SOME THERMODYNAMIC PARAMETERS OF TWO INDIGENOUS MINERAL DYES APPLIED ON WOOL MATERIAL

Bulletin of Pure and Applied Sciences.Vol.27C (No.2)2008:P.1-24

SOME THERMODYNAMIC PARAMETERS OF TWO

INDIGENOUS MINERAL DYES APPLIED ON WOOL

MATERIAL

Adebayo, G.B

* , Adekola, F.A

** , Olatunji, G.A

** and Bello, I.A

***

*Chemistry Department, Kwara State Polytechnic, Ilorin

P.M.B. 1375, Ilorin, Nigeria

ABSTRACT

Some thermodynamic parameters governing the dyeing process of two potential indigenous mineral dyes applied on wool fabric have been investigated. These parameters included percent exhaustion

(%E), partition coefficient (K), standard affinity (-∆µ 0 ), enthalpy change (∆H 0 ), entropy change (∆s 0 ), diffusion coefficient (D

T

) and activation energy of the diffusion(E

D

) . Relevant physicochemical properties such as solubility, melting point, pH, λ max

and elemental analysis were also discussed. The range of values of %E, K, -∆µ 0 ,

∆H 0 , ∆s 0, D

T

, and E

D

obtained for the two dyes were : 92.8-98.7%, 20.5 to 73.1lkg

-1 , -1036.0 to -2626.0cal/mol, -14451 to -6043cal/mol, -15.42 to -48.88cal/molK 1.2- 4.1x10

-3 cm 2 /min and 3.75 - 4.03kcal/mol respectively. The implication of the values of each parameter on the dyeing of fabric material were discussed and used to predict some important properties of the two dyes.

Key words: Mineral dye, exhaustion, wool, Standard affinity, Enthalpy, Entropy, Partition

coefficient diffusion coefficient and activation energy.

INTRODUCTION

The application of colour producing agents to materials usually fibrous or film in order to impart a degree of colour permanency demanded by the projected end user is called dyeing[1].True dyeing covers mechanisms in which molecules of materials to be dyed becomes involved by various means with the molecules of the colouring matter. Materials which are commonly dyed include textile, fibres, plastic films, anodized aluminum, wood, paper, leather, hair, fur and some foodstuff [2-12]. The term affinity is used to describe the various types of attraction between the materials to be coloured and the dye.

Affinity may be caused by attraction between charged dye particles and oppositely charged dye-site on the materials by various types of chemical attraction, such as hydrogen bonds, non-polar or van der walls’ forces, electrostatic or ionic forces and covalent bond. Recent study has reported that an acid dye anchored by two sites parallel to the surface of the adsorbent [13, 14,

15]. The involved hydrogen bonds have recently been proposed for the adsorption of acid dye on polyamide [16, 17] to have been realized between the

CO of the support and NH

2

, NH or OH groups of the dye or realized between the NH group of the support and CO, NO

2 and O groups of the dye. These attractions seldom act in isolation; usually at least two operate in any dyeing

*Author for Correspondence, Tel. 08033851631. E-mail. adebayochem@yahoo.com

**Chemistry Department, University of Ilorin, P.M.B.- 1515, Ilorin, Nigeria.

***Chemistry Department, Ladoke Akintola University Technology, Ogbomoso, Nigeria

process. Further more, the so-called hydrophobic bond may be involved [18]. It is often useful to express the attraction of dyes for fibres in terms of standard affinities. Dyeing in most fibres are thermodynamically reversible processes involving desorption and sorption [1].Dyeing process is an exothermic process which may be simply represented thus:

Dye solution + material (substrate) → dyed material+ heat.

This simplified equation explain, the universally known fact that dye has a greater tendency to bleed into hot water than into cold water. It also points out that more dye will ultimately be absorbed by a fiber or film at low temperature than at higher temperatures when equilibrium is finally reached. The effect of a change in temperature on the rate of dyeing is determined by the activation energy of dyeing. The higher the activation energy of any dyeing process, the faster is the rate of dyeing.[1].

Although the amount of heat liberated is extremely small when a dye is absorbed by textile materials, it is possible to measure it directly if a very sensitive calorimeter is used [18].

Affinity (-∆µ o ) is measurable according to the principles of thermodynamics and may be expressed in energy unit (kjoules/mole). It is the most basic thermodynamic parameter of the dye in dyeing solution towards fiber substrate. The value of -∆µ o has been described as the measure of tendency of the dye to move from its standard state of the solution to its standard state of the fiber [16]. The greater the degree of exhaustion at equilibrium the greater is the affinity [18]. It has been recently established that adsorption of dye quantity at saturation decreases when the temperature increases [17]. Concentrations of the dye bath also affect exhaustion at equilibrium; at higher concentration the exhaustion is always low because of the size of the dye molecules. If the volume of the dye bath is high, the molecules of dye will be able to diffuse well into the fabric than when the volume is low and hence is concentrated [1]. Large negative value of ∆H 0 indicates high affinity. ∆μ 0 is termed the standard affinity and it is a measure of the tendency of the dye to move from its standard state in the dye bath on to the fiber. In most dye-fiber system ∆H 0 is negative i.e dyeing is an exothermic process, so raising the temperature leads to lower affinity and less dye being absorbed of equilibrium.

