Variation in the effectivity of fixing agents in dyeing process

Dyeing is one of the prominent applications of chemistry that people unknowingly observe every day. Dyeing garments is the most important application of dyeing. The clothes people wear has different color and pattern which comes after dyeing the fabric or material of the cloth. My home town, Pune, has one of the oldest dyeing industries in the country. As most of my family members are into this industry, I have decided to decipher few of my interests in the chemistry of dyeing as my chemistry internal assessment. The color fixation is a very vital parameter which involves economic factors of the company as well. Owing to my research, I came across several dye fixing agents that are usually used in several dyeing industries; however, I was more interested to understand an intrinsic factor of the dye fixing agent and its effect on color fixation. As studied in chemical kinetics of IB Chemistry, pH chemical has significant effect in the rate and yield of product of any chemical reaction. Thus, in this exploration, I have decided to build the relationship between the intensity of color fixation and pH of different dye fixing agents used to come up with the best economically favorable dye fixing agent.

How does the pH of different fixing agents (Sodium bicarbonate, Caustic soda, Potassium hydroxide, Soda ash, and a mixture of one third Caustic soda and two third soda ash) affect the color strength of cotton fabric, which is dyed using Reactive Red Dye?

It combines with the cellulose group of cotton fabric by covalent bonds. Reactive dye consists of four parts: chromogen - responsible of coloration; reactive system – responsible for chemically reacting with cellulose group of cotton; bridging system – responsible for connecting chromogen and reactive group; solubilizing group – responsible for solubilizing the dye in water.

In the process of dyeing, as all the dye molecules couldn’t be fixed on the surface of the fabric, fixing agents were used to fix those molecules on the fabric. As these chemicals are usually alkaline in nature, these are added to the dye bath in the process of dyeing to neutralize the acidic solution and form covalent bonds to fix the unbonded dye molecules with the cellulose of the cotton fabric.

The process of dyeing consists of four parts. They are as follows:

• The fabric is treated with water and sodium chloride (salt).
• The fabric is then dyed as per requirement.
• Fixing agents are added into the dye bath.
• Washing of dyed cloth.

The chromogen present in the dye forms the coloration. When the reactive system reacts with the terminal hydroxyl group of the cellulose of the cotton material, the chromogen molecules are made fixed with the cellulose molecule of the cotton fabric by covalent bonds. The chromogen molecules which are not bonded a fixed by the fixing agents (alkaline). The acid – base neutralization reaction connects the remaining unfixed chromogen molecules with the cellulose group of the fabric by covalent bonds. Due to this reaction, hydrogen ion and hydroxyl ions are liberated by the breakdown of water molecules present in the dye bath. The liberated hydroxyl ions react with cellulose and forms cellulosate ion which lose the capability of combining with chromogen. Hence, the alkalinity of the fixing agents should sufficiently high so that the cellulosate ions could form and terminate the reaction.

The cloth will be firstly dyed using reactive red dye and five different fixing agents. Apart from that, in one trial, no color fixing agents would be used.

Spectrophotometer was used to determine the intensity of color fixing in this exploration. The intensity of darkness of color in the fabric was expressed using K/S value where K is the light absorbance of the dyed cloth and S is the scattering of light. The device determines the above-mentioned ratio for light of different wavelengths of the visible spectrum. More the value of K/S, darker is the cloth.

Null Hypothesis: There is no effect in the color strength of cotton fabric when it is dyed in presence of different fixing agents with varying pH.

Alternate Hypothesis: There is significant effect in color strength of cotton fabric when it is dyed in presence of different fixing agents with varying pH.

According to the information provided above, it could be stated that dye may not be fixed on the cotton cloth if the fixing agents are either highly alkaline or highly acidic. Hence, the predicted curve would be as follows:

The pH of fixing agent used during the process of dyeing was considered as the independent variable of the exploration. To vary the pH of fixing agents, those agents were chosen in such a way that their individual pH vary over a significant range. The fixing agents that were used in this exploration along with their pH are as follows:

The color absorbance expressed in terms of K/S value, obtained using a spectrophotometer was considered as the dependent variable of this exploration.

