. The precipitation of natural dyes is known as color lakes. These are insoluble pigments that are suitable for artistic purposes, but not for dyeing textile products. As already described, pigments as insoluble color bodies no longer have any affinity for the substrate and are therefore unsuitable as dyes. The precipitation of tannin with aluminum salts to form insoluble aluminum complexes is known and is used for example as an anti-fouling component in boat paints.

The formation of soluble aluminum complexes with anthocyanin dyes has also been described in the literature. Although such complexes may be significant in terms of color engineering, the problem of the low concentration of complex in the extract remains even with knowledge of complex formation in solution, so that again an enrichment step is required.

Also known is the possibility to produce stain-colored complexes with natural dyes on the fiber. This can be done by different methods (pre-etching, meta-pickling = addition to the dyebath, Nachbeize), but in this case arises again insoluble metal complex, which remains on the fiber. Virtually all available metal salts have been proposed in the art for textile dyeing purposes. Important representatives are titanium, iron, aluminum, calcium, magnesium, tin, zinc, manganese, copper salts. When using these substances form insoluble fixed metal complexes with the addition of the pickling on the goods. Use of such dyeing complexes is not possible due to their insolubility. The unfixed portions of metal complex are washed out.

Often, the pickling process by the dyeing process is carried out separately as a pre- or Nachbeize, since here at least the pickling baths can be reused. If the meta-pickling process is used, the stain is added directly to the dyebath, making re-use of the dyebath impossible due to the presence of undissolved pigments. A crucial difficulty in the use of natural dyes therefore lies in the problem of either having to use dilute aqueous solutions or to spend a large amount of resources for concentration. Both solutions limit or prevent the more extensive use of natural color fabrics as sustainable dye systems.

The use of insoluble color lakes does not provide a solution to the issue, since the insoluble pigments are not suitable for dyeing and therefore only for use as painter pigments etc. can be used.

GB 1857 01390 A (Cowper) describes the preparation of solutions and extracts of madder and other plant materials. By adding metal ions, a precipitation of the dissolved dye takes place. GB 1 119 359 describes the extraction of dyes from grape skins in hydrochloric acid solution and the subsequent precipitation with CaCl ₂ . The precipitate can then be redissolved in HCl. In the introduction to the specification, DE 172 662 mentions a process in which a lake of color is prepared by adding metal ions from a woodlog or yellow wood extract. The paint can be resumed by organic acids. A similar process is disclosed in GB 1877 00674.

Object of the present invention is to provide methods of the type mentioned, in which the disadvantages of the prior art are reduced.

This object is achieved by a process for preparing a solution containing a dye, characterized by the steps (in this order):

a. Transferring the dyestuff from biological material into an aqueous medium, b. Precipitating the dye from the aqueous medium by adding a suitable precipitating agent, the precipitant forming part of the precipitate, c. Separating the dye precipitate from the aqueous medium and

d. Transferring the dye from the dye precipitate in an aqueous solution by adding a releasing agent, wherein the release agent is a complexing agent selected from the group of polycarboxylates, polycarboxylic acids, aminopolycarboxylic acids, such as NTA or EDTA, oxalate, gluconate, citrate, phosphate, polyphosphate or combinations thereof.

This object is further achieved by a method for dyeing a substrate, preferably textile, characterized by the steps (in this order):

d. Dyeing the substrate with an aqueous solution by releasing the dye from the dye precipitate by adding a releasing agent to the aqueous solution, wherein

the release agent is a complexing agent selected from the group of polycarboxylates, polycarboxylic acids, aminopolycarboxylic acids, such as NTA or EDTA, oxalate, gluconate, citrate, phosphate, polyphosphate or combinations thereof.

The present invention thus overcomes the problem of the low concentration of the dye in the extract by providing a method for resource-saving production of a dye concentrate by precipitation and enrichment, wherein the precipitates are carried out so that the dye in the dyeing process according to the invention is soluble again and thus on the to be dyed Can raise well.

The step of the present invention is primarily to provide a suitable dye recovery process, a suitable dye formulation, and a suitable dyeing process which can usefully utilize these precipitates.

