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Title
Chemical changes of cellulose pulps in the processing to viscose dope
Authors
P. STRUNK A. LINDGREN B. ELIASSON and R. AGNEMO
Received
November 30, 2011
Published
Volume 46, Issue 9-10 November-December
Keywords
aging, cellulose pulp, hemicelluloses, long fiber, short fiber, sulfate, sulfite, mercerization, molecular weight, reactivity, viscose
Abstract
A selection of cellulose pulps was investigated for their chemical changes during the required process steps to viscose
dope. The selection of the pulps was based on pulping process, original wood type and intrinsic viscosity. In total, five
sulfite pulps and four sulfate pulps were chosen, of which all but one sulfate pulp were of dissolving grades. The
physical and chemical properties of the pulps were analyzed as well as important qualitative parameters of the cellulose
intermediates during mercerization, pre-aging and in the final viscose dope. Pre-aging curves were reported as a
measure of each pulp’s reactivity with respect to oxidative degradation, where high hemicellulose content and small
pore area and pore diameter were found to hamper cellulose degradation. The correlations in pre-aged pulps of intrinsic
viscosity to Mz, Mv and Mw were found to be ambiguous and show the need for a description of total molecular
weight distribution of the alkali celluloses to better understand the degradation behavior of each pulp, instead of only
intrinsic viscosity. It was also shown that R18 and R10 are insufficient analyses to determine pulp, and to predict
viscose quality. Further, many pulps, independently of initial hemicellulose content, reached the same level of
hemicellulose content after mercerization. The presence of crystalline hemicelluloses could be a possible cause for this
level-off behavior, combined with hemicelluloses resistant to caustic lye treatment. The change of both low-molecularweight celluloses and PD in the process to viscose dope was investigated due to the importance of these variables on dope spinnability and viscose fiber strength. Caustic resistance of cellulose and hemicelluloses and a more rigid fiber
structure in some pulps are suggested to contribute to the different degradation behavior.
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