A cleaner and eco-benign process for wool dyeing with madder, Rubia ...

Int. J. Environ. Sci. Technol. (2016) 13:2569–2578 DOI 10.1007/s13762-016-1060-x

ORIGINAL PAPER

A cleaner and eco-benign process for wool dyeing with madder, Rubia tinctorum L., root natural dye L. Mehrparvar1 • S. Safapour1

•

M. Sadeghi-Kiakhani2 • K. Gharanjig2

Received: 26 September 2015 / Revised: 26 March 2016 / Accepted: 27 June 2016 / Published online: 12 July 2016 Ó Islamic Azad University (IAU) 2016

Abstract In this study, an alternative cleaner process over traditional metallic mordanting process for wool dyeing with madder, Rubia tinctorum L., root natural dye was presented. Wool surface was modified with novel ecofriendly and biocompatible cationizing agent having numerous free amine groups, namely chitosan–polypropylene imine dendrimer hybrid (CS-PPI). Modified wool demonstrated remarkable increase in dye uptake as compared to raw wool. Optimal dyeing results were obtained when CS-PPI 7 %, madder dye 20 % and dyeing pH 7 were employed. Dyeing results such as percent dye exhaustion and color depth emphasized auxiliary agents, i.e., metallic mordant and acid could be eliminated from wool dyeing process with madder dye. Saturation point shifted to lower dye concentrations in the treated wool suggested the same color depth could be obtained using lower amount of crude dye material. Wool modification with CS-PPI demonstrated no adverse impact on other properties such as colorfastness and color shade characteristics. In addition, treated wool exhibited excellent antimicrobial activity (nearly 100 % microbial reduction) against two common pathogenic microorganisms, Escherichia coli and Staphylococcus aureus which were almost durable after dyeing and subsequent repeated washes. In general, the results of this investigation showed that CSThe present research work was developed during 2014–2015 in Carpet Faculty, Tabriz Islamic Art University, Tabriz, I.R. Iran. & S. Safapour [email protected] 1

Faculty of Carpet, Tabriz Islamic Art University, PO Box 51385-4567, Tabriz, Iran

2

Department of Organic Colorants, Institute for Color Science and Technology, PO Box 16765-654 Tehran, Iran

PPI can be employed as an alternative eco-friendly ‘‘biomordant’’ as well as effective antimicrobial finishing material in wool dyeing with madder dye. Keywords Antimicrobial finishing Bio-mordant Chitosan–polypropylene imine dendrimer hybrid Ecofriendly Natural dyeing Wool surface modification

Introduction Wool has a unique combination of properties, including high water absorption, fire resistance, softness, luxury, resilience, high elasticity, stain resistance, easiness to clean, comfortable to wear, bulkiness, recyclability, texture retention, good dyeability and colorfastness, durability and the ability to moderate temperature and humidity by absorbing and releasing moisture, and for many centuries it has found use in clothing and floor coverings (Gashti et al. 2013). Wool is very important for human being to live in the eco-friendly world. Due to these facts, eco-friendly processing of wool (pre-treatments, dyeing and post-treatments) is critical to the added value of the resulting materials. Dyeing is an integral part of processing of textiles performed to add color and sophistication to textiles as well as raise product value. Until the twentieth century, natural dyes were the only source of color available, extensively used and traded. Nevertheless, natural dyes are seldom used in modern dyeing, except by specialist companies and craft dyers. Recently, most of the colorants used in commercial textile dyeing are synthesized by various means from by-products of fossil fuels, e.g., aniline and other aromatic derivatives. Nonetheless, oil supplies are limited and non-renewable resources (Kasiri and Safapour 2013). Currently, there is a move to find renewable resources to reduce the depletion of

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Int. J. Environ. Sci. Technol. (2016) 13:2569–2578

