Sustainable route to prepare functional lignin-containing cellulose