Structural changes in wood pulp treated by 55 wt% aqueous calcium thiocyanate solution

Abstract

Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN)2) solution at room temperature. For this purpose, X-ray, DSC, and CP/MAS 13C 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 soln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose-calcium thiocyanate addition compound. The interplanar spacing of (110), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time td of 90min. From DSC thermograms of cellulose-55wt% aq Ca(SCN)2 soln. mixture, exothermic heat ΔH for the formation of the addition compound was estimated to be ca. 11 kcal mol-1, which was far lower 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-I) and hydrated cellulose (Cell-II), while the methanol and acetone recovered only Cell-I. After one day the structure of the recovered cellulose from the system was: water, Cell-II; methanol, Cell-I; acetone, almost amorphous cellulose.