Dissolution of dissolving pulp in alkaline solvents after steam explosion pretreatments

In this project different aqueous based solvent systems were investigated for the dissolution of steam exploded (STEX) dissolving pulps prior to a coagulation step for preparation of textile fibers. The pulp samples studied could, to a large degree, be dissolved in a NaOH/urea/thiourea system, but there are always residuals, irrespective of the conditions. The dissolution process appeared to be kinetically controlled, as prolonged retention time decreased the amount of residuals. A pre-cooled NaOH/urea/thiourea system, and a retention time of 60 h generated the lowest amount (6%) of residuals of the STEX pretreated dissolving pulp studied. Some fundamental results are described and a model for dissolution of dissolving pulp fibers is proposed.