Caustic treatment importance

Another important advantage of true HWM fibers is their better resistance to caustic soda. Although garments made of rayon are not normally subjected to exposure to strong caustic solutions, fabric preparation, such as dyeing, bleaching, etc., sometimes requires caustic treatment. In HWM blends with cotton, fabrics are sometimes mercerized or treated... 

Waste segregation is an important step in waste reduction. Process wastewaters containing specific pollutants can often be isolated and disposed of or treated separately in a more technically efficient and economical manner. Highly acidic and caustic wastewaters are usually more effectively adjusted for pH prior to being mixed with other wastes. Separate equalization for streams of highly variable characteristics is used by many plants to improve overall treatment efficiency [7]. 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

The substrate also has an important influence on diffusion of the dye. The diffusion rate increases with caustic soda treatment or mercerization of cotton. However, with regenerated cellulose fibers, which have a marked skin-core structure, the outer parts of the fiber can act as a diffusion barrier. 

Cotton can be causticized or half-mercerized to increase the dye uptake and economics up to 25% may be realised. Semi-mercerization or causticization is carried out in caustic soda solution between 25 and 30 Tw at a temperature of 20-25 C, sometimes without stretching the cloth to restore original dimensions. Sodium hydroxide solution above 30 Tw the rate of colour absorption decreases. Semi-mercerization is also an important step where heavy shades are required with the expensive vat colours. Better results are also observed with aniline black on goods which have received a semi-mercerization treatment. 

In a phenol/cresols or xylenols plant, using the conventional sulfonation and caustic fusion technologies, inorganic chemicals which are recovered are sodium sulflte, sodium sulfate and hydrated calcium sulfate also known as gypsum. These are all sellable by-products and depending on the method of treatment and recovery will fetch reasonable prices, and more importantly, will ensure a better eco-system. 

On the other hand, the esters of the polypeptides are of the greatest importance and they are prepared by the action of alcoholic hydrochloric acid. Hydrolysis of the polypeptide does not occur if prolonged heating be avoided, nor does hydrolysis occur when the esters are saponified by dilute cold caustic alkali. The esters have served in particular for the further synthesis of polypeptides and for the isolation of dipeptides from mixtures on treatment with alcoholic ammonia, the dipeptide esters are converted into their diketopiperazines. They are not soluble in petroleum ether and they are soluble with difficulty in ether, and they thus differ from amino acid esters. Chloroform dissolves them, and in this solvent their combination with acid chlorides has been generally effected. 

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