1. Welcome to My Classent on Wet Processing
Asif Shahriar
B.Sc. Engg. (Textile), M.Sc. Engg. (Textile)
PGD (Knitwear Industry Management), MIEB
PhD (Textile Engineering, DUET)-(On Going)

2. Pretreatment on Wet Processing
Asif Shahriar
B.Sc. Engg. (Textile), M.Sc. Engg. (Textile)
PGD (Knitwear Industry Management), MIEB
PhD (Textile Engineering, DUET)-(On Going)

3. Pretreatment:
In textile wet processing, pretreatment is a processes applied on textile material (fibers, yarn, woven and knit fabrics) to prepare the material for dyeing, printing or finishing.

4. Object of Pretreatment:
Good desizing effect
Removal of seed husks
Removal of foreign substances from the fibers
Lowest possible fiber damage
High degree of Whiteness
Good Physical/Technological ratings
Levelness of the effects
High and even Hydrophilicity

5. Pre-treatment Machine
All the processes if this
stream are carried out in an aqueous medium
Pre-treatment Machine
Singeing Machine
Desizing Machine
Scouring Machine
Bleaching Machine
Mercerizing Machine

6. Singeing Burning the projecting fiber from yarn or fabric.
Objective
Burning the projecting fiber from yarn or fabric.
Fabric / yarn surface become smooth, even and clean
To develop luster in textile material.

7. Singeing Help to create to create smart design
Objective
Help to create to create smart design
Help to create smart design by printing.
To make the textile material suitable for next process

8. Singeing Result

9. Singeing Method Plate Singeing Roller Singeing Gas Singeing
Gas Singeing is most popular because this type of singeing burn both side of fabric.

10. Desizing
De-sizing is the process of removing the size material from warp yarns after a textile fabric is woven. Desizing is an essential part of the purification process for woven fabric. Size performs an adhesive and lubricating function. After drying, the size forms a protective film on the surface of the warp yarns, bounding the protruding fibrils to produce a smoother yarn with improved tensile strength and abrasion resistance.

11. Sizing Agent Natural sizing agent Synthetic sizing agents
Natural sizing agents are based on natural substances and their derivatives:
Starch and starch derivatives
Cellulosic derivatives: carboxymethylcellulose (CMC)
Protein-based starches: glue, gelatin, albumen
Synthetic sizing agents
Modified polyesters
Polyvinyl alcohols (PVA)

12. Objective of Desizing To remove starch from the fabric.
 To increase the absorbency of the fabric. 
 To increase the lustre of dyeing and printing. 
 To make the fabric ready for the following subsequent process. 

13. Enzyme
Enzymes are living organisms based on the protein which is used as Bio-catalyst. Its molecular weight is high. 
The action of enzymes is controlled by temp, concentration, time, and pH of the solution. Its primary function is the fermentation of starch.  Enzymes are soluble in water but insoluble in acid and alcohol.

14. Scouring
Normally natural fiber contains dust, oil, wax, minerals and many impurities as well. we have to cleanse these for further process. So the way of removing those impurities is called scouring. The most important wet process used on textile products before dyeing or printing is scouring.

15. Scouring Result

16. Object of Scouring
Natural and synthetic oils, fats, and waxes are removed from clothing products
Improve hydrophilicity
Improve absorbency
Prepare for the next process
To get uniform bleaching result

17. Chemical used in Scouring
1. Caustic soda (NaOH): Neutralizes acidic materials, saponify glycerides (waxes and oils), solubilize silicates.
2. Sodium silicate: Penetrate and breakdown lignin in motes. These penetrant’s are added, commonly, when fabrics have large contents of motes and other assorted materials.
3. Wetting agent: Reduce surface tension and minimize interfacial tensions.
4. Detergents: Emulsify fats, oils and waxes; remove oil borne stains; suspend materials after they have been removed.
5. Chelating (sequestering agents): Deactivate metal ions.
6. Builder (salt): Cause detergents to become increasingly effective.

18. Bleaching
Bleaching of textiles has been practiced for a very long time. Textile bleaching process is a chemical treatment employed for the removal of natural coloring matter from the substrate. The source of natural color is organic compounds with conjugated double bonds, by doing chemical bleaching the discoloration takes place by the breaking the chromophore, most likely destroying the one or more double bonds with in this conjugated system. The material appears whiter after the bleaching. In spite of these processes whiteness would have been impossible without optical brightening agents. However, the degree of whiteness is not only the main criterion bin evaluation of bleaching, but also absorbency.

19. Object of Bleaching
The main objectives of bleaching are to get a sufficiently high and uniform degree of whiteness in the textile materials.
To get a high and uniform absorptivity in the textile materials.
Bleaching agent occur some damage to the textile materials. So bleaching must be accompanied with minimum fiber damage.
To preserve a good user and technological properties of the textile materials.
The process must be ecologically and financially sensible.
To accelerate the next dyeing process.

20. Mercerization
Mercerization is a textile finishing treatment for cellulose fabric and yarn, mainly cotton and flax, which improves dye uptake and tear strength, reduces fabric shrinkage, and imparts luster.

21. Mercerization Results

22. Objective of Mercerization
i. To improve the luster of cotton materials ii. To increase the ability to absorb dye and moisture of the cotton iii. To improve reactions with a variety of chemicals for different stages iv. To improve the dimensional stability of materials v. To improve strength elongation and mechanical properties of the cotton vi. To improve the smoothness of the cotton

23. Mercerization Chemicals
Mercerization is a finishing treatment where the cotton yarn is treated with a strongly alkaline solution of Caustic Soda (Sodium Hydroxide), under appropriate tension and ambient temperature, to impart qualities such as improved luster, dye uptake, strength, etc.

24. Remember… Safety First!
Thanks Everybody