The dye which is absorbed by a fiber can be thought of as being dissolved in the solid phase and distributed between the solid and liquid phases. With two miscible liquids, the equilibrium concentration in one liquid divided by the concentration in other is termed the distribution coefficient or the partition ratio

(K). Constant K have been obtained for disperse dyes distributing themselves between water and either cellulose acetate polyester fibre, nylon, wool, cellulose or polypropylene. The Value of K varies with the temperature and is a function of liquour ratio. The higher the liquour ratio the higher the value of K. it also


2

SOME THERMODYNAMIC PARAMETERS OF TWO INDIGENOUS

MINERAL DYES APPLIED ON WOOL MATERIAL varies with temperature. The values of K could be used to predict the wet fastness properties of fibres. The higher the value of K, the higher the wet fastness of the dye [18] .

The present study is aimed at investigating dyeability of wool material in terms of the thermodynamic and kinetic properties, such as standard affinity

(∆µ o ), enthalpy change (∆H o ), entropy change (∆S o ), diffusion coefficient (D

T

) and activation energy of the diffusion(E

D

) of two indigenous mineral dyes. The dyes under investigation are presently being used to dye hair. Since hair and wool have similar composition as both of them are made up of protenious materials

[1], having disulphide, amino and amide groups in them . It is therefore of interest to investigate the potential of the mineral dye in dyeing a fabric material such as wool. Hence, a standard wool material from American textile company Dupont

Yorkshire has been chosen for the investigation, and we believe, the results obtained on wool could be extended to hair.

2. EXPERIMENTAL

2.1. Source of the Materials

Two samples of rock-like mineral dyes were obtained from a local market in

Ilorin, Kwara Sate, Nigeria. The local names of the dyes are Yombo-tumtum (YT) for black and Yombo-fita (YF) for white. The original sources of the samples were traced to the coastal area of Ghana. These mineral dyes are widely used for various purposes including dyeing of hair and clothing materials, in the West

African Sub-region.

The wool material used is a model material from the American textile company

Dupont Yorkshire. The material was used without further treatment. The liquor to fabric ratio was 150: 1.

2.2. Solubility Test

Solubility test of sample YT was investigated in fourteen different solvents as it was previously reported for YF [22]. The solvents are: Deionized water,

Hydrogen peroxide, Acetone, Benzaldehyde, Acetaldehyde Ethanol. Pet-ether, conc. HNO

3

, Conc. HCl, Methanol, Diethyether, Ethyacetate, Acetic acid and

Aniline.

The test was carried out by adding 10mg of the well ground (<80µm) to 5cm 3 of each of the above solvents in a test tube at room temperature. Where the dye was not soluble in the cold, a gentle heat was applied placing the test-tube inside a heated water-bath [19]

2.3. Melting Point: This was determined by Gallenkamp heated block apparatus using the capillary tube method.


3

2.4. Elemental Analysis of the Dyes:

Sample YT was crushed and ground in a Tungsten carbide Spex Mill and analyzed for trace elements as previously reported for sample YF [20, 22] using energy dispersive X-ray fluorescence (EDXRF) Spectrophotometer a Canberra model SL 12170 silicon solid state detector and the associated pulse processing electronic which are coupled to ADC-Card. Quantification of the concentrations of detectable elements was done using a modified version of emission transmission method [21].

2.5. Preparation of standard dyes solution

A 1% dye solution was prepared by dissolving 1g of each of the dye (YF and YT) in 50cm 3 of distilled water and made up to 100cm 3 in a standard volumetric flask.[1]. All other solutions were prepared from the standard solutions of the dyes.

2.6. Determination of the λmax of the dyes

The absorbance of the standard solution of the dyes (1%) were scanned between

400-700nm to determined their λmax using UV-VIS spectrophotometer, model

Aquamate V4.60

2.7. Preparation of dye bath

A 1%dye solution was prepared as stated previously 0.100g of bleached wool fabric was dyed in each case to 1% depth by conventional methods [1]. Glauber’s salt-anhydrous sodium sulphate and acetic acid were used to vary and maintain the pH desired. The liquor to fabric ratio was 150:1 for different period of equilibrium exhaustion of the dye. The recipe for the dyebath of 150:1 liquour to fabric ratio is as given below:

2.8. Dye stock solution 1% w/v:

Volume of the dye = 0.1cm

3

Mass of fabric = 0.100g

Volume of H

2

SO

4

= 0.1cm

3

Volume of Na

2

SO

4

(5%) = 1.0cm

3

Buffer solution (CH

3

COOH/CH

3

COON a

) = 2.4cm

3

Water = 11.3cm

3

= 15.0cm

3 Total

2.9. Adsorption isotherm

The wool fabric (0.1g) was dyed in solution containing 0.0667g/l of the dyes at various temperatures of 35, 50, 60 and 70 0 C until equilibrium adsorption was


4


MINERAL DYES APPLIED ON WOOL MATERIAL obtained. The dyeing process involved dipping of 0.1g fabric in the dye liquor

(15cm 3 ) at a given temperature for varying periods of 3, 5, 10, 20, 30, 45 and 60 mins. The absorbance (At) of the solution at the end of different duration of dyeing of the fabrics was measured using spectrophotometer. One of the dye baths was left without fabric to serve as blank dye bath or the control. The absorbance, (A

0

) of the blank dye bath was noted. Percent Exhaustion (%E) was calculated for each bath using the expression below:

%E = A o

- A t

x 100 (1).

A o

The %E was then used to calculate amount of dyes uptake in g per kg of the fabric, from which the sorption capacity was graphically deduced.

2.10. Partition coefficient and standard affinity

If μ of + RT In (D) f

and μ 0s + RT In(D) s

are the respective free energies of the dye retained in the fiber and the dye left in dyeing bath, both energies are equal at equilibrium since the free energy of the dye must be the same in both phases.

The partition coefficient (K) of the dye between the fiber ([D] f

) and the dyeing solution ([D]

S

) were obtained from the adsorption isotherm. The standard affinities (-∆μ 0 ) of the dyes were calculated using equation (2).

-∆μ 0 = - ( μ 0f - μ 0s ) = RT In (D) f

(D) s

-∆μ 0 = RTInK (2).

-∆μ 0 , standard affinity(cal/mol); standard chemical potential of dyes in the fiber , standard chemical potential of dyes in the solution, R, gas constant(1.9872cal/mol); T, ,absolute temperature(K); [D] f

, dye concentration in the fiber (g/Kg); [D]

S, dye concentration in the solution

(g/L) and K , partition coefficient. K can also be determined from equation (3):

K =liquor ratio x %E/%R (3).

Where %E = Percentage exhaustion/adsorption at equilibrium and %R = (100 - %E)

2.11. Enthalpy Change

The enthalpy change ∆H o in adsorption process is obtained from the empirical


5

plot that shows the relationship between -∆μ 0 /T and 1/T using Eq. 4.

∆H o = δ(-∆μ 0 /T) / δ(1/T)

∆H o /T = -∆μ 0 /T + C (4).

Where ∆H o is heat of adsorption (cal/mol); --∆μ 0 absolute temperature (K); and C , integral constant.

2.12. Entropy of dyeing

The entropy change ∆S o is calculated using Eq. 5

-∆μ 0 = ∆H o - T∆S 0 (5).

-∆μ 0 is standard affinity (cal/mol); ∆H O , heat of adsorption; ∆S O , change in entropy (cal/mol K); and T, absolute temperature (K).

2.13. Dyeing rate:

For dyeing rate, the wool fabric (0.1g) was dyed in a solution containing

0.0667g/l of the dye at the temperatures of 35, 50, 60 and 70 0 C. The liquor ratio was fixed at 150: 1.

2.14. Diffusion coefficient

Diffusion coefficient (D

T

) was calculated from the plot of variation of C t

/C eq

with t 1/2 at the initial stage of dyeing

C t

/C eq =

4√D

T

/A (6).

Where C t

, is dye exhaustion at time t (g/dm 3 ); C eq

, dye exhaustion at equilibrium (g/dm 3 ); D

T

, diffusion coefficient(cm 2 /min), and A, surface area of fabric (cm 2 ).

2.15. Activation energy of diffusion

The activation energy of the diffusion (E

D

) was calculated from the relationship between lnD

T

and 1/T using Eq. 7 lnD

T

= lnD

0

- E/RT (7). where(D

T

) is diffusion coefficient at a temperature T (cm 2 /min),D

0 constant; E

D

, activation energy; R, gas constant(1.9872cal/molK); and T, absolute temperature(K).


6


MINERAL DYES APPLIED ON WOOL MATERIAL

3. RESULTS AND DISCUSSION

Physicochemical characterization

3.1. Solubility

The results of solubility of the sample YF in fourteen different solvents have been recently reported [22]. Similar results were summarized in table

1 for sample YT. The solvents are:- deionized water, Hydrogen peroxide, acetone, benzaldehyde, acetaldehyde, Ethanol, Pet. Ether, conc. HNO

3

, conc. HCl, Methanol, Diethyl ether, Ethylacetate, Acetic acid, and Aniline.

