Regeneration of cellulose fibers

Considerable quantities of sodium sulfate and zinc sulfate are also formed f ri sg regeneration of cellulose fibers. Part of the sodium and zinc sulfates is discharged from the spinning bath together with the viscose fibers and enters the wastewater through the aftertreatment of the fibers. 

An alternate procedure used in a few specialty applications is the cuprammonium process. This involves stabilization of cellulose in an ammonia solution of cupric oxide. Solubilization occurs by complex formation of cupric ion with ammonia and the hydroxyl groups of cellulose. Regeneration of cellulose, after formation of the desired products, is accomplished by treatment with acid. The main application of the cuprammonium process is for the synthesis of films and hollow fibers for use in artificial kidney dialysis machines. The cuprammonium process yields products with superior permeability and biocompatibility properties compared to the xanthation process. Less than 1% of all regenerated cellulose is produced by the cuprammonium process. 

After precipitation and regeneration of cellulose have been completed and raw rayon fiber has been formed, the subsequent steps must be controlled so that differences in treatment are minimized otherwise such sensitive properties... 

Fig. 55. Scanning electron micrograph of a cellulose-cellulose con osite. (A) and (B) Rayon fiber-cellulose acetate composites, after regeneration of cellulose acetate in aUcahne conditions, showing the poor quality of the interface. (C) and (D) Acetylated rayon fiber-ceUulose acetate composites after coregeneration in alkaline conditions, showing disappearance of the interfece.

Microdialysis is also a feasible option for purifying DNA fragments [15]. In this procedure the sample is injected into a regenerated hollow cellulose fiber and a countercurrent flow of the dialysis solvent is maintained through the annular space between a Teflon tube and the cellulose fiber. 

High-intensity ultrasonication can be considered as a mechanical method for producing cellulose nanofibers with hydrodynamic forces [72]. In this process, ultrasonic waves create strong mechanical stress because of cavitations, and therefore, cause the disaggregation of cellulosic fiber to nanofibers [73]. Several attempts have been made to isolate cellulose nanofiber by ultrasonication from various cellulose sources such as microcrystalline cellulose, regenerated and pure cellulose fibers [72], kraft pulp [74], flax, wood, wheat straw and bamboo [75] (Figure 11.5), para rubberwood sawdust [76], and poplar wood powders [15]. 

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