Acid hydrolysis, regenerated cellulose

Acid hydrolysis, regenerated cellulose, 341/ Activation energies, warp and weft yams, 68 ... 

The resultant yellow sodium cellulose xanthate is dispersed in an aqueous caustic soda solution, where some hydrolysis occurs. This process is referred to as ripening and the solution as viscose . When the hydrolysis has proceeded sufficiently the solution it transferred to a hopper from which it emerges through a small slit on to a roller immersed in a tank of 10-15% sulphuric acid and 10-20% sodium sulphate at 35-40°C. The viscose is coagulated and by completion of the hydrolysis the cellulose is regenerated. The foil is subsequently washed, bleached, plasticised with ethylene glycol or glycerol and then dried. 

The carbonate salts investigated by Siegfried and Howwjanz were decomposed instantly by dilute acetic acid, whereas the moderate stability of the 0-(sodium thiolthiocarbonyl) derivatives toward this reagent has been a valuable aid to their purification. In mineral acids, however, the 0-(metal thiolthiocarbonyl) compounds are also rapidly attacked, with regeneration of the carbohydrate, a property utilized in the cellulose Viscose process. The 0-(sodium thiocarbonyl) derivative of cellulose is less resistant to acid hydrolysis than its thiolthiocarbonyl analog. 

Figure 5. Data regarding heterogeneous hydrolysis of regenerated cellulose in 1 N hydrochloric acid at different temperatures. (Reproduced with permission from Ref. 16. Copyright 1966 TAPPI.)...

Viscose rayon is inherently a weak fibre, particularly when wet, therefore it is highly susceptible to damage if enzymatic hydrolysis is not controlled. The enzymatic hydrolysis of viscose fibres causes a decrease of the intrinsic viscosity from 250 to 140 ml/g and an increase in crystallinity from 29 to 39% after 44 h [34]. Strong changes of the structure, however, are not typical for the enzymatic hydrolysis of cellulosic materials. Neither cotton nor wood pulp show an essential decrease of the DP during enzymatic hydrolysis [35-37]. The kinetics of the enzymatic hydrolysis of regenerated cellulose fibres before and after acid prehydrolysis changes the kinetics from a monophasic to a biphasic first order reaction [38]. 

The preparation of microcrystalline cellulose by acid hydrolysis of native and regenerated fibers has been studied extensively (3) and developed into a commercial process by Battista et ah (4). The resulting products are used as aqueous gels with high water-bonding capacity, inert food and drug additives, viscosity regulators, and stabilizers in colloidal... 

The finished xanthate, colored a strong red-orange by the trithiocarbonate by-product, is dissolved in dilute caustic to.form viscose (ts ically, 6-9 per cent cellulose and 5-8 per cent sodium hydroxide plus by-products of carbon disulfide hydrolysis, of viscosity 30-50 poises at 20°C). Viscose, in turn, yields regenerated cellulose fibers or film when extruded into an acid coagulating and regenerating bath. The instability of the xanthate halfester under acid conditions makes rapid regeneration possible. 

ANP of elliptical shape can be obtained by acid hydrolysis of regenerated cellulose with the following ultrasound disintegration (loelovich, 2013a, 2014a). Due to the amorphous structure, the ANP acquires such specific features as increased content of functional groups, high accessibility and enhanced sorption ability. 

Increasing the SA concentration to more than 65 wt% led to further diminution in yield, crystallinity, and DP of the regenerated particles. After hydrolysis of the initial sample with 67 wt% SA the yield of the particles was zero because the hydrolyzed and dissolved cellulose cannot be regenerated from the acidic solution by dilution with water. This was caused by the fast acidic depolymerization of cellulose with 67 wt% SA and forming of the water-soluble ohgomers. 

Cumberbirch, R.J.E. and Mack. C. (1961) A quantitative theory of the loss of strength of regenerated cellulose filaments on hydrolysis by acids. J. Textile Inst., 52 T382-T389. 

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