It is of interest to note that the two samples were soluble in almost all the solvents with the resulting solutions having different colours. Some of the colour appeared to be unstable as they evolved after 24 hours. The colours range from brown, red, yellow and black. The colour observed may be attributed to the existence of certain complexes involving some elements within the sample and organic species acting as ligands. The pHs (8.3 -

8.6) of the resulting aqueous solutions show that the sample solutions were slightly alkaline. The maximum absorption band obtained at

461.5nm for YF and 464.0nm for YT within the visible region of electromagnetic spectrum are of interest, probably indicating the presence of colour imparting chromophores in the samples [23] and therefore explained their use as dye. The spectra for the two dyes are shown in figures.1 and 2.


7

Figure 1: The spectrum for the λ max

of sample YF.


8



Figure 2: The spectrum for the λmax of sample YT


9

Table 1: Solubility of dye YT in Different Solvents with the Observed Colour

Change after 24 Hours.

10

11

12

13

14

1

2

3

4

5

6

7

8

S/No

9

Solvent Solubility Colour of solution

Colour after

24hour

Deionized water Soluble

Hydrogen peroxide Soluble

Acetone

Benzaldehyde

Acetaldehyde

Ethanol

Pet. Ether

Conc. HNO

Conc. HCl

3

Soluble

Soluble

Soluble

Light brown

Brown

Reddish

Black

Brown

Wine red

Brown

Red

Dark brown Black

Soluble

Sparingly soluble Colourless

Soluble

Light brown Reddish brown

Brownish

Light yellow

No change yellow

Sparingly soluble Cloudy White

Methanol

Diethyl ether

Ethylacetate

Acetic acid

Aniline

Soluble

Soluble

Soluble

Soluble

Soluble whitish mixture sediment?

Light brown Black

Colourless Residue

Light brown Dark red

Faint yellow Faint purple

Brown Brown

3.2. Melting point:

The wide ranges of melting point range (125-145 o c for YF and 130- 147 0 C for YT) shows that the dyes are complex mixtures.

3.3. Elemental Analysis by XRF Technique

The results of XRF analysis of sample YF has been reported (22). Similar results for YT are summarized in Table 3. Twenty elements were recorded and their concentrations range from major to ultra-trace levels. The major elements include potassium (K) and sodium (Na), minor elements are Ti, V, Cr, Zn, Mn and Fe trace elements are Co, Ni, Cu, As, Pb, Nb and Zr, and lastly, the ultra-trace elements include Rb, Sr, Y and Mo.

The major difference between the two is found in the concentration of Zn, Fe, Br, and Nb. These elements exhibited higher concentration in mineral dye YF than

YT, except Zn which was higher in sample YT. The higher concentration of

Bromine (Br) suggests marine origin for YF. The results of XRF also reveal that, these dyes could have certain degree of toxicological effect due to the presence of some toxic elements such As, Pb, Cr, Co and Zn in the two samples. This has


10


MINERAL DYES APPLIED ON WOOL MATERIAL been put into evidence in a recent study (22). It is of interest to note that all of the first series transition elements except scandium (Sc) were recorded. The colour of each of the sample can therefore be linked with the formation of coloured complex compounds by some of these transition elements [24].

Table 2: Results of Elemental Analysis of Samples YT by XRF Techniques

Element Concentration of the element

K

Ca

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

0.43(p)

0.26(p)

0.07(p)

348

204

151

125

66.0

42.0

43.0

Zn

As

Pb

Br

Rb

123

23.0

33.0

8.00

7.00

Sr

Y

Zr

7.00

7.00

11.0

Nb

Mo

15.0

5.00

(p) Indicate values in percentage, others are in ppm.

Organic matter in the dyes YF and YT was determined by ashing to be 49% and

47% respectively;

3.4. Percentage exhaustion (%E).

Tables 3 and 4 show the percentage exhaustion of dyes YF and YT by the fabric at different temperatures of 35, 50, 60 and 70 o c and different time intervals of 3,5,10,

20, 30, 45 and 60 minutes respectively for this investigation. It was discovered that the %E of the two dyes were generally high 92.8-98.7%. Two factors determine %E of any dye; concentration of dye bath and the temperatures, at higher concentration the exhaustion is always lower compare to lower concentration when the dye molecules will be able to diffuse well into the fabric due to high volume of the dye bath( 1). The liquor to fabric ratio for this investigation is 150:1 which is relatively high, this probably explain high %E at


11

all temperatures. These values of %E were then used to calculate the amount of dyes uptake by the fabric from the dye bath [D] f

(/kg ) and used to compare the diffusion of the two dyes on the wool fabric. The dyeing rate was obtained at various temperatures of 35, 50, 60 and 70 0 C. Figures 3 and 4 show the dyeing rate of YF and YT on the wool fiber at various temperatures. However, the %E at equilibrium decreases as the temperature increases (Table 5).

