298
Cationization as Tool for Functionalization of Cotton
linked. From dyeing perspective, anionic nature of cotton poses a problem while
taking up dyes which are also anionic in nature. Because negative dye/chemical and
fibre surface repel each other, the electrolyte is added in the dyeing process to neutralize the electronegativity of fibre surface. When alkalinity is introduced functional
group of reactive dye forms a covalent bond with fibre [44]. These electrolytes, however, do not get absorbed during the dyeing process and such a high concentration of
electrolytes is discharged. It is not acceptable by environmental norms as it disturbs
aquatic life. It also has an adverse effect on dye solubility. Lowering or eliminating
the concentration of electrolytes including alkali does not give satisfactory fixation
of the anionic dyes on the cotton substrates. Similar issues arise in case of finishing process as negative surface nature of cotton also restricts the anionic chemical
agents to be applied on its surface. Anionic softeners cannot get attached on the
cotton. Hence, it is necessary to perform cationic surface modification of cotton.
In textile industry various surface modification techniques like grafting, inorganic
chemical addition, biopolymer addition etc. are used but most of these treatments
are not economic and effective. They are not durable as there is no strong linkage
between surface of substrate and target chemical agent.
The durability of any finishing process is the most important criteria in textile
processing, where strong and permanent linkage of cationic chemical on the surface
of the substrate is the necessity, so the cationization of cotton is important surfacemodifying treatment [45]. The cationization process has a high ecological impact as
for processing like dyeing and finishing. By cationization, chemical consumption to
dye cotton can be reduced by 50% compared to conventional processing.
3.3 Mechanism
The process of cationization is a simple technique, where a cationic agent is chemically reacted with hydroxyl ions of cotton to develop new cationic sites on the
fibre surface. The nucleophilic substitution reaction takes place between nucleophile
i.e. hydroxyl group of cotton and a cationic group of cationizing agent. When such
cationized cotton is further treated with anionic dyes or finished with a finishing
agent, the coulombic attraction takes place between the positive charge on the fibre
and the negative charge on the dyes or finish [46].
The efficiency of the cationization is directly proportional to the concentration of
the cationizing agent and the capacity of the cotton surface. In a simple way, more is
the amount of cationizing agent applied, more is the degree of cationization (Fig. 6).
3.4 Application
Cationization can be achieved on fibre, yarn or fabric form and the reaction depends
upon parameters like time, temperature and pH. The temperature and time can be
Cationization as Tool for Functionalization of Cotton
linked. From dyeing perspective, anionic nature of cotton poses a problem while
taking up dyes which are also anionic in nature. Because negative dye/chemical and
fibre surface repel each other, the electrolyte is added in the dyeing process to neutralize the electronegativity of fibre surface. When alkalinity is introduced functional
group of reactive dye forms a covalent bond with fibre [44]. These electrolytes, however, do not get absorbed during the dyeing process and such a high concentration of
electrolytes is discharged. It is not acceptable by environmental norms as it disturbs
aquatic life. It also has an adverse effect on dye solubility. Lowering or eliminating
the concentration of electrolytes including alkali does not give satisfactory fixation
of the anionic dyes on the cotton substrates. Similar issues arise in case of finishing process as negative surface nature of cotton also restricts the anionic chemical
agents to be applied on its surface. Anionic softeners cannot get attached on the
cotton. Hence, it is necessary to perform cationic surface modification of cotton.
In textile industry various surface modification techniques like grafting, inorganic
chemical addition, biopolymer addition etc. are used but most of these treatments
are not economic and effective. They are not durable as there is no strong linkage
between surface of substrate and target chemical agent.
The durability of any finishing process is the most important criteria in textile
processing, where strong and permanent linkage of cationic chemical on the surface
of the substrate is the necessity, so the cationization of cotton is important surfacemodifying treatment [45]. The cationization process has a high ecological impact as
for processing like dyeing and finishing. By cationization, chemical consumption to
dye cotton can be reduced by 50% compared to conventional processing.
3.3 Mechanism
The process of cationization is a simple technique, where a cationic agent is chemically reacted with hydroxyl ions of cotton to develop new cationic sites on the
fibre surface. The nucleophilic substitution reaction takes place between nucleophile
i.e. hydroxyl group of cotton and a cationic group of cationizing agent. When such
cationized cotton is further treated with anionic dyes or finished with a finishing
agent, the coulombic attraction takes place between the positive charge on the fibre
and the negative charge on the dyes or finish [46].
The efficiency of the cationization is directly proportional to the concentration of
the cationizing agent and the capacity of the cotton surface. In a simple way, more is
the amount of cationizing agent applied, more is the degree of cationization (Fig. 6).
3.4 Application
Cationization can be achieved on fibre, yarn or fabric form and the reaction depends
upon parameters like time, temperature and pH. The temperature and time can be