Oxidative steeping:Starch and other added impurities are hydrolyzed through oxidation process followed by washing process. Following oxidising agents may be used:

Sodium Hypochlorite: 2.0-5.0 gm/lit. at room temperature at pH 7.0

Hydrogen peroxide:3.0-6.0 gm/lit of H2O2 and 7.0-15.0 gm/lit Sodium Hydroxide, 40 degree C for 12-16 hours

Drawback: It is a time consuming process and some time bleaching of fabric occured which other wise not required. As in the process, oxidising agents are used , there are chance of fibre damage.

Enzymatic desizing: The enzymatic desizing is the most widely practiced method of desizing starch based sizing material. Enzymes are high molecular weight protein biocatalyst that are very specific in their action. This means that a given enzyme only will work on a certain substrate and only do a very particular job. Secondly it should be remembered that, although they take part in a chemical (enzymatic) reaction, they do not change during that reaction. They are what we call biological catalysts that accelerate or facilitate chemical reactions.Enzymes are named after the compound they break down. Some of the examples are given below:

• Amylase breaks down amylose and amylopectin,
• Maltase breaks down maltose and
• Cellulase breaks down cellulose.

The starch based desizing is carried out using amylase and maltase enzymes.

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