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P. S. Kumar et al.
10 Pretreatment Techniques
Several pretreatment techniques are performed in the textile industry and its requirement varies with the fabric production method. The basic need for pretreatment
is to remove impurities that adhere to the fabric material and also to improve its
surface characteristics such as uniformity and reactivity with coloring agents (dyes).
A detailed description of the pretreatments involved are discussed in the following
section.
10.1 Singeing
Singeing is the process that is designed to burn off the surface fibers from the fabric
to produce fine smoothness.
10.2 Desizing
Desizing is the process that involves the removal of chemicals that were added in the
sizing operation. These chemicals inhibit the dyeing and printing of fabrics as these
chemicals might react with the dyestuff to result in unwanted by-products. Either
hydrolytic or oxidative processes are employed to remove these chemicals from
the fabric material. The hydrolytic method includes rot, alkali, acid, and enzymatic
stepping, while the oxidative method includes bromide, chloride, and ammonium
persulphate desizing. The acid stepping process uses inorganic acid such as dilute
hydrochloric or sulphuric acid for hydrolyses. However, this method of desizing
affects the fiber configuration in cotton fiber. Enzymatic hydrolysis is also emphasized in the desizing operation which utilizes enzymes attained from vegetables and
animals. Enzymes are target specific species that act efficiently in the removal of
sizing agents, thus the number of enzymes required will be very less. The problem
with enzymatic hydrolysis is that it loses its activity due to poisoning by foreign
substances. The oxidative method uses oxidizing agents for the removal of starch
from fabric materials. It is highly effective in degrading the sizing agents, however,
when used in the excess amount it destroys the structure of the fiber. After the
desizing operation, the surface of the fabric is washed thoroughly to separate the
traces of sized materials. After washing, the material is subjected to thermal drying
in steam producing apparatus.
P. S. Kumar et al.
10 Pretreatment Techniques
Several pretreatment techniques are performed in the textile industry and its requirement varies with the fabric production method. The basic need for pretreatment
is to remove impurities that adhere to the fabric material and also to improve its
surface characteristics such as uniformity and reactivity with coloring agents (dyes).
A detailed description of the pretreatments involved are discussed in the following
section.
10.1 Singeing
Singeing is the process that is designed to burn off the surface fibers from the fabric
to produce fine smoothness.
10.2 Desizing
Desizing is the process that involves the removal of chemicals that were added in the
sizing operation. These chemicals inhibit the dyeing and printing of fabrics as these
chemicals might react with the dyestuff to result in unwanted by-products. Either
hydrolytic or oxidative processes are employed to remove these chemicals from
the fabric material. The hydrolytic method includes rot, alkali, acid, and enzymatic
stepping, while the oxidative method includes bromide, chloride, and ammonium
persulphate desizing. The acid stepping process uses inorganic acid such as dilute
hydrochloric or sulphuric acid for hydrolyses. However, this method of desizing
affects the fiber configuration in cotton fiber. Enzymatic hydrolysis is also emphasized in the desizing operation which utilizes enzymes attained from vegetables and
animals. Enzymes are target specific species that act efficiently in the removal of
sizing agents, thus the number of enzymes required will be very less. The problem
with enzymatic hydrolysis is that it loses its activity due to poisoning by foreign
substances. The oxidative method uses oxidizing agents for the removal of starch
from fabric materials. It is highly effective in degrading the sizing agents, however,
when used in the excess amount it destroys the structure of the fiber. After the
desizing operation, the surface of the fabric is washed thoroughly to separate the
traces of sized materials. After washing, the material is subjected to thermal drying
in steam producing apparatus.