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
Highlights
The demand for viscose fibers is increasing because of the increase in world population, prosperity as well as demand for fashion and other related consumer products
Na-Cell is easy to depolymerize by means of the oxidation that occurs in the aging step prior to xanthation, which is done in order to adjust the degree of polymerization (DP) to the requirements of the viscose fiber product aimed for
The high level of cellulose II (Cell II) in LFk-hp was supposed to be connected to the high purity level with regard to hemicellulose, which often demands an alkaline purification step in the fiber line
Summary
The demand for viscose fibers is increasing because of the increase in world population, prosperity as well as demand for fashion and other related consumer products. More than 90% of today’s seven million tons of viscose fiber are produced using dissolving pulp derived from wood (DWP). This increasing demand is met by an extension of global DWP capacity. The first process step in producing viscose is the alkalization (steeping) and subsequent pressing of the pulp (Gotze 1967). A side effect of pressing the slurry of pulp and aqueous alkali is purification of the pulp dedicated for xanthation by means of alkali extraction. This process ensures, on one hand, the purification from short-chained, xanthation-chemical-consuming polymers. Purification causes a yield loss for the viscose mill, which depends on the recovery strategy of the press lye
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
