What Is Desizing in Textile?
Desizing is the first wet-processing textile finishing technology employed to remove the sizing material from the fabric.
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Objectives of Desizing
Common Size Materials
- Starch: Corn, Potato, Sago, Hydroxy ethyl starch.
- Natural gums: Tragacanth, locust beam, etc.
- Proteins: Glue, Gelatin.
- Synthesis sizing agent: PVA, PVC, PAN, PAA.
- Additives: Defoamers, Thinners, Tallow, Oils, and waxes.
Types of Desizing
- Rot steeping
- Alkali steeping
- Acid steeping
- Enzymatic steeping
- Bromite desizing
- Chlorite desizing
- Ammonium persulfate desizing
Rot Steeping
- Starch is removed by rotting. It is the very oldest method when men cannot know the use of enzymes or other special chemicals.
- No special chemicals are required.
- In this method, the fabric is passed through a padding mangle containing warm water of 40-60℃, and the fabric is kept for prolonged stocking.
- If the warm water temperature is 40℃ then the fabric is stored for 24 hours stocking and if the warm water temperature is 60℃ then the fabric is stored for 12 hours.
- Pectin and organism are naturally present in water-produced starch-liquefying enzymes which remove the starch. But starch is not completely removed and other size materials are removed.
- To remove more starch more time is required. But if the fabric is allowed to stock very long time then enzymes may attack the cellulose. After washing, desizing is completed.
- Here the temperature is mainly to be controlled.
Alkali Steeping
In this method, the starch is removed by alkaline hydrolysis. The fabric is treated with 0.4-0.6% caustic soda solution at 60℃ to 70℃ and stored for 8 to 10 hours.
Acid Steeping
In this method, 0.5-1.0% dilute sulphuric acid solution or HCL acid at 40-60℃ is used for 4-6 hours to hydrolyze the starch from the sized fabric.
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| Hydrolytic Desizing ©Textile Pad |
Enzymatic Steeping
- Enzymes are living organisms.
- It is based on protein.
- Its main function is the fermentation of starch.
- Soluble in water but insoluble in acid and alcohol.
- No risk of hydro cellulose formation during pilling.
Types of Enzymes: Mainly Two Types
- Cellulose enzymes (degrade cellulose and if more time then cellulose is damaged and converted into glucose).
- Amylase enzymes: Outstanding features are- only hydrolyzed the starch but do not attack cellulose. So it is used for desizing.
Types of Extracting of Enzymes
- Malt extract/malt preparation enzymes.
- Bacterial extract enzymes.
- Pancreatic Analysis Enzymes.
1. Malt Extract/Malt Preparation Enzymes
Malt enzymes are obtained by extraction of corns. Concentration, temperature, pH and are very important for the efficiency of enzymes. If the temperature is raised to the upper limit it becomes destroyed (not useable). Best result at 60℃ and destroyed at 75℃.
- Disastafor
- Ferment D
- Terhyd MD etc.
2. Bacterial Extract Enzymes
Fermented rice produces bacteria → Extract → Grow → Enlarge → Prepared.
The best result is at 70-75℃ and destroyed at 95-100℃
- Rapidase
- Biolase
- Bactolase
- Gelatase
- Aery
3. Pancreatic Analysis Enzymes
Pancreatic (animal) enzymes are prepared from the pancreas of slaughtered animals. A characteristic feature of the pancreatic is that forms milky-emulsion water and is capable of modifying starch, albumen, pectins, and fats.
- Fermosol
- Novofermosol DS
- Degonmma etc
- Viveral
Conditions of Desizing With Different Extracted Enzymes
Desizing Machines
Padding Mangle for Impregnating the Cloth (One Dip One Nip)
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| One Dip One Nip ©Textile Pad |
Then the fabric is passed- through two squeezing rollers i.e one rubber and the other ebonite. When the fabric is passed into rollers, desizing occurs i.e nip is done. As the fabric at first dips in the tank and then is squeezed/ nipped by the roller, so this process is one dip and nip process.
Padding Mangle for Impregnating the Cloth (Two Dip Two Nip)
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| Two Dip Two Nip ©Textile Pad |
In this machine, the fabric is two dips and two nips.
Enzymatic Desizing Process/Continuous Desizing Process
Continuous process of cotton desizing by enzymatic process as below:
Recipe:
- Enzyme = 3-5 g/L
- Time = (for stronger solution 5 min) = 20-30 min
- Temperature = 60-65℃
- Common salt= 5-10 g/L
- pH = 6-7
The whole process of desizing is completed in the following stages.
1. Preparation of Desizing Mixture
- Water
- Wetting agent
- Salt
- Acid or alkali
- Chelant if necessary
- Malt extract enzymes.
The above chemicals dissolve completely in a mixture.
2. Padded in Padding Mangle
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| Continuous Desizing ©Textile Pad |
3. Storing
After padder the material, the fabric is squeezed and passed over the winch roller. Then the fabric is stored in the storage bath by folding it for (3-4 hours) or 5 minutes at room temperature. Here malt extracts with a starch material, and decomposes into glucose.
4. Washing
Temperature, concentration, and pH of the enzyme, the mixture must be controlled otherwise desizing will be uneven.
Controlling Points of the Desizing Machine
- Pipelines
- Faults bottom
- Steam line
- Multitubular heater
- Inlet outlet pipe
- Bulb
- Temperature
- pH
Desizing Test
- Potassium Iodide (KI) - 0.24 gm
- Lodine (1) - 0.13 gm
- And water to make a 100 ml solution.
- Deep blue: present of starch
- Violet- partially degraded starch (dextrin)
- Brown - completely degraded dextrin.