Oxidative Desizing Process of Cotton: Desizing Effect Easy Testing Procedure

What is Oxidative Desizing Process?

Desizing is a process where sizing materials are removed by using desizing agent. Oxidative desizing is a process where an oxidizing agent is used as desizing agent to remove the sizing materials from the fabric. Hydrogen peroxide (H₂O₂) is an oxidizing agent. The desizing with hydrogen peroxide offers several advantages. It can break the ring structure of starch and produce higher oxidative smaller fragments. It also cleaves the PVA sizes, which are not broken down by amylase enzymes. The oxidative desizing process is considerably faster than the biological process and where the cycles are short.

Typical Recipe of Oxidative Desizing of Cotton

Chemical	Amount (gm/l)
Wetting agent	0.5-1.0
Sequestering agent	0.5-1.0
Soda ash	3.0-5.0
Sodium silicate	1.0-2.0
Hydrogen peroxide (H₂O₂)	4.0-6.0
Temperature	65-75⁰
Time	15-30 min
pH	10-11
M:L	1:20
Fabric weight	5 gm
Stock solution for all chemicals	2%

Table 1: Typical recipe of oxidative desizing of cotton

Recipe Calculation

For Recipe calculation following formula is required.

The following steps are shown for the recipe calculation of oxidative desizing process.

Total amount of liquor= 5×20= 100 ml
Required wetting agent= {total amount of liquor× recipe amount (gm/l)} ÷ (1000×stock solution) = (100×1) ÷ (1000× 2%) = 5 ml
Required sequestering agent= (100×1) ÷ (1000× 2%) = 5 ml
Required soda ash= (100×4) ÷ (1000× 2%) = 20 ml
Required sodium silicate = (100×2) ÷ (1000× 2%) = 10 ml
Required hydrogen peroxide= (100×5) ÷ (1000× 2%) = 25 ml
Required water= {100- (5+5+20+10+25)}= 35 ml

Process Curve (Oxidative Desizing of Cotton)

Process curve for oxidative desizing process of cotton — Figure 1: Process curve (oxidative desizing process of cotton )

Procedure of Oxidative Desizing

At beginning, set the machine according to the parameter of the recipe.
Subsequently, add all chemicals at room temperature to the pot and check the pH.
Now, load the pot in the machine and raise the temperature to 65-75⁰ C
Run the bath for approximately 15-30 min at 65-75⁰ C.
After that time, cool down and unload the pot from the machine.
Rinse the sample with hot water (60⁰ C) and again rinse with cool water for 3 min.
Finally, add 0.5-1.0 gm/l acetic acid (65%) for neutralize the alkali at 40-50⁰ C for 5 min. Then drop the bath and squeeze the sample. Now dryer the sample.

De-sized Sample

Advantage of Oxidative Desizing Process

Oxidative de-sizing degrades and removes starch (PVA, CMC) easily from the fabric.
It also effective for tapioca starches.
Oxidative desizing is faster than enzymatic process. Because, here desizing time is low than enzymatic desizing.
As hydrogen peroxide and soda ash are used as desizing agent, hence, some scouring and bleaching actions are obtained here.

Disadvantage of Oxidative Desizing Process

Strong oxidizing agents can degrade cellulose fiber. Therefore, fabric strength may reduced. So, oxidative desizing should be carefully controlled.
Strong oxidizing chemicals pose risks to workers.
This process generates harmful effluents which impact on environment.

Desizing Effect Testing

Desizied fabric should be checked after desizing process for confirmation of size materials removal. It is very crucial because residual size materials can impact on sequence process. The following two testing methods are described by which one can show the presence of starch and PVA in fabric.

1. Iodine Test Method

A. Starch identification

At first, make a 0.02 N iodine solution where added few crystals of potassium iodide. Now, put one or two drops of this iodine solution on the fabric. If starch present in the fabric, it creates bluish to violet color.

B. Starch and PVA Identification

To identify both starch and PVA presence, 3 solutions need to prepare.

Solution-a : Take 10 ml 0.1 N iodine, 100 ml 1,4-dioxane, and 1 gm boric acid. After boiling the solution for 30 min, add necessary amount of 1,4-dioxame to make it to 100 ml, and then add 7 ml distilled water.
Solution-b: This is made up by adding 52 gm potassium chromate, 735 ml sulfuric acid, and 265 ml distilled water.
Solution-c: This is made up by taking 39 gm sodium hydroxide in a container and making it to 100 ml solution by adding the necessary amount of distilled water.

Observation:

Put 1-2 drops solution-a on the fabric and it produces a violet or blue stain on the fabric which indicates both starch and PVA are present in the fabric.
Add 1 drop of solution-b on the fabric and immediately add 3 drops of solution-c on it. Rub the created stain with the end of a glass rod. A brown coloration confirms the presence of PVA and a yellow or yellow-green color indicates the presence of starch.

2. Tegewa Rating Method

Tegewa rating process is perfect for factory to identify desizing effect. Because, by using this method, desizing effect can identify quickly.

Solution preparation

Take 10 gm of potassium iodide (100%) in a biker. Then add 100 ml of water to make a 100 ml solution of potassium iodide(KI).
Now, add 0.6358 gm of iodine (100%) to the biker.
Subsequently, stir the solution until iodine is dissolved in the potassium iodide solution.
After totally dissolved, add 800 ml of ethanol. Then add water to make 1000 ml of the total volume of the solution.

Testing method:

At first, 1 or 2 drops above solution put on the fabric. Now, rub it with glass rod and assessment the color change as per the TEGEWA scale. Rember, fabric should be cold and free from alkali.

Assessment:

No color change	No starch size present
Pale blue to bluish	Presence of starch size or blend
Violet	Starch size with synthetic size

Conclusion

This article discussed oxidative desizing process with recipe and recipe calculation. Here also discussed desizing effect testing procedure. If you have any questions about this article, you can knock me in below comments box.

References

Hossain, M. F. (2015). Practice of Textile Coloration, Volume-I. Dhaka: Books Fair Publications.
Hossain, M. S. (2014). Introduction to Textile Engineering. Dhaka: Books Fair Publications.
Kabir, D. S. (2016). Chemistry of Dyes & Pigments. Dhaka: Books Fair Publications.
Kadolph, S. J. (2006). Textiles. New Delhi: Pearson Education.
Kaplan, N. (2006). Textile Fibres. New Delhi: Abhishek Publications.