Desizing Process in Textile industry | Desizing application practical

Desizing Process in Textile industry

Ingredients such as starch,gum,carboxymethyl celluose,polyvinyl alcohol, polyacrylate etc , applied during sizing of warp yarn.

And then in desizing we remove more or less  size material from the warp yarn as required.

1. Inefficient desizing less to the problem of patchy dyeing .
2. In case of colored woven fabrics, starch left on the fabric reacts with the alkali and form products wich will lead to bleeding of colors.
3. In desizing,starch is degraded to soluble products.
4. Degradation of starch is brought about by water,acid, oxidising  agent and enzymes.
5. Normally, desizing is carried out using enzymes,  hence the process control aspects about enzymes desizing are discussed.
6. Enzymes are biocatalyst.
7. Enzymes which degrade starch are called amylases.
8. There are three types of enzymes 

• Malt 
• Bacterial 
• Pancreatic 

Out of these the last two are largely used in our country 

These enzymes are starch degrading agents of the formation process which occors when starched fabrics stored in wet condition at slightly elevated temperature because infected by micro-organisms.

the optimum condition for PH and temperature for different types of enzymes and their susceptibility to sodium chloride an calcium chloride are summarized in table . It can be said that a pancreatic enzymes is ineffective in the absence of salt and to reach full activity sodium and calcium chloride of concentration not less then 0.03 must be added
The presence of calcium chloride also activates bacterial and malt (alpha) enzymes.
Heavy metal ions , such as mercury, copper , zinc , lead , iron and silver are strong inhibitors for all analyses.
The residual starch content on weight Fabric(owf) after de-sizing should be less then 1.0% the presence of starch (amylose) can be detected qualitatively on the de-sized and washed fabric by treating with iodine (iodine in potassium iodide solution ). the formation of blue color indicates the presence of starch.

OPTIMUM OPERATION CONDITION FOR AMYLASE

Starch is poly-alpha-glucopyranase , in which straights chain (amylose) and branched chain (amylopectin) polymers are present.

Amy lose and amylopection  are insoluble in water but can solubilised by hydralysis these polymers.

Methods OF De-sizing

The Methods of desizing may be classified as followers

1. Hydrolytic De-sizing  

•  Acid De-sizing
• Rot De-sizing
• Enzyme Desizing

LAB WORK :-

Aim :- To Desize Given Cotton Grey Fabric By Enzymatic Desizing and Calculate the Percentage Loss Weight Of Fabric 

Chemical and Conditions :-

 Material Liquid Ratio -   1:40   (in lab)

                                   Desizing Agent - 2-3 % (of weight of material )

                         Nacl (common salt ) - 5 % ( of weight of material )

                                                            PH  -  6.5-7 (adjusted by Acetic Acid ) 

Temperature  -  80*c

              Time  -  1 hour 

Theory :-  

 The Main Objective Of Desizing is to remove size from the fabric i.e, to make the fabric size free  

 To Accelerate Desizing Enzymes are used for Forthcoming process . In Enzymatic Desizing , Enzymes are used for the Degradation of starch molecule into the sample compounds which can be washed away from fabric . Enzymes are bio catalyst product and they degrade starch , so called Amylase .

They are sensitive to  continuous processing and successfully operate within limit of temp. and PH they can attack starch molecule in random way by breaking them in small parts , which are water soluble.

Procedure:-

Take Weight of the fabric sample accurately , by removing all extra threads.

then calculate the quantity of Nacl ( common salt )  and Desizing Agent .

prepare the desized bath in the water as per MLR (material liquor ratio).

Now add all the required chemical in Desized bath .

Check and adjust the PH of the bath upto 6.5-7 by acetic acid .

set the bath at 80 degree C.

now enter well wetted fabric  sample in the desized bath and run the bath for 1 hr.

Take out the material for Hot and Cold Water Rinsing and dry the fabric and now take the weight of sample again and calculate the % age loss in weight .

Solution Used :-

Chemical Quantity - weight of material  × Required concentration  

                    prepared concentration

 Result :-  percentage %age loss in weight of fabric is ______.

 

1.  Oxidative De-sizing

• Chlorine Desizing
• Chlorine De-sizing
• Bromite Desizing