Thermodynamic Parameters of Two Azo Dyes on Nylon Fabric. Synthesis, Application and Determination

Research Paper (undergraduate), 2016

11 Pages, Grade: 2.3

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Materials and method

Discussion of Results
Effect of temperature on % exhaustion
Effect of Time on % exhaustion
Thermodynamic of dyeing




Two dyes namely p-hydroxyazo-3-benzene carboxylic acid and 1-(3-hydroxyphenyl azo )-2-naphthol were synthesized. The dyeing performance of these dyes were evaluated on nylon fabric at three different temperature i.e (50 oC, 70 oC and 90 oC).The thermodynamics parameters such as percentage dye exhaustion (%E), Partition coefficient (K), change in Standard affinity ( ),Standard enthalpy change( ) and Standard change in entropy( ) of these dyes on nylon fabric were investigated. The results showed that the thermodynamic parameters values of these dyes on nylon fabric vary directly with temperature. Dye p-hydroxyazo-3-benzene carboxylic acid and 1-(3-hydroxyphenyl azo )-2-naphthol had (82% and 65%)%E, (19.86 KJmol-[1] and 16.79 KJmol-[1] ) , (-15.32 and -12.83 KJmol-[1]) and (0.097 and 0.078 Jmol‑[1]K-[1]) at 90 oC respectively.

Keywords; Azo Dye, Thermodynamic, Enthalpy, Percentage exhaustion and partition coefficient.


Dyes are type of organic compounds that con provide bright and lasting colour to other substance (Gong et al., 2005) there are more than 100,000 dyes available commercially, which are specially designed to resist fading upon, exposure to light water and oxidized agent s and, as such are very stable and difficult to degrade (Nigam et al., 2000). Synthetic dyes have been increasingly used in textile, leather, paper, rubber, plastic, cosmetic, pharmaceuticals and food industries (Said et al., 2012).

In general, acid dyes have attracted much attention to nylon substrates due to their interaction mechanism and easy method for application (Yoon et al., 2001). However, to achieve satisfactory levels of wash fastness, recourse is required to an after treatment with a commercial system and other fixing systems. While after treatment of the dyed nylon substrates can be improve wash fastness, this treatment can impart a change in shade of ground colour but also it is temporary in nature (Burkin shaw and Son, 2001). Most acid dyestuffs acquire their acidity from the present of sulphonic acid groups (-SO3) or nitro (-SO2) groups in the molecules (Nkeonye, 1987). Acid dyes being water soluble anionic dyes are applied primarily to nitrogenous fivers such as wool, silk and nylon, all of which contain basic groups. They provide a complete colour range, Varying from yellow to black, many of the being very bright (David, 1990). Out of different classes of dyes, azo dyes constitute the largest group of colourants used in industry (Zollinger, 1987). Azo dyes do not occur in nature and are produced only through chemical synthesis (Maynard, 1983). The emergence of diverse classes of synthetic dyes including azo-dye occurred due to constant effort to find specific dye or a particular class of dye for application an diverse materials of industrial importance mainly textile fibres, aluminum sheet, leather, electro optical devices, Ink-jet printers etc. (catino and Farris, 1985) .

Materials and method

2.1 Materials

Nylon fibre


2.2 Method

The principal method of forming of forming azo involves Diazotization of primary amines followed by coupling with hydroxyl or amino derivatives of aromatic hydrocarbons or with certain aliphatic keto compound.


Diazotization is the process of converting an amine into diazonium salt. When a cold solution of primary aromatic amines in a dilute mineral acid (Hcl) is treated with cold solution of nitrous acid at about 0-5[0]C, a diazonium salt is formed. Nitrous acid (HNO2) is formed when sodium nitrite and mineral acid (HCl) reacted together

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Ar is an aryl group, Aryl diazonium chloride

2.2.2 Coupling

Azo compounds are prepared by the interaction of a diazonium salt with a coupling agents like Phenol in the presence of NaOH or with an amino in the presence of sodium acetate (CH3COONa) The Coupling reaction is an electrophilic substitution involving the diazonium ion which reacts at the position of greatest electron availability i.e position ortho or para to the electron releasing phenoxyl or amino groups.

2.3 Experimental synthesis of P-hydroxy azo-3- benzene carboxylic acid

2.3 1 Diazotization : 3- benzene carboxylic acid .

45 ml of aniline was measured and poured into 40 ml of HCl, the solution was heated gently in a hot temperature.1 M NaNO2 solution was produce by measured 6.90 g of NaNO2 in 100ml of water stirred and kept in an ice bath. It was stirred rapidly and continuously to facilitate cooling to less temperature of 5 [0]C

2.3.2 Coupling of 3- benzene carboxylic acid .

6.91 g (0.05mol) of salicylic acid was dissolved in 38ml of 2.5.M NaOH. The mixture was stirred at (0-5)[0]C for 15minutes. It was then heated in hot water bath until solid dissolved. 17.65 g of NaCl was added to further decrease the solubility of the product.

