Sizing has been considered an ‘invention of the devil’ because it is the main source of many processing problems. Size paste is added to the grey fabric in a weaving preparatory process to reduce frictional properties, decrease yarn breakages and improve weaving efficiency.
The sizing agents can be divided into two main types:
a) Natural sizing agents– which include native and degraded starch and starch derivatives, cellulose derivatives and protein sizes.
b) Synthetic sizing agents– which include polyvinyl alcohols, polyacrylates, and styrene-maleic acid copolymers.
Starch-based sizing agents are commonly used for cotton yarns because it is economical and gives satisfactory weaving performance. Other products are also used, alone or in combination with starch sizes when the higher cost can be offset by improved weaving efficiency. Some auxiliaries are also used.
The desizing procedure depends on the type of size. Therefore, it is necessary to know what type of size is on the fabric before desizing. So this is easily determined by appropriate spot tests.
The sizing material present on warp yarns can resist dyes and chemicals in textile wet processing. It must therefore be removed before any further wet processing of the fabric.
Different methods of desizing are:
a) Enzymatic desizing
b) Oxidative desizing
c) Acid steeping
d) Rot steeping
Desizing with hot caustic soda treatment
The most used methods for cotton are enzymatic desizing and oxidative desizing. Acid steeping is a risky process and may result in the degradation of cellulose while rot steeping, hot caustic soda treatment, and hot washing with detergents are less efficient for the removal of the starch sizes. Enzymatic desizing consists of three main steps:
Application of the enzyme—digestion of the starch —- removal of the digestion products.
The common components of an enzymatic desizing bath are as follows:
· Chelating agent
· Salt
· Surfactant
· Optical brightener
· Amylase enzyme
· pH stabilizer
Enzymatic desizing offers the following advantages:
· No damage to the fibre
· No usage of aggressive chemicals
· Wide variety of application processes, and
· High biodegradability
Disadvantages of enzymatic desizing include:
Lower cleaning effect towards other impurities, no effect on certain starches (e.g. tapioca starch), and possible loss of effectiveness through the poisonous enzyme. Every problem has a cause and a remedy for it. So here are some of the problems that occur in enzymatic desizing, their causes, and countermeasures to prevent those problems.
1. Incomplete desizing
CAUSES:
· It is caused due to inadequate enzymes.
· It is caused due to inappropriate desizing baths.
· It is caused due to inappropriate desizing bath pH
· It is caused due to insufficient fabric pickup.
· It is caused due to poor enzyme activity.
· It is caused due to incompatible wetting agent.
· It is caused due to deactivation of the enzyme due to the presence of metals or their contaminations.
· It caused due to insufficient digestion time.
REMEDIES:
· Using a sufficient amount of enzyme in the desizing bath.
· Appropriate temperature should be maintained.
· Optimum pH should be maintained
· Optimum squeeze pressure and wetting agent should be used.
· Good quality of enzymes must be used
· Compatible wetting agent must be used.
· Use soft water or to use an appropriate sequestering agent.
· Optimum digestion time.
2. Uneven desizing (widthways)
CAUSES:
· It is caused due to uneven pad pressure (across the width).
· It is caused due to non-uniform pad temperature.
· It is caused due to non-uniform chemical concentration in the bath.
REMEDIES:
· By maintaining uniform squeeze pressure
· Uniform bath temperature.
· Uniform chemical concentration.
3. Uneven desizing(lengthways)
CAUSES:
· It is caused due to uneven pick-up (along the length).
· Drying of outer layers of the batch.
· Temperature variation during digestion.
REMEDIES:
· Uniform pick-up along the fabric length.
· Covering the batch with polythene or other suitable sheet or by keeping the batch rolling.
· Covering the batch with polythene or other suitable sheet or by keeping the batch rolling.
4. Uneven desizing(random)
CAUSES:
· Poor wetting agent.
· Inappropriate bath temperature.
· Foaming in the bath.
· Improper use of defoamer.
· Uneven liquor distribution during padding.
· Non-uniform washing after desizing.
REMEDIES:
· Use of effective wetting agent.
· Optimum bath temperature.
· Use of appropriate defoamers.
· Uniform liquor distribution during padding.
· Thorough and uniform washing after desizing.
At Polly Industries, we take care of all these aspects which engineering the formulations of our chemicals. Our products provide various advantages and the benefits are very well time-tested at hundreds of processes.
POLLYZYME-15 – Highly effective; safe on fabrics; Alpha-amylase-based desizing agent; imparts 100% removal of size, ensures efficiency in dyeing, printing, and finishing.
POLLY-THERMO – Highly effective; Stable at high temperatures; safe on fabrics; Alpha-Amylase based desizing agent; imparts 100% removal of all types of starch including PVA, polyacrylic acid and CMC; ensures efficiency in dyeing, printing and finishing