Table 3: Percentage exhaustion (%E) at equilibrium of YF by the wool fabric.

Time at 35C at 50C at 60C at 70C

3 97.3 95.7 93.7 92.8

5

10

20

30

45

60

97.7

98.5

98.7

98.7

98.6

98.3

96.3

97.2

98

98

98

97.6

96.6

97

97.3

97.3

97.2

97.1

93.3

94.2

95.5

95.5

95.5

95.3

Table 4: Percentage exhaustion (%E) at equilibrium of YT by the wool fabric.

20

30

45

60

Time at 35C at 50C at60C at 70C

3

5

10

96.1

97.5

98.4

92.9

95.6

96.5

94.3

95.8

96.7

93.5

94.9

95.1

98.5

98.5

98.4

98.2

97.7

97.7

97.6

97.5

96.8

96.8

96.7

96.5

95.3

95.3

95.2

95

Table 5: Percentage Equilibrium exhaustion (%E) at different Temperatures for

sample YT and YF

Temp.kel

vin

308

323

333

343

YT

98.5

97.7

96.8

95.3

YF

98.7

98.0

97.3

95.5

The results show that the dyeing rate decreases with increase in temperature with maximum at 35 0 C. This is expected since the dyeing process is exothermic, the dyes have greater tendency to bleed into hot water than cold water hence more dye will ultimately be absorbed by the fabric at low temperature than at higher temperature when equilibrium is finally reached. It has been reported that greater degree of exhaustion at equilibrium indicates greater affinity of the dye

(1), hence high %E of the two dyes could be explained to mean that they are of


12

0.065

0.0645

0.064

0.0635

0.063

0.0625

0.062


MINERAL DYES APPLIED ON WOOL MATERIAL high affinities and possibly high substantivities as affinity has been described as the quantitative measure of substantivity[18].

Figure 3: Dyeing rate of YF on wool material at 35 o C, 50 o C, 60 o C and 70 o C.

0.066

0.0655

35 C

50 C

0.0615

0 10 20 30 40 50 60 70

Time(min)

3.5. Partition Coefficient (K) and Standard Affinity

The partition coefficients of the two dyes samples were found to be decreasing as the temperature increases from 73.1- 20.5. The values of K were obtained from ratio of amount of dyes uptake [D] f

to amount in solution [D] s.

K values for YF are relatively higher than YT (Table 6). The high values of K may probably due to higher volume of dye bath (150:1) which lead to faster rate of migration of dye molecules to the fabric hence high sorption of the dyes molecules by the fabric. It has been reported that the values of K can be used to predict the wet fastness properties of dyes to the fibres. Higher values of K indicate higher fastness and substantivity properties of the dyes and vice versa. However, value of K decreases with increase in temperature, since the rate of desorption is usually high at higher temperatures.(18). The higher values of K could be taken to mean that the two dyes have high fastness properties which may justify their use as hair dyes.(18). The standard affinities for the wool fiber by the two dyes were calculated from Eq.(2) and the corresponding values for YF and YT are shown in

Table 6. The standard affinities of YF are a little higher than those of YT. The finding explains that YF has higher tendency to move from the solution to the


13

wool fabric than YT which may be due to high mineralization of YT compare with YF as it is observed from their melting point differences. It could also be as a result of favorable intermolecular interaction. As the temperature increases, the standard affinity decreases for the two dyes. This observation has been explained in terms of the exothermic nature of the adsorption of dyes towards fiber resulting in higher dyeing temperature given a negative effect on the thermodynamic adsorption [25]

Figure 4: Dyeing rate of YT on wool material at 35 o C, 50 o C, 60 o C and 70 o C.

0.066

0.0655

0.065

0.0645

0.064

0.0635

0.063

0.0625

35 C

50 C

60 C

70 C

0.062

0.0615

0 10 20 30 40 50 60 70

Time(min)

50

60

70

0

Table 6: Amount of dyes uptake [D] f, amount in solution [D] s

, partition

coefficient K and the standard affinity (-∆μ)of YT and YF on wool

material at equilibrium at 35, 50, 60, 70 0 C.

Temp.

