Synthesis and Characterization of MC-MCNT Fibers

Microcrystalline cellulose (MC) (average particle size of 20 µm, purchased from Sigma-Aldrich, Leverkusen, Germany) was dissolved with the Ionic liquid (IL) 1-ethyl-3-methylimidazolium chloride (EMIMCl, >97%). The MCNTs (MWCNT, Baytubes^®; length > 1 µm, inner diameter 4 nm, and outer diameter 12 nm) were purchased from Bayer Material Science (BMS, Leverkusen, Germany) and used as supplied. After 12 h stirring at 85 °C, the MCNTs (MCNT, 50 wt.%) were added to the suspension and ultra-sonicated at room temperature for 30 min. The mixture was then placed in a syringe (760 µm inner diameter) and extruded in anti-solvent (Milli-Q+, Tallinn, Estonia) using a procedure that was shown in detail in a previous study [11 (link)]. To remove excess EMIMCl, the MC-MCNT fibers were washed with ethanol several times and then dried in an oven at 40 °C at 2 mbar. The MC-MCNT fiber had a cylindrical form with a diameter of 965 ± 75 µm and a length of 4.5 ± 0.3 mm. The diameter of the MC-MCNT fibers was measured with a screw gauge (Eisco Labs, Rochester, NY, USA) after they had been stored in different electrolytes for 24 h. The applied electrolytes (0.1 M) were dissolved in propylene carbonate (PC, 99%) with the chosen salts, 1-ethyl-2,3-dimethylimidazolium trifluoro-methanesulfonate (EDMICF₃SO₃, EDMITF, 95%), lithium triflouro-methanesulfonate (LiCF₃SO₃, LiTF, 99%), and tetrabutylammonium triflouro-methanesulfonate (TBACF₃SO₃, TBATF, 98%). The MC-MCNT fibers applied in this research weighed 1.2 ± 0.1 mg with an estimated MCNT weight of 500 ± 48 µg, resulting in a density of MC-MCNT fibers in the range of 0.33 ± 0.03 g cm⁻³. To ensure reproducibility, at least three fibers were formed independently of each other and investigated. The EMIMCl, PC, EDMITF, LiTF, TBATF, and ethanol (technical degree) were obtained from Sigma-Aldrich (Taufkirchen, Germany) and used as supplied.