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.