global supplies of fossil fuels, which has initiated research into natural products from plants (Bechtold and Mussak 2009). The revival interest in the use of natural dyes is also a result of the stringent environmental standards imposed by many countries in a response to the toxic and allergic reactions associated with synthetic dyes (Ghaedi et al. 2014; Kasiri and Safapour 2014). The major parts of natural dyes are anthraquinone, anthocyanin and flavonoid dyes, or polyphenolic compounds most of which have yellow, red and brown shades (Bechtold and Mussak 2009). Anthraquinone dyes belong to the group of most durable dyes, so they are often used in products that must satisfy strict requirements. Anthraquinones are relatively stable and lightfast, and they give a bright color (Bechtold and Mussak 2009). Dyer’s madder, Rubia tinctorum L., is one of the oldest and most popular red pigments found in nature on the Eurasian supercontinent. Madder has been used since antiquity for dyeing textiles in particular in Europe, the Middle East and India where the plant was indigenous. Madder has been considered as the most popular source of red color shades and also served to obtain pink, orange, purple, gray, brown and the most precious black and brunette shades with high color depth. Numerous papers dealing with various aspects of wool dyeing with madder natural dye have been published in the disclosed literature (Bechtold and Mussak 2009; Gashti et al. 2013; Kasiri and Safapour 2014; Manian et al. 2016). The pigment is extracted from the dried roots of the plant. The roots contain 2–3.5 % of di- and tri-hydroxyanthraquinone glycosids. Typical contents of alizarin found in different cultivars vary from 6.1 to 11.8 mg/g of roots. Average values for the amount of anthraquinones in 3-year-old cultivars of R. tinctorum L. are: pseudopurpurin 7.4 mg/g, munjistin

6.2 mg/g, alizarin 8.7 mg/g, purpurin 3.5 mg/g and nordamnacanthal 13.4 mg/g. The composition of the extracted anthraquinones differs between the varieties of Rubia (Fig. 1) (Goverdina et al. 2004). In the European madder (R. tinctorum L.), the major component forming the natural dye is alizarin (1,2-dihydroxyanthraquinone) (Gupta et al. 2001). In addition to coloring properties, antimicrobial activity against various pathogenic gram-positive and gram-negative bacteria, yeasts, filamentous fungi and actinomycetes has been reported for R. tinctorum L. extracts (Kalyoncu et al. 2006). Furthermore, improved insect resistance for the carpet beetle was shown for the wool dyed with madder natural dye (Park et al. 2005). A major problem of natural dyes is their relatively low affinity to the wool, which leads to considerable proportion of not exhausted pigment in the used dye bath. Thus, aspects of bath reuse and recycling have been investigated to decrease the amount of plant crude material needed for coloration of a certain amount of textile material. Generally, in wool dyeing with madder, a metallic salt so-called mordant is necessary for satisfactory dyeing and colorfastness properties (Kasiri and Safapour 2015). Furthermore, some assistant materials such as acetic acid, formic acid, oxalic acid, cream of tartar (potassium hydrogen tartrate) may be used for dyeing pH regulation, color shade extension, colorfastness improvement, and so on (Mortazavi et al. 2012). Mordants comprised heavy metal ions such as chromium, copper, iron, tin, cobalt, nickel and aluminum. A considerable portion of these metal ions remains unabsorbed after dyeing process which results in serious environmental pollution (Ghaedi et al. 2013a, b; Kasiri and Safapour 2013). Also, colored effluents of dyeing units generate a considerable amount of polluted wastewater which causes considerable

Fig. 1 Chemical structures of some coloring components found in the madder root demonstrating variety of hydroxyl (-OH), carboxyl (-COOH) and carbonyl (-CO-) functional groups (Goverdina et al. 2004)

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damage to the environment if discharged untreated. To reduce the above drawbacks and improve the affinity and dye absorption, numerous technologies, techniques and materials have been explored to alter wool surface properties. These include hydrolysis by enzymes and reagents, grafting with monomers, application of supercritical carbon dioxide in scouring and dyeing, micro- and nano-encapsulation of compounds, corona discharge treatment, gamma and UV irradiation treatment, ultrasound energy, plasma treatment. However, these methods, on the one hand, may often impair some physical, chemical and mechanical properties of wool, and on the other hand, in some cases, there may be a need to scale up processing machinery from the laboratory to the industrial scale which may restrict their application for wool wet processing in carpet production (Gashti et al. 2013; Zhang and Wang 2015). Recently, it is well accepted that in order to obtain satisfactory dyeing and fastness properties, complete penetration of dye into the fiber is essential. The rate at which penetration occurs is controlled by the rate of dye diffusion across the fiber surface and then throughout the whole interior. The rate can be markedly affected by altering the net charge on the fiber. In this context, a more susceptible alternative may be surface modification of wool with compounds containing cationic groups (Holme 2003; Arivithamani et al. 2014). Nonetheless, in this regard, a special attention should be paid in the selection of suitable cationizing agent, more especially, from the environmental point of view, since most of these materials produce hazardous effluents (Fang et al. 2013). Lately, various aspects of chitosan biopolymer and its derivatives have been explored as the best candidates for modification of properties of textiles (Lim and Hudson 2003; Enescu 2008). Chitosan is deacetylated derivative of chitin obtained from crustaceans like crab and shrimp shell wastes. It has many useful chemical and physical properties such as biodegradability, non-toxicity, antimicrobial activity, antioxidant properties (Lim and Hudson 2003; Jocic et al. 2005; Yang et al. 2010). In textile industry, chitosan has been widely investigated to impart antimicrobial properties, enhance dyeability and prepare beneficial fibers (Lim and Hudson 2004; Sadeghi-Kiakhani et al. 2015). In addition, chitosan can be used to increase the cationic nature of wool surface, thanks to poly-amino groups present in its chemical structure. It is reported that chitosan pre-treatment successfully reduces the difference in dyeing performance between damaged and undamaged wool fibers through the increasing of dyeing rate and dyeability (Jocic et al. 2005). Dendrimers are novel biologically active macromolecules which possess branched structure, many reactive end groups, and highly ordered compacted shape. This peculiar structure creates best places for host molecules between the branches

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(Calabrett et al. 2007). Recently, dendrimers and their hybrid materials have been used in dye removal from colored effluents (Sadeghi-Kiakhani et al. 2013a), modification of dyes (Sadeghi-Kiakhani and Safapour 2015b, 2016a) and modification of textiles (Klaykruayat et al. 2010). Chitosan can be modified with dendrimers containing numerous active amine groups to enhance its cationic nature (Sadeghi-Kiakhani et al. 2013a). Recently, polypropylene imine dendrimer-modified chitosan (CS-PPI), as a novel biocompatible compound, has been used in dye removal from colored solutions (Sadeghi-Kiakhani et al. 2013a), antimicrobial finishing (Sadeghi-Kiakhani et al. 2013b; Sadeghi-Kiakhani and Safapour 2016b), salt-free reactive dyeing of wool (Sadeghi-Kiakhani and Safapour 2015a) and cotton (Sadeghi-Kiakhani and Safapour 2015c) and cochineal dyeing of wool (Mehrparvar et al. 2016). To the best our knowledge, thus far, dyeing characteristics of CS-PPI-altered wool with Rubia tinctorum L. root natural dye have not been investigated yet. In continuation of our ongoing interest in the extension of the application of CS-PPI potentiality in textile field, therefore, in this study, the dyeing characteristics, color quality and colorfastness properties of CS-PPI-treated wool with madder root natural dye were investigated with the aim at the possibility of replacing metallic mordants with eco-friendly CS-PPI treatment. In addition, antimicrobial activity against two common pathogenic gram-positive and gramnegative bacteria, namely Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), respectively, was investigated and deliberated.

Materials and methods Commercial scoured 100 % woolen yarn (200Tex/four folds) was supplied by Azar Barf Yarn Co., Iran. Chitosan (degree of deacetylation 85 %, MW 1000 kDa) was provided by Kitotak Co., Iran, and polypropylene imine (PPI) dendrimer (Generation 2, MW = 770 g/mol) was prepared by Ciba Ltd. Acetic acid, sodium carbonate, citric acid, sodium hypophosphite, aluminum sulfate and carbon tetrachloride supplied by Merck, Germany, were used. Madder’s, R. tinctorum L., finely pulverized dried roots, cultivated in Yazd Province, Iran, as crude natural dye source was supplied from a local carpet traditional dyeing workshop. All solutions were prepared by distilled water. All chemicals used in this study were of analytical laboratory grade. Preparation of CS-PPI hybrid Five grams of chitosan (1, Fig. 2) was dissolved in 80 mL water/methanol 1/1 (V/V) and 1.5 mL acetic acid solution, and then, 0.5 mL ethyl acrylate was added to the solution.

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Fig. 2 Schematic representation for preparation of CS-PPI; (1) chitosan; (2) N-carboxyethyl chitosan ethyl ester; (3) N-carboxyethyl chitosan; (4) chitosan–polypropylene imine dendrimer hybrid (CS-PPI); (Sadeghi-Kiakhani et al. 2013a)

After stirring at 50 °C for 10 days, the reaction mixture was quenched and precipitated in 80 mL acetone saturated with NaHCO3. The precipitate was separated by filtration, and then, the filtrates dispersed in 20 mL water saturated with NaHCO3. The resulting mixture was dialyzed against 4L water and lyophilized to obtain N-carboxyethyl chitosan ethyl ester (2, Fig. 2). For the preparation of N-carboxyethyl chitosan (3, Fig. 2), the prepared compound (2, Fig. 2) was added to 50 mL NaOH solution; the mixture was stirred for 2 h, dialyzed and lyophilized as above. The precipitated powders were obtained in quantitative yield of 95 %. One hundred milligrams of the compound (3, Fig. 2) was dispersed in 50 mL methanol; poly(propylene imine) (PPI) (G = 2) was then added to the prepared suspension, and the mixture was stirred at room temperature. After 3 days, the mixture was evaporated to dryness, dispersed in NaOH solution (0.2 M) at room temperature for 2 h, dialyzed and lyophilized to obtain CS-PPI. The summarized preparation of CS-PPI is shown in Fig. 2 and was explained in detail in the previous work (Sadeghi-Kiakhani et al. 2013a). Instrumentation Wool dyeing was performed using a laboratory high-temperature (HT) dyeing machine. Ultraviolet (UV)–visible Spectronic Helios Alpha double-beam spectrophotometer

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was used to measure absorption spectra of dyeing solutions. The reflectance characteristics of the dyed samples were measured through Color-Eye XTH Spectrophotometer, X-Rite Inc., USA (under D65 illumination, 10° standard observer). The spectrophotometer was equipped with software able to automatically calculate CIEL*a*b*, color difference and color strength (K/S) values from the reflectance values at the appropriate wavelength for each dyed sample. The colors are given in CIEL*a*b* coordinates: L* corresponding to the brightness (100 = white, 0 = black), a* to the red–green coordinate (? = red, - = green), b* to the yellow–blue coordinate (? = yellow, - = blue), C* to color purity or vividness– dullness (100 = vivid, 0 = dull) and h° to hue angle. Surface modification of wool with CS-PPI Wool yarns were scoured in a solution containing 5 g/L nonionic detergent and 3 g/L Na2CO3 at 50 °C for 30 min. Hydrophobic greasy layer of wool was removed by treatment with absolute carbon tetrachloride solution at room temperature for 10 min. Then, woolen yarns were removed, thoroughly squeezed and air-dried at room temperature. Required amount of fine powder of CS-PPI was dissolved in acetic acid solution (pH 4–5). Modification of wool with CS-PPI was performed according to the dip-dry-


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cure method as follows: Grafting solutions containing CSPPI [1–10 % owf (on weight of the fiber)], citric acid (8 % owf), as cross-linking agent, and sodium hypophosphite (8 % owf) were prepared. The scoured wool was soaked in grafting bath for 6 h at 70 °C. After that, yarns were removed and dried for 5 min at 70 °C, cured in an oven at 110 °C for 5 min and washed with distilled water at room temperature for 15 min to remove any surface unattached material. Raw and modified wool were dyed with madder natural dye (1–50 % owf) and then characterized.

K=S ¼

ð1 RÞ2 2R

ð2Þ

where R is the reflectance of an infinitely thick layer of material illuminated with light of a known wavelength, K is the absorption coefficient, and S is the scattering coefficient. The function K/S is directly proportional to the concentration of colorant within the substrate. Fastness tests

Scoured yarns were mordanted prior to dyeing (pre-mordanting) with aluminum sulfate 10% owf, pH 5, liquor ratio 40:1, temperature of 95 °C, time 60 min. After mordanting, the yarns were removed, thoroughly rinsed with tap water, squeezed and air-dried.

Wash fastness was measured by the standard ISO 105 C06 C2S:1994 (E) method. Washing was conducted for 30 min at 60 °C, rinsed with cold water, air-dried and analyzed using gray scale. Lightfastness tests were performed by ISO 105 B02:1988 (E) standard with the xenon arc lamp. The results were evaluated using blue scale reference samples and reported.

Extraction of madder natural dye

Durability of treated wool against washing

A weighed amount of finely pulverized crude madder root was extracted with distilled water using a laboratory dyeing machine. In the standard procedure, the mass ratio of crude dye material to the volume of liquid was 1:20; extraction was performed at 90 °C for 60 min. The pH value of the extract was around 6. The solution was then filtered by filter paper, so that a clear natural dye solution was obtained.

To study the durability of applied finish (CS-PPI) against washing, modified yarns were treated for five washing cycles in accordance with ISO Standard 105-C06. Samples of 1.5 g were introduced into a laundry solution bath with a volume of 100 mL with ten stainless steel balls. When the cycle was finished, the samples were washed twice with distilled water. After that, the samples were dried under ambient conditions. Then, antimicrobial properties of treated samples were examined according to the procedure described in the following.