In the procedure according to the invention, an aqueous dye extract of the biological material is first prepared (step a). The step a, ie the transfer of the dye from biological material into an aqueous medium is carried out by pure water or at most with the auxiliaries mentioned below. Anyway, this step should be done without organic solvent. By addition of suitable precipitant takes place the formation of an insoluble precipitate (step b). However, the precipitation should proceed in such a way that at least part of the precipitant forms part of the precipitate, ie it is incorporated in the precipitate. This can be done according to the invention in two ways. On the one hand, the precipitant can chemically react with the dye and form the precipitate. For example, the precipitating agent may comprise metal ions which form a complex or salt with the dye. The precipitant in this case is selected such that the complex or salt has a lower solubility product than the dye with the other materials in the solution. Part of the precipitant (eg the metal ions) is thus chemically bound in the precipitate. On the other hand, the precipitant itself can form a precipitate and absorb the dye without chemical bonding. In this case, the dye is adsorbed on the precipitate.

The precipitate is concentrated by separating it from the aqueous medium (step c).

When selecting the precipitating agent, care should be taken that the precipitate can be dissolved again in the following step without adversely affecting the dyeing process.

In processes for preparing a solution containing a dye, a solution with a higher concentration of dye is actually prepared than can be obtained by simple extraction (step a). An essential step is the final transfer of the dye from the dye precipitate in an aqueous solution by adding a release agent. Thus, the desired concentration of dye in the aqueous solution can be adjusted.

The dyeing process is modified in the procedure according to the invention so that the dye concentrate or the pigment preparation first releases the dye again, then the dyeing process is carried out. However, the release of the dye can also be carried out in the presence of the substrate (step d in the process for dyeing a substrate). The dye concentrate or pigment concentrate is precipitated as a dye preparation by precipitation of the dye from the aqueous extract of the plant material by using precipitants, preferably metal salt ions, particularly preferably salts of the cations iron, calcium, aluminum, magnesium, titanium. In the preparation of the extracts and also in the precipitation of the dye precipitates, adjuvants such as caustic soda, soda, ammonia, inorganic and organic acids for pH adjustment, as well as other chemicals that promote precipitation, such as phosphates, silicates or polyelectrolytes, can be added. These adjuvants may serve to improve the extraction yield and / or to favor the precipitation of the extracted dye.

In a preferred form, in addition to the metal salt addition, the precipitation pH is adjusted. In a particularly preferred embodiment, only the addition of the metal salt takes place in dissolved form. Typical examples of precipitants are FeSO ₄ , KA 1 (SO ₄ ) 2 or (NH ₄ ) 2 Fe (SO ₄ ) 2. The amounts of precipitant used in the precipitation depend on the extract strength, usually concentrations below 100 g / l precipitant, preferably to use metal salt, advantageous concentrations below 50 g / l precipitant, preferably metal salt, in a particularly preferred embodiment are between 5 , 0 and 0.1 g / l precipitant, preferably metal salt used. The pH of the solution depends on the solubility behavior of the metal ions used and the need for chemicals to adjust the pH. A working range between pH 2 and pH 12 is advantageous, and the precipitation takes place particularly advantageously at pH values between 4 and 10.

The insoluble dye product formed by precipitation is concentrated by sedimentation and filtration and can be provided as an aqueous dispersion or as a dried and ground product for the following dyeing process. Other forms of concentration are possible, e.g. Centrifugation, spray drying etc.

Plant dyes which are suitable for the procedure according to the invention originate, for example, from the group of flavonoid dyes, but others may also be used Dyes, for example anthraquinoid dyes, indigoid dyes and dyes from the group of polyphenols can be obtained and used by the process according to the invention. With knowledge of the procedure of the present invention, it will be readily apparent to one of ordinary skill in the art to devise suitable working conditions for a selected natural dye plant in terms of precipitant, precipitation conditions, and dye preparation, as well as staining procedures.

For the dye preparation of the invention, it is advantageous if the selection of the precipitant is done carefully. It is advantageous to use such precipitating agents that are compatible for the desired dyeing process, do not interfere with the dyeing process during the dissolution of the pigment, or can be so blocked / masked during the dyeing process that it is not hindered.

When preparing the dye for the dyeing process in the inventive procedure, the treatment of the pigment with a suitable chemical, which is able to cleave the dye pigment and release the original dye again. Particularly suitable for this purpose are complexing agents from the group of polycarboxylates and polycarboxylic acids, aminophenylcarboxylic acids such as NTA (nitrilotriacetic acid) and EDTA (ethylenediaminetetraacetate), oxalate, gluconate, citrate and phosphates or polyphosphates, which can dissolve a precipitate formed. In addition, it is also possible to admix acids which are particularly preferably selected from the group consisting of acetic acid, hydrochloric acid, citric acid, gluconic acid and oxalic acid.

