E. Pasquier and J. Ruwoldt
Journal of Bioresources and Bioproducts 10 (2025) 325–335
tion reactions happened. In the case of CTMP fibers, lignin self-condensation improved the self-adhesion of the fibers and the strength of the substrates. Similar phenomena likely occurred here in the presence of the added lignin; however, additional data would be needed to corroborate this. For the wet strength, the type of flocculant did not have a significant impact. Sanchez-Salvador et al. (2024) studied the effect of cationic starch as the flocculant for lignin in paper. It was shown that the combination of starch and lignin was needed to improve the wet strength, as compared to their individual effect. As for the dry strength, the size of the lignin particles only had an impact on the wet strength when the substrates were pressed at low moisture. Here, the complete melting of the lignin at high humidity was also responsible for the decreased sizing effect. The tensile modulus increased from 200 to 938 MPa (PL) and from 186 to 930 MPa (SL) ( Figs. 6 b and S4) with the increase of wet pressing. Stiffening is usually linked to a decrease in elongation, but here the elongation was not affected. The toughness was thus increased, which means that the materials tolerated higher stresses and could absorb higher amounts of energy before breaking. The dimensional stability was thus increased. This also showed the ductility of the lignin-containing network.
4. Conclusions
The addition of lignin to cellulose substrates that were subsequently thermopressed had a positive impact on their dry and wet strength. Increasing the moisture during pressing from 10 % to 50 % showed an increase in wet strength by a factor of 4 in the presence of the added lignin. The flocculant used to retain the lignin with the cellulose did not affect the final strength, while the lignin particle size had a significant effect only when the substrates were pressed at low moisture (10 %). When the substrates immersed in water, limited swelling of the substrates was correlated with increased tensile wet strength. Melting of the lignin was likely enhanced by the high moisture, filling in voids and providing improvement in overall contact areas. These results are promising for the further development of molded pulp products with improved resistance to water.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
CRediT authorship contribution statement
Eva Pasquier: Methodology, Visualization, Formal analysis, Investigation, Data curation, Writing –original draft, Writing –review & editing, Visualization. Jost Ruwoldt: Conceptualization, Methodology, Formal analysis, Resources, Writing –original draft, Writing – review & editing, Supervision, Project administration, Funding acquisition.
Acknowledgments
The research in this article was supported by funding from the Research Council of Norway . We want to acknowledge the basic funding “Grunnfinansering ” of Norwegian research institutes by the Norwegian government.
Supplementary materials
Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jobab.2025.05.001 .
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