What Is Desizing in Textile?
Desizing is a preparatory wet processing operation used mainly for woven fabrics to remove size materials applied to warp yarns during weaving. Sizing agents protect warp yarns from abrasion and help reduce yarn breakage on the loom. However, these materials must be removed before many subsequent wet processing operations to ensure proper absorbency and uniform treatment.
Why Is Desizing Necessary?
Size materials can create a barrier on the fabric surface and interfere with wet processing. Proper desizing helps improve fabric absorbency and prepares the material for scouring, bleaching, dyeing or printing.
Common Sizing Materials Removed During Desizing
- Starch and modified starch.
- Polyvinyl alcohol (PVA).
- Carboxymethyl cellulose (CMC).
- Other water-soluble or synthetic sizing agents.
The suitable desizing method depends on the type of sizing material used during weaving.
Methods of Desizing
1. Enzymatic Desizing
Enzymatic desizing commonly uses amylase enzymes to break down starch-based size materials into smaller, water-soluble products. The process requires suitable pH, temperature and treatment time according to the enzyme supplier's recommendations.
2. Oxidative Desizing
Oxidative methods use suitable oxidising chemicals to degrade certain sizing materials. Chemical selection and process control are important to avoid unwanted fibre damage.
3. Acid Desizing
Acid desizing may be used for selected starch-containing fabrics under controlled conditions. It requires careful control because excessive acid exposure can damage cellulosic fibres.
4. Hot Water or Washing Desizing
Water-soluble sizing agents such as PVA may be removed through suitable washing processes. The required temperature, time and washing efficiency depend on the size formulation and fabric construction.
Desizing Process Flow Chart
- Grey fabric inspection.
- Identification of sizing material.
- Fabric preparation and batching.
- Preparation of desizing liquor.
- Application of the selected desizing treatment.
- Required dwell or reaction time.
- Washing and rinsing.
- Inspection of desizing performance.
- Transfer to the next pretreatment process.
Important Parameters in Desizing
- Type and concentration of sizing material.
- Enzyme or chemical concentration.
- Process temperature and pH.
- Treatment time and fabric speed.
- Washing efficiency and water quality.
- Fabric construction and absorbency requirement.
Quality Control After Desizing
Desizing quality should be checked before the fabric moves to the next process. A common method for evaluating starch removal is the iodine test. The result helps indicate the presence of residual starch, although the test method and interpretation should follow the laboratory procedure.
Other checks may include fabric absorbency, appearance, residual size and consistency across the fabric width and length.
Common Desizing Problems and Remedies
| Problem | Possible Cause | Corrective Action |
|---|---|---|
| Incomplete desizing | Insufficient treatment or unsuitable method | Verify size type and process conditions |
| Uneven desizing | Uneven chemical application or fabric movement | Check liquor application and machine settings |
| Residual starch | Inadequate enzyme action or washing | Review pH, temperature, time and rinsing |
| Fibre damage | Excessive chemical exposure | Control chemical concentration and treatment conditions |
Desizing is an important part of textile pretreatment. For related wet processing topics, read our guides to slasher dyeing and the carbonising process.
Conclusion
Desizing removes weaving size materials and prepares woven fabric for subsequent wet processing. The correct method must be selected according to the sizing agent, fabric composition and process requirements. Proper washing and quality testing are essential for consistent results.
Frequently Asked Questions
What is the main purpose of desizing?
The main purpose is to remove sizing materials applied to warp yarns during weaving.
Which enzyme is commonly used for starch desizing?
Amylase is commonly used to break down starch-based sizing materials.
How can residual starch be checked?
An iodine test is commonly used to check for residual starch on fabric.
Is desizing necessary for every fabric?
Desizing is mainly required for woven fabrics that contain sizing materials. The need and method depend on the fabric construction and processing route.
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