Flexible cellulose nanopaper with high wet tensile strength, high toughness and tunable ultraviolet blocking ability fabricated from tobacco stalk via a sustainable method

Cellulose nanopaper (CNP) is of great interest to researchers mainly due to its renewability, excellent mechanical properties and optical properties. However, CNP is usually sensitive to water, resulting in the loss of strength and durability. To overcome this issue, in this work, an efficient and sustainable route, which involved ammonium sulfite cooking and formic acid hydrolysis, was reported to isolate lignin-containing cellulose nanofibrils (CNFs) from tobacco stalk. The resultant CNFs were directly used to fabricate strong, flexible, and water resistant CNP without any complex chemical modification. The residual lignin was found to act as a reinforcing agent between CNFs in CNP. The tensile strength and toughness of the lignin-containing CNP (255 MPa and 19.7 MJ m(-3)) were much higher compared with those of the one without lignin (179 MPa and 12.8 MJ m(-3)). The water-resistance of the CNP was also improved extraordinarily, and its maximum wet tensile strength reached up to 83 MPa which is the highest value in comparison with the reported CNP. Compared to the lignin-free CNP, the lignincontaining CNP also showed the better thermal stability and excellent UV-blocking properties. The present work designed a new route to prepare lignin-containing CNFs and CNP, which are potential candidates to replace petroleum-based materials in many advanced applications.