The dye pigment which is unsuitable for dyeing is thus dissolved in the dissolution step, for example by treatment with, for example, acid or complexing agents, by mobilizing the precipitation agent causing the precipitation, such as the metal ion, by pH shift or complex formation. The conditions to be used are advantageously selected so that the dye molecule is not adversely affected. The dyestuff solution thus obtained can now be used for dyeing by adding it to the prepared dyebath. The dyeing is carried out according to the usual dyeing process for natural dyes, it can be used as desired pickling and pickling. When using metal stains care must be taken that the chemicals used to dissolve the dye pigment do not bind the added stain as well. However, knowing the procedure according to the invention, this can be easily corrected by using a sufficiently increased amount of pickling that the amount of free metal ion required for pickling dyeing is available.

It can further be provided that precipitants and / or release agents are added to the substrate during the dyeing step to determine the desired shade. It is thus possible to adjust the color on the substrate at any time. By suitable release agents, or precipitants, in addition to the different brightness and other shades can be released. For example, the precipitation of the dyes extracted from goldenrod can be accomplished by the addition of iron salts to the olive-dark precipitate, after complexation of the iron upon redissolution of the salt, e.g. by oxalate, then a yellow dyeing on wool can be done using aluminum stains.

In a particularly preferred method, the dissolution of the pigment form is carried out by acid without complexing agent and the restoration of the complex on the fiber to be dyed by simply raising the pH in the dyebath.

The procedure described allows the energy and resource-saving production of a concentrated natural dye product, as it is particularly suitable for the market of ecologically oriented manufacturers and consumers.

The formation of precipitate leads to a very high concentration, so that the application of the product is also suitable for processes which require relatively high dye concentrations, eg. continuous dyeing and printing techniques. With respect to the dyeable substrates, there are no limitations, the method is therefore suitable for all classes of textile fibers, particularly preferred are high-receptivity materials for natural color fabrics such as wool, silk, linen, polyamide. Also for the user in the textile industry, in contrast to the currently proposed in the prior art on-site extraction of the plant material no investment costs, since the handling of the conventional solvent technique of synthetic dyes is similar. Standardization and storage are also greatly simplified for the plant dye manufacturer.

Application examples:

In the following application examples, the extract of the goldenrod is described as an example. To the knowledge of the invention, it is readily apparent to one of ordinary skill in the art to apply the technique to other plant extracts, e.g. of bark, madder, resede and to optimize. The examples are therefore representative of the technology.

Application Example 1

125 g dried Canadian goldenrod are boiled in 2.5 1 extract for 1 hour. The undissolved plant parts are filtered through a cotton cloth. To 500 ml of the extract is added 50 ml of a solution of 50 g / l FeSO ₄ , KAl (SC ₂ ) ₂ or (NH ₄ ) ₂ Fe (SO ₄ ) ₂ . The resulting precipitate is filtered off and dried, another fraction is obtained after a precipitation time of 1 week. 0.76 to 2.2 g of olive-colored solid residue are obtained. 0.1 g of the precipitate are then dissolved in 50 ml of various aqueous acid solutions (concentration 1 g / l each). The solution thus obtained is used without further treatment for dyeing 2.5 g of wool yarn (45 min at about 84-89 ° C).

The color change is characterized by measuring the color coordinates as CIELab values. (L * = brightness (0 = black, 100 = white) a * = red - green (- value = green, + value = red) b * = yellow - blue (- value = blue, + value = yellow) The CIE Lab system is a color space defined by the International Commission on Illumination (Commission Internationale d'Eclairage, CIE 1976). Table 1 shows the color coordinates of the colorations obtained after dissolution of the precipitate in various acids (oxalic acid, gluconic acid, citric acid and hydrochloric acid) on woolen yarn.

Table 1

For purposes of comparison 5 g of wool in 100 ml extract at 84-89 ⁰ C. after the pickling process meta- or without pickling colored. In the pickling process, 5 ml of the 50 g / l pickling solution are added. The color coordinates are shown in Table 2.

Table 2

(Averages of two stains)

A comparison of the color coordinates of the dyeings 2a and 5 or 7 shows that even without complex correction of the color intensity, similar color coordinates are already obtained. In particular, the advantageous use of oxalic acid to dissolve the precipitate can be seen in sample 2a.

