Textile Wet Processing:
Textile materials in different forms, such as fiber, yarn, woven fabric, knitted fabric or garment may be subjected to different textile wet processing operations. In which way grey fabric is dyed is called wet process technology. Normally wet processing depends on buyer’s demand. Suppose your buyer wants the more precised dyed fabric; so in this fact you should mercerize your fabric during the dyeing pre-treatment process. Basically if the buyer don’t want that so called particular fabric there is no need to mercerize your fabric. Some processes may be combined, for example scouring or bleaching may be combined in one operation; similarly dyeing may be combined with some chemical finishing or finishes may be done directly after bleaching.
In textile wet processing, pretreatment is a processes applied on textile material (viz. fibers, yarn, woven and knit fabrics) to prepare the material for dyeing, printing or finishing. As the grey material will have lot of impurities, these impurities hampering the subsequent processes has to be removed and made absorbent to ease the further processes like bleaching, dyeing, finishing, etc. For all practical purposes pretreatments are carried out in continuation of dyeing or printing and their equipment is part of the wet processing plant.
The main objective of fabric preparation or pretreatments is to remove any impurities or contaminants from the fabric and make it ready for the subsequent operations such as optical brightening, dyeing, printing or finishing. The overall objectives of fabric preparation include removal of fabric impurities such as protruding fibers, sizing agents, cotton seed husks, fats, oils, waxes, dirt, dust, lubricants, etc.; improved absorbency and / or whiteness of the fabric; minimum fiber damage; uniform residual size, pH, alkalinity, whiteness, absorbency and moisture content.
Flow Chart of Textile Wet Processing Technology
Grey Fabric Inspection
Sewing or Stitching
All above textile wet processing process are described briefly:
Grey Fabric Inspection:
After manufacturing fabric it is inspected in an inspection Table. It is the process to remove neps, warp end breakage, weft end breakage, hole spot.
Batching is the receiving section of grey fabric, where the fabrics which should be dyed and processed for a particular lot of a particular order are grouped, assembled together and the length is increased. From batching section, the grey fabric is sent to the dyeing section for dyeing. Flow chart of batching section is given as follows:
Fabric received and stored
Fabric divided according to width or tube diameter after buyer’s recommendation
Supervisor batches the fabric according to quantity by calculation
Send for bleaching and/or dyeing
To increase the length of the fabric for making suitable for processing is called stitching. It is done by plain sewing machine.
To remove the dirt, dust, loose fiber and loose ends of the warp and weft threads is known as brushing.
Shearing / Cropping:
The process by which the attached ends of the warp and weft thread is removed by cutting by the knives or blades is called shearing. Shearing is done for cotton and cropping for jute. After Shearing or cropping fabrics goes under singeing process.
The process by which the protruding / projecting fibers are removed from the fabrics by burning / heat to increase the smoothness of the fabric is called singeing. If required both sides of fabric are singed. The main objective of the singeing process is to produce a clean fabric surface and reduce fabric pilling tendency by removing the protruding fibers from the fabric surface. There are three different methods of singeing such as hot plate singeing, hot rotary cylinder singeing and gas flame singeing. However, gas flame singeing is the most commonly used singeing methods because of better singeing efficiency.
The process by which the sizing materials (starch) are removed from the fabric is known as desizing, which are usually applied on the warp yarns before weaving. Removal of sizing materials after weaving is necessary in order to make the fabric more absorbent for dyes and other chemical processing agents. This must be done before printing.
The process by which the natural impurities (oil, wax, fat etc) and added/external/adventitious/acquired impurities (dirt, dust etc) are removed from the fabric is called scouring. It is done by strong NaOH. Main purpose of scouring is to make them more absorbent and suitable for subsequent processes such as bleaching, dyeing, printing or finishing. Main parameters of the scouring process include type and amount of alkali, type and amount of detergent, type and amount of sequestering agent, temperature and time of the treatment.
The process by which the alkali is removed from the scoured fabric with dilute acid solution is known as souring.
The process by which the natural colors (nitrogenous substance) are removed from the fabric to make the fabric pure and permanent white is known as bleaching. It is done by bleaching agent. The main parameters for bleaching with hydrogen peroxide include concentration of hydrogen peroxide, concentration of alkali (e. g. NaOH), type and concentration of bleaching stabilizer (e. g. sodium silicate), type and concentration of sequestering agent, pH, temperature and treatment time.
The process by which the cellulosic materials/substance are treated with highly conc. NaOH to enhance various properties such as increase in dye affinity, chemical reactivity, dimensional stability, tensile strength, luster and fabric smoothness is known as mercerizing. It is an optional process. If the fabrics are 100% export oriented then it is done by highly conc. NaOH (48-52° Tw). Mercerization process is performed using caustic soda. Although caustic soda is also used in scouring cotton fabrics but the concentration of caustic soda is very low in scouring (e. g. 5–10 %) while the concentration in mercerization may be up to 22–25 %.
A process of coloring fibers, yarns, or fabrics with either natural or synthetic dyes. Dyeing can be defined as a process during which a textile substrate is brought in contact with the solution or dispersion of a colorant, and the substrate takes up the said colorant with reasonable resistance to its release form the substrate. Dyeing is the most important coloration process of textile.
A process for producing a pattern on yarns, warp, fabric, or carpet by any of a large number of printing methods. The color or other treating material, usually in the form of a paste, is deposited onto the fabric which is then usually treated with steam, heat, or chemicals for fixation. Printing can be considered as “localized dyeing” and comprises the application of one or more dyes or pigments on textile materials in the form of a design or pattern. Unlike dyeing, printing designs or patterns are usually printed on only one side of the fabric.
Finishing comprises final processes in the textile wet processing sequence to improve the appearance, hand-feel or other aesthetics of the textiles or to add any extra functionality such as water repellency or flame retardancy, etc. Textile finishing treatment are done according to buyer requirements and then folding, packaging, and at last delivery.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.