**Table 4.**

*Colour Difference Index (CDI) and Relative Compatibility Rating (RCR) for application of selected binary pairs of synthetic dyes of jute fabric.*

Make Model SC 5100A] along with associated Colour-Lab plus software employing Kubelka Munk [2, 6–8] equation and CIE-Lab equations against a particular undyed (bleached) sample set as standard followed by calculating the K/S values with the help of relevant software.

The relevant color parameters measured for each sample of varying dyeing conditions are detailed in **Table 5** and plots of each dyeing process variables vs. K/S values are shown in **Figure 7** for 3 selected reactive dyes applied on jute under varying conditions of dyeing, to optimize dyeing conditions of each dye.

Finally, data in **Table 6** indicate the relevant optimised dyeing parameters for each reactive dyes studied and reported here as optimised dyeing conditions for those respective dyes applied on Jute fabric by conventional reactive dyeing method.

#### **3.8 Precession grading of colour fastness of dyed textiles by colorimetric measurement of total colour difference (dE\*) values after fading/staining in colour fastness test procedure**

In color fastness test for washing, rubbing or crocking or perspiration, or gas fading or any other agencies, the assessment is done two ways—(i) assessing change of colour/loss of depth of shade and (ii) assessing staining on a same or multifiber white fabric after colour fastness test s by fading under different agencies/conditions as per standard test method and followed by assessing colour loss or staining amount by comparing with two types of grey scale as said. But this assessment is sometimes misleading to one grade upper or lower and is debatable unless quantitative measurement of amount of colour change or amount of staining occur is done and checked not fully depending on visual assessment with the said two types of grey scale.

Colour changing grey scale card consists of colour fastness rating for the colour change with a corresponding decreasing scale of grey chroma, which is standardised in 5-grade levels or nine grades system including half grades, where grade 5 representing the best Colour Fastness and grade 1 representing the worst colour fastness. The middle levels are assessed as half grade: like grade 45 and grade 34 and then it consists of nine levels.

Similarly, stained grey scale card consists of standard scale of white with a corresponding group of increasing grey chroma having standardised mainly by five grades (1–5), or nine grades system including half grades, where grade 5 implies


#### *Colorimetric Evaluations and Characterization of Natural and Synthetic Dyes/Pigments… DOI: http://dx.doi.org/10.5772/intechopen.104774*

*Plots of dyeing process variables Vs K/S values for three reactive dyed jute fabric dyed with varying dyeing conditions as per Table 5.*

#### **Table 5.**

*Surface colour strength (K/S) data showing the effects of dyeing process variables on colour yield of different reactive dyed jute fabric.*

#### *Colorimetry*

*Plots (a-i) showing dyeing process variables vs. K/S curves for three reactive dyes-for varying. (a) Dye concentration; (b) Salt concentration; (c) Dye Exhaustion Time (Min); (d) Dye Exhaustion Temp (<sup>o</sup> c); (e) Soda Ash (gpl); (f) Dye fixing time (Min); (g) Dye fixing Temp (o c); (h) pH; and (i)MLR.*

virtually no staining representing best colour fastness while grade 1 signifies the worst colour fastness, and the middle grade are assessed as half grade, like grade 4–5 and grade 3–4. But these grey scale grading is comparative visual assessment of grades and may not always be true.

Hence later, as per ISO-105-A02—1993 Textiles- Test for Color fastness test part -A02, Grey scale for assessing change in color and ISO-105-A03–2019 -


*Colorimetric Evaluations and Characterization of Natural and Synthetic Dyes/Pigments… DOI: http://dx.doi.org/10.5772/intechopen.104774*

#### **Table 6.**

*Optimised conditions of dyeing process variables by conventional method of reactive dyeing of jute fabric using three selected reactive dyes.*

Textiles- Test for Color fastness test- part-A03, Grey scale for assessing staining, the quantitative data for dE\* values for both types of grey scale are shown in **Table 7** with given tolerances. So precision and correct color fastness grading is now possible matching with the values of measured DE\* values after fading/ staining on each type of colour fastness tests under different agencies instead of using visual comparative assessment by grey scales only. Thus, colorimetric measurement of these cases is found to be useful for correct/precision color fastness grading.

