Application of a rubber, (polyvinyl chloride) or PU (Polyurethane) paste on one or both faces of a fabric. As soon as the coating is dry, it is firmly bonded to the fabric. As an example of coated fabrics, one can mention tarpaulin. Several coating processes (in solvant or aqueous medium) are possible.
Chemical Treatments
- Chemical treatment to add particular qualities and characteristics to fabrics. The most commonly used treatments are
- Crease-resistant treatment, allowing to avoid the tendency to crease of cotton fabrics.
- Shrink-resistant finish limits the tendency to shrink of cotton.
- By applying the water repellent and oil repellent finish, one avoids that fabrics absorb water and oil
- Other finishes add specific properties to fabrics to starch and reinforce them.
- The softening finish improves the touch of the fabric
Aesthetic Finishing
- Aesthetic treatments improve the appearance or touch (sensation) of the fabric. chemical treatments are considered as wet treatments and mechanical treatments as dry treatments.
- Temporary - The finish is removed by washing or dry-cleaning; e.g. calendaring (similar to pressing).
- Renewable - Finishes that may be applied again. Examples of this type of treatment are starch and dirt repellent finishes.
- Durable - A treatment that will last the entire life of the product but with decreasing efficiency.
- Permanent - Finish remaining entirely the same during the entire life of the product.
Functional Finishing
Functional finishing improves the product's performance under conditions of specific use
Chemical Finishing
Chemical) finishing adds qualities to fabrics which they lack; it eliminates certain flaws or improves their touch and aspect.
Stages at which cellulose can be Mercerised
Mercerisation is possible -
Woven fabrics are mercerized in full width, knitted fabrics in full width or in rope form.
The sodium hydroxide concentration varies from 20% - 30%. The process, done in a continuous way, consists of the following steps: - padding of the textile with the lye - drafting of the textile - washing (under tension) - acidifying, rinsing. The main ecological impact in mercerising is the high concentrated residual dye.
- On Greige Goods
- After Desizing
- After Desizing and Scouring
- After Bleaching
- After Dyeing
Woven fabrics are mercerized in full width, knitted fabrics in full width or in rope form.
The sodium hydroxide concentration varies from 20% - 30%. The process, done in a continuous way, consists of the following steps: - padding of the textile with the lye - drafting of the textile - washing (under tension) - acidifying, rinsing. The main ecological impact in mercerising is the high concentrated residual dye.
Sodium Hypochlorite (NaClO) Bleaching
- The NaClO bleaching is characterized in that the bleaching is performed at room temperatures without requiring a heating apparatus such as a steamer, and that the chemical cost is low. However, the disadvantages of the NaClO bleaching include relatively low bleaching whiteness and embrittlement of fabrics.
No particular pH adjustment is required in the NaClO bleaching. The NaClO bleaching is usually employed for bleaching fabrics after Kier-scouring, or for bleaching towels. For towels, the two-step bleaching comprising the NaClO bleaching and the H2O2 bleaching is preformed to obtain full whiteness. The NaClO bleaching is also employed for jeans fade adjustment, etc. Note here that a dechlorination process needs to be provided as in the NaClO2 bleaching. Since 'chlorine free' is a recent trend, like PRTR, a method without using chlorine is being examined. The same applies to NaClO.
One-Bath Desizing and Bleaching
- Desizing agent -BIOGEN 300
- Bleaching auxiliary -BIOGEN NN
- Dechlorination agent -BRITE CL-B
Sodium Chlorite (NaClO2) Bleaching
- The NaClO2 bleaching is performed after pH adjustment to 3.5 with an acid such as a formic acid. It provides soft hand with less embrittlement of cotton. Compared with the H2O2 bleaching, some insist that even bluish whiteness can be achieved with the NaClO2 bleaching.
Note here that a special reducing agent, sodium thiosulfate (hypo), or hydrogen peroxide (so-called, cosmetic bleaching) is used for the dechlorination purposes.
- Sodium chlorite low-temperature activator -BRITE FB CONC
Hydrogen Peroxide Stabilizer
- BRITE NIK -Contains sodium silicate; Effective in dispersing silica scales.
- BRITE W -Contains no sodium silicate
- APPEAGEN TOP -Improved version of BRITE W
Hydrogen Peroxide (H2O2) Bleaching
The H2O2 bleaching is the most common bleaching method, and is environmentally friendly (degradable into water and oxygen). The best bleaching whiteness can be obtained at pH 11 adjusted using caustic soda.
However, if metal ions, such as iron ions and copper ions are present in fabrics or in water, catalytic action of these metal ions causes abnormal degradation of H2O2, which may sometimes cause embrittlement of fabrics until holes (pin-holes) are generated due to the excessive degradation.
Usually, the abnormal degradation of H2O2 and the resulting generation of pin-holes are prevented by adding a chelating agent. Also, as a stabilizer for H2O2, sodium silicate has been conventionally employed. The obtained bleaching whiteness is favorable. However, the use of sodium silicate has the following disadvantages. Silica scales are generated due to calcium ions and magnesium ions reacted with silica ions. The generated silica scales are adhered to machinery, damaging fabrics, or undermining hand of the fabrics.This case, however, suffers from a contradiction that complete removal of calcium ions and magnesium ions will undermine the stability of H2O2.
To solve the disadvantages and contradiction, a non-silicate type stabilizer containing no sodium silicate has been developed, although the cost is higher than sodium silicate.
Furthermore, when dyeing is performed without a drying process after the H2O2 bleaching, the problem of residual H2O2 arises. 10ppm of residual H2O2 or more causes dyeing problems, although it depends on a type of dye. To degrade the residual H2O2, a reducing agent or the like, or an enzyme (catalase) can be used. The enzyme appears as a current mainstream.
Chelating Agents
- CHELATE HC -Chelating Agent
- FN-5000 -Chelate Dispersing Agent
- FN-6602 - Chelate Dispersing Agent
Scouring Agents
- DESCO SOFT 900 -Soft-type Scouring and Penetrating Agent
- DESCO DN-40 -Low-foaming Scouring and Penetrating Agent
- DESCO SOFT UC CONC - Soft-type Scouring and Penetrating Agent/ Low-Foaming
- DESCO KRA -Scouring Agent/ Alkali-Resistant
Removal of Water-Soluble Sizes
Fabrics containing water soluble sizes can be desized by washing using hot water, perhaps containing wetting agents (surfactants) and a mild alkali. The water replaces the size on the outer surface of the fiber, and absorbs within the fiber to remove any fabric residue.
Acid Desizing
Cold solutions of dilute sulphuric or hydrochloric acids are used to hydrolyze the starch.However, this has the disadvantage of also affecting the cellulose fiber in cotton fabrics.
Oxidative Desizing
In oxidative desizing, the risk of damage to the cellulose fiber is very high, and its use for desizing is increasingly rare. Oxidative desizing uses potassium or sodium persulfate or sodium bromite as an oxidizing agent.
Enzymatic Desizing
- Enzymatic desizing is the classical desizing process of degrading starch size on cotton fabrics using enzymes. Enzymes are complex organic, soluble bio-catalysts, formed by living organisms, that catalyze chemical reaction in biological processes. Enzymes are quite specific in their action on a particular substance. A small quantity of enzyme is able to decompose a large quantity of the substance it acts upon. Enzymes are usually named by the kind of substance degraded in the reaction it catalyzes.
Effective enzymatic desizing require strict control of pH, temperature, water hardness, electrolyte addition and choice of surfactant.
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