C

35

YF

[D] f g/kg

.0658

[D] s

K

YT

-∆μ(cal/mol) [D] f g/kg g/l

.0009 73.1 2626.0 .0657

[D] s g/l

K

.0654

.0649

.0637

.0013 50.3

.0018 36.1

.0030 21.2

2495.6

2355.0

2065.7

.0652

.0646

.0636

.001

.0015

.0021

.0031

-∆μ(cal/mol)

65.7 2561.5

43.5 2301.9

30.8 1141.4

20.5 1036.0


14

-4

-5

-6

-9

-10

-7

-8



Figure 5: Relationship between ∆µ/T and 1/ T on enthalpy change for YF and

YT

0

0.0029 0.0029 0.003

0.003 0.0031 0.0031 0.0032 0.0032 0.0033 0.0033 0.0034

-1

-2

-3

R = 0.972

R = 0.932

YF

YT

1/T(1/K)


15

Figure-6 : Relationship between ∆μ(cal/mol)and Temp(K)on entropy change

for YF and YT

0

305 310 315 320 325 330 335 340 345

-500

R = 0.931

-1000

YF

YT

-1500

-2000

R = 0.958

-2500

-3000

Temperature (K)

3.6. Enthalpy and Entropy change

Figure 5 and Eq, 2 shows the linear relationship between ∆µ/T and 1/T on enthalpy change (∆H 0 ) for the two dyes respectively. ∆H 0 for the two dyes determined from the slope of figure 5 are -14451.0calmol

-1 and - 6042.9calmol

-1 for

YF and YT respectively. ∆H 0 is the heat content between that needed to free one mole of dye from solvent, and that required to free the same quantity of adsorbed molecules from the surface or from the interior of the solid by thermal agitation. The amount of exothermic energy depends on the dyeing conditions, such as fibers, dyes, dyeing media etc[26]. The enthalpy change (∆H 0 ) is also considered as a measure of the adsorption strength of dyes. Large negative values of ∆H o therefore correspond somewhat to high potential affinity and a more thermodynamically favorable condition. The entropy change (∆S 0 ) in dyeing on the other hand, represents the entropy difference of the dye molecules within the fiber [25]. The entropy change shows negative values in most dyeing process, because adsorbed dyes become more restrained within fiber molecules than dyeing solution, hence the value of the entropy change could be regarded as the measure of immobility of dyes within the fibers[26]. Figure 6 and Eq. 5 show the linear relationship between ∆µ 0 and T from which the entropy can be obtained. The enthalpy and the entropy change obtained are summarized in

Table 7. According to Table 7, YF showed higher negative value of ∆H 0 (-14451.0) and lower negative value of ∆S 0 (-15.42), while YT showed lower negative value


16


MINERAL DYES APPLIED ON WOOL MATERIAL of ∆H 0 (-6042.9) and higher negative value of ∆S 0 (-48.88). The negatively larger value of enthalpy change has been described to represents that the dye molecules were more strongly embedded within the polymer molecules[26]. In this context, it is proposed from Table 7 that YF is more adsorbed by the wool and hence exhibiting higher potential affinity than YT. The entropy change shows the extent of the reduced freedom of molecules after the completion of dyeing [25].The negatively larger value of the entropy change represents the phenomenon that the mobility of the dye molecules significantly reduced after dyeing. In this study, it can be proposed that YT has a more decrease mobility after dyeing than

YF; hence it can be said to have high substantivity. It has been reported that dyes with high affinity tend to be of large molecular size and are adsorbed at relatively lower rate than dyes of lower affinity. The results of elemental analysis actually revealed that these dyes are heterogeneous and complex materials, with high molecular sizes. Also the ∆H 0 for the two dyes are relatively high compare to some commercial dyes, for instance ∆H 0 and ∆S 0 for a typical acid dye at 50 0 C are 7.6 kcalmol -1 and - 7.2calmol

-1 k -l hence they could be said to have high affinity [18]. The high value of entropy change may also be due to its high mineral contents as revealed by its melting point.

Table 7: The enthalpy change (∆H 0 ) and the entropy change (∆S 0 ) of YF and

YF on wool fabric.

Dy e l

∆H

-1

0 calmo

1

(∆S 0 calmol -

K

YF -14451.0 - 15.42

YT - 6042.9 - 48.88

3.7. Dyeing rate and diffusion coefficient

It has been generally agreed that dyeing process involves three continuous steps

[26]. The first step is the diffusion of dye through the aqueous dyebath on to the fiber. The second step is the adsorption of dye into the outer layer of the fiber.

And the last step is the diffusion of dye into the fiber from adsorbed surface. The second step, the actual adsorption process, is generally assumed to be much rapid than either of the other diffusion steps. Of the two diffusion steps, the diffusion into the inner layer is much slower than the movement of dye through the aqueous solution due to physical obstruction of diffusion of dye presented by the network of fiber molecules [16].


17

Figure 7a: Relationship between C t

/ C eq and t 1/2 on diffusion coefficient at 35 and 50 0 C for YF.

0.502

0.5

0.498

0.496

0.494

0.492

0.49

0.488

0.486

R=0.922

R=0.999

308k

323k

0.484

0 1 2 3 4 5 6 t

1/2

(min

1/2

)

For the dye molecule to diffuse into the fiber, it is expected that the free volume could be formed within the substrate. This free volume is regarded as temporarily formed within the polymers by the thermal movement of molecular chains and the dye molecules penetrate into this empty space [27].

