Kinetics and thermodynamics of dye extracted from Arnebia nobilis Rech.f. on wool

Indian Journal of Fibre & Textile Research Vol. 37, June 2012, pp. 178-182 Kinetics and thermodynamics of dye extracted from Arnebia nobilis Rech.f. on wool Anjali Arora 1,a, Deepti Gupta 2, Deepali Rastogi 1 & M L Gulrajani 2 1 Department of Fabric and Apparel Science, Lady Irwin College, Delhi University, Delhi 110 001, India 2 Department of Textile Technology, Indian Institute of Technology, Delhi 110 016, India Received 25 November 2010; revised received and accepted 10 June 2011 Kinetic and thermodynamic studies have been conducted with the crude dye extract of A. nobilis on wool fabric. On comparing the dyeing results of this dye with those of other natural dyes (juglone, lawsone and Rheum emodi), it is found that the diffusion coefficient of this dye is slightly lower. The dyeing mechanism corresponds to the partition mechanism, confirming that this naphthoquinonoid based colourant is adsorbed by wool fabric as a disperse dye. The dyeing process is exothermic. The rate of dye uptake, diffusion coefficient, standard affinity, heat of dyeing and entropy have also been calculated and discussed. Heat of dyeing and entropy are found to be negative. Keywords: Arnebia nobilis Rech.f., Dyeing, Kinetic studies, Natural dye, Thermodynamic studies, Wool 1 Introduction Arnebia nobilis Rech.f., referred to as Ratanjot in India, has traditionally been an important natural source of red colour in the field of pharmaceuticals, cosmetics and food 1, 2. Investigations have already been carried out by the authors to isolate and identify the components of Arnebia nobilis Rech.f. Alkannin β, β-dimethylacrylate was identified as the major component constituting ~ 25 % of the crude extract 3. In a previous paper, the results of the effect of ph and temperature on the crude dye have been reported 4. The dye showed acute sensitivity to ph. The dye was also heat sensitive and showed degradation above 80 C. Different textile substrates, viz nylon, polyester, acrylic, wool, silk and cotton, were dyed at different ph. All substrates showed good affinity with nylon dyed in blue, polyester dyed in pink and other substrates in purple colour at ph 4.5. According to Indrayan et. al. 5 and Kyu and Soo 6, the active coloured ingredient in Arnebia nobilis is present in quinonoid form in acidic medium. In alkaline medium, the phenolic proton of quinonoid form gets dissociated from the naphthoquinone nucleus and is converted to benzenoid form which is responsible for blue colour. This has been demonstrated in Fig. 1. Previous studies have been conducted on natural dyes of different chemical structures towards establishing the mechanism of dyeing synthetic fibres. a To whom all the correspondence should be addressed. E-mail: aarora_18@yahoo.com Few detailed studies have been carried out on quinonoid dyes. Two naphthoquinone based isomeric dyes namely lawsone and juglone (2- hydroxyl and 5-hydroxy naphthoquinones respectively) were found to give linear isotherms when used to dye synthetic fibres (nylon and polyester). Both these dyes exhibited very high affinity for hydrophobic fibres 7, 8. There have been some investigations on the naphthoquinones of Onosma echioides, also referred to as Ratanjot in literature. It was found that the dye is adsorbed by both nylon and polyester in the same manner as a disperse dye 9, 10. The natural anthraquinone-based colourants obtained from madder roots also showed good affinity for nylon and polyester. The dyeing mechanism corresponded to the Nernst isotherm 11, 12. However, differing results were obtained when nylon and polyester were dyed with long, conjugated carotenoid molecule Bixin. Dyeing of nylon corresponded to Langmuir isotherm while dyeing of polyester corresponded to Nernst isotherm 13. Berberine Fig. 1 Possible dye reaction taking place on different substrates which is responsible for different hues

