Liquid ammonia mercerization

Variety Temperature Scouring and bleaching Caustic mercerization Liquid ammonia treatment Removal techniques... 

Fig. 8. Internal volume (1 ) that is accessible to sugars as functions of the cotton molecular diameters (89). (a) Batting A greige , scoured-bleached , caustic mercerized , liquid ammonia treated, (b) Fabric o, scoured-bleached T, cross-linked.

Thus, further experiments were performed with two hydrolytically degraded linters powders subsequently disintegrated to different particle sizes (Filtrak, FNA and FND, VEB Spezialpapierfabrik Niederschlag, GDR), the lateral order of these samples being varied by liquid ammonia treatment or by mercerization with 18% aqueous NaOH. A posthydrolysis of these samples with aqueous acid (5% HC1, 2 hr, 100°C) resulted in changes in DP and in residue as indicated in Table IX and as to be expected from previous publications (11,16). 

These techniques have been used to elucidate the effects of variety [289], temperature [287], scouring-bleaching [290], caustic mercerization [290-292], liquid ammonia treatment [290,292,293], cross-linking with different agents under varying conditions [294-298], dye-ability [296,299], and treatment with cellulases [300-302], on the cotton. The trends observed are summarized in Table 5.8. 

It has been suggested that the great depth of color or dye yield found with mercerized cotton is due to the caustic treatment inducing an abundance of large pores in the fiber. In contrast, the high level of resilience associated with liquid ammonia treatment has been ascribed to a low level of large pores in the fiber [292]. 

Strong alkali solutions acting on cellulose (at room temperatures) produce alkali cellulose. The studies on the structure of alkali cellulose [43] obtained with 20-40% NaOH solutions indicated that the substance is not a true alcoholate but an addition complex, RceiiOH NaOH. A true alcoholate can be obtained, for example, from dry cellulose and Na in liquid ammonia. Alkali cellulose has a large range of applications as an intermediate product in the preparation of cellulose ethers, and xanthate (dithiocarbonate), as well as in cellulose mercerization. 

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,... 

In this test a mixture of red and green direct dyes is used to compare the maturity of cotton fibre samples. Immature fibres dye red, and mature fibres green. Mercerization increases the fibre s affinity for green compound and causticization number can be assessed related to the strength of the green hue. Fabric treated with liquid ammonia under industrial mill condition dyes red. 

The fibre is immersed in iodine solution (20 g iodine in 100 ml of standard KI solution) for 3 min and rinsed thoroughly. Mercerized cotton is stained bluish black and unmercerized cotton remains white. Cotton fibres in the yam bundle can be counted using a microscope and the ratio of dyed to undyed fibres can be used to determine the degree of mercerization. The iodine sorption value shows the largest increase for those samples treated in liquid ammonia with NH removal by evaporation, followed by caustic mercerized samples, and last by those samples NH treated and water quenched. Generally only minor differences in iodine sorption value are found between samples mercerized slack or under tension. 

Dilute alkali penetrates only accessible regions of the fiber causing intercrystalline or interfibrillar swelling. The latter is much more profound in that it brings about changes in crystal structure of the fibers, as evidenced by mercerization (in the case of alkali) and the formation of ammonia cellulose (in the case of liquid ammonia). 

Waterless mercerization can be accomplished by the use of liquid ammonia, which is all recovered and reused. Mercerization is effective and is practiced on a fairly wide commercial scale. 

Typical one-step commercial mercerization of cotton yam with caustic or liquid ammonia causes only partial conversion to cellulose II or cellulose III. Cotton cellulose is partially converted to cellulose II by repeated mercerization, the swelling of cellulose in strong alkali (eg, 23% NaOH), followed by rinsing and drying. Cellulose III results from treatment of cellulose with liquid ammonia (ammonia mercerization) or amines. Cellulose III can be made from either cellulose I or II. When treated with water, cellulose III can revert to its parent stmcture. Cellulose IV can be prepared by treating cellulose I, II, or III in glycerol at temperatures 260°C. Conversion of the crystal form in cotton fibers to cellulose IV can be effected by heat treatment of ethylamine-treated cotton cellulose in either saturated steam or formamide with minimal fiber degradation (86). Like cellulose III, cellulose IV preparations can revert to their parent stmctures. 

Conversion to cellulose II and cellulose III via caustic mercerization and liquid ammonia treatment are commercial textile processes that are discussed later. Figure 7 shows the characteristic diffractograms (Cu Ka radiation) of native cellulose, cellulose mercerized with sodium hydroxide, and cellulose treated with liquid ammonia. 

Scouring and bleaching slightly increase the accessible internal volume, liquid ammonia treatment of the scoured-bleached cotton decreases it slightly, caustic mercerization substantially enhances accessibility, and cross-linking to impart durable press properties reduces the accessible internal pore volume substantially. 

Bertoniere, N. R., King, W. D. (1989), Effect of scouring/bleaching, canstic mercerization, and liquid ammonia treatment on the pore stmcture of cotton textile fibers. Textile Res. J.,59(2), 114-21. 

Other processes of structural modification of cellulose, e.g., mercerization, treatment with amines or liquid ammonia, and regeneration from solutions, lead to a decrease in crystallinity, length, and lateral size of crystallites these treatments cause transformation of the initial cellulose structure into another structure in which small crystallites are surrounded by non-crystalline matrix [Fig. 7.28]. 

Permanent press, 100% cotton fabrics are produced via a licensed process involving mercerization in a bath of liquid anhydrous ammonia. This Sanfor-Set process was commercialized in 197557. 

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