Stereoselectively water resistant hybrid nanopapers prepared by cellulose nanofibers and water-based polyurethane

Abstract

Cellulose nanopapers, known for excellent mechanical properties, loses 90% of their stiffness in the wet conditions. In this study, we attempt to improve the wet mechanical properties of cellulose nanopaper by incorporating polyurethane by a novel and ecofriendly method. Water based PU was dispersed along with CNFs in water and hybrid nanopapers were prepared by draining water under vacuum followed by forced drying. These hybrid nanopapers have a gradient interpenetrating structure with PU concentrated towards one side and CNFs towards the other, which was confirmed by scanning electron microscopy, x-ray photoelectron spectroscopy and contact angle measurements. Because of this, the nanopapers are water resistant on one surface (PU rich side) and hydrophilic on the other (cellulose rich side), making them stereoselectively water resistant. When wetted with water on the PU side, the hybrid nanopaper with 10% PU is able to retain 65% modulus; on the other hand, the reference retains only 10% of the modulus. Similar results are seen in the tensile and the yield strength. Additionally, the hybrid nanopapers have higher elongation and improved thermal stability. The reported material is relevant to the applications such as flexible electronics and transparent displays.

Vitrimer Chemistry Meets Cellulose Nanofibrils: Bioinspired Nanopapers with High Water Resistance and Strong Adhesion

“…Pristine CNF nanopapers display the lowest degree of movement, corroborating the mechanical tensile data. Although water stability in cellulose nanocomposites have been studied, ,,− to our knowledge this is one of the first attempts to obtain water resistance in CNF-based nanocomposites by activation of thermo-induced exchange and cross-linking reactions. Hence, this opens the opportunity to continue developing the design further.…”

Nanocomposites from Clay, Cellulose Nanofibrils, and Epoxy with Improved Moisture Stability for Coatings and Semistructural Applications

“…Some examples of such “active” components include vitrimer nanoparticles activated by thermal curing, algal polysaccharides entangled within the CNF network and locked in the wet state with cation treatment, or physical cross-linking by chitosan during base treatment . One may also include intrinsically hydrophobic, but colloidally stable particles such as water-based latexes − or positively charged species such as quaternary alkylammonium . Water repellence can also be achieved by chemical modification after materials preparation. , …”