Specification of Alkali Soluble Pulp Suitable for New Cellulosic Filament Production

In order to produce a new type of cellulosic filament using caustic soda solution as solvent, the dissolved pulp available for the spinning was specified in view of solubility. Steam exploded six kinds of sulfite and two kinds of kraft pulps with viscosity-average degree of polymerization DPv lower than 600 were dissolved into the aqueous sodium hydroxide solution by the two step method reported in previous paper (C. Yamane et al. this journal Vol. page). The solubility of these pulps was investigated measuring volume (mL) of indissoluble component (Rc) in the solution. The sulfite pulp prepared from broadleaf as well as coniferous trees showed far lower Rc, value than that of the kraft pulp. This relatively high solubility of the sulfite pulp was plausibly explained in terms of its high degree of breakdown of intermolecular hydrogen bonds, which is estimated by CP/MAS13C-NMR, in the cellulose solid. Rc of the sulfite pulp into aqueous 7.6wt% NaOH solution is fairly well described as a function of DPv and cellulose content C in range of DPv=215-320 and C=3-7wt% as follows: Rc=6.82×10-26×DPv8.9×C5.7 The sulfite pulp with DPv ranging from 200 to 320 is sufficiently useful to the industrial spinning from the point of view of solubility and degree of polymerization.