Emodin and dermocybin natural anthraquinones as high-temperature dispere dyes for polyester and polyamide
Pure natural anthraquinones, emodin and dermocybin, isolated from the fungus Dermocybe sanguinea, are for the first time used as disperse dyes for polyester and polyamide fabrics using a high-temperature dyeing method, accompanied with a reference dyeing with CI Disperse Red 60. The color of each dyed material is investigated in terms of the ciELAB L*, a*, and b* values, and color fastness to light, washing, and rubbing are tested according to the *so standards. Emodin dyes polyester bright yellow and dermocybin bright reddish-orange, and the fabrics show excellent color-fastness results. Emodin and dermocybin successfully dye polyamide brownish-orange and wine-red, respectively, but the fastness results are only moderate. This study shows that pure natural anthraquinone compounds can produce bright hues and color-fastness properties equivalent to those of synthetic disperse dyes, and thus providing useful alternatives to the synthetics.
Colors are an important part of our everyday life, and since prehistoric times, colors have had profound anthropological, psychological, aesthetic, functional, and economic impacts on society. Since the discovery of Mauveine by Perkin in 1856, the development of synthetic organic dyes has been enormous. In recent years, the harmful effects of synthetic dyes and their industrial by-products on humans and the environment have become a question of debate. Thus, along with technical and economic considerations, ecological concern has gained increasing importance .
In the food industry, natural colorants have been used increasingly to replace synthetic ones [4, 14, 15], even though they are more expensive, require more material to achieve an equivalent color strength, and are not as easily applicable as the synthetic colorants . In textile applications, signs of a renaissance of natural dyes can be seen in the rising demand for ecologically safer textiles and an interest in dyeing with natural dyes [6, 10, 21]. According to some researchers [3, 5, 21], natural dyes cannot compete with synthetic dyes in the textile industry because their color-fastness properties are in most cases reported to be inadequate and the material costs are high compared with synthetic dyes. Admittedly, economics and availability factors are dominant at the moment, but research together with new techniques and changing attitudes will influence the scene [6, 10].
Nature produces potential dyes that could be used more widely. Plants and fungi serve as a renewable source of raw material from which natural pigments can be isolated using advanced techniques. Furthermore, in the future, natural dyes offer an alternative to dwindling fossil resources, particularly enzyme technology combined with genetic engineering or cell cultures [10, 18]. The results from this study suggest that pigments isolated from fungi provide, without modification, good alternatives to synthetic dyes. It is also possible to modify natural dyes chemically .
At any rate, there is increasing interest in developing textile dyes from natural sources. In most studies, efforts have been made to improve and optimize the dyeing methods using natural dyes for natural fibers [1, 2, 8, 13, 17, 21, 26]. Some applications of natural dyes can be found for synthetic fibers as well [16, 21, 26]. For example, polyester has been dyed with natural dyes using high-temperature (Hr) dyeing. In these studies, the natural dyes were obtained by extracting leaves, bark, roots, etc., and so the dye liquors were more or less complex mixtures of different colorants . This is probably the reason that the results, ie., the hues and light-fastness properties of the dyed materials, have been discouraging or only moderate.
Instead of using crude plant extracts, we are interested in using pure natural compounds as dyes for textile materials. Compared with higher plants, we consider fungi a more ecological and interesting source of pigments, since we know that some fungal species are rich in stable colorants such as anthraquinones [7, 20, 23-25]. In our previous studies 2 [11, 19], we isolated anthraquinone pigments from the fungus Dermocybe sanguinea and, after thorough purification, characterized the compounds by spectrometric methods. For the dyeing experiments, the two main pigments, emodin and dermocybin, were preparatively separated by multiple liquid-liquid partition. In this paper, we will describe their application as disperse dyes in the HT dyeing of polyester and polyamide fabrics. We measure the color of each dyed material in terms of the cELAB L*, a*, and b* values, and we test the color fastness to light, washing, and rubbing according to the iso standards. The results for dyed polyester are excellent and for polyamide moderate. We discuss the dyeing properties of emodin and dermocybin and compare them with a commercially available, synthetic anthraquinone dye, CI Disperse Red 60.
