Superbase ionic liquids for effective cellulose processing from dissolution to carbonisation

Abstract

A range of superbase derived ionic liquids (SILs) was synthesised and characterised. Their ability to dissolve cellulose and the characteristics of the produced fibres were correlated to their specific structural and solvent properties. 17 ionic liquids (ILs) (including 9 novel) were analysed and six ILs were selected to produce fibres: 1-ethyl-3-methylimidazolium acetate [C2C1im][OAc], 1-ethyl-3-methylimidazolium diethyl phosphate [C2C1im][DEP] and the SILs 1-ethyl-1,8-diazabicyclo[5.4.0]undec-7-enium diethylphosphate [DBUEt][DEP], 1,8-diazabicyclo[5.4.0]undec-7-enium acetate [DBUH][OAc], 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] and 1-ethyl-1,5-diazabicyclo[4.3.0]non-5-enium diethylphsophate [DBNEt][DEP]. The mechanical properties of these fibres were investigated. The obtained fibres were then carbonised to explore possible application as carbon fibre precursors. The fibres obtained using a mixture of 1,5-diazabicyclo[4.3.0]non-5-enium based SILs with acetate and hexanoate anions (9 : 1), [DBNH][OAc][Hex], showed a promising combination of strength, stiffness and strain at failure values for applications in textiles and fibre reinforcement in renewable composites. Using Raman spectroscopy it is demonstrated that these fibres exhibit a relatively high degree of structural order, with fewer defects than the other materials. On the other hand, analogous fibres based on imidazolium cation with acetate and hexanoate anions (9 : 1), [C2C1im][OAc][Hex] showed a decline in the quality of the produced fibres compared to the fibres produced from [C2C1im][OAc], [C2C1im][DEP] or [DBNH][OAc][Hex]

Room-temperature dissolution and chemical modification of cellulose in aqueous tetraethylammonium hydroxide–carbamide solutions

“…The dissolution and regeneration of cellulose can decrease the DP of cellulose depending on the utilized solvent and dissolution conditions (e.g., temperature and time). For example, a slight decrease in the DP of MCC has been observed with various ionic liquids (Kuzmina et al 2017). Here, the DP of the cellulose regenerated from carbamide-based solvents was observed to be similar to that of the original MCC (Table 1).…”

“…Dissolution of higher MCC concentrations and high-molecular-weight cellulose Although 5 wt% cellulose solution has been efficiently used, for example, to produce cellulose filaments, which were further used to produce carbon fibers by carbonization (Kuzmina et al 2017), higher cellulose concentrations are desirable to fabricate strong regenerated cellulose fibers and films. Therefore, the production of solutions with higher cellulose concentrations was studied.…”

Superbase-based protic ionic liquids for cellulose filament spinning

“…After studying systematically the influence of the composition (Ma et al 2016a, b) and molecular weight distribution (Michud et al 2015b) of the lignocellulosic solute on the spinnability, we now looked at alternative superbase-based ILs: 1,8-Diazabicyclo[5.4.0]undec-7-enium acetate ([DBU-H]OAc), an amidine-based IL, and 7-methyl-1,5,7triazabicyclo[4.4.0]dec-5-enium acetate ([mTBDH]OAc), a guanidine-based IL. Similar to DBN, both DBU and mTBD ILs are capable of dissolving high cellulose contents (Parviainen et al 2013;Kuzmina et al 2017;Elsayed et al 2020). Herein, we report on the suitability of these ILs as spinning solvents and compare their performance with NMMO monohydrate as a benchmark.…”

Effect of Alkyl Chain Length in Anions on the Physicochemical Properties of Cellulose-Dissolving Protic Ionic Liquids

“…[16,17] The (DpK a ¼ 8.46) dissolves 27 wt-% cellulose. These differences may be attributed to the alkyl chain of the carboxylate ion, according to the report by Kuzmina et al [18] The carboxylate ions are thought to disrupt the hydrogen bond network of the hydroxy groups in cellulose, therefore enabling the dissolution of cellulose in carboxylate-based ILs. The longer, hydrophobic alkyl chains would prevent interactions between carboxylate ions and hydroxy groups, thus decreasing cellulose solubility with increasing alkyl chain length in the carboxylate ion.…”