University of Oulu

Ari Ämmälä, Ossi Laitinen, Juho Antti Sirviö, Henrikki Liimatainen, Key role of mild sulfonation of pine sawdust in the production of lignin containing microfibrillated cellulose by ultrafine wet grinding, Industrial Crops and Products, Volume 140, 2019, 111664, ISSN 0926-6690,

Key role of mild sulfonation of pine sawdust in the production of lignin containing microfibrillated cellulose by ultrafine wet grinding

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Author: Ämmälä, Ari1; Laitinen, Ossi1; Sirviö, Juho1;
Organizations: 1Fiber and Particle Engineering Research Unit, University of Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 1.1 MB)
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Language: English
Published: Elsevier, 2019
Publish Date: 2019-08-27


Cheaper methods and raw materials are currently being sought for the production of microfibrillated cellulose. Presently microfibrils with high lignin content have attracted increasing interest. Wood residues, like sawdust, are good candidates due to their abundancy and low price but the recalcitrant nature of the lignocellulose complex is an obstacle for the mechanical separation of microfibrils directly from wood. The purpose of this study was to investigate whether the mild sulfonation pretreatment of pine sawdust with sodium sulfite in neutral and mild alkaline conditions could enhance mechanical fibrillation in ultrafine wet grinding. Sawdust sulfonated at pH 7 and 9 resulted in a lignin sulfonation degree of 0.5–0.6% with a yield loss of 5–6%, approximately half of which was due to the dissolution of extractives from the initial content of 4.7% to 1.3–1.5%. Sawdust (with and without sulfonation) was pre-ground first in a twin-screw extruder, followed by ultrafine grinding with a friction grinder at a temperature of 80 °C. The viscosity and size distribution of the microfibrillated sample suspensions were determined. Additionally, the samples were filtered on a membrane, dried, and the mechanical properties of the sheets made from the samples were measured. The results showed that the sulfonation of softwood sawdust is a promising economic and environment-friendly method to produce microfibrillated cellulose with high lignin content (above 28%), having excellent strength properties, low viscosity, and fast dewatering rates. The sheets made from the sulfonated samples yielded an almost twofold increase in tensile strength and Young’s modulus (100 MPa and 7–7.5 GPa, respectively) compared to the reference sample without sulfonation (52 MPa and 4.3 GPa) at an applied net grinding energy of 7 MW h per ton. It was found that the size of the fibrils was at a similar level with and without sulfonation, but the bonding ability of the sulfonated samples was clearly better.

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Series: Industrial crops and products
ISSN: 0926-6690
ISSN-E: 1872-633X
ISSN-L: 0926-6690
Volume: 140
Article number: 11164
DOI: 10.1016/j.indcrop.2019.111664
Type of Publication: A1 Journal article – refereed
Field of Science: 215 Chemical engineering
Funding: We thank Mr. Jarno Karvonen for his contribution to the experiments and laboratory analyses. Council of Oulu Region (grant aided by the European Regional Development Fund), Ha-Sa Oy, Junnikkala Oy, Keitele Forest Oy, Kuhmo Oy, Pölkky Oy and Westas Group Oyare gratefully acknowledged for their financial support of this work.
Copyright information: © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (