Abstract
Alkali extraction of cellulose material is a common treatment for several industrial processes—especially the viscose process, which produces fibers for textile applications. This study investigated different generic dissolving wood pulps by means of alkali extraction (10–18 wt% aq. NaOH at 20–50 °C). The regenerated residue of the pulps was characterized for its chemical composition, molecular structure, and cellulose conformation. The investigated pulps had in common that glucan was most intensely extracted at low temperature and low concentration of aqueous alkali, xylan was most intensely extracted at high temperature and high concentration of aqueous alkali, and mannan was most intensely extracted at a concentration of aqueous alkali > 14 wtwt% at all temperatures applied. The degree of transformation via alkali cellulose to cellulose II as determined with Raman spectroscopy was found to be maximized for all pulps at high alkali concentration and temperature had no major influence. Maximum yield for all investigated pulps was found when extraction was done with 18 wt% aq. NaOH. The importance of temperature differed for the investigated pulps. The reason for the differences in extraction behavior or different absolute levels of resulting properties was found to be related to differences in the homogeneity and purity of the pulps. A conclusion of interest for industrial applications was that extracting the pulps with 18 wt% aq. NaOH led to an optimal alkalization result for yield, purity, and conversion. The steeping temperature chosen was found to be important to balance the yield and the purity of xylan-containing pulps.
Graphic abstract
Examining the Hofmeister Series through Activation Energies: Water Diffusion in Aqueous Alkali-Halide Solutions
