Hot mercerization

In hot mercerization fabric is either padded through hot caustic solution or at ambient temperature and then passed through steamer where the fabric is steamed. The process sequence of two step hot mercerization is as follows  

Another possible method of hot mercerization consists of wet-in-wet impregnation of fabric immediately after washing at 95 C and a subsequent hot squeezing with high speed steam injected. The heated fabric is then impregnated with caustic solution at 30 C in the first step and 20 C in the second step. These offer the stabilisation. Sequence is normally carried out under tension controlled condition. 

The various factors changing the properties of cotton due to hot mercerization are slightly different from that of conventional mercerization. The degree of swelling of individual fibre is lower at higher temperatures [100] as the process is an 

---

Hot mercerization allows better penetration of the alkali into the fibers than the ambient temperatures used normally [312]. However, to obtain optimum improvement in properties the caustic has to be washed out after the fabric is cooled. 

The properties and swelling processes of cotton fibres after treatment with liquid ammonia are compared with conventional and hot mercerized cotton in Table 9.3. The nature of the improvement in properties resulting from the treatment of cotton with liquid ammonia depends on the conditions of its removal from the fibre. Dry removal of ammonia after treatment converts Cellulose I to Cellulose III,... 

Hot dilute or cold concentrated acids disintegrate the fiber, similar u> cotton. Strong alkaline solutions cause swelling and reduce strength. Can be mercerized. 

Cotton is attacked by cold concemiuied acids and by hot dilute acids. Alkalis cause mercerization, but without damage. Cotton is quite resistant to most solvents. 

The structure has primary and secondary alcohol groups uniformly interspersed throughout the length of the polymer chain. These hydroxy units impart high water absorption characteristics to the fiber and can act as reactive sites. The cotton fibers are hydrophilic and swell in water. It is hydrolyzed by hot acid and swollen by concentrated alkali. The cotton is treated with caustic soda solution (12 to 25 percent) under tension to develop a silk-luster and stop longitudinal shrinkage. This process is called mercerization. Mercerized cotton exhibits increased moisture and dye absorption. 

Mercerizing Liquors.—Quantities of liquor will vary considerably with the process of washing used in each plant, and a reasonable average will give 2 gal. of 6°Twaddell waste liquor for each pound of cotton mercerized. These liquors are usually concentrated to from 70 to 80 Twaddell in a triple- or quadruple-effect evaporator of the horizontal-tube or rapid-circulation type. The capacity is from 2H to 3H gal. per square foot, with a steam pressure of from 10 to 15 lb. Special construction and entrainment separators are necessary to prevent losses by foaming. The last effect will frequently show incrustations of sodium carbonate which can be dissolved in hot water or weak hquor. Evaporators are usually built of steel with steel or charcoal-iron tubes. 

The same phenomena were observed for soda celluloses. Na-oellulose Ij prepared from the I family under conditions of low swelling (high temperature or with stretching) could be converted to cellulose I with hot water. Na-cellulose Ijj prepared from cellulose II under the same conditions was converted to cellulose II (7-10). In ordinary mercerization of native cellulose a mixture of Na-cellulose Ij and Ijj was obtained both decomposed to cellulose II with cold water. Na-cellulose Ij was transformed irreversibly into Na-cellulose Ijj. 

---