ARORA et al.: KINETICS & THERMODYNAMICS OF DYE EXTRACTED FROM A. NOBILIS ON WOOL 179 (C I Natural Yellow 18), a natural basic dye, was sorbed by acrylic by site mechanism indicated by Langmuir isotherm 14. Wool and silk were dyed with the dye extracted from Rheum emodi. The dyeing corresponded to partition mechanism, confirming the anthraquinonoid structure 15. Dye extracted from red sandalwood showed good affinity for nylon and wool fibres and the mechanism corresponded to partition type like that of disperse dye on hydrophobic fibres 16. It was observed that majority of the naphthoquinone and anthraquinone based natural dyes studied exhibited high substantivity for synthetic fibres. The dyes were reported to behave as disperse dyes and exhibited partition mechanism on synthetic substrates. Not much work has been reported in literature on elucidating the mechanism of dyeing natural fibres with disperse dyes. As the studies reported in previous paper showed positive results on wool 4, it offered an interesting opportunity to conduct kinetic and thermodynamic studies of crude dye extracted from Arnebia nobilis Rech. f. on wool to understand the theoretical basis of dyeing. A comparison of diffusion coefficients of the dye with those of the other naphthoquinone natural dyes has also been made. 2 Materials and Methods 2.1 Materials Dried root material of Arnebia nobilis Rech.f. was procured from Nature and Nurture Healthcare Private Limited, Delhi, India. Roots of A. nobilis were ground to coarse powder, air dried and extracted with n-hexane in soxhlet apparatus at 50 C till the entire colour was extracted. A deep red viscous residue amounting to ~5 % on the dry weight basis of roots was obtained after evaporation of solvent. Kinetic and thermodynamic studies of dyeing were carried out on wool fabric. The specifications of the substrate are: weight 179.9 g/m 2, ends/inch 66 and picks/inch 60. The substrate was prepared for dyeing by scouring with 1gpl non-ionic detergent (Lissapol N) at 50 C for 1 h, followed by repeated rinsing in hot and cold water and drying. A shaker bath, SW22 (Julabo, USA) was used to carry out all the dyeing studies. Ultraviolet-visible spectra were recorded on Lambda 25 (Perkin Elmer, US). 2.2 Methods 2.2.1 Kinetic Studies For measurement of rate of dyeing (dyeing kinetics), an aqueous dispersion of dye was prepared (100% on weight of material) and buffered with sodium acetate and acetic acid to give a constant ph of 4.5 ± 0.2. The kinetic studies were carried out for the time periods ranging from 15 min to 48 h, keeping the material-to-liquor ratio 1: 1000 at 80 C. The dyed fabric was dissolved in 5% sodium hydroxide solution and the amount of dye was determined from the absorbance values of the above solution with the help of calibration curve previously constructed using standard dye solution. 2.2.2 Calculation of Diffusion Coefficient The apparent diffusion coefficient of the dye extracted from Arnebia nobilis on wool fabric was calculated by Hill s equation for an infinite bath and the approximations given by Rais and Militky and Urbanik. 2.2.3 Thermodynamic Studies For thermodynamic studies, dyeing was carried out using a range of dye concentrations (0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 g/l) over a period of 48 h at 70 C, 80 C and 90 C, keeping the material- to- liquor ratio at 1: 1000. Dye liquor was buffered as before to get a ph of 4.5. The amount of dye in the fabric was estimated colourimetrically using the same procedure as described in kinetic study. 3 Results and Discussion Kinetic and thermodynamic studies were carried out on wool with the dye extracted from A. nobilis. The parameters were calculated and discussed. 3.1 Kinetic Studies 3.1.1 Rate of Dyeing The dye uptake by wool fabric dyed at 80 C for various time periods has been determined. The time of half-dyeing (t 1/2 ) is calculated as 60 min. It is observed that as the time of dyeing increases from 15 min to 600 min (10 h), the dye uptake increases from 10 g of dye/100 g of fabric to 80 g of dye/100 g of fabric. A further increase in time to 1500 min (25 h) leads to a slight increase in dye uptake of about 90 g of dye/ 100 g of fabric. However, no significant dye uptake is observed thereafter, as the dyeing time approaches infinity i.e. 2880 min (48 h), thus indicating that the equilibrium is achieved. It has been reported by Das et al. 15 that the nonpolar hydrocarbons of the protein fibres are considered to be chiefly responsible for the incorporation of the non-polar dye in the structure of wool.

