Increasing the Possibilities of TEMPO‐Mediated Oxidation in the Production of Cellulose Nanofibers by Reducing the Reaction Time and Reusing the Reaction Medium

Abstract

2,2,6,6‐Tetramethylpiperidine‐1‐oxyl (TEMPO)‐mediated oxidation of cellulose is the most effective pretreatment to obtain highly fibrillated cellulose nanofibers (CNFs). However, the associated environmental impact and the high operational costs have limited its implementation at large scale. This study aims to improve the effectiveness of this pretreatment by reducing the oxidation time and reusing the reaction medium, with the ultimate objective of upscaling a more viable sustainable process. The results show the possibility of reducing the reaction time by 85% and 60% in the case of cotton and eucalyptus pulps, respectively, without altering the properties of the obtained CNFs (carboxyl groups, nanofibrillation yield, cationic demand, and morphology). The reuse of 75% of the reaction medium for ten cycles, do not alter the properties of the CNFs either. With this approach, the consumption of TEMPO and NaBr is reduced by 67%, while that of NaClO is decreased by 42% and 22% in the oxidation of cotton and eucalyptus cellulose, respectively. At the same time, the environmental concerns derived from the disposal of the catalysts are considerably reduced.

Critical comparison of the properties of cellulose nanofibers produced from softwood and hardwood through enzymatic, chemical and mechanical processes

“…Finally, although the final oxidation degree of both pretreated pulps with TEMPO-mediated oxidation was similar in terms of carboxyl groups, the morphology resulted to be very different. As explained in a previous publication [13], once the pulp has been oxidized at a certain point, the electrostatic repulsion induced by the carboxyl groups causes the breaking of the fibers in those areas close to the crystalline regions. Thus, it makes sense to think that this breaking would reach a higher degree in the pulps with longer crystallites, i.e.…”

“…Since the percentages were approximately the same in both pulps, BKSP and BKHP, this effect was attributed to some residual salts derived from the oxidation reaction. Two main reasons could have governed this behavior: first, the oxidation reaction gives NaCl as a product [13], that could have remained attached to the fibers even after washing. Second, some industries have generally added NaCl to the commercial NaClO just to improve its stability during storage [61], and this low proportion could have remained also together with the fibers.…”

“…Among them, chemical oxidation, via carboxylation using 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and NaBr as catalysts, and NaClO as oxidant, is one of the most used processes to obtain a homogenized sample with mostly individual fibrils, high aspect ratio, and diameters below 10 nm [10,11]. However, this reaction presents some drawbacks related to the high cost of TEMPO catalyst, or its recovery at the end of the process, which would help to increase its profitability and reduce the environmental impact due to the alkaline waste streams associated with the reaction medium that has a high amount of salts [12,13].…”

Enhanced Morphological Characterization of Cellulose Nano/Microfibers through Image Skeleton Analysis

“…Nevertheless, the carboxyl content in T15 was similar in all samples, around 1360–1390 mmol/g, except in jute where there was a lower content, around 1300 mmol/g. At this dosage, most of the C6 positions may have been oxidized and a proportion of the more oxidized and amorphous sample could have remained in dissolved or colloidal form [ 38 ]. As showed in Table S1 , the values of CD in CMF/CNFs increased gradually with the severity of the homogenization for all sources.…”

Gel Point as Measurement of Dispersion Degree of Nano-Cellulose Suspensions and Its Application in Papermaking

“…Several effective methods have been applied to disintegrate cellulose fibers into substructures with micro-or nano-size dimensions as cellulose micro/nanofibrils (CMFs/CNFs) or micro/nanocrystals [ 1 , 2 , 3 , 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 , 6 , 7 , 8 ]. CMF/CNF applications have been thoroughly studied in several fields such as papermaking [ 9 , 10 , 11 ], food packaging [ 12 , 13 ], anti-microbial films [ 14 ], biomedical applications [ 15 , 16 , 17 ], wastewater treatments [ 18 , 19 ], or cement-based materials [ 20 ].…”