Towards the efficient preparation of tough cellulose nanopapers

Cellulose nanopapers are attractive materials with outstanding mechanical and optical properties, yet their production is slow. The use of non-aqueous suspension media, in particular ethanol, for nanopaper production reduced filtration times by 73 %. Nanopapers prepared from ethanolic suspensions possessed higher porosities than those prepared from aqueous suspensions, reducing their transparency and tensile properties. Rewetting nanopapers prepared from ethanolic suspensions with water and subsequent drying yielded nanopapers with densities essentially the same as those prepared from aqueous suspensions, which in turn greatly increased mechanical properties and transparency. The strain to failure of rewetted and dried nanopapers prepared from ethanolic suspensions increased from 2.8 % to 7.5 %. The strain to failure of rewetted and dried nanopapers prepared from ethanolic suspensions was also greater than that of nanopapers prepared from aqueous suspensions (3.3 %) albeit at the expense of a 20 % decrease in tensile strength and modulus, which was shown to be attributable to a lower bonding contribution between fibrils in the network. The increased strain to failure results in significantly increased work of fracture. The rewetting and drying treatment also yielded nanopapers with high total luminous transmittance and haze.