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.
Highlights
Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; so far, the role of the coagulation solvent has not been systematically elucidated in this context
We systematically investigated the influence of coagulation agent on the spinnability of TOCNF suspensions, considering the coagulation and drying times
It is reasonable to assume that due to the low affinity with ethanol and acetone, a dense semi-solidified shell formed via interfibrillar aggregation, which proceeded into the core, leading to the densification of the filaments, as discussed previously[15,22]
Summary
Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; 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. In this study, we investigated the influence of the coagulation system on the wet-spinning of TOCNF and the final properties of the spun filaments This is a subject that has not been addressed systemically in such contexts. Coagulation is applied in film formation (wet-casting) and fiber spinning (dry-jet or wet- spinning), where phase separation of a polymer solution occurs in the bath by mass transport and exchange between the solvent and non-solvent[26,27]. Two types of coagulation agents have been applied in wet-spinning of CNF, including organic solvents (such as ethanol, acetone, and tetrahydrofuran) as well as aqueous electrolytes (CaCl2, HCl). The electrolytes species can displace the counterions in the Spinning bath Ethanol Acetone NaCl (1 M) CaCl2 (1 M) HCl (pH 2)
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