The analytical-reagent grade chemicals included sodium hydroxide and formic acid (98%) from E. Merck (Darmstadt, Germany), and sodium dihydrogen phosphate and ammonium sulphate from J. T. Baker Chemicals B. V. (Deventer, Holland). All water was distilled.
The 100% polyamide knitted fabric from Orneule (Orivesi, Finland) and the 100% polyester satin woven fabric from Finlayson (Forssa, Finland) were both bleached. To avoid shrinking in the dyebath, thus ensuring uniform dye diffusion, the polyester fabric was heatset before dyeing by keeping it at 180 deg C for 2 hours and then letting it cool in the oven till the next day. For dyeing experiments, the fabric was cut into 10 g pieces and held in the oven at 50 deg C for 2 hours. After cooling in a desiccator, the exact dry weights were measured.
Emodin and dermocybin (Table 1) were isolated from the fungus D. sanguinea by a new enzymatic method developed by Hynninen . In the method, the endogenous beta-glucosidase enzyme [EC 22.214.171.124, beta-D-glucoside glucohydrolase] of the fungus was used to catalyze the hydrolysis of the O-glycosyl linkage in emodin- and derinocybin-1-beta-glucopyranosides. A 10.5 kg amount of fresh fungi yielded 56 g of fraction 1 (94% of the total pigment amount), containing almost exclusively emodin and dermocybin at a ratio of about 3:1, and 3.3 g of fraction 2 (8%), containing mainly hydroxy– anthraquinone carboxylic acids [11, 19].
The emodin and dermocybin in fraction 1 were preparatively separated from each other by multiple liquid-liquid partition (MLp)2. The stationary organic phase consisted mainly of isopropylmethyl ketone (Mtc) and the mobile aqueous phase of 0.1 M sodium phosphate buffer with a stepwise pH-gradient. Approximately two-thirds of the dermocybin was distributed into the aqueous phase at pH 9.1 (K = c^sub aq^/c^sub org^ = 1.58), whereas emodin remained at this pH totally in the organic phase.2 It is also possible to partition the emodin and dermocybin between the PAK phase and the aqueous phosphate buffer phase in a separatory funnel using a slightly higher pH than that used in the MLLP, i.e. pH 9.5. According to the results from the uv/vis and mass spectrometric measurements , the purity grades of emodin and dermocybin were 99%.
To compare the dyeing properties of the natural anthraquinones with those of synthetic disperse dyes, we used a commercial anthraquinone preparation (Terasil Red FB(TM), from Ciba Specialty Chemicals, Finland) of CI Disperse Red 60 (Table I) as a reference.
A 10 g sample of polyester fabric was dyed with a 1% (of the weight of the fiber) dye solution in 0.05 M sodium phosphate buffer adjusted to pH 3.5 with 98% formic acid. The liquor to fabric ratio was 20:1 and the dyeing occurred in an Original Hanau Linitest laboratory machine.
To prepare a homogenous dye dispersion, 100 mg emodin or dermocybin was first dissolved in 200 ml distilled water, the pH of the solution was adjusted to 10.5 with 10% NaOH, and the temperature of the dye solution was raised to 50 deg C. The pH of the solution was then lowered to 4.0 by adding 1.380 g sodium dihydrogen phosphate, which caused formation of a finely divided dye dispersion. The color of the dispersion was yellow for emodin and yellowish-orange for dermocybin. After that, the pH was adjusted to 3.5 with 98% formic acid. The thoroughly wetted fabric sample was immersed in the dye dispersion and the vessel was closed. The temperature of the dyebath was raised from 50 deg C to 130 deg C at 2 deg C/minute, maintained at 130 deg C for 1 hour, and then lowered to 60 deg C in 10 minutes. The dyed fabric sample was rinsed with water and dried at room temperature.
The dye dispersion for the reference dyeing processes was prepared according to the manufacturer’s instructions. A 100 mg amount of CI Disperse Red 60 and 400 mg ammonium sulphate were placed into a vessel and a 200 ml volume of water was added. The pH of the dye dispersion was adjusted to 4.5 with 98% formic acid. No other auxiliaries were used. The dyeing conditions for the fabric sample were the same as for the natural anthraquinones.
