Pulp reactivity during dissolution: from assessment to activation

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School of Chemical Technology | Doctoral thesis (article-based) | Defence date: 2022-08-26
Degree programme
84 + app. 62
Aalto University publication series DOCTORAL THESES, 88/2022
The market of man-made cellulosic fibers (MMCF) is expanding. From 2000 to 2019, the global production of these fibers has increased by ca. 4400 TMT, and a further increase is expected in the future. However, the dissolution of cellulosic natural fibers, which is a fundamental step for the manufacturing of MMCF, is hindered by the recalcitrance of cellulose. If the dissolution is not sufficiently thorough, the undissolved matter can slow down the downstream process and affect the quality of the final fibers. "Reactivity" is a somewhat ill-defined, but important, characteristic of pulp that relates to its dissolution behavior in a compatible solvent.This thesis studies whether it is possible to assess pulp reactivity by monitoring the rheological behavior of fiber suspensions during dissolution. Secondly, the pulp features that affect reactivity are examined. Finally, methods to increase pulp reactivity are investigated.The Dissolution-Based Torque Reactivity (DTR) test was developed to measure pulp reactivity by tracking the torque of a fiber suspension while dissolving in cupriethylenediamine at a constant shear rate. The dissolution produces a rheogram with torque as a function of time which reaches a plateau when the dissolution is complete. The rheogram was analyzed in terms of dissolution time (DT) and torque plateau. Faster dissolutions corresponded to higher reactivity. The DT could rank the pulps consistently with the current industrial understanding of pulp reactivity. The average coefficient of variation of DT and plateau measured ca. 8 and 3%, respectively.Plateau and DT increased with the molar mass of pulp. The DT increased with hornification (lowered swelling). The plateau was affected by the xylan content and the amount of undissolved matter. The DTR test was compared to the Treiber test for some dissolving pulps. The DTR test was less sensitive than the Treiber test for undissolved material, and the two tests are not interchangeable. However, for pulps with similar molar mass, the plateau increased with the decrease of the Kr filterability value, indicating a certain correlation between the methods. Moreover, the DTR test is much faster and less laborious than the Treiber test.Enzymatic treatments targeting the selective depolymerization of cellulose or hemicellulose could shorten the DT of paper- and dissolving-grade pulps. Cellulose was depolymerized with endoglucanase and lytic polysaccharide monooxygenase (LPMO), while hemicelluloses with mannanase and xylanase. Activation by endoglucanase and LPMO was due to cellulose depolymerization and the increase in porosity and surface area. Activation was most effective when hydrolysis was performed at high solids content. TrCel45A endoglucanase shortened the dissolution of softwood Kraft pulp more than TrAA9A LPMO, but even shorter dissolution was achieved with TrCel45A and TrAA9A together. Xylanase and mannanase reduced the dissolution time of dissolving pulp even if the changes to the molar mass distribution were modest and the removal of part of the hemicelluloses caused hornification.   
Supervising professor
Maloney, Thaddeus, Prof., Aalto University, School of Chemical Engineering, Finland
Thesis advisor
Maloney, Thaddeus, Prof., Aalto University, School of Chemical Engineering, Finland
pulp reactivity, dissolution, activation, andoglucanase, LPMO, xylanase, mannanase
  • [Publication 1]: Ceccherini, Sara; Maloney, Thaddeus C. 2017. Novel CED-based rheological test to evaluate pulp reactivity. In: Batchelor W. and Söderberg D., Advances in Pulp and Paper Research, Oxford 2017, Trans. of the XVIth Fund. Res. Symp. Oxford, 2017. FRC, Manchester. Volume 2. Pages 909–927
  • [Publication 2]: Ceccherini, Sara; Maloney, Thaddeus C. 2019. Assessing wood pulp reactivity through its rheological behavior under dissolution. Springer Netherlands. Cellulose, volume 26, issue 18, pages 9877–9888.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202001021143
    DOI: 10.1007/s10570-019-02750-0 View at publisher
  • [Publication 3]: Ceccherini, Sara; Rahikainen, Jenni; Marjamaa, Kaisa; Sawada, Daisuke; Grönqvist, Stina; Maloney, Thaddeus C. 2021. Activation of softwood Kraft pulp at high solids content by endoglucanase and lytic polysaccharide monooxygenase. Elsevier. Industrial Crops and Products, volume 166, issue August, pages 113463.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202104206223
    DOI: 10.1016/j.indcrop.2021.113463 View at publisher
  • [Publication 4]: Ceccherini, Sara; Ståhl, Marina; Sawada, Daisuke; Hummel, Michael; Maloney, Thaddeus C. 2021. Effect of enzymatic depolymerization of cellulose and hemicelluloses on the direct dissolution of prehydrolysis Kraft dissolving pulp. ACS. Biomacromolecules, volume 22, issue 11, pages 4805-4813.
    DOI: 10.1021/acs.biomac.1c01102 View at publisher