Influence of DP and MMD of the pulps used in the Ioncell® process on processability and fiber properties

In this study, we have demonstrated for the first time the ability of the Ioncell fiber spinning process to produce high-quality regenerated cellulose fibers from dissolving pulps with a wide range of intrinsic viscosity from 140 to 1300 mL g⁻¹ and different molecular mass distributions prepared by the applied acid, enzyme and sequential acid-enzyme pretreatments. To minimize the influence of the hemicellulose content, only dissolving pulps with a hemicellulose content of less than 4% were used. The rheological properties exhibited certain threshold values beyond which the spinnability of the prepared dope can be severely affected. A spinning dope with a dynamic modulus higher than 6000 Pa s or less than 1600 Pa s is not spinnable or results in an acceptable draw ratio. The best spinnability can be obtained at a crossover point for the dynamic moduli between 2800 and 3500 Pa and for the angular frequency between 0.4 and 1.2 rad s⁻¹. In these ranges, the highest draw ratios of the spun filaments can be obtained for pulps with a viscosity of 420 to 500 mL g⁻¹ and the lowest linear density (fiber titer) for pulps with viscosity from 500 to 730 mL g⁻¹. The strength of the spun fibers is strongly DP dependent. The fiber tenacity gradually decreases with reducing pulp viscosity until non-spinnable dopes are prepared at a pulp viscosity below 300 mL g⁻¹. Compared to acid-treated pulp, fibres made from enzyme-treated pulp generally have lower strength, which is due to a high polydispersity expressed in a high proportion of short-chain cellulose. At a suitable pulp viscosity between 360 and 820 mL g⁻¹ and a cellulose concentration in the spinning dope of 11 to 15 wt%, Ioncell fibres with excellent tensile strength and toughness properties can be produced.