#### **3.9 Determination of rate of dyeing, dyeing isotherm and dyeing kinetics parameters by colorimetric analysis**

Rate of dyeing can be understood by colorimetric analysis of dye in fibre (rest are dye in solution) at specific dyeing time and its temperature dependence and dyeing isotherm is understood by Din Fibre vs. Dye in solution plots and dye in fibre with respect to different dyeing temperature indicates its bearing on heat of dyeing. All these can be easily calculated by colorimetric analysis of dye absorbed in fibre (out of total dye added in bath) by analysis of dye concentration left in dyeing bath at any time span and even after different dyeing time and temperature, if dye % added in bath solution before dyeing is known. This must be done in UV VIS absorbance spectrophotometer after obtaining calibrated dye concentrations curve for specific dye. Discussion of a case study will bring more clarity in it to understand it practically. Hence, an example of determining rate of dyeing, dyeing isotherm and dyeing kinetics are briefly mentioned as a case study facilitating both offline and on line colour control in relation to computer aided colour control and matching [21] for textiles.

CASE STUDY 9: An example of determining rate of dyeing, dyeing isotherm [Dye in fibre vs. Dye in Solution curves] and dyeing kinetics (determining half dyeing time, heat of dyeing or dyeing enthalpy, bond energy etc] are briefly mentioned here as case study. Relevant data and the rate of dyeing curve [Df (amount of Dye exhausted to the fibre) vs. td (time of dyeing)] for jute fabric for dyeing with madder (also known as Manjistha/Rubia) after double pre-mordanting with 20% harda (myrobolan) and 20% Al2(S04)3 applied in sequence followed by subsequent


#### **Table 7.**

*Colour fastness grading in terms of colour difference values (dE\*) as equivalent to grades of grey scale with tolerances for precision grading of colour fastness assessment.*

dyeing with madder/Manjishtha under a pre-optimized conditions of dyeing are shown in **Table 8** and **Figure 8**.

Relevant Data in **Table 8** also shows the dye exhaustion to the fibre for different dyeing temperature indicating rate of dyeing for application of madder extract on the said double pre-mordanted jute at lower temperature (at 50°C) and at higher temperature (at 90°C), where differences of dye up take at these two temperature are found to be higher at lower dyeing temperature of dyeing and gradually the differences reduces for use of higher temperature, viz. data in **Table 8**.

Relevant curves in **Figure 8**, using data of **Table 8**, indicate that with increase in dyeing time, the dye uptake (Df) increases measurably up to 60 min of dyeing time and then gradually slows down and almost levels off in between 90 and 120 min. Since, purpurin and manjistin are present as the two main colouring components of in Indian Madder [a natural dye], both these colouring components [having -OH and -COOH functional groups] gradually starts reacting by attachment to mordant with increasing of dyeing time and temperature, while its exhaustion to the mordanted fibre might have levelled off after possible saturation of such dyemordant-fibre complex forming reaction and possible hydrogen bonding etc. for dye fixation is completed and no further increase in temperature or time can increase dye up take further.

*Colorimetric Evaluations and Characterization of Natural and Synthetic Dyes/Pigments… DOI: http://dx.doi.org/10.5772/intechopen.104774*


#### **Table 8.**

*Dye exhaustion to the fibre [Df] for different dyeing time indicating rate of dyeing for application of Madder/ manjistha as natural dye on double pre-mordanted bleached jute fabric.*

**Figure 8.** *Rate of dyeing plot as function of time for dyeing of pre-mordanted jute fabric with Madder at 50 and 90°C.*

**Figure 9.**

*Plot showing the dyeing isotherm for pre-mordanted jute fabric dyed with Madder/Manjistha at 90°C.*

While, **Figure 9** is the Plot between Dye in solution (Ds) Vs Dye in Fibre (Df) at a particular time and temperature (here at 90°C) represent at saturation or equilibrium as corresponding dyeing isotherm.

The chemical affinity (Δμ) for the dye molecule or dyeing affinity for Madder/ Rubia/Manjistha towards mordants for pre-mordanted bleached jute fabric when dyed at optimized dyeing conditions for different durations at two different dyeing temperatures (50 and 90°C) is shown in Table 5.2.9. Low but measurable increase in chemical affinity of the said colourant is observed for increase in dyeing

temperature from 50–90°C, albeit, higher increase in chemical affinity is expected for increase of dyeing temperature. This moderate value and low increase of chemical affinity for enhancement of dyeing temperature showed that dyeing of bleached and mordanted jute fabric with madder/manjistha do not occur as rapidly as expected and maybe there is low extent of formation of Fibre-Mordant-Dye coordinated complex, while it may be presumed that dyeing occur through weak hydrogen bonding formation in a slower speed. While it is reported in earlier literature [22] that some synergistic effects for application of double pre mordanting with 10% natural potash alum and 10% harda (myrobolan) on cotton before dyeing with madder (Manjistha) due to additional coordinating power of chebulinic acid of harda as a mordanting assistant, facilitates more number of strong and giant bigger complex formation amongst the said fibre (cotton) mordanting assistants (harda)—metallic mordant (natural alum)—natural dye (madder) to develop higher colour strength and higher Colour fastness to wash as an optimised and better option, which however do not happen in case of dyeing jute fabric with madder/manjistha, after double pre-mordanting with 20% harda (myrobolan) and 20% Al2(S04)3 applied in sequence in this case, may be due to acidity of jute do not allow chebulinic acid of harad (myrobolan) to be attracted/ absorbed to jute fibre, as required.

