Water-resistant nanopaper with tunable water barrier and mechanical properties from assembled complexes of oppositely charged cellulosic nanomaterials
2021
Zhang, Kaitao | Ismail, Mostafa Y. | Liimatainen, Henrikki
Owing to the intrinsic hydrophilicity of nanocellulose, films and nanopapers prepared from cellulosic nanomaterials exhibit weak mechanical strength when exposed to high-moisture conditions. In this study, an approach for designing a water resistant, assembled nanopaper through controlled and irreversible aqueous complexation of oppositely charged cellulose nanoconstituents, i.e., cationic cellulose nanocrystals (AH-CNC) and anionic cellulose nanofibers (TO-CNF), is proposed. The fabrication process and features of the nanopaper can be adjusted by altering of the AH-CNC/TO-CNF ratio. For example, the draining time during the filtration of a nanopaper decreased dramatically (480–10 min) when the dosage of nanocelluloses resulted in charge compensation. This dosage also reduced the swelling of the nanopaper. After all charged groups were neutralized, a nanopaper with a wet strength of 11 ± 3 MPa was obtained when immersed in water for 24 h. Furthermore, the electrostatic interaction between the charged nano-entities enhanced the mechanical properties of the nanopaper in dry state (the maximum of tensile strength was 174 ± 3 MPa) and resulted in improved water barrier properties (water vapor transmission rate of 1683 g μm m⁻² d⁻¹). This straightforward method based on simply aqueous mixing of two oppositely charged nanomaterials may provide a new pathway for the fabrication of various functionalized films and sheets with advanced characteristics from different type of charged nanoparticles and colloids.
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