nanomaterials
Article Synergies between Fibrillated Nanocellulose and Hot-Pressing of Papers Obtained from High-Yield Pulp Carlos Negro 1, * , Gunilla Pettersson 2 , Amanda Mattsson 2 , Staffan Nyström 2 , Jose Luis Sanchez-Salvador 1 , Angeles Blanco 1 and Per Engstrand 2
1 Department of Chemical Engineering and Materials, University Complutense of Madrid, Avda Complutense s/n, 28040 Madrid, Spain; ablanco@ucm.es (A.B.) 2 Department of Engineering, Mathematics and Science Education (IMD), Mid Sweden University, SE-85170 Sundsvall, Sweden; amanda.mattsson@miun.se (A.M.); per.engstrand@miun.se (P.E.) * Correspondence: cnegro@ucm.es; Tel.: +34-91-394-42-42 Abstract: To extend the application of cost-effective high-yield pulps in packaging, strength and barrier properties are improved by advanced-strength additives or by hot-pressing. The aim of this study is to assess the synergic effects between the two approaches by using nanocellulose as a bulk additive, and by hot-pressing technology. Due to the synergic effect, dry strength increases by 118% while individual improvements are 31% by nanocellulose and 92% by hot-pressing. This effect is higher for mechanical fibrillated cellulose. After hot-pressing, all papers retain more than 22% of their dry strength. Hot-pressing greatly increases the paper’s ability to withstand compressive forces applied in short periods of time by 84%, with a further 30% increase due to the synergic effect of the fibrillated nanocellulose. Hot-pressing and the fibrillated cellulose greatly decrease air permeability (80% and 68%, respectively) for refining pretreated samples, due to the increased fiber flexibility, which increase up to 90% using the combined effect. The tear index increases with the addition of nanocellulose, but this effect is lost after hot-pressing. In general, fibrillation degree has a small effect which means that low- cost nanocellulose could be used in hot-pressed papers, providing products with a good strength and barrier capacity.
Citation: Negro, C.; Pettersson, G.; Mattsson, A.; Nyström, S.; Sanchez-Salvador, J.L.; Blanco, A.; Engstrand, P. Synergies between Fibrillated Nanocellulose and Hot-Pressing of Papers Obtained from High-Yield Pulp. Nanomaterials 2023 , 13 , 1931. https://doi.org/ 10.3390/nano13131931
Keywords: hot-pressing technology; microcellulose; cellulose nanofibers; nanocellulose; high-yield pulp; CTMP; paper quality; packaging
1. Introduction High-yield pulps (HYP) have become a key material in sustainable products because of their resourcefulness and cost efficiency [1] and the potential to manufacture products which achieve certain important properties, such as a high bulk in paperboard and high light scattering in printing papers. They are produced at a yield of over 90% from different wood sources (or annual plants) by means of mechanical or combined chemical and mechanical processes [2,3]. One of the driving forces has been the fact that if high-yield processes can be used to a higher extent, it will be possible to manufacture more products from the same amount of wood since the corresponding yield for chemical pulps is around 50%. In addition, due to HYPs being a traditional and mature sector, industrial interest in this area is growing since new applications have been developed over the last few years. The market reduction, especially in printing products, due to digitalization, has forced the sector to search for other possible market strategies, transforming the processes and developing new HYP-based which includes their application for packaging to replace fossil-fuel-based plastic products [4]. Consequently, the research interest in improving the quality of papers obtained from HYPs has increased significantly in recent years [5,6]. The hot-pressing of various wood-based materials, such as wood, plywood, particle board, and fiberboard, has been used over the years to improve their material proper- ties [7,8]. Song et al. (2018) showed that with a combination of chemical pre-treatment and
Academic Editor: Linda J. Johnston
Received: 30 May 2023 Revised: 20 June 2023 Accepted: 23 June 2023 Published: 25 June 2023
Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).
Nanomaterials 2023 , 13 , 1931. https://doi.org/10.3390/nano13131931
https://www.mdpi.com/journal/nanomaterials
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