Nanomaterials 2023 , 13 , 1931
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CMNF and 92% by hot-pressing. This effect is more pronounced for mechanical fibrillated cellulose. It is important to note that after hot-pressing, all papers retain a wet strength 22% higher than that of the dry strength, even at high NC dosages. Furthermore, the combined effect also increases the SCT values, related to paper’s ability to withstand compressive forces applied in a short period of time, by 110% while hot-pressing produces an increase of 84% compared to the reference paper. The tear index increases with the addition of nanocellulose, but this effect is lost after hot-pressing. In general, the fibrillation degree has a low effect, which means that low-cost nanocel- lulose could be used in hot-pressed papers to provide products with a good strength and barrier capacity. Data show that it is possible to extend the application of cost-effective high-yield-pulp packaging through improving strength and barrier properties by using CMNF as a bulk additive and by hot-pressing the obtained papers. This shows that in hot-pressing technology, fiber bonding plays a key role, as well as the new covalent bonds formed at high temperature, possibly in a crosslinking structure within the lignin and/or between the lignin and carbohydrates. As lignin could play an important role in the en- hanced properties of hot-pressed paper, it is recommended to explore the possibility of using lignin-based nanoparticles to obtain more knowledge on this theory. Author Contributions: Conceptualization, C.N. and P.E.; methodology, A.B., C.N., A.M. and G.P.; validation, C.N. and P.E.; formal analysis, A.M., G.P., A.B. and C.N.; investigation, A.M., G.P., A.B., J.L.S.-S., S.N. and C.N.; resources, P.E. and C.N.; data curation, C.N., A.M., A.B. and C.N.; writing— original draft preparation, A.M., G.P., A.B., J.L.S.-S. and C.N.; writing—review and editing, A.M., G.P., A.B., J.L.S.-S. and C.N.; visualization, A.M., G.P., A.B., J.L.S.-S., C.N. and P.E.; supervision, P.E.; project administration, C.N. and P.E.; funding acquisition, C.N. and P.E. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the mobility grant received from the Spanish Minister of Universities, ref: PRX21/00600. We also want to acknowledge the funding of the project nr. 20180234 by the Swedish Foundation: Familjen Kamprads Stiftelse. Data Availability Statement: Data available on request. Acknowledgments: The authors want to express their gratitude to SCA R&D Center (Sundsvall) for allowing the use of its facilities for hand sheet preparation and its characterization. Conflicts of Interest: The authors declare no conflict of interest.
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