molecules
Article In Situ Production and Application of Cellulose Nanofibers to Improve Recycled Paper Production AnaBalea 1 , Jose Luis Sanchez-Salvador 1 , M. Concepcion Monte 1 , Noemi Merayo 1,2 , Carlos Negro 1 and Angeles Blanco 1, * 1 Department of Chemical Engineering and Materials, Universidad Complutense de Madrid (UCM), Av. Complutense s / n, 28040 Madrid, Spain; anabalea@ucm.es (A.B.); josanc03@ucm.es (J.L.S.-S.); cmonte@ucm.es (M.C.M.); nmerayoc@ucm.es (N.M.); cnegro@ucm.es (C.N.) 2 Department of Mechanical, Chemical and Industrial Design Engineering, ETSIDI, Universidad Polit é cnica de Madrid (UPM), Ronda de Valencia 3, 28012 Madrid, Spain * Correspondence: ablanco@ucm.es; Tel.: + 34-91-394-4247
Received: 3 April 2019; Accepted: 7 May 2019; Published: 9 May 2019
Abstract: The recycled paper and board industry needs to improve the quality of their products to meet customer demands. The refining process and strength additives are commonly used to increase mechanical properties. Interfiber bonding can also be improved using cellulose nanofibers (CNF). A circular economy approach in the industrial implementation of CNF can be addressed through the in situ production of CNF using side cellulose streams of the process as raw material, avoiding transportation costs and reducing industrial wastes. Furthermore, CNF fit for use can be produced for specific industrial applications.This study evaluates the feasibility of using two types of recycled fibers, simulating the broke streams of two paper machines producing newsprint and liner for cartonboard, to produce in situ CNF for direct application on the original pulps, old newsprint (ONP), and old corrugated container (OCC), and to reinforce the final products. The CNF were obtained by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated oxidation and homogenization at 600 bar. Handsheets were prepared with disintegrated recycled pulp and di ff erent amounts of CNF using a conventional three-component retention system. Results show that 3 wt.% of CNF produced with 10 mmol of NaClO per gram of dry pulp improve tensile index of ONP ~30%. For OCC, the same treatment and CNF dose increase tensile index above 60%. In both cases, CNF cause a deterioration of drainage, but this e ff ect is e ff ectively counteracted by optimising the retention system.
Keywords: nanocellulose; cellulose nanofibers; recycled paper; mechanical properties; drainage; retention; circular economy
1. Introduction Papermaking is an industrial sector characterized by its commitment to develop sustainable production processes [1,2]. In Europe, 52.4% of the papermaking industry’s raw materials come from recovered paper, which corresponds to a paper recycling rate of 72.3% [3]. Nevertheless, the quality levels required in the utilization of secondary fibers are continuously increasing according to the customer demands. Besides, paper consumption has decreased due to the replacement of paper by other supports for the information, causing cost pressures in the paper and board industry. Despite the fact that natural and synthetic strength additives are commonly used in recycled paper, the main source of complaints is still the poor tensile strength. Therefore, other strategies to improve interfiber bonding have been explored, and the use of cellulose nanofibers (CNF) is a promising alternative to increase mechanical properties of recycled products with some additional advantages, such as their renewable nature, biodegradability, high surface area, and high availability.
Molecules 2019 , 24 , 1800; doi:10.3390 / molecules24091800
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