Rot Steeping: This is an oldest method of desizing. In this method no chemical is used. Under this, the fabric which need to be desized, is stored in water at 40-60 degree C for overnight. Due to reaction with water, starch based sizing material get dissolved. 

                                   Padding            Storing                Washing

In this process fabric is first padded with warm water for 100% pickup and then kept for 12-24 hours. During that process microorganism present in water get multiplied and generate starch hydrolyzing enzymes. These enzymes break down starch and dissolve it in to the water. Finally cloth is washed. This process has following two main draw backs. 

1. Process is time consuming and 
2 One can not be sure that in the overnight dipping in water would remove sizing material completely.
3. Requirement of big space 
4. Some time mildew generated during processing attack the cloth and leaves stains

Acid Steeping: In this process acid is used to hydrolyze starch in to lower molecular weight glucose. The most common acids used in this process are Sulphuric and hydrocholoric acids. Fabric is treated 0.25 to 0.50% acid at room temperature around 30 to 40 degree C. To perform this process fabric is padded in acid and then stored for around 12 hours after that fabric is washed.

This process is also economical. There is no need for adjusting pH. The sizing material is removed completely. It take less time than Rot steeping.

The main disadvantage  associated with this process:

• If the material dried during storage the concentration of acid concentration increases which results tendering of cellulose material.

Desizing:Desizing is the process of removing the size material from the warp yarns in woven fabrics. Before understanding desizing process, one has to understand sizing process.

Sizing/Slashing: Slashing is the process where Size chemicals are applied to the warp yarns, to make the yarns weavable. The purpose of size  is to protect the yarn from the abrasive action of the loom parts. The process is carried out on a Slasher machine and the application procedure is called Sizing or Slashing.

Sizing agents: 

1. Natural sizing agents: Starch and starch derivatives; native starch, degradation starch and chemical modified starch products such as Cellulose derivatives, carboxymethylcellulose (CMC), methyl cellulose and oxyethylcellulose etc.

2. Synthetic sizing agent: Polyacrylates,  Modified polyesters, Polyvinyl alcohols(PVA) etc.

Desizing Starch: Once a starch solution dries, the resulting film will not readily re-dissolve in water; therefore, to completely remove starch from a fabric, the polymer must be chemically degraded to make it water  soluble. Following four chemical methods can be used to convert/degrade starch into water soluble compounds.  These are:

•Rot steeping

•Acid steeping

•Oxidative desizing

•Enzymatic desizing

Major Desizing Processes: The main desizing processes are given below:

•Rot steeping

•Acid steeping

•Oxidative desizing

•Enzymatic desizing

Rot steeping:   

                         In this process fabric is stored at 40-60 degree Celsius for overnight in water. It                         removes starch and water soluble impurities with natural reaction.

 Following are main drabacks associated with this  process:

                      

                           - It is time consuming process
                           - It is not certain that in the given duration, sizing material will remove or not.

Acid Steeping:

                           Here acid behave as hydrolysing agent. It reacts with bigger molecule and hydrolyze                  it to smaller molecules. For example starch, which is important ingredient of sizing                      recipe react with acid and  is hydrolyzed to glucose. In acid steeping, fabric is treated                  with sulphuric acid (0.5% to 1.0%) or Hydrochloric acid. The main drawback                              associated with this process is that the fabric get tendered or damaged if acid is                            remained in the treated fabric.

Oxidative desizing: 
                
                          Starch and other added impurties are hydrolysed through oxidation process.                                  Following oxidizing agesnts may be used for this purpose:

                           -Sodium hypochlorite: 2.0-5.0 g/l at room temperature at around pH 7.0
                           -Hydrogen peroxide: 3.0- 6.0 g/L  and 7-15 g/l Sodium hydroxide at 40 degree                             Celsius for 12-16 hours. 

Following are the drawbacks involved with this process:

                        
                            -It is a time consuming process
                            -In this process, bleaching effect is also produced which some time not                                          required.

Enzymatic desizing: 

                            Enzymatic desizing is carried out using amylase enzyme as the main                                            constituent of starch is amylose. Following recipe may be used for desizing

                            

                                       -0.5% to 2.0% Enzyme  on weight of fabric (OWF) in water                                                          -Require quantity of Common salt
                               - pH should be neutral and Fabric should run continuously in the machine                                          loaded with enzyme solution

    

Preparation of textiles for wet processing i.e Bleaching or Dyeing or Printing:

The preparation of textiles for bleaching/dyeing/printing is just like same as we do preparation for examination. Why we do preparation for examination? The answer may be  to pass the exam. Therefore when we have certain goal in mind, we do prepare our self to achieve the same. In similar way, in the textile, our goal may be to get bleached or dyed or printed fabric. To achive this goal we ahve to prepare textile material to make it ready to bleach/dye/print.

Following are the processes for preparation of textile material for bleaching/dyeing/printing:

Desizing: Removal of sizing chemicals such as starch/poly vinyl alcohol (PVA) etc from the fabric . To understand desizing we must know sizing process.

           Sizing: Sizing is a process in which we apply starch or PVA or other ingredient on the warp                 yarn (Just like a coating) to improve warp yarn strength without affecting its elongation                       properties much so it can stand stress and strain during weaving process. Please note that                  sizing is carried out only in weaving not in Knitting. 

Desizing process: There are four methods for desizing. These are:

1. Rot steeping
2. Acid steeping
3. Oxidative desizing
4. Enzymatic desizing