MAXIMUM DYE-UPTAKE MEASUREMENTS
Spectrophotometric dye-uptake measurements were performed for each natural anthraquinone in the dyebath at the end of the dyeing process. Five standard solutions representing dye uptakes of 0, 25, 50, 75, and 100% were prepared by first measuring 1.00, 0.75, 0.50, 0.25, and 0.00 ml of fresh dye solution into five test tubes. Then 0.00, 0.25, 0.50, 0.75, and 1.00 ml distilled water were added, respectively, to give five standard solutions of 1.0 ml each. These standards were further diluted to 5.0 ml with water, which gave for the strongest solution an A^sub MAX^
COLOR FASTNESS TESTING
The color of the dyed material was determined as the Cm,B L*, a*, and b* values using a Chromameter CR-210 equipped with a ciE illuminant C (Minolta, Japan).
Color fastness to light was determined according to the ISO 105-1302-1978 standard using an Original Hanau System Cassela apparatus provided with a xenon arc lamp and a side-changing mechanism. The exposure time for the samples was 500 hours. The rating values varied in the range 1-8, 8 being the best value.
Color fastness to domestic and commercial laundering was determined according to the ISO 105-C06-1994 standard. The color-fastness test was performed as a single C2S test at 60 deg C for 30 minutes using 25 steel balls. The ECE reference detergent for color-fastness testing, without fluorescence indicator, was used. A multi-fiber adjacent fabric containing wool (wo), cellulose acetate (cA), silk (SE), polyamide (PA), cotton (co), and triacetate (cTA) was used to test staining of polyamide. Two single-fiber adjacent fabrics, cotton and polyester (PEs), were used for polyester. The numerical rating for staining was given by the gray scale numbers 1-5, 5 being the best value. The color change of the specimen was given by the gray scale numbers 1-5. The change in color was, in addition, determined by the cLt.AS values, DeltaE, DeltaL, Deltaa*, and Deltab*, using the unwashed dyed material as standard. The DeltaE values were converted to equivalent gray scale ratings according to the literature .
Color fastness to rubbing was tested according to the ISO 105-X12-1993 standard. The numerical rating for dry and wet staining was given by the numbers 1-5, where 5 is the best value.
Results and Discussion
DYE UPTAKE AND SPECIMEN COLOR
Our experiments showed that the natural hydroxyanthraquinones, emodin and dermocybin, used as HT-disperse dyes for polyester fabric, gave uniform dyeings with good color yields and excellent color-fastness results. Spectrophotometric measurements of the dyebath at the end of dyeing showed that there was no dye left in the mother liquor. The A^sub MAX^, values of 0.013 for emodin and 0.014 for dermocybin indicated that the adsorption of dye molecules onto the polyester fibers was higher than 99%. The result for CI Disperse Red 60 was similar. Emodin and dermocybin successfully dyed knitted polyamide fabrics, but the color-fastness results were not as promising as for polyester. Spectrophotometric measurements of the dyebath containing the polyamide samples showed that the dye uptake was higher than 99% for emodin and 97% for dermocybin. The better uptake for emodin compared with dermocybin might be because emodin is a slightly flatter and smaller molecule than dermocybin and hence can penetrate and diffuse more easily into the fibers. Both polyester and polyamide are hydrophobic and highly crystalline fibers. The better adsorption and color-fastness properties of polyester compared with polyamide can be explained by several structural differences. Polyamide contains alkyl chains, which have a negligible effect on dye substantivity . In contrast, the aromatic a-electron system of the terephthalic acid unit in the polyester molecule may interact with the iT-electron system of the anthraquinone molecule. Thus, higher dye uptake and better fastness properties are possible.
Table II summarizes the CIELAB color values for the natural anthraquinones and CI Disperse Red 60. Emodin dyed polyamide brownish-orange and dermocybin winered, but on polyester the colors were totally different: bright yellow and bright reddish-orange, respectively. The colors of CI Disperse Red 60 on polyester and polyamide were somewhat alike, but the hues were lighter and brighter for polyester.
Table III summarizes the color-fastness properties of the dyed fabrics. For polyester, the test of color fastness to light gave value 7 for emodin, 6 for dermocybin, and 7 for CI Disperse Red 60. In the test, there was a slight change from bright yellow to orange with emodin, probably due to the photochemical decay of the dye molecule. In the case of polyamide, the values of color fastness to light were poor for emodin and dermocybin and moderate for CI Disperse Red 60.