To understand the chemistry of attachment of this particular natural colorant specifically whether the dye molecules from madder or manjistha has been bonded to the fibre-mordant system through pre-dominant H-bonding or through coordinate/chelating complex formation, dyeing isotherm indicate that there is formation of more intermolecular H-bonding between dimeric association of – OH groups of madder component and mordanting assistant like harda (myrobolan) used in double mordant attached through metallic mordant of aluminium sulphate and the jute fibre forming intermolecular H-bonds, and less or no Dye-Mordant Fibre Complex formation occur predominantly as expected. Hence the dyeing isotherm observed is Nernst type (and not Langmuir type) is observed in **Figure 9** like dyeing of non-polar disperse dyes to hydrophobic polyester fibre. However, some metallic chelate formation cannot be excluded fully and need to be explored by FTIR scan etc.

For dyeing of bleached jute after double pre-mordanting with harda (myrobolan) and Al2(SO4)3, applied in sequence, heat (enthalpy) of dyeing is found to be positive, showing medium magnitudes of positive values. Thus, this dyeing process may be considered as endothermic and therefore more dye would be adsorbed with increase of dyeing temperature up to equilibrium. In case of double pre-mordanting with harda (myrobolan) and Al2(SO4)3 applied in sequence and subsequent dyeing at pH 11.0, K/S value initially increases with increase in dyeing temperature up to 90°C, and above which, the K/S value levelled off. From observed data in **Table 9**, it is indicated that at dyeing temperature between 50–90° C, the ΔH values (required heat of dyeing, as a measure of bond energy/forces of attraction responsible to bind natural dye molecules to the fibre by bridging through the metallic mordant) are always positive in this case but showing lower magnitude of ΔH values within 6.91 to 29.52 kJ/mol. This bond energy values nearly matches with the usual range of bond energy (10–40 kJ/mol) [23] of hydrogen bond formation indicating formation of a weaker dye-fibre bond that has been taken place instead of coordinated co-valent bonds. The +ve sign of ΔH values might have indicated this dyeing process as an endothermic process, which actually occur for hydrogen bond formation between the dye and mordanted fibre. However, metallic mordanting is also essential to increase the attraction of the dye to the fibre in the dye bath during dyeing to increase their chemical affinity and exhaustion of this natural dye towards jute.


*Colorimetric Evaluations and Characterization of Natural and Synthetic Dyes/Pigments… DOI: http://dx.doi.org/10.5772/intechopen.104774*

#### **Table 9.**

*Thermodynamic parameters for dyeing pre-mordanted jute with Madder/Manjistha after double premordanting with harda plus Aluminium sulphate.*

Changes in dyeing entropy (ΔS) and dyeing enthalpy (heat of dyeing) are the main indicator of dye absorption and dye fixation force. From observed results in **Table 9**, it is indicated that for different Df (dye in Fibe) and Ds (dye in solution) values, there is some changes in dyeing entropy at the initial stage of dyeing, with measurable small changes in ΔH values (heat of dyeing), as dyeing time progresses. Df values continues to increase slowly with increase in dyeing time from 30 to 60 min at 90°C in case of said double mordanting system using harda and Al2(SO4)3 in pre-mordanting. This slow increase in K/S value, for increase in dyeing time may be due to only physical absorption of dye molecules in fibre by hydrogen bonding with less possibility of Fibre -Mordant-dye co-ordinated complex formation for the dye fixation even on the pre-mordanted fibre, thus without much affecting ΔH and ΔS values.

#### **3.10 Estimation of soil removal efficacy of different detergents used for textiles**

For estimation of degree of soiling and soil removal efficiency by standard domestic laundering by selective detergent [24], first the clean white or light coloured fabrics are to be artificially soiled under standard conditions by dipping and running the clean fabric under an oil in water emulsion with water+ coconut oil/carbon tetrachloride with addition of recommended dosages of graphite powder or carbon black powder and the changes in reflectance value after artificial soiling gives degree of soiling as depicted in the following Eq. 25;

$$\text{Degree of Soliding} \left( \% \text{Sooling} \right) = \frac{\text{R}\_0 - \text{Rs}}{\text{Rs}} \times 100 \tag{25}$$

Where **R0** is the Initial Reflectance value of clean (unsoiled) white/light coloured fabric and **Rs** is the Reflectance value of artificially soiled white or light coloured fabric.

Further, estimation of soil removal efficacy % of any detergent, can be similarly calculated by change of Reflectance of corresponding soiled fabric sample before and after washing at specified standard conditions in launder-o-meter, represented by following Eq. 26:

$$\frac{\text{Degree of soil removal efficiency} \left(\%\right)}{\text{Or Percent soil removal Efficiency}} = \frac{\text{R}\_{\text{L}} - \text{Rs}}{\text{R}\_{\text{0}} - \text{Rs}} \times 100\tag{26}$$

where **Rs** is the Reflectance value of artificially soiled white or light coloured fabric before laundering and **RL** is Reflectance values of the standard soiled fabric after Laundering for given numbers of cycles of wash under specified washing conditions of domestic wash under lauder-o-meter. Also, to determine degree of soil redeposition %, AATCC Test Method 151 can be used to estimate the degree of soil redeposition likely to occur during laundering as soil removal efficiency is never 100% and gradual redeposition of soil on fabrics under wash always occurs. The fabrics to be tested are exposed to initially to a standard soiling method (preferably taking fabric swatches with both dry soiling followed by fabric pretreated with a standard oily soil) and then subjected to laundering to determine both soil removal efficacy and soil redeposition during a laundering simulated with a standard domestic wash with selective detergent. The change in reflectance of the fabric before and after laundering for the soiled fabric under testing is an indication of the % soil redeposition potential of the fabric as well as soil removal efficacy percent of the corresponding detergent.

#### **4. Concluding remarks**

The application of above said colorimetric analysis with few case studies for textile industry are a small glimpse only considering this vast subject of colorimetry and hence, this can be applied in makeshift way to other different industry as well. In the colorimetric analysis, besides conventional old model of colorimeter (which is almost abandoned) UV VIS absorbance spectrophotometer and UV VIS Reflectance spectrophotometer, both took major role for colorimetric analyses of all types of Liquid and solid coloured samples used in textile industry, paint industry, food industry, chemical industry, cosmetic industry, pharmaceutical industry etc., where colour information could be obtained with different type of sensor/detector to quantify the colour variation in different colour spaces such as CIE L\*a\*b\* colour space and other recent few more colour space used such as CIE-LUV, RGB, CMC etc., Besides the conventional approaches of colorimetric analysis, nonconventional approaches are now being applied on liquid samples for detection of chlorine in water, to check ripeness estimation of different fruits, to check colour differences in blood to determine blood shading date (or age) for forensic purpose, to determine efficacy of UV active agents like Bluing agents or optical brighteners/ UV absorbers used in textile industry etc., where quantification of required colour parameters are calculated using analytical formulas extracted from different colour space concepts defined and measured using UV VIS absorbance spectrophotometer and UV VIS Reflectance spectrophotometer. Presently Portable Reflectance spectrophotometer are the industry's major choice due to its handy use and carrying capability from one place to other.

As an alternative to UV-VIS spectrophotometric analysis, colorimetry is also widely used in many applications including food allergen testing, albumin testing in urine analysis, blood analysis, pH quantification and water monitoring in different industry.

Over the last decade, scientist has made possible that smartphones may also be used in a variety of scientific fields as spectrometers or as colorimeters, if provided with optical sensor. Smartphone optical spectrometers uses the wavelength scan components, which give spectral information at 400 to 700 nm for the collimated light from the optical source which is dispersed after interaction with samples and corresponding results are recorded. The colour spectrum image of the sample taken in a smart phone is transformed into various colour spaces for the extraction of quantitative colour data. The wavelength of the spectrum generally changes

#### *Colorimetric Evaluations and Characterization of Natural and Synthetic Dyes/Pigments… DOI: http://dx.doi.org/10.5772/intechopen.104774*

between 400 and 700 nm because of the optical filters set in front of the camera in the manufacturing process which serves the purpose of using this Spectral information in many applications from smart phone.

Smartphone-based spectrometer and colorimetry have been gaining popularity and current relevance due to the widespread advances of these type of small sized and multipurpose smart devices with increasing computational and spectral recording power having relatively low cost and portable designs with very much user-friendly interfaces, and compatibility with data acquisition and processing facility. They find applications in interdisciplinary fields, including but not limited to textiles or paints or pharmaceutical industry, agriculture industry chemical industry and biological and medical purposes too.