Mordanting of wool

Dyeing procedure Woolen yarns were dyed with liquor-to-good ratio of 40:1. The samples were immersed for 5 min in the dye bath at 30 °C prior to the addition of dye solution. After the addition of dye, the temperature was raised to simmering temperature (around 90 °C) with heating rate of 2 °C/min, kept at this temperature for 60 min and then cooled down to 70 °C with cooling rate of -2 °C/min. Dyed samples were then removed from dye bath, rinsed with hot and then cold water, and air-dried at the ambient temperature. Optical density of dye solution was recorded at maximum absorption wavelength (kmax) of dye (410 nm) prior to and after dyeing. Then, the percentage dye exhaustion (E%) was calculated using Eq. 1. E%¼

ðA0 A1 Þ 100 A0

ð1Þ

where, A0 and A1 are the absorbance of dye solution prior to and after dyeing process, respectively. Color strength (K/S) of dyed samples was calculated at kmax for each sample using Kubelka–Munk equation (Eq. 2):

Antimicrobial assay Antimicrobial activity of woolen samples was examined according to ASTM E2149-01, which is a quantitative antimicrobial test method performed under dynamic contact conditions. Both gram-negative and gram-positive organisms, namely E. coli and S. aureus, were tested. In this procedure, a number of test tubes, each containing 5.0 mL of Muller–Hinton broth (MHB, Difco, England), were autoclaved for 15 min at 121 °C. Bacterial inoculums (1.0 ± 0.1 mL) were then added to the circular swatches (1.0 g). These inoculums were nutrient broth cultures containing 106–107 mL-1 CFU (colonyforming units) of bacteria. Positive control tubes contained 5.0 mL of the nutrient broth medium with tested bacterial concentrations of 105–106 CFU/mL, while negative control tubes contained only the inoculated broth. All samples were incubated for 24 h at 37 °C at a constant temperature of incubator. Then, 100 lL of solution was taken from each incubated sample and

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70

ð3Þ

where, A and B are the surviving cells (CFU/mL) for the flasks containing test samples (treated wool) and the reference sample, respectively. To assure repeatability and accuracy of all experimental data, at least three individual measurements were taken, averaged and reported along with sample standard deviation for each sample.

Results and discussion

65 60 55 50 45 40 0

In this section, the impact of some important parameters, i.e., CS-PPI concentration, madder dye concentration and dyeing pH which may affect the dye uptake on wool, have been investigated and discussed. Effect of CS-PPI concentration Figure 3a demonstrates the percentage dye absorption versus CS-PPI concentration. It is clearly observed that modification of wool resulted in a substantial raise in dye absorption which enhanced by the increase in CS-PPI concentration and reached a maximum at around 7 % owf CS-PPI. This behavior can be related to the increased number of free amine groups on the surface of treated wool as dye absorbing sites and thus the enhanced ionic (carboxyl groups) interactions, hydrogen bondings (carboxyl, hydroxyl, and carbonyl groups) or hydrophobic interactions with madder pigments. This fact, indeed, resulted in sequential dye up-take improvement (SadeghiKiakhani and Safapour 2015b). Gradual decrease in dye absorption at the highest CS-PPI concentration may be explained by the accumulation of CS-PPI on wool surface, possible obstruction of active dye-absorbing sites and/or a decrease in specific area of adsorption by accumulation. Therefore, according to absorption data, 7 % owf CS-PPI was selected as the most appropriate concentration for modification of wool in natural dyeing with madder root dye.

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4

7

10

(B) 80 70 60 50 40 30 20

Raw Wool

10 0

Dyeing properties

1

CS-PPI concentraon (%owf)

Percent dye exhauson

BA R% ¼ 100 B

(A) Percent dye exhauson

distributed over an agar plate. All plates were incubated again for 24 h, and the colonies formed on them were counted. The antimicrobial activity was expressed in terms of percent bacterial reduction after contacting test specimen compared to the number of bacterial cells surviving after contacting the control. The percent bacterial reduction (R%) was calculated using (Eq. 3) as follows:

0

10

20

30

Modified wool 40

50

Dye concentraon (%owf) Fig. 3 Percent dye exhaustion as a function of a CS-PPI concentration (30 % owf madder dye was used); b madder dye concentration [raw(reference) and modified (CS-PPI 7 % owf) wool]

