Structural Changes in Wood Pulp Treated by 55 wt% Aqueous Calcium Thiocyanate Solution

Abstract

ABSTRACT:Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN)z) solution at room temperature. For this purpose, X-ray, DSC, and CPIMAS 13 C NMR were used to measure changes of crystalline structure and formation of cellulose-solvent complex. X-Ray data indicated that 55 wt% aq Ca(SCN)2 so ln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose--calcium thiocyanate addition compound. The interplanar spacing of (ITO), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time td of 90 min. From DSC thermo grams of cellulose-55 wt% aq Ca(SCN)z soln. mixture, exothermic heat !'J.H for the formation of the addition compound was estimated to be ca. II kcal mol-1 , which was far iower than that for generation of cellulose sodium salt. The cellulose recovered from the system has quite different crystalline structure depending on treatment time and the reagents used for recovery. Up to td = 90 min, water recoverd the mixture of natural cellulose crystal (Cell

Aqueous Calcium Thiocyanate Solution as a Cellulose Solvent. Structure and Interactions with Cellulose

“…5 Such molecular adducts of cellulose have been reported also for aq lithium thiocyanate 6 and aq zinc chloride solutions. 7 However, the structures of all these cellulose adducts have not been clear yet.…”

“…LJH might include contribution from energies necessary to form adducts with cellulose and break hydrogen bonds within cellulose solid. 5 The above formula could explain the fact that LJH is 0 for aq Ca(NCS)z solution with Ccar = 48.5 wt% (stable 4 hydrate type) and becomes larger when aq Ca(NCS)z solution with higher CcaT (hydration number is less than 4) interacts with cellulose so as to satisfy 4 hydrates-like thiocyanate. In other words, cellulose might act as a supplier of R-0-R moiety like water (H-0-H moiety) directly interacting with aq Ca(NCS)z with evolution of heat.…”

Solubility and Dissolved Cellulose in Aqueous Calcium- and Sodium-Thiocyanate Solution

“…The insoluble CP sample shows no peak during heating, but the soluble sample CAR-2, cellulose regenerated from cuprammonium soln., reveals an endothermic peak near dissolution temperature. In the previous paper 12 we reported that cellulose-55 wt% aq Ca(SCN)z soln. exhibits an exothermic DSC peak attributable to cellulose-aq Ca(SCN)2 complex formation far below the dissolution temperature and shows no peak near the actual dissolving temperature.…”

Direct Dissolution of Cellulose: Background, Means and Applications

“…In water, only cellulose II is recovered, but in methanol the product is mainly cellulose I. Upon precipitation in acetone the product is amorphous [77]. The interaction between cellulose and salt hydrates have also been examined using Raman spectroscopy [74], and of course different NMR spectroscopy techniques [78].…”