Effects of non-solvents and electrolytes on the formation and properties of cellulose I filaments

Abstract

Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; however, so far, the role of the coagulation solvent has not been systematically elucidated in this context. This work considers organic non-solvents (ethanol, acetone) and aqueous electrolyte solutions (NaCl(aq), HCl(aq), CaCl2(aq)) for the coagulation of negatively charged cellulose nanofibrils via wet spinning. The associated mechanisms of coagulation with such non-solvents resulted in different spinnability, coagulation and drying time. The properties of the achieved filaments varied depending strongly on the coagulant used: filaments obtained from electrolytes (using Ca2+ and H+ as counterions) demonstrated better water/moisture stability and thermomechanical properties. In contrast, the filaments formed from organic non-solvents (with Na+ as counterions) showed high moisture sorption and low hornification when subjected to cycles of high and low humidity (dynamic vapor sorption experiments) and swelled extensively upon immersion in water. Our observations highlight the critical role of counter-ions and non-solvents in filament formation and performance. Some of the fundamental aspects are further revealed by using quartz crystal microgravimetry with model films of nanocelluloses subjected to the respective solvent exchange.

Mesoporous Carbon Microfibers for Electroactive Materials Derived from Lignocellulose Nanofibrils

“…The oxidation yields thinner and more flexible fibrils. TOCNF with high aspect ratio (>100) and surface charges, can induce both fibril entanglement and osmotic repulsion between the fibrils, which enhance wet-spinning into fibres (Iwamoto et al 2011;Walther et al 2011;Torres-Rendon et al 2014;Lundahl et al 2016a;Wang et al 2019b, a). With optimized parameters, fibres have been manufactured with high stiffness (86 GPa) and tensile stress (1.57 GPa) (Mittal et al 2018); these values are much higher compared to the properties of known natural or synthetic biopolymeric materials.…”

Microfibers synthesized by wet-spinning of chitin nanomaterials: mechanical, structural and cell proliferation properties

“…Similar behavior was observed between acetone and CNF microbers coagulated in electrolyte solutions. 34 Besides the differences observed at the macroscale, all the spun microbers possessed a hierarchical structure. Using F AC as an example, ChNF assembled randomly and formed several brous units, which further formed into layers.…”

“…4 illustrates that the coagulants led to microbers of different cross-section. Compared with F Na and F AM , F AC was irregular; however, this is likely the results of an artifact, as discussed for CNF systems: 34,40 That is, the microbers coagulated in alkaline solution, F Na and F AM, where free to form in the coagulation bath, with no inuence of the bottom solid surface in the bath, which otherwise would have attened the micro-ber. Similar behavior was observed between acetone and CNF microbers coagulated in electrolyte solutions.…”

“…Consequently, ChNF lost water, underwent phase separation, and settled down, at the bottom of the bath, given the densication process. 34 Aer coagulation, the microber required quick withdrawal from the coagulation bath since it would otherwise stick to the bottom surface (e.g., glass, metal or plastic). For diluted ChNF suspensions, a longer coagulation time was needed and the formed microbers adhered more strongly to the bottom surface of the bath.…”

“…Similar behavior was reported for negatively charged CNF (TOCNF). 34 An aqueous alkaline electrolyte (NaOH and ammonia) solution was applied as coagulants. When the positively charged ChNF was extruded in alkaline solution, the primary protonated amine groups were neutralized (from NH 3 + to NH 2 ).…”