Application Example 2:

50 g of goldenrod are boiled in 1 liter of water for 60 minutes and filtered through a cloth. 100 ml of extract were with 10 ml of a pickling with 50 g / l salt concentration (FeSO ₄ , KA1 (SO ₄ ) ₂ or (NH ₄ ) ₂ Fe (SO ₄ ) ₂ ) precipitated and with ammonia solution to pH 5, 7 or 9 set. The solution is heated for a further 35 minutes on the water bath at 80-90 ⁰ C and then allowed to stand overnight at room temperature. The next day, the precipitate is filtered through a paper feeder. Depending on the precipitation conditions, 1.1 to 1.5 g of a yellow-olive precipitate are obtained (Table 3).

Table 3

0, 1 g of the dried extract are dissolved in 50 ml lg / 1 oxalic acid in a hot water bath for 10 min, then 2.5 g wool yarn are added, dyed at 85-90 ⁰ C for 10 min, then 2.5 ml of a 5 g / l pickling added and further treated at elevated temperature for 35 min, after dyeing, the samples are rinsed with water and dried in air. For comparative purposes, dyeings are also carried out in which no stain is added in addition. Table 4 shows the color coordinates of the patterns.

Table 4

Three precipitation pH values were investigated for each of the precipitants selected. After the redissolution of the precipitate shows that the full color depth after renewed addition of stain can be achieved in the dyebath. Therefore, the patterns 11, 12, 13 are substantially darker than the comparison patterns 8, 9, 10, which were dyed without addition of beech, the same applies to the patterns 17, 18, 19 with respect to the patterns 14, 15, 16, as well as the patterns 23, 24, 25 with respect to the patterns 20, 21, 22.

In order to confirm the procedure, comparative experiments with precipitate (dye product) without addition of acid, ie without previous dissolution, were also carried out 26, 28, 30 as well as with additional addition of additives 27, 29, 31. The bright color values in comparison with the samples carried out according to the invention confirm the described Procedure. In the samples 27, 29, 31 it should be considered that the added mordants also have a certain acid character, which observed here, in comparison to samples 26, 28, 30, somewhat stronger stains are here on the process claimed in the invention, namely attributed to the treatment of precipitation with acidic substances.

Claims

claims

A process for preparing a solution containing a dye characterized by the steps of:

a. Transferring the dyestuff from biological material into an aqueous medium, b. Precipitation of the dye from the aqueous medium by addition of a suitable precipitant, wherein at least a portion of the precipitant forms part of the precipitate,

c. Separating the dye precipitate from the aqueous medium and

d. Transferring the dye from the dye precipitate into an aqueous solution by adding a releasing agent, wherein the releasing agent is a complexing agent selected from the group of polycarboxylates, polycarboxylic acids, aminopolycarboxylic acids such as NTA or EDTA, oxalate, gluconate, citrate, phosphate, polyphosphate or combinations thereof ,

2. A process for dyeing a substrate, preferably textile, characterized by the steps:

c. Separating the dye precipitate from the aqueous medium and

d. Dyeing the substrate with an aqueous solution by releasing the dye from the dye precipitate into the aqueous solution by adding a releasing agent, the releasing agent being a complexing agent selected from the group consisting of polycarboxylates, polycarboxylic acids, aminopolycarboxylic acids such as NTA or EDTA, oxalate, Gluconate, citrate, phosphate, polyphosphate or combinations thereof.

3. The method according to claim 2, characterized in that are added to determine the desired color on the substrate precipitating agent and / or release agent during the dyeing step.

4. The method according to any one of claims 1 to 3, characterized in that the transfer of the dye from the biological material into an aqueous medium by aqueous extraction of the biological material.

5. The method according to any one of claims 1 to 4, characterized in that the precipitant comprises at least one kind of metal salt ions.

6. The method according to claim 5, characterized in that the metal salt ion is selected from the group of ions of iron, calcium, aluminum, magnesium, titanium or combinations thereof.

7. The method according to any one of claims 1 to 6, characterized in that at least during a step a) to d) a Hilfssto ff is added.

8. The method according to claim 7, characterized in that the Hilfsssto ff is selected from the group sodium hydroxide, soda, ammonia, the phosphates, the silicates, the polyelectrolytes, inorganic acids, organic acids or combinations thereof.

9. The method according to any one of claims 1 to 8, characterized in that at least during a step a) to d), the pH is adjusted.

10. The method according to claim 9, characterized in that the precipitation step at a pH of 2 to 12, preferably from 4 to 10, is made.

11. The method according to any one of claims 1 to 10, characterized in that as an additional release agent, an acid is used.

12. The method according to claim 11, characterized in that the acid is selected from the group acetic acid, hydrochloric acid, citric acid, gluconic acid, oxalic acid or mixtures thereof. Method according to one of claims 1 to 12, characterized in that the biological material is of plant origin