High-strength cellulose nanofibers producedviaswelling pretreatment based on a choline chloride–imidazole deep eutectic solvent

Abstract

A deep eutectic solvent (DES) based on choline chloride and imidazole (CCIMI) was investigated for swelling of cellulose fibers prior to mechanical disintegration into cellulose nanofibers (CNFs). The dimensions of the DES treated and washed fibers were investigated after various treatment conditions (time, temperature, and cellulose consistency) using DES based on choline chloride-urea (CCUrea) and pure imidazole as references. Even mild treatment conditions (15 minutes at 60°C) with CCIMI increased the diameter of the fibers from 18.1 to 18.9 μm, and a maximum diameter of 19.9 μm was obtained after three hours at 100°C. Overall, CCIMI resulted in a higher degree of swelling compared to both references. In addition, pure imidazole caused a decrease in the degree of polymerization of cellulose, whereas cellulose degradation in CCIMI was negligible. The mechanical disintegration of CCIMI-treated fibers resulted in the production of CNF films with very good mechanical properties-specific tensile strength and work capacity being over 200 kNm kg −1 and 10 kJ kg −1 , respectively-whereas CNFs films produced using choline chloride-urea had notably lower values (182 kNM kg −1 and 7 kJ kg −1 , respectively). In addition, CNF films exhibited good oxygen barrier properties, even at an elevated relative humidity level (80%). CCIMI could be recycled without any effect on the mechanical properties of CNF films. The results presented here indicate CCIMI is a highly efficient pretreatment media for swelling and further nanofibrillation of cellulose, even at mild treatment conditions. † Electronic supplementary information (ESI) available: Fiber width and CWT at various concentrations, DRIFT spectra, photograph of CNF aerogels, and TGA curves. See

Mechanochemical and thermal succinylation of softwood sawdust in presence of deep eutectic solvent to produce lignin-containing wood nanofibers

“…The WNF films obtained from the mechanochemical succinylated sawdust exhibited relative low mechanical properties, for example, specific tensile strength ranged from 63 to 32 kNm/kg (Table 2). For the CNF films obtained from bleached cellulose, the specific tensile strength over 200 kNm/kg has been reported (Salajkova et al 2013;Yang et al 2020;Sirviö et al 2020a). In addition, although films produced from WNFs with a high lignin content usually have lower mechanical properties than CNFs, specific tensile strengths of 83 (Sirviö and Visanko 2017) The tensile test results indicate that mechanochemical succinylation is not ideal for production of high-strength biobased materials.…”

“…Many DESs have negligible vapor pressure and, therefore, do not contribute to the volatile organic component emission and are safer to handle than many common solvents (i.e., minimal exposure to toxic fumes and low flammability). Low or negligible vapor pressure also allows for removal of volatile chemicals from DESs, thus enabling their recycling (Mukesh et al 2014;Li et al 2018;Sirviö et al 2020a). Depending on their chemical constitutions, DESs exhibit low toxicity and are readily biodegradable (Wen et al 2015).…”

“…Cellulose nanofibers (CNFs) are well-known lignocellulose-based nanomaterials, generally produced from bleached, ligninfree cellulose pulp by using enzymatic, chemical, and mechanical methods, or their combinations (Klemm et al 2018). In the preparation of CNFs, DESs are used as a swelling agent to obtain non-chemically modified CNFs (Sirviö et al 2015(Sirviö et al , 2020aLi et al 2017b;Hosseinmardi et al 2017). The swelling of cellulose fibers results in loosening of the fiber structure, thus allowing for a more efficient CNF production by mechanical disintegration.…”

A conductive polymer composed of a cellulose-based flexible film and carbon nanotubes

“…1). In recent years, DES has been widely used in the preparation of cellulosic materials, [21][22][23][24] which is a low-temperature eutectic mixture composed of hydrogen bond acceptors (such as quaternary ammonium salts) and hydrogen bond donors (such as carboxylic acids, polyols) in a certain molar ratio; its synthesis requires simple mixing and stirring of the components, no other purication treatment is required. [25][26][27] Compared with the common treatment method of removed wood lignin/hemicellulose by used a mixed alkaline solution of Na 2 SO 3 or NaClO 2 and NaOH, the treatment process of DES is more gentle, and it is inexpensive, green and environmentally friendly, and will not produce toxic gases in the experiment.…”

Deep eutectic solvent for curing of phthalonitrile resin: Lower the curing temperature but improve the properties of thermosetting

“…10,15,16 Deep eutectic solvent (DES) is an ionic liquid analog achieved by simply mixing together the hydrogen bond donor and acceptor, which are capable of forming a eutectic mixture at the temperatures below the melting point of each component. 17,18 DES is considered as a promising, green, cheap and easy-to-prepare medium for application in many fields (metal plating, 19 material extraction, 20,21 reaction medium or catalyst, [22][23][24] materials synthesis, 25,26 electrolyte, 27,28 etc.). Thus, DES has also gained attention for the development of thermosetting resins.…”