180 INDIAN J. FIBRE TEXT. RES., JUNE 2012 Table 1 Kinetic and thermodynamic parameters of various naphthoquinones and anthraquinones on wool Dye structure Name of dye Diffusion coefficient 10-11, cm 2 / s Standard affinity, Enthalpy Entropy J/mol/ K Reference Anthraquinone Rheum emodi 0.20 (90 C) 7.69 (60 C) 9.65 (90 C) Naphthoquinone Juglone 6.08 (100 C) 28.73 (85 C) 29.95 (100 C) Naphthoquinone Lawsone 2.58 (100 C) 26.83 (70 C) 29.15 (100 C) 14.06 65.38 15 0.65 82.0 8-0.29 77.34 7 Table 2 Diffusion coefficient and thermodynamic parameters of nylon and polyester dyed with Onosma echioides (Ratanjot) Substrate Nylon (90 C) Polyester (100 C) Polyester (130 C) Diffusion coeff. 10-11 cm 2 /s Standard affinity Enthalpy Entropy J/mol/K Ref. 56.4 39.95 74.03 314 9 1.86 38.88 07.71 393 9 1.43 - - - 10 3.1.2 Diffusion Coefficient The apparent diffusion coefficient of the crude dye of A. nobilis is found to be 0.25 10-11 cm 2 /s according to Hill s equation, 0.22 10-11 cm 2 /s according to Urbanik approximation and 0.21 10-11 cm 2 /s as per Rais and Militky approximation. Values obtained from all the equations are found to be comparable. The D app values obtained for crude extract of A. nobilis are compared with those of other naturally occurring naphthoquinone and anthraquinone dyes on wool. The diffusion coefficients of all these dyes are listed in Table 1. The D app value of the dye (~ 0.2 10-11 cm 2 /s) is found to be comparable to that of Rheum emodi (0.2 10-11 cm 2 /s). However, it is found to be much lower than that of Juglone and Lawsone which has D app values of 6.08 10-11 and 2.58 10-11 cm 2 /s respectively. On comparing the diffusion coefficient of the crude dye extracted from A. nobilis on wool with those on other synthetic substrates dyed with the same dye, it is found that the diffusion coefficient of this dye on wool is much less than that on nylon and polyester (56.4 10-11 cm 2 /s and 1.86 10-11 cm 2 /s respectively) (Table 2). This may be because the rate of diffusion increases with temperature. Hence, higher diffusion coefficient is obtained on nylon and polyester which are dyed at 90 C and 130 C respectively as compared to wool which was dyed at 80 C. Fig. 2 Adsorption isotherm for dyeing of wool with A. nobilis 3.2 Thermodynamic Studies 3.2.1 Adsorption Isotherm Quantitative estimation of the dye in fabric and that in dyebath was done and results are plotted as adsorption isotherm. To predict the nature of the isotherm, the best fit line for three models of dye sorption viz. Nernst, Langmuir and Freundlich was drawn, which, in turn, was used to define the theoretical model for a particular dyeing system. The model thus serves as a basis for the calculation of thermodynamic parameters. The dye molecule of A. nobilis is believed to be very small and simple and has no ionic groups. These are characteristics of a disperse dye and, therefore, theoretically the isotherms should conform to the linear or partition mechanism of dyeing. Figure 2 shows the isotherm for wool fabric. The best fit isotherm is linear, with a high correlation coefficient (R 2 = 0.967 0.973), which indicates the partition mechanism of dyeing or Nernst model. This model is generally observed in dyeing hydrophobic fibres with disperse dyes. Linear isotherms were also obtained by Das et al. 15 in dyeing of natural protein fibres with anthraquinone dyes and by Gupta and Gulrajani 7,8 in dyeing of wool with juglone and

ARORA et al.: KINETICS & THERMODYNAMICS OF DYE EXTRACTED FROM A. NOBILIS ON WOOL 181 Table 3 Slopes and statistical parameters of isotherms Parameter 70 C 80 C 90 C Slope 80.72 119.6 69.57 Correlation coefficient (R) 0.973 0.967 0.976 lawsone. The dye uptake at equilibrium is found to be highest at 80 C. The slope of the isotherm, which is indicative of partition ratio, increases from 80.72 to 119.6 as the dyeing temperature is increased from 70 C to 80 C. However, it is observed that the slope of the adsorption isotherm decreases to 69.57 as the dyeing temperature is increased to 90 C. This may be due to the decomposition of the dye molecule at higher temperature 4. The slopes and results of statistical analysis for best-fit isotherms are given in Table 3. During dyeing, it is observed that a large amount of dye is being taken up by the fabric at higher concentrations of dye liquor and during longer hours of dyeing. Fabrics which are red during initial hours of dyeing become brownish black to black when dyed up to the equilibrium with infinite solutions. This shade build-up may be due to the aggregation of dye inside the fibre. 3.2.2 Thermodynamic Parameters Dyeing of wool with Arnebia nobilis corresponds to the partition mechanism, and hence the standard affinity ( µ ) of the dye for wool fabric was calculated using the following equation: - µ = RT ln ([D] f /V [D] s ) = RT ln K v.... (1) where R is the universal gas constant (kj/ K); T, the temperature of dyeing (K); [D] f, the concentration of the dye in the fibre (g/100 g of fabric); [D] s, the concentration of dye in solution (g/l); and V, the volume term representing the effective volume of water in the substrates (L/kg). The value of V for wool is 0.31 L/kg. The standard affinity values were obtained from Eq. (1) at 70 C, 80 C and 90 C. It is found that the value of standard affinity increases from 15.92 to 17.8 as the dyeing temperature increases from 70 C to 80 C. A further increase in temperature by 10 C leads to the decrease in standard affinity to 15.48. This trend is also evident from the adsorption isotherms. The affinity of many natural dyes on wool dyed at temperatures varying between 80 C and 100 C has been found to vary from 7 to 29 7,8,15,16. An affinity of 17.8 kj/ mol of A. nobilis at 80 C is found to be comparable. 3.2.3 Heat of Dyeing Heat of dyeing ( H ) was calculated using the following equation: H = [T 2 µ 1 T 1 µ 2 ]/(T 2 T 1 ) (2) where T 1 and T 2 are the temperatures of dyeing at 70 C and 90 C; and µ 1 and µ 2, the standard affinity at temperatures 70 C and 90 C. H value is calculated as -23.48 kj/ mol using Eq. (2). It is found that for dyeing of wool with this dye, the heat of dyeing is negative (-23.48 ), i.e. the dyeing process is exothermic and therefore, less dye will be adsorbed in equilibrium at increased temperature 17. On comparing the heat of dyeing of Onosma echioides (Ratanjot) on synthetic substrates (nylon and polyester), it is found that the process of dyeing is endothermic (Table 2). The heat of dyeing is considered as a measure of bonding force of the dye with the fibre. The enthalpy of heat ( H ) is depicted as energy of broken bonds energy of formed bonds. The greater the value of energy of bonds formed between the fibre and the dye, the more stable the dyeing will be. If this value is greater than the energy of broken bonds, the heat of dyeing is negative 18. Thus, more bonds are formed resulting in negative heat of dyeing of A. nobilis on wool. 3.2.4 Entropy of Dyeing The third thermodynamic parameter, entropy of dyeing ( S ), was calculated by the following equation: µ = H - T S... (3) The calculated value of entropy is -22.05 J/ mol/k. The entropy of dyeing is also found to be negative. Vinod et al. 19 attributed the negative entropy to a uniformly order distribution of dye in the substrate. According to Treigiene et al. 18, when the dye molecules are absorbed by the fibre, they arrange themselves in the interior in an orderly manner and are oriented in a longitudinal axis to the fibre. They have less state of movement and the state of probability will be minor, therefore the entropy will be reduced, resulting in negative entropy. However, entropy of nylon and polyester dyed with Onosma echioides is found to be positive (Table 2). 4 Conclusion The dye extracted from A. nobilis Rech.f. exhibits good affinity for wool fabric. The dyeing mechanism

182 INDIAN J. FIBRE TEXT. RES., JUNE 2012 corresponds well to partition mechanism, confirming that this naphthoquinonoid based dye is absorbed by wool as a disperse dye. Heat of dyeing is found to be negative and the dyeing process appears to be exothermic. The entropy is also found to be negative. References 1 Martinez M J A & Benito P B, Studies in Natural Product Chemistry: Bioactive Natural Products (Part K), edited by A U Rahman ( B V Elsevier, New York ), 2005, 303. 2 Li K & Wang Z, China Pat CN 1116923 (to Faming Zhuanli Shenqing Gongkai Shoumingshu), 18 March 1995. 3 Arora A, Rastogi D, Gulrajani M L & Gupta D, Coloration Technol, (in press). 4 Arora A, Rastogi D, Gulrajani M L & Gupta D, Indian J Fibre Text Res, 37 (2012) 91. 5 Indrayan A K, Yadav V, Kumar R & Tyagi P K, J Indian Chem Soc, 81 (2004) 717. 6 Kyu L W & Soo Y G, Yakhak Hoechi, 24 (3-4) (1980) 151. 7 Gupta D B & Gulrajani M L, J Dyers Colour, 110 (1994) 112. 8 Gupta D B & Gulrajani M L, Indian J Fibre Text Res, 18 (1993) 202. 9 Gulrajani M L, Gupta D & Maulik S R, Indian J Fibre Text Res, 24 (1999) 294. 10 Bairagi N & Gulrajani M L, Indian J Fibre Text Res, 30 (2005) 196. 11 Gupta D, Kumari S & Gulrajani M L, Coloration Technol, 117 (2001) 328. 12 Gupta D, Kumari S & Gulrajani M L, Coloration Technol, 117 (2001) 333. 13 Gulrajani M L, Gupta D & Maulik S R, Indian J Fibre Text Res, 24 (1999) 131. 14 Gulrajani M L, Gupta D & Maulik S R, Indian J Fibre Text Res, 24 (1999) 223. 15 Das D, Maulik S R & Bhattacharya S C, Indian J Fibre Text Res, 33 (2008) 163. 16 Gulrajani M L, Bhaumik S, Oppermann & Hardtmann G, Indian J Fibre Text Res, 27 (2002) 91. 17 Johnson A, The Theory of Coloration of Textiles, edited by H H Sumner (Society of Dyers and Colourists, England), 1989, 255. 18 Triegiene R & Musnickas J, Chemija, 14 (3) (2003) 145. 19 Vinod K N, Puttaswamy, Gowda K N N & Sudhakar R, Indian J Fibre Text Res, 35 (2010) 159.