Effect of dye concentration Generally, an increase in dye concentration in dye bath increases the chemical potential of dyeing solution and thus driving force of dye molecules to move toward textile surface where to be adsorbed. Percent dye exhaustion of raw and modified wool as a function of dye concentration in dyeing solution has been demonstrated in Fig. 3b. For both wool samples, dye absorption increased with increasing of dye concentration until the saturation point was attained. After that, the changes in dye absorption were almost negligible. Furthermore, modified wool exhibited quite higher dye absorption and saturated at relatively lower dye concentration. This behavior can be explained by the changes in net charge of wool surface which promote higher dye adsorption. According to the graphs in Fig. 3b, the modified wool reached equilibrium at around 20 % owf madder dye, while the untreated wool still required higher amount of dyes (30–50 % owf) to be saturated. This finding emphasizes that the same results (dye uptake and/or color depth) with the use of lower concentration of madder dye can be achieved. A decrease in dye saturation concentration as well as dye uptake enhancement is of substantial importance in studying a particular dye/textile system since considerable amount of dye and chemicals


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could be saved which is very important both in ecological and economical standpoints. Effect of dyeing pH The pH is an important factor that controls the adsorption of dyes from aqueous solution onto wool fibers (Jocic et al. 2005). In this study, two different pH values (below and above isoelectric point of wool) are investigated, and the results are shown in Fig. 4. Interestingly, as it is clear from dye exhaustion data, the pH role in madder dye absorption is very prominent and strongly dependent on the type of wool. Raw wool showed low percent dye absorption at pH 7. With pH changed to 4, the dye absorption increased by 21.52 %. This phenomenon emphasizes the necessity of the use of an acid such as acetic or formic as pH regulating auxiliary agent in dyeing in order to achieve better dyeing yield. On the other hand, contrary to raw wool, modified wool showed higher dye absorption at neutral medium (pH 7), which was even higher than that of the raw wool dyed at acidic medium (pH 4). Such somewhat unusual behavior in dye absorption may rely on the different accessibility of dye-absorbing sites to the dye molecules and/or different interactions and binding of the dye onto the substrates, as explained in the following: Analysis of dye absorption by raw wool Madder dye absorption dependency to pH and its increase with pH decrease suggests that the dye absorption is primarily controlled by electrostatic interaction between anions of dye molecules (Fig. 1) and protonated amine groups (amino groups) of wool. Taking into account the isoelectric point of wool (pH 4.2), below this point, wool is positively charged principally because of the presence of basic groups in lysine and arginine, whereas above that, the carboxyl groups give a net negative charge on the wool. When pH is 70

Raw Wool

Modified wool

Percent dye exhauson

65 60 55 50 45 40 35 4

7

Dyeing pH Fig. 4 Effect of dyeing pH on quantity of dye exhaustion (30 % owf madder dye was used)

below 6, the amine groups inside the wool will be always present in protonated (amino) form. At the pH values higher than 6, almost all carboxyl groups in wool will be present as carboxylate anions (Jocic et al. 2005). Furthermore, some functional groups of dye molecules, principally carboxyl groups will exist in carboxylate anion form at pH 4 (Bechtold and Mussak 2009). Hence, the weak carboxylate anion of the dye replaces that of acid via an ion-exchange reaction due to its higher affinity. Due to the complicated character of madder pigments, when bound on the wool, further kinds of interactions may take place together with electrostatic interactions. This electrostatic attraction would enhance the dyeability of wool. Nonetheless, at pH 7, the number of protonated terminal amine groups of wool decreased, and therefore, the electrostatic interactions and the dye absorption decreased accordingly. Meanwhile, in the absence of electrostatic attractions, hydrogen bonding, van der Waals forces and hydrophobic interactions would be responsible for absorption of madder dye by wool. At pH 4, almost all the terminal amine groups were protonated, and so, the maximum dye absorption was obtained. Analysis of dye absorption by CS-PPI-modified wool Unexpected trend in dye absorption in the case of modified wool is clear from Fig. 4. Hypothetically, in acid solutions, it is expected CS-PPI behaves as a cationic polyelectrolyte due to protonation of the amine groups (Sadeghi-Kiakhani et al. 2013b). Hence, almost all the amine groups of the CSPPI will be protonated at pH 4 to form cationic amino groups, but at pH 7, CS-PPI should have very low positive charge (Sadeghi-Kiakhani et al. 2013a). Although, incorporation of CS-PPI onto wool surface enhanced dye absorption, opposite trend in dye absorption took place, i.e., dye absorption at pH 7 (unprotonated form of amine groups) was markedly higher than that of acidic dyeing at pH 4. This fact suggests that more effective interaction forces other than electrostatic forces should be involved in dye adsorption process. Taking into account the chemical structure of madder colorants (Fig. 1), there are numerous carboxyl, hydroxyl and carbonyl groups which are very prone to establish hydrogen bonds with amine groups of CS-PPI (4, Fig. 2). This hypothesis becomes more strengthened when absorption data in two pH values were compared. In fact, at pH 4, because of the protonation and loss of pair electrons of amine groups, the possibility of hydrogen bonding formation between dye and wool substrate is decreased, and that is why better dye absorption was obtained at pH 7. Comparable or even higher dye absorption value for treated wool at pH 7 suggested that acid can be eliminated from wool dyeing with madder dye through wool pre-treatment with CS-PPI. This finding is of great importance in ecological and cleaner dyeing process points of view.

