This
paper investigates a strategy to convert hydrophilic cellulose
nanofibrils (CNF) into a hydrophobic highly cross-linked network made
of cellulose nanofibrils and inorganic nanoparticles. First, the cellulose
nanofibrils were chemically modified through an esterification reaction
to produce a nanocellulose-based macroinitiator. Barium titanate (BaTiO3, BTO) nanoparticles were surface-modified by introducing
a specific monomer on their outer-shell surface. Finally, we studied
the ability of the nanocellulose-based macroinitiator to initiate
a single electron transfer living radical polymerization of stearyl
acrylate (SA) in the presence of the surface-modified nanoparticles.
The BTO nanoparticles will transfer new properties to the nanocellulose
network and act as a cross-linking agent between the nanocellulose
fibrils, while the monomer (SA) directly influences the hydrophilic–lipophilic
balance. The pristine CNF and the nanoparticle cross-linked CNF are
characterized by FTIR, SEM, and solid-state 13C NMR. Rheological
and dynamic mechanical analyses revealed a high dregee of cross-linking.
A strategy is devised to synthesize zwitterionic acetylated cellulose nanofibrils (CNF). The strategy included acetylation, periodate oxidation, Schiff base reaction, borohydride reduction, and a quaternary ammonium reaction. Acetylation was performed in glacial acetic acid with a short reaction time of 90 min, yielding, on average, mono-acetylated CNF with hydroxyl groups available for further modification. The products from each step were characterized by FTIR spectroscopy, ζ-potential, SEM-EDS, AFM, and titration to track and verify the structural changes along the sequential modification route.
Tunable dynamic networks of cellulose nanofibrils (CNFs) are utilized to prepare high‐performance polymer gel electrolytes. By swelling an anisotropically dewatered, but never dried, CNF gel in acidic salt solutions, a highly sparse network is constructed with a fraction of CNFs as low as 0.9%, taking advantage of the very high aspect ratio and the ultra‐thin thickness of the CNFs (micrometers long and 2–4 nm thick). These CNF networks expose high interfacial areas and can accommodate massive amounts of the ionic conductive liquid polyethylene glycol‐based electrolyte into strong homogeneous gel electrolytes. In addition to the reinforced mechanical properties, the presence of the CNFs simultaneously enhances the ionic conductivity due to their excellent strong water‐binding capacity according to computational simulations. This strategy renders the electrolyte a room‐temperature ionic conductivity of 0.61 ± 0.12 mS cm−1 which is one of the highest among polymer gel electrolytes. The electrolyte shows superior performances as a separator for lithium iron phosphate half‐cells in high specific capacity (161 mAh g−1 at 0.1C), excellent rate capability (5C), and cycling stability (94% capacity retention after 300 cycles at 1C) at 60 °C, as well as stable room temperature cycling performance and considerably improved safety compared with commercial liquid electrolyte systems.
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