Analytical monitoring of xanthation in the viscose process along with xanthate group analysis in the viscose material is a long‐debated problem in cellulose chemistry. The task is rendered extremely ...intricate by the lability of the starting material and the harshness of the reaction medium, which adds to a lack of suitable analytical approaches. In a four‐years' endeavor in our lab, a method is being developed which allows to analyze the distribution of xanthate groups in viscoses relative to the anhydroglucose units and along the cellulose chain.
In a first step the xanthate groups are stabilized by alkylation, which was optimized towards quantitative conversion. In a second step, the remaining free hydroxyl groups are protected by carbanilation, followed by selective removal of the stabilized xanthate groups. Steps two and three thus generate an inverse image of the initial xanthate pattern. In the forth and fifth step, the liberated hydroxyl groups are methylated, and the carbanilates are removed, so that in the overall process the xanthates were replaced by methyl groups. All reaction steps have been comprehensively tested with regard to completeness of conversion and orthogonality of the protecting groups.
In a long development of solvents for cellulose dissolution and fiber spinning, ionic liquids represent the youngest category with great potential both from an environmental and technical point of ...view. Herein, we report on 1,5‐diazabicyclo4.3.0non‐5‐ene‐1‐ium acetate – a nonimidazolium based ionic liquid – as excellent solvent for a wide set of lignocellulosic solutes to prepare composite fibers of cellulose, hemicellulose, and lignin. The viscoelastic properties of the polymer solutions that are governed by the cellulosic constituents have to be within defined limits to assure good spinnability. The solutions are processed in a Lyocell‐type dry‐jet wet spinning procedure that allows for a filament draw in the air gap. The draw was found to be a major factor controlling the mechanical properties of the resulting fibers. However, the effect of the draw was dependent on the solute composition. With a high share of cellulose, a small draw led already to high tensile strength and modulus. All fibers showed high tenacities and moduli even when containing a high share of noncellulosics. The elongation at break was affected significantly only at high lignin content. A distinct relationship was found between the cellulose content and the mechanical properties.