Synthesis of 1-(3-hydroxyphenylazo) -2- naphthol

2.3.3 Diazotization: 3-aminophenol

10.9 g of 3-aminophenol was placed into 250 ml of water in a 500 ml beaker. 40 ml of concentrated hydrochloric acid was slowly added until 3-aminophenol dissolve completely. The solution was cooled in the ice bath. 3-aminophenol precipitates out upon cooling while the solution kept at (0-5)[0]C NaNO2 was slowly added with a dropper and stirred thoroughly for 2-3 minutes

2.3.4 Coupling of 3-aminophenol

7.2g of 2-Naphtol was dissolved in the sodium hydroxide solution and the mixture was stirred until complete dissolution, the solution was cooled in an ice bath. The benzene diazonium salt solution was slowly added to the 2-naphthol solution. A brick red precipitate is formed.

Discussion of Results

Effect of temperature on % exhaustion

It is evidently clear from table 1 and 2 that temperature change affects dyeing and percentage exhaustion. All dyes showed high % exhaustion at temperature near the boiling point. The percentage exhaustion increased with increased in temperature. This is so, because, there is grater segmental mobility of the fibre polymer chains action of the dye molecule into the fibre (Moncrieff, 1975). At 50o % exhaustion of dye 1 and2 are (48% and68%), at 70oc % exhaustion of dye 1 and 2 are (53% and 72%), while % exhaustion at 90oc are (65% and 85%) respectively, this shows that the adsorption of dyes 1 and2 on nylon improved with rise in temperature up to 90oc for the dyes indicate that high temperature favoured the dye adsorption into nylon fibre (Ali et al., 2009). The increase in temperature increase the mobility of large dye, as well as produced swelling effect with the internal structure for more, thus enabling the large dye molecule to penetrate further (Yoshida et al., 1993, venkatet et al., 2007). This may also due to an increase in the mobility of dye molecules with an increase in their kinectic energy and improved the rate of intra particle diffusion of sorbate with rise in temperature (Ezeribe et al., 2013)

Effect of Time on % exhaustion

Its shown from table 1 and 2 that there is an increase in the percentage exhaustion with increase in time of dyeing, this indicate that the longer the time of dyeing, the greater the amount of dye molecules absorbed by the fibre on till an equilibrium is attained, more dye molecules penetrating into the nylon at longer dyeing time resulting in high percentage exhaustion of dye 1 and 2. Thus, percentage exhaustion increases with time (Bello et al. 2009).

Thermodynamic of dyeing

The thermodynamics parameter from table 1 and 2 show that as the temperature increases, the partition coefficient of dye increases for nylon. This indicate that the absorption of dye toward the nylon fibre as an exothermic reaction process resulting higher dying temperature gives a positive effect on thermodynamics absorption (El Gabry. 2004).

The change in standard affinity of the dye in dyeing solution towards the substrate. This parameter was defined as the differences between the chemical potential of the dye in the fibre and the chemical potential of dyeing solution. This value measures the tendency of the dye to form its standard state of the solution to its standard state of the fibre (Vicker staff, 1954). It was shown from the table above that, the standard affinities increases as the temperature increases. The enthalpy change means the amounts of the released thermal energy when dye molecules are absorbed on fabric, the enthalpy change considered as the measured of the absorption strength of the dyes (Trotman, 1984). The enthalpy change of dye 1 and 2 are (-12.55 and - 15.29) kjmol-[1] respective. Because of the negative sign of the enthalpy shows that the dyeing reaction is exothermic (Banchero, 2013; MaO et al.2013).

The entropy values for the sorption of the dyes into nylon 6 fibre were found to be (78 and 95) Jmol-[1]K-[1] respectively from table 1 and 2. Mean while, the entropy change show the extent of the reduce freedom of the dye molecules after the completion of dyeing and represent the entropy difference of the dye molecule the fibre (Kim et al.2007). The positive entropy change values suggested that the solid/solution interface during sorption increase the diffusion rate of dyes (Otutu et al.2008).


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TABLE 1 Thermodynamic parameters of Dye 1(p-hydroxyazo-3- benzene carboxylic acid) on nylon

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TABLE 2 Thermodynamic parameters of Dye 2[1-l(3-hydroxylphenyls azo)-2-naphthol] on nylon.

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Scheme 1

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Scheme 2

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Thermodynamic Parameters of Two Azo Dyes on Nylon Fabric. Synthesis, Application and Determination
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thermodynamic, parameters, dyes, nylon, fabric, synthesis, application, determination
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Adekunle Jelili Olaoye (Author), 2016, Thermodynamic Parameters of Two Azo Dyes on Nylon Fabric. Synthesis, Application and Determination, Munich, GRIN Verlag,


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