nanomaterials
Article Gel Point as Measurement of Dispersion Degree of Nano-Cellulose Suspensions and Its Application in Papermaking
Jose Luis Sanchez-Salvador , Ana Balea , Carlos Negro , Maria Concepcion Monte and Angeles Blanco *
Chemical Engineering and Materials Department, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain; josanc03@ucm.es (J.L.S.-S.); anabalea@ucm.es (A.B.); cnegro@ucm.es (C.N.); cmonte@ucm.es (M.C.M.) * Correspondence: ablanco@ucm.es; Tel.: +34-91-394-42-47 Abstract: The dispersion degree of cellulose micro and nanofibrils (CMFs/CNFs) in water suspen- sions is key to understand and optimize their effectiveness in several applications. In this study, we proposed a method, based on gel point (Ø g ), to calculate both aspect ratio and dispersion degree. This methodology was validated through the morphological characterization of CMFs/CNFs by Transmission Electronic Microscopy. The influence of dispersion degree on the reinforcement of recycled cardboard has also been evaluated by stirring CMF/CNF suspensions at different speeds. Results show that as stirring speed increases, Ø g decreased to a minimum value, in which the aspect ratio is maximum. Then, Ø g increased again. Suspensions with lower Ø g , in the intermediate region of agitation present very good dispersion behavior with an open and spongy network structure, in which nanofibril clusters are totally dispersed. Higher stirring speeds shorten the nanofibrils and the networks collapse. Results show that the dispersion of the nanocellulose at the minimum Ø g before their addition to the pulp, produces higher mechanical properties, even higher than when CNFs and pulp are agitated together. This method allows for the determination of the CMF/CNF dispersion, to maximize their behavior as strength agents. This knowledge would be crucial to understand why some industrial trials did not give satisfactory results.
Citation: Sanchez-Salvador, J.L.; Balea, A.; Negro, C.; Monte, M.C.; Blanco, A. Gel Point as Measurement of Dispersion Degree of Nano-Cellulose Suspensions and Its Application in Papermaking. Nanomaterials 2022 , 12 , 790. https:// doi.org/10.3390/nano12050790 Academic Editors: Giuseppe Lazzara and Rushdan Ahmad Ilyas
Keywords: nanocellulose; dispersion degree; gel point; cellulose nanofibers; aspect ratio; papermaking; mechanical properties
1. Introduction Several effective methods have been applied to disintegrate cellulose fibers into substruc- tures with micro-or nano-size dimensions as cellulose micro/nanofibrils (CMFs/CNFs) or micro/nanocrystals [1–4]. Among them, the use of CMFs/CNFs has gained attention due to their high surface area, high strength, or their excellent barrier properties [5–8]. CMF/CNF applications have been thoroughly studied in several fields such as papermaking [9–11], food packaging [12,13], anti-microbial films [14], biomedical applications [15–17], wastewater treat- ments [18,19], or cement-based materials [20]. However, although their effect has been highly successful at lab scale, these data are not always replicable. This is the case of the reinforcement of recycled cardboard for packaging, where improvements above 60% in the Tensile Index has been achieved at lab scale using 3% of CNF prepared from the same raw material, pretreated with 10 mmol/g of NaClO in TEMPO-mediated oxidation and then homogenized [10,11]. However, the uncertainty of pilot trials has limited the industrial application, especially when nanocellulose was not produced on-site [21,22]. This fact is still not fully understood. CMF/CNF gels production has been widely studied during the last decade; never- theless, their characterization is an area still under development. Many parameters have been developed to characterize CMFs/CNFs in terms of morphology, rheological prop- erties, composition, carboxyl or aldehyde content, nanofibrillation degree, etc. [2,5,23,24].
Received: 30 December 2021 Accepted: 22 February 2022 Published: 26 February 2022
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Nanomaterials 2022 , 12 , 790. https://doi.org/10.3390/nano12050790
https://www.mdpi.com/journal/nanomaterials
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