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Effect of mordant Metallic salts are being used for different purposes in natural dyeing of wool such as extension of color shade, improvement in colorfastness properties, enhancement of natural dye affinity and uptake. Among them, aluminum salts were frequently used. Aluminum mordants are colorless and generally do not change color hue, but improve dye uptake and color vividness. Hence, in this study, aluminum sulfate (10 % owf) as an example of mordants was applied on wool by pre-mordanting method. Then, the impact of mordant on dye uptake change in terms of color strength was investigated and compared with those values of raw and CS-PPI-treated wool, and the results are shown in Fig. 5. It is observed that mordanting with aluminum resulted in an appreciable increase in color strength by 32.67 %, owing to the enhanced affinity of madder natural dye. Also, appreciable improvement in dye uptake for CS-PPI-modified wool (34.66 %) was observed in comparison with dyed raw wool. Interestingly, it is clear that K/S value of CS-PPI-modified wool was a little higher than that value of the mordanted wool. This finding emphasizes that the CS-PPI-treated wool can be dyed with substantial higher color depth with no aid of aluminum mordant. In other words, the CS-PPI can be used as an alternative bio-mordant in place of metallic mordant in wool dyeing. Therefore, not only the mordant is eliminated from madder dyeing of wool, but also, the lower amount of dye is required to achieve a desired color depth. This finding is worthwhile from environmental stand point making wool dyeing eco-friendlier over traditional dyeing methods with less hazards of discharged effluents. Colorfastness properties Colorfastness against wash and light are examined, and the results are presented in Table 1. It can be seen that wash fastness rating for staining of adjacent wool fabric and color change is very good. In addition, staining on cotton is 17

good. No color change was observed using different CSPPI concentrations. Washing fastness remained unchanged, indicating the independency of fastness properties from CS-PPI concentrations. Lightfastness increased around 1–2 grades indicating wool modification resulted in an enhancement in lightfastness presumably owing to the intrinsic characteristics of dendrimers generally used to improve the optical stability of the materials (SadeghiKiakhani and Safapour 2015a, 2016a). In general, fastness data confirmed that the CS-PPI had no adverse effect on colorfastness of dyed modified wool. Colorimetric properties Colorimetric values for dyed wool samples are presented in Table 2. Data showed no appreciable changes in lightness (L*), and redness–greenness (a*) of the dyed modified wool took place, while the yellowness (?b*) and vividness of the color (C*) gradually increased. Color data emphasized that in general wool modification with CS-PPI did not induce appreciable color change which is very important from textiles modification standpoint. Antimicrobial properties Numerous standard methods are nowadays being used to examine the bactericidal properties of textiles. In this study, antimicrobial activity of the samples were investigated according to ASTM E2149-01, a quantitative antimicrobial test method performed under dynamic contact conditions against two pathogenic bacteria E. coli and S. aureus, and the results are presented in Table 3. Results show that bactericidal activity of raw (untreated) wool increased to some extent after dyeing with madder presumably due to biological activity of natural ingredients present in the madder root (Kalyoncu et al. 2006). Furthermore, undyed treated wool showed excellent antimicrobial activity against both organisms. Such prominent improvement in bactericidal activity may be ascribed to the presence of the CS-PPI on the wool surface with numerous

Color strength (K/S)

16 15

Table 1 Colorfastness data of raw and modified wool dyed with madder dye (30 % owf)

14 13

CS-PPI (%owf)

12 11

Wash fastness CC

10 9 8 7

Raw Wool

Al-mordanted wool

Modiﬁed wool

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SC

b

Light fastness SW

c

Nil (raw wool)

4–5

4

4–5

4–5

7

4–5

4

4–5

6

10

4–5

4

4–5

6

a

Fig. 5 Color strength of raw (reference), Al-mordanted (10 % owf) and CS-PPI-modified (7 % owf) wool dyed with 30 % owf madder dye

a

Color change

b

Staining on cotton

c

Staining on wool

Int. J. Environ. Sci. Technol. (2016) 13:2569–2578 Table 2 Colorimetric data of raw and modified wool dyed with madder dye (30 % owf)

CS-PPI (%owf)

L*

a*

b*

C*

h°

K/S

Nil (raw wool)

35.71 (0.41)§

30.57 (0.26)

20.46 (0.23)

36.78 (0.34)

33.79 (0.07)

12.03 (0.33)

7

34.92 (0.87)

30.82 (0.86)

23.88 (0.03)

39.88 (1.59)

37.76 (0.76)

16.20 (0.48)

10

34.47 (1.22)

32.32 (0.25)

25.60 (0.23)

41.23 (0.05)

38.38 (0.46)

16.23 (0.56)

§

Table 3 Antimicrobial activity of raw and modified wool in three different conditions against E. coli and S. aureus microorganisms

2577

Numbers within parentheses represent sample standard deviation

Samples

Undyed Dyed Washed five cycles after dyeing

Reference (untreated wool)

Modified wool

E. coli

E. coli

S. aureus

S. aureus

5 (1.05)§

1 (0.10)

100 (0.00)

99.8 (0.26)

19.4 (1.55)

6.1 (0.71)

96.4 (2.12)

88.1 (2.23)

7.6 (1.08)

2.8 (0.82)

51.2 (3.32)

38.7 (3.41)

Data given in table are in terms of percent bacterial reduction (R%) for each sample §

Numbers within parentheses represent sample standard deviation

active amine groups which may have come into contact with the bacterial cell surface and prevented the leakage of intracellular components (Kalyoncu et al. 2006; SadeghiKiakhani et al. 2013b). The most accepted mechanism for bacterial inhibition by CS-PPI may be the interaction of the positively charged amine (NH2 ? NH3?) groups with the negatively charged residues at the cell surface of bacteria, which causes extensive alteration of cell surface and cell permeability. This causes the leakage of intracellular substances such as electrolytes, UV-absorbing materials, proteins, amino acids, glucose and lactate dehydrogenase. As a result, CS-PPI inhibits the normal metabolism of microorganisms and finally leads to their death. In the case of S. aureus, a gram-positive bacterium with a thicker cell wall, more reluctance and resistance to CS-PPI are observed as compared to gram-negative E. coli (SadeghiKiakhani and Safapour 2016b). Nevertheless, antimicrobial activity of treated wool decreased somewhat after dyeing. This fact can be ascribed to the obstruction of several amine groups of CS-PPI by madder colorants and/or partial detachment of CS-PPI at elevated temperatures during dyeing process. Bactericidal property of dyed modified wool was retained to a great extent after five wash cycles presumably owing to strong attachment of CS-PPI onto wool (Sadeghi-Kiakhani et al. 2013b). Above results clearly demonstrate the potentiality of madder dyed modified wool for hygienic textile applications.

Conclusion The results of this investigation clearly demonstrated that chitosan–polypropylene imine dendrimer hybrid (CS-PPI) can be employed as a biocompatible material for cleaner

modification and antimicrobial finishing of wool. Using CS-PPI-modified wool, acid and metallic mordant was eliminated form madder dyeing process, dye saturation point shifted to lower dye concentrations, the quantity of dye required to achieve a desired color depth was minimized, and substantial antimicrobial activity against two pathogenic bacteria E. coli and S. aureus with good durability was achieved on wool substrate. Color data and fastness test results emphasized wool modification not only did not deteriorate color hue and colorfastness against wash, but also increased colorfastness against light by 1–2 grades. Overall and based on the results, it is concluded that CS-PPI can be used as alternative ‘‘bio-mordant’’ in place of metallic mordant traditionally used in wool dyeing with madder dye as well as a promising antimicrobial finishing compound for production of hygienic colored wool textiles. Therefore, the problems associated with the use of acid, metallic mordant and bacterial infections would be obviated. Acknowledgments This paper has been extracted from thesis submitted for master degree in ‘‘Carpet materials and dyeing’’ in Carpet Faculty of Tabriz Islamic Art University. Hereby, the authors would like to express their gratitude for ‘‘Tabriz Islamic Art University’’ for all the supports. Also, cordial thanks go to ‘‘Institute for Color Science and Technology’’ for sincere collaboration throughout this research work.

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