nanomaterials
Article Fit-for-Use Nanofibrillated Cellulose from Recovered Paper AnaBalea 1 , M. Concepcion Monte 1 , Elena Fuente 1 , Jose Luis Sanchez-Salvador 1 ,QuimTarr é s 2 , PereMutj é 2 , Marc Delgado-Aguilar 2 and Carlos Negro 1, *
1 Department of Chemical Engineering and Materials, University Complutense of Madrid, Avda Complutense s/n, 28040 Madrid, Spain; helenafg@ucm.es (E.F.) 2 LEPAMAP Research Group, University of Girona, Maria Aur è lia Capmany, 6, 17003 Girona, Spain; pere.mutje@udg.edu (P.M.); m.delgado@udg.edu (M.D.-A.) * Correspondence: cnegro@ucm.es; Tel.: +34-913944242 Abstract: The cost-effective implementation of nanofibrillated cellulose (CNF) at industrial scale requires optimizing the quality of the nanofibers according to their final application. Therefore, a portfolio of CNFs with different qualities is necessary, as well as further knowledge about how to obtain each of the main qualities. This paper presents the influence of various production techniques on the morphological characteristics and properties of CNFs produced from a mixture of recycled fibers. Five different pretreatments have been investigated: a mechanical pretreatment (PFI refining), two enzymatic hydrolysis strategies, and TEMPO-mediated oxidation under two different NaClO concentrations. For each pretreatment, five high-pressure homogenization (HPH) conditions have been considered. Our results show that the pretreatment determines the yield and the potential of HPH to enhance fibrillation and, therefore, the final CNF properties. These results enable one to select the most effective production method with the highest yield of produced CNFs from recovered paper for the desired CNF quality in diverse applications.
Keywords: recycled fibers; nanocellulose; enzymatic pretreatments; TEMPO-mediated oxidation; refining; high-pressure homogenization
Citation: Balea, A.; Monte, M.C.; Fuente, E.; Sanchez-Salvador, J.L.; Tarrés, Q.; Mutjé, P.; Delgado-Aguilar, M.; Negro, C. Fit-for-Use Nanofibrillated Cellulose from Recovered Paper. Nanomaterials 2023 , 13 , 2536. https://doi.org/10.3390/ nano13182536
1. Introduction Papermaking is one of the most sustainable industries contributing to the circular economy [1]. Recovered paper is widely recognized as an efficient and eco-friendly cel- lulose source for paper and board production. In Europe, 55.9% of raw materials come from recovered paper, which corresponds to a paper recycling rate of 70.5% [2]. In Spain, these values are even higher (92% and 71%, respectively). The use of recovered paper as raw material presents several challenges, due to the relatively low quality of the secondary fibers after several recycling cycles, which mainly affect the mechanical properties of the recycled paper due to shortening and hornification of the fibers during each recycling process. To enhance the quality of the recycled fibers and achieve the desired properties in the final product, papermakers use fiber refining and strengthening additives. In this context, extensive research has been carried out in the last decade to explore the potential of nanocellulose-based products as paper-reinforced additives. A lot of different nanomate- rials have been development during the last three decades, such as carbon nanotubes, 2D mono-elemental graphene-like materials, and 2D β -Indium sulfide nanoplates [3,4]. Some of these have been combined with nanocellulose to improve paper properties or to develop new materials [5]. It is well known that CNFs improve interfiber bonding, significantly increasing the mechanical properties of the recycled products [6]. However, the use of CNF is still limited at industrial scale. This is mainly due to the high cost of nanocellulose products and to some limits in their application mainly due to their effect on drainage and the dispersion degree of the 3D network as has been recently demonstrated [7]. To
Academic Editor: Hirotaka Koga
Received: 4 August 2023 Revised: 6 September 2023 Accepted: 8 September 2023 Published: 11 September 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 , 2536. https://doi.org/10.3390/nano13182536
https://www.mdpi.com/journal/nanomaterials
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