To compare the diffusion of YF and YT dyes on the wool fiber, the dyeing rate was obtained at 35, 50, 60 and 70 0 C. Figures 3 and 4 show the dyeing rate of YF and YT on wool fiber at these temperatures. The results show that the dyeing rate decreases as the temperature increases. This could be attributed to the exothermic nature of the dyeing process.

According to Eq. 6, C t

/C eq varies linearly with the t 1/2 . The diffusion coefficient

(D

T

) could be obtained from the slope of the relationship. Figures7a and 7b,and

8a and 8b show the relationship between C t

/C eq and t 1/2 on wool fiber at 35, 50,

60 and 70 0 C for YF and YT respectively . In addition, the diffusion coefficients

(D

T

) of the two dyes obtained graphically are presented in Table 8 .


18



Table 8: The diffusion coefficient (D

T

) of YF and YT on wool fiber

50

60

70

0

Temp.

C

35

D

T n)

YF

(cm

1.7X10

2.2X10

2.0X10

4.1X10

2

-3

-3

-3

-3

/mi D

T

YT

(cm

1.2X10

3.1X10

2

-3

/min)

2.4X10

-3

2.0X10

-3

-3

Table 8 shows that the values of the diffusion coefficient increased as temperature increases. This finding indicates that the mobility of the wool polymer chains greatly increased with increasing temperature. Similar observation has been reported for C. I .Disperse Violet 1 on three polyester fibers at 90,110 and 130 0 C [26].

Figure -7b: Relationship between C t

/ C eq and t 1/2 on diffusion coefficient at 60

and 70 0 C for YF.

0.502

0.5

0.498

0.496

0.494

0.492

0.49

0.488

0.486

0.484

0.482

0.48

0

R=0.795

R=1

1 2 3 t

1/2

(min

1/2

)

4 5 6


19

333k

343k

Figure 8a: Relationship between C t

/ C eq and t 1/2 on diffusion coefficient at 35 and 50 0 C for YT.

0.5

0.498

0.496

0.494

0.492

0.49

0.488

R=999

R=1

308k

323k

0.486

0 1 2 3 t1/2(min1/2)

4 5 6

3.8. Activation energy of the diffusion

The activation energy of the diffusion has been calculated from the Arrhenius equation (eq. 7). This parameter gives the dependence of the diffusion coefficient on the dyeing temperature and also represents the energy barrier that a dye molecule should overcome to diffuse into the polymer molecules [28]. The activation energy of the diffusion can be obtained from the slope of the linear relationship between lnDT and 1/T shown in the in Fig.9. The calculated values of activation energy are 3.7 and 4.03 Kcal/mol for YF and YT respectively.

The effect of temperature on the rate of dyeing is governed by its activation energy. The higher the activation energy of any dyeing process, the more rapidly does its rate increase as the temperature is raised.[1]. The activation energies of the two dyes YF and YT were relatively lower compared to those of some commercial dyes such as equalizing acid dyes on wool (22kcal/mol) and Milling acid dyes (29kcal/mol)[18]. It can be proposed that during dyeing process the relaxation of the wool polymer chains was less affected by the temperature than the case of wool used in the literature [26 ].


20



Figure8b: Relationship between C t

/ C eq and t 1/2 on diffusion coefficient at 60

and 70 0 C for YT

0.502

0.494

0.492

0.49

0.488

0.5

0.498

0.496

R=0.866

R=0.908

0.486

0 1 2 3 t

1/2

(min

1/2

)

4 5 6


21

333k

343k

Figure 9: Relationship between lnDT and 1/T on activation energy for YF and

YT.

-2

-3

0

0.00285

0.0029

0.00295

0.003

0.00305

0.0031

0.00315

0.0032

0.00325

0.0033

0.00335

-1

-6

-7

-4

-5

R=0.832

R=0.897

YF

YT

-8

1/T (1/K)

4. CONCLUSION

The determination of some important thermodynamic parameters has revealed the practical significance of the dyes such as affinities, substantivities for fabric and wet fastness properties. They can be said to be of high affinities and wet fastness. The various values of thermodynamic parameters have shown that the application of the dyes on the wool fabric is exothermic. The results obtained from the study compared favorably well with some commercial dyes as shown in Table 10.

Table -10: Comparison of the Thermodynamic parameters of commercial dyes with the two indigenous mineral dyes YF and YT at 60 0 C

Dye -∆μ 0 Cal/mol at 60 0 C

Disperse dye(18) 3020.0

Acid dye(18)

YF

YT

4130.0

2355.0

1141.4

-

∆H 0 Kcal/mol

5.40

7.20

6.04

14.45

-∆S 0 Cal/mol/K

5.30

17.70

15.42

48.88

From the Table 10, it can be proposed that YF has higher affinity than YT but lower than any of commercial Disperse or Acid dye .The larger negative values of ∆H 0 and ∆S 0 of


22



YT, however indicate that YT molecules were more strongly embedded within the polymer molecules and have more restricted mobility within the fiber after dyeing.

Hence, YT could be said to have higher substantivity than YF and any of the commercial dyes in the Table 10.

REFERENCES

1. Charles Hugh Giles: A Laboratory Course in Dyeing 3 rd edn. The society of Dyers and colourist. Bradford York Shire. BD1 2 JB 1974.

Bancroft . J S DC.1939. 55, 11 2.

3 Gill. Ibid. 1939. 64, 213.

4 Collins and Gilesl JSDC (review) 1952.68 , 421,

5 Anstead , ibid Cosmetics 1960. 76, 573.

6 Giles, Rahaman and Smith Text. Research J., 1961.31, 679.

7 Musgrave. J.S.D.C, 1961 77, 638.

8

9

Smith. J.S.D.C., 1962, 78, 222.

Mckay. Text Research J., ( review) 1963. 33,381

10 Marsden and Nursten . Soc. Leather Trades Chem. 1967. 51, 315.

11 Corbett . J.S.D.C 1968. 84, 556.

12 Nusten. Rev Prog. Coloration, 1973, 4, 7.

13. Baouab. M.H.V, Gauthier. R, Gauthier. H, Chabert. B, Rammah.M.B. J.

Appl. Polym.Sci. 2000. 77:171.

14. Khalfaoui. M, Baouab. M.H.V, Gauthier. R, Ben Lamine .A. Adsorpt. Sci.

Technol. .2002. 20, 33.

15. Giles. C. H, Nakwa S. N, McEwan. T.H, Smith. D . J. Chem. Soc. 1960,

3973.

16. Vickerstaff T. physical chemistry of Dyeing. Edinburgh and London.

Oliver and Boyd 2 nd edn. (1984);

17 . Khalfaoui. M, Baouab. M.H.V, Gauthier. R, Ben Lamine .A. J. Colloid

Interface Sci. . elsevier.com/locate/jcis. 2005.

18. Bird C. L. and Boston W. S. The Theory of Coloration of Textiles, Dyers

Company Publications Trust , 1975. pp 163- 234.

19. Adetuji A.O. Popoola, A.V,. and Lajide. L. Isolation and A colouring

Potentials of leaf extract of Teak plant (Tectone Grandis). J Chem. Soc.

Nigeria .2003.l. 28, 1, Pp 34-39.


23

20. Potts P.I. Energy Dispersive X-ray Spectrometry. In A Handbook of

Silicates Rock Analysis Blackie, Glasgow. 1993. Pp 286-325

21. Potts P.J Webb P.C and Waston J.S (1984): Energy Dispersive X-Ray

Fluorescence Analysis of Silicate Rock, for Major and Trace Elements Xray Spectrom . 1984. 13, pp. 2-15

22. Adebayo G .B, Sunmonu T .O, Adekola F.A and Olatunji G.A Effect of white African mineral hair dye on the activities of Phosphatases and

Malondialdehdye level in selected tissues of albino rats. J.Tox. and

Env.Chem, Taylor and Francis Group, Germany 2005, 87(3), 399-406,

23. William Kemp. Organic Spectroscopy ELBS Edition, Hong Kong 1986.

24. Liprot G.F. Modern Inorganic Chemistry 4 th Ed. pp 351-352 ELBS

Publication, London. 1974.

25. Trotman E.R. Dyeing and chemical technology of textile fibres. 6 th ed. Ne w York: John Wiley and Sons, Inc; 1984. p.279 -85.

26. Tae-Kyung K, Young-A . Son and Yong-Jin Lim. Thermodynamic parameters of disperse dyeing on several polyester fibers having different molecular structures. Dyes and pigments, , Science@ Direct, Elsevier.

2005. 67, P 22 9- 234.

27. Weigmanm HG, Scott M G, Rebenfeld L. Textile Res. J .1977. 47; 745- 54.

28 Alan J. The theory of coloration of textiles 2 nd ed.`West Yorkshire: Society of Dyers and Colourists. 1989. p.396-400.


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SOME THERMODYNAMIC PARAMETERS OF TWO INDIGENOUS MINERAL DYES APPLIED ON WOOL MATERIAL

SOME THERMODYNAMIC PARAMETERS OF TWO

INDIGENOUS MINERAL DYES APPLIED ON WOOL

MATERIAL

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SOME THERMODYNAMIC PARAMETERS OF TWO INDIGENOUS MINERAL DYES APPLIED ON WOOL MATERIAL

SOME THERMODYNAMIC PARAMETERS OF TWO

INDIGENOUS MINERAL DYES APPLIED ON WOOL

MATERIAL

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