Sulfur-free dissolving pulps and their application for viscose and lyocell |
| |
Authors: | Gabriele Schild and Herbert Sixta |
| |
Institution: | (1) Kompetenzzentrum Holz GmbH, St.-Peter-Str. 25, 4021 Linz, Austria;(2) Lenzing AG, Werkstra?e 1, 4860 Lenzing, Austria;(3) Department of Forest Products Technology, Helsinki University of Technology, Vuorimiehentie 1, 02015 Espoo, Finland |
| |
Abstract: | In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving
pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E)
both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification
in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully
replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive
viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed
a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell
wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular
viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher
molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant
to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted
from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of
the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high
molecular weight xylan of the CCE-treated pulps even took part in fiber forming. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|