In the case of polyester, the test of color fastness to washing gave excellent results for emodin and dermocybin as well as for CI Disperse Red 60. The DeltaE, DeltaL, Deltaa*, and Deltab* values (Table II) of the washed materials indicated that only slight changes in the color values were detected. For the DeltaE values, the corresponding gray scale numbers are listed in Table III, which also shows the visually assessed numbers for color changes. For emodin, dermocybin, and CI Disperse Red 60, the change in color was not manifested visually (rating 5 for all), but the numbers converted from DeltaE gave slightly different results (4, 4-5, and 4-5, respectively). Differences between the light source in the instrument (illuminant C) and that used for visual assessment (D^sub 65^ may explain these differences. Another reason for the differences might originate from the variations in fluorescent species derived from the bleaching agents . The distribution of the bleaching agent in the specimen, the test liquor, and the adjacent fabric during the washing test may also partly explain the anomalous instrumentally obtained ratings . For polyamide dyed with emodin, the changes in DeltaE, DeltaL, Deltaa*, and Deltab* values after washing were noticeable and the change in color was easily manifested visually (rating 1-2, Table III). Instrumentally and visually assessed changes in the color values differed for dermocybin and CI Disperse Red 60. The visually assessed values were slightly lower than those obtained instrumentally. It is possible that the change in the color shade affected the visual gray scale rating, so that the change in color was overestimated (Table III). For polyester, washing fastness to staining was excellent with all dyes used and, for polyamide, the corresponding results were moderate (Table III).
In the case of polyester, color fastness to rubbing was somewhat better for emodin than for dermocybin, and the results for CI Disperse Red 60 were identical to those for emodin (Table III). The lower rubbing fastness for dermocybin indicates that the molecules were adsorbed on the surface of the fiber and diffused only partly into the interior. It is possible that the der-mocybin aggregates were larger than the emodin aggregates, because dermocybin has more hydroxyl groups available for hydrogen bonding and one methyl group out of the macrocycle plane, thus hindering its absorption into the fiber. For polyamide dyed with the natural anthraquinones and with CI Disperse Red 60, color fastness to rubbing reached the best values of the properties tested.
The results of this investigation indicate that emodin and dermocybin natural anthraquinones are very suitable as HT-disperse dyes for polyester fabrics. They dye polyester bright yellow and bright reddish-orange, respectively. The color-fastness properties of dermocybin on polyester are satisfactory, even though, in the rubbing and light fastness tests, dermocybin reaches slightly lower results than emodin and CI Disperse Red 60.
The natural anthraquinones successfully dye polyamide using the HT method, but the color-fastness results are not as good as for polyester. Thus, an interesting study would be to investigate the dyeing properties of polyamide with natural anthraquinones using the methods of normal disperse dyeing and metal-complex dyeing.3
We were interested in applying pure natural compounds to textile materials to avoid weak and uneven dyeing with crude extracts of natural dyes, which in most cases are variable mixtures of several chemical compounds. Note also that the impurities can have an undesirable effect on the color-fastness properties as well as on the shades of the colors. Our study shows that pure natural anthraquinones can provide bright hues and color-fastness properties comparable to those of synthetic disperse dyes, thus providing good alternatives for the latter dyes. They can serve as a noteworthy source of raw material in the future. Chemical modification of natural compounds could be an interesting field of study, as it could appreciably facilitate the syntheses of dye molecules.
We gratefully acknowledge the financial support from the Foundation for Research of Natural Resources in Finland.
1 To whom correspondence should be sent.
2 P. H. Hynninen and R. Raisanen, manuscript in preparation.
3 R. Raisanen, P. Nousiainen, and P.H. Hynninen, manuscript in preparation.
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Manuscript received November 3, 2000; accepted December 19, 2000.
Department of Home Economics and Craft Science and Department of Chemistry, University of Helsinki, FIN-00014 Helsinki, Finland
Institute of Fibre Materials Science, Tampere University of Technology, FIN-33101 Tampere, Finland
PAVVO H. HYNNINEN1
Department of Chemistry ( A.I. Virtasen Aukio 1), University of Helsinki, FIN 00014 Helsinki, Finland
Copyright Textile Research Institute Oct 2001
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