• Rubber gloves were worn throughout to experiment to avoid skin exposure to any chemical.
• Aprons and thermal gloves were worn throughout the exploration, to avoid thermal burns while touching any hot or warm object.

• All the materials used in this exploration were purchased and utilized at optimum amount to avoid loss or wastage of chemical products and also to decrease the cost of products.
• The NaCl (sodium chloride) used in this exploration was obtained dyeing unit treatment plant to avoid wastage of chemical.

The experiment was performed in a laboratory with an Effluent Treatment Plant. Hence, all the water used in the dyeing process was purified before disposal or reuse.

• Sodium chloride was taken and 8 g of it was measured using a digital mass balance.
• A beaker was taken and it was washed with distilled water and dried using clean cloth.
• 100 cm³ of water was added into the beaker.
• The measured sodium chloride was then transferred into the beaker with 100 cm³ of water.
• The NaCl solution in the beaker was stirred until dissolved.
• A cotton cloth was taken and 10 g of it was taken after measuring it using a digital mass balance.
• The 10 g sample of cotton cloth was kept under running water until it was completely wet.
• The wet cloth was then transferred into the NaCl solution containing beaker.
• The solution and the cloth in the beaker were then stirred for 5 minutes at a temperature of 25℃ using a Lab Infracolor Dyeing Machine.
• The fabric was then taken from the beaker and the excess liquid was rinsed out into the beaker.

• In the beaker containing sodium chloride solution, 0.6 g of dye was added.
• The content of the beaker was stirred for 5 minutes at a temperature of 50℃ in a Dyeing Machine.
• The content of the beaker was then filtered using a filter paper.
• The filtrate was then transferred into a separate beaker and kept to cool until it reached to a temperature of 25℃.
• The sample cloth, drenched in sodium chloride solution was transferred to the beaker and it was stirred for 20 minutes in the Dyeing Machine.
• The fabric was then taken from the beaker and the excess liquid was rinsed out into the beaker.

• Sodium bicarbonate was taken and 2.4 g of it was measured using a digital mass balance.
• It was then transferred to the remaining solution of the beaker as obtained in Part 2.
• The solution was stirred until the sodium bicarbonate has completely dissolved.
• The sample cloth was again transferred into the beaker and stirred for 5 minutes.
• The content of the beaker was stirred for 15 minutes in a Dyeing Machine with a gradually increase in temperature till 60℃ (4℃ per minute).
• The fabric was then removed and washed under running water for five times.

• Acetic acid was of 0.1 cm³ volume was pipetted out.
• A beaker was taken and it was washed with distilled water and dried using clean cloth.
• The obtained acetic acid was transferred into the beaker.
• The sample cloth was again transferred into the beaker.
• The sample cloth was transferred to the beaker and it was stirred for 10 minutes in the Dyeing Machine at a temperature of 35℃.
• The fabric was then taken from the beaker and the excess liquid was rinsed out into the beaker.
• Another beaker was taken and it was washed with distilled water and dried using clean cloth.
• Soaping oil of 0.2 cm³ volume was pipetted out and transferred into the beaker.
• The sample cloth was transferred to the beaker and it was stirred for 10 minutes in the Dyeing Machine at a temperature of 80℃.
• The fabric was then removed and washed under running water for three times.
• The readings of spectrophotometer were noted.

The above steps were repeated four more times for each fixing agent. Furthermore, the entire experiment was repeated by changing the fixing agents as mentioned in the independent variable section (refer to section Variables). Other than that, the experiment was repeated without using any fixing agent which is referred as Control Condition.

