Production of New Cellulosic Filament Spun from Cellulose/aqueous NaOH Solution. (Part 1). Industrial Preparation Method of Cellulose-Alkali Dope with High Solubility.

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Abstract
The cellulose aqueous alkali solution dope with sufficient solubility and stability for spinning was successfully prepared. The solubility of exploded pulp was remarkably increased by using two steps dissolution method; preparing the cellulose slurry in aqueous 2-5wt% NaOH solution, followed by an addition of aqueous NaOH solution to let the NaOH content against the solvent to be 7-9wt%. A kinetic analysis on dissolution process indicated that diffusion of the caustic soda into the cellulose fibril defines the rate of dissolution at early stage. The progressive accumulation of the cellulose gel formed near the surface prevents the caustic soda from further diffusion, resulting in termination of the dissolution. Therefore, fine pulverization of cellulose and strong agitation during the dissolution, which promotes removal of the swollen gel from the surface, are found to be very effective for the increase in the solubility of cellulose. Application of the wet pulverization and the two steps dissolution methods made it possible to prepare the dope with dissolved cellulose content up to 99.9% for the pulp with degree of polymerization of ca. 300. When the concentration of NaOH is 7.6wt%, the dope does not occur gelation and was stable at least for one month, contrary to the case of viscose dope which turns to gel in about one week.

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