TY - JOUR
T1 - An improved, less erroneous protocol for the classical “cuen”, “cuoxam” or “cadoxen” viscosity measurements of pulps
AU - Zaccaron, Sara
AU - Ahn, Kyujin
AU - Henniges, Ute
AU - Potthast, Antje
AU - Rosenau, Thomas
N1 - Funding Information:
Lenzing AG, Sappi, Mondi AG and Zellstoff Pöls AG are gratefully acknowledged for donation of cellulosic pulps and interesting discussions. We would like to thank the Austrian research promotion agency (FFG) for financially supporting this work in the framework of the project series “Chromophores” (Projects #847169, 855644, and 861863). The financial support by the Austrian Biorefinery Center Tulln (ABCT) is gratefully acknowledged.
Publisher Copyright:
© 2022, The Author(s).
PY - 2022/5
Y1 - 2022/5
N2 - Correctness and reliability of molar mass data by viscometry in organometallic solvents (cuen, cuoxam, cadoxen) are compromised by the alkalinity of these solvents which causes immediate depolymerization especially in the case of pulps with higher carbonyl content (oxidative damage). The viscosity values thus correspond to the molar mass after the beta-elimination reactions that underly these degradative processes, which is sometimes significantly smaller than the molar mass determined by gel permeation chromatography (GPC) in the non-degrading solvent system DMAc/LiCl. Despite this well-known drawback, viscosity measurements have become a standard approach for molar mass measurements due to their ease and fastness, especially in the pulp and paper industries. A potential way to reduce the inherent error of these molar mass determinations via viscosity measurements is a reductive treatment prior to dissolution of the pulp in the organometallic solvents, which converts the labile, alkali-sensitive carbonyl structures back to the respective alcohols. Using sodium borohydride (NaBH4) on different types of cellulosic pulps, we demonstrate the beneficial effects of such a reduction step on the determined degree of polymerization (DP) for all three common solvents: cuen, cuoxam and cadoxen. Molar mass distributions and profiles of carbonyl groups were determined by GPC and by carbonyl selective fluorescence labeling (“CCOA method”). Such a reductive treatment was especially valuable for hemicellulose-containing pulps. While the decreased measurement error according to the new protocol is beyond doubt, an immediate acceptance in the pulp and paper industries is at least questionable, because the new, more correct data would not agree with the old – wrong, but consistent – numbers accumulated over years and decades. In the long run, however, the new, improved protocol will prevail here as well due to its lower error rate.
AB - Correctness and reliability of molar mass data by viscometry in organometallic solvents (cuen, cuoxam, cadoxen) are compromised by the alkalinity of these solvents which causes immediate depolymerization especially in the case of pulps with higher carbonyl content (oxidative damage). The viscosity values thus correspond to the molar mass after the beta-elimination reactions that underly these degradative processes, which is sometimes significantly smaller than the molar mass determined by gel permeation chromatography (GPC) in the non-degrading solvent system DMAc/LiCl. Despite this well-known drawback, viscosity measurements have become a standard approach for molar mass measurements due to their ease and fastness, especially in the pulp and paper industries. A potential way to reduce the inherent error of these molar mass determinations via viscosity measurements is a reductive treatment prior to dissolution of the pulp in the organometallic solvents, which converts the labile, alkali-sensitive carbonyl structures back to the respective alcohols. Using sodium borohydride (NaBH4) on different types of cellulosic pulps, we demonstrate the beneficial effects of such a reduction step on the determined degree of polymerization (DP) for all three common solvents: cuen, cuoxam and cadoxen. Molar mass distributions and profiles of carbonyl groups were determined by GPC and by carbonyl selective fluorescence labeling (“CCOA method”). Such a reductive treatment was especially valuable for hemicellulose-containing pulps. While the decreased measurement error according to the new protocol is beyond doubt, an immediate acceptance in the pulp and paper industries is at least questionable, because the new, more correct data would not agree with the old – wrong, but consistent – numbers accumulated over years and decades. In the long run, however, the new, improved protocol will prevail here as well due to its lower error rate.
KW - Aging
KW - Beta-elimination reaction
KW - Cellulose
KW - Gel permeation chromatography
KW - Molar mass distribution
KW - Oxidative damage
KW - Paper
KW - Pulp
KW - Reduction
KW - Viscosity measurement
UR - http://www.scopus.com/inward/record.url?scp=85126549419&partnerID=8YFLogxK
U2 - 10.1007/s10570-022-04505-w
DO - 10.1007/s10570-022-04505-w
M3 - Article
AN - SCOPUS:85126549419
SN - 0969-0239
VL - 29
SP - 3733
EP - 3744
JO - Cellulose
JF - Cellulose
IS - 7
ER -