Desizing Process of Cotton Fabric
Desizing Process:
Grey cotton fabric contains natural impurities as well as ‘size’ added to the fabric to facilitate weaving. The size is added to grey fabric in a weaving preparatory process called ‘sizing’. The added matter or size is removed from the fabric by a process called ‘desizing’.
Sizing components such as starch, thin-boiling starch, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), vegetable oils, mutton tallow, etc., applied to cotton warp yarn to strengthen it before weaving, make the fabric unsuitable for dyeing as the fabric becomes hydrophobic. Hence this unwanted size has to be removed for successful wet processing by making the fabric hydrophilic in nature.
The object of desizing is to remove size that is applied to the grey fabric as a part of the weaving process so that the fabric becomes free of the added matter and can be effectively scoured and bleached. Hydrolysis of starch:
Starch → Dextrin→ Maltose → Glucose
(high molecular weight) → (low molecular weight)
Objects of Desizing:
Different methods of desizing are given in below figure.
The most commonly used methods for cotton are enzymatic desizing and oxidative desizing. Acid steeping is a risky process and may result in the degradation of cotton cellulose while rot steeping, hot caustic soda treatment and hot washing with detergents are less efficient for the removal the starch sizes.
Enzyme Desizing:
In enzymatic desizing, enzymes liquefy starch in the fabric. An enzyme is essentially a protein produced by living cells. It acts as a catalyst in chemical reactions. In almost all instances, enzymes are very specific in action, i.e., each enzyme catalyses’ only one reaction or type of reaction. Classification of desizing enzymes:
Enzymes suffer from the disadvantage that if the conditions of temperature and pH are not maintained, little or no desizing takes place.
Important information about desizing:
Desizing Procedure of Cotton Fabric:
Grey cotton fabric contains natural impurities as well as ‘size’ added to the fabric to facilitate weaving. The size is added to grey fabric in a weaving preparatory process called ‘sizing’. The added matter or size is removed from the fabric by a process called ‘desizing’.
Sizing components such as starch, thin-boiling starch, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), vegetable oils, mutton tallow, etc., applied to cotton warp yarn to strengthen it before weaving, make the fabric unsuitable for dyeing as the fabric becomes hydrophobic. Hence this unwanted size has to be removed for successful wet processing by making the fabric hydrophilic in nature.
The object of desizing is to remove size that is applied to the grey fabric as a part of the weaving process so that the fabric becomes free of the added matter and can be effectively scoured and bleached. Hydrolysis of starch:
(C6H12O5)n→ (C6H12O5)x →C12H22O11→ C6H12O16
Starch → Dextrin→ Maltose → Glucose
(high molecular weight) → (low molecular weight)
Objects of Desizing:
- To remove the starch material from the fabric.
- To increase the affinity of the fabric to the dry chemicals.
- To increase the absorbency power of the fabric.
- To increase the luster of the fabric increase of dyeing and printing.
- To make the fabric suitable for the next process.
Different methods of desizing are given in below figure.
 |
| Figure: Methods of desizing |
Enzyme Desizing:
In enzymatic desizing, enzymes liquefy starch in the fabric. An enzyme is essentially a protein produced by living cells. It acts as a catalyst in chemical reactions. In almost all instances, enzymes are very specific in action, i.e., each enzyme catalyses’ only one reaction or type of reaction. Classification of desizing enzymes:
Enzyme
|
Concentration
|
Temperature
|
pH
|
Malt extracts
|
3-20
|
50-60
|
6-7.5
|
Pancreatic
|
1-3
|
50-60
|
6.5-7.5
|
Bacterial
|
0.5-1
|
60-70
|
5.5-7.5
|
Enzymes suffer from the disadvantage that if the conditions of temperature and pH are not maintained, little or no desizing takes place.
Process flowchart of desizing:
Batch
↓
Entry J-scary
↓
Desizing chamber
↓
Steamer (95°c - 100°c)
↓
Metallic guider
↓
Hot wash (95°c)
↓
Hot wash (95°c)
↓
Hot wash (95°c)
↓
Cold wash or oxalic acid wash
↓
Exit J-scray
↓
Batching
Batch
↓
Entry J-scary
↓
Desizing chamber
↓
Steamer (95°c - 100°c)
↓
Metallic guider
↓
Hot wash (95°c)
↓
Hot wash (95°c)
↓
Hot wash (95°c)
↓
Cold wash or oxalic acid wash
↓
Exit J-scray
↓
Batching
Important information about desizing:
- Machine used: Menzeldesizing machine
- Speed of machine: 70m/min – 100m/min
- Length of machine: 220m
- Capacity of desizing chamber: 1000L
- Temperature maintained while desizing: 65°c - 70°c
- pH maintained while desizing: 5.5-6.5
- Pick up%: 80%
- Dwell time: 8-12 min
- Chemical Brand used: IGSURF
Sl.No
|
Chemicals Used
|
Chemical name
|
Quantity in gpl
|
1
|
Bacterial enzyme
|
3120DE
|
5-7
|
2
|
Wetting agent
|
3160CE
|
3-4
|
3
|
Sequestering agent
|
3120CI
|
2-3
|
4
|
Anti-tinting
(in Y/D fabric)
|
3199FI
|
1-2
|
Desizing Procedure of Cotton Fabric:
- Cloth is taken from the batch into the entry J-scray and through the guiders to the desizing chamber.
- The fabric is arranged inside the desizing chamber in S-threading. Temperature is maintained at 65°c-70°c. There are 7 rollers above and 8 rollers below the chamber. The length of fabric inside the desizing chamber is 24m, which have a capacity of holding 1000L of liquor.
- The fabric is then passed into the steamer using a squeezer and bow roll/expander to remove crease. The capacity of steamer is 350 kg. The threading length is 84m arranged in a double S-threading.
- The dwell time varies from 8min for yarn dyed fabric to 12min for bleached fabric. The temperature is maintained at 95°c-100°c. The temperature at lower compartment of steamer is slightly less to avoid formation of cloud.
- The fabric is then passed through a metallic guider to washing chamber having water holding capacity of 1000L.
- After three consecutive hot wash at 95°c, the fabric is cold washed or washed with oxalic acid at 55°c (if online route is taken) and passed to the exit J-scray.
- From where it is taken through the guiders and guide rollers to the winding roller and finally batching is done.