Sample Calculation for Control Condition:

Mean = \(\frac{8.5+8.5+8.4+8.5+8.6}{5}\) = 8.5

Standard Deviation = \(\sqrt{\frac{(8.5-8.5)^2+(8.5-8.5)^2+(8.5-8.4)^2+(8.5-8.5)^2+(8.5-8.6)^2}{5}}\) = 0.1

Percentage Uncertainty = \(\frac{±0.1}{8.5}\) × 100 = ± 1.2 %

From the above-mentioned graph, the variation of color fixing (in terms of K/S value) with respect to pH of fixing agent has been established. The intensity of color fixation in K/S was plotted along Y – Axis, and the pH of fixation agent was plotted along X – Axis. The intensity of color fixation increases from a pH of around 8 till a pH of around 11. With further increase in pH of fixing agent, the color fixation decreases. From the graph, it is clearly observed that, when the pH of fixing agent increases from 8 to 11, the intensity of color fixation in K/S ratio increases from 4.6 to 24.1. However, with further increase in pH of fixing agent to 13.3, the color fixation decreases to 9.2. Hence, it could be stated that the color fixation is optimum at a pH of around 11.

How does the pH of different fixing agents (Sodium bicarbonate, Caustic soda, Potassium hydroxide, Soda ash, and a mixture of one third Caustic soda and two third soda ash) affect the color strength of cotton fabric, which is dyed using Reactive Red Dye?

The color fixation is greatly affected by the pH of fixing agent used in the dyeing process of cotton fabric using Reaction Red Dye. The color fixation is optimum when the pH of the fixing agent was 10.73. Fixing agent having a pH of less or greater than that has yield in less color fixation.

• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value when no fixing agent was used was 8.5.
• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value sodium bicarbonate was used was 4.6.
• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value when soda ash was used was 24.1.
• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value when a mixture of one third of caustic soda and two third of soda ash was used was 18.0.
• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value when potassium hydroxide was used was 11.1.
• The color fixation of cotton fabric dyed using Reactive red dye in terms of K/S value when caustic soda was used was 9.2.
• The color in the fabric were most deep when the mixture of one third of caustic soda and two third of soda ash was taken which came out to be very deep pink.
• The color in the fabric were least deep when no fixing agent was taken which came out to be light pink.

The experiment was performed in a Lab Infracolour Dyeing Machine which is why all the external and internal conditions was controlled efficiently.

The materials required in this exploration was obtained from valid sources which provide chemicals and dyeing agents to various dyeing industries so that the exploration could be error free and reliable.

The pH of fixing agents mentioned in the Variable section were measured using pH meter prior to the experiment.

Method of triangulation was obtained while collecting raw data. Five trials for each fixing agent were obtained and the mean of the trials were considered for the exploration to nullify the random error or other human error. It has made the exploration more coherent.

In the exploration, a relationship between the pH of fixing agents used and color fixing intensity of reactive red dye on cotton fabric was established. As a lot of variables were controlled in this exploration, which also conveys an idea of the effect of each of those controlled variables on the color fixation (dependent variable). Apart from that, it could also be stated that the pH of the fixing agents would have significant impact on color fixation if any one of those controlled variables was made to be the independent variable. Hence, I would extend the idea of this exploration not only within the boundaries of one dependent versus one independent variable, rather, I would like to further explore the effect of pH of fixing agents on intensity of color fixing for different fabrics such as silk, cotton, polyester, and wool.

The research question would be framed as: How does the pH of different fixing agents (Sodium bicarbonate, Caustic soda, Potassium hydroxide, Soda ash, and a mixture of one third Caustic soda and two third soda ash) affect the color strength of cotton fabric, silk fabric, polyester and wool, which is dyed using Reactive Red Dye and hence determining the effect of pH of fixing agent on different fabric material?

The procedure would be similar to that of the current exploration. Sample of four different cloth materials of equal mass, thickness and area would be obtained and would be firstly dyed using reactive red dye and five different fixing agents. Apart from that, in one trial, no color fixing agents would be used.

Spectrophotometer was used to determine the intensity of color fixing in this exploration. The intensity of darkness of color in the fabric was expressed using K/S value where K is the light absorbance of the dyed cloth and S is the scattering of light. The device determines the above-mentioned ratio for light of different wavelengths of the visible spectrum. More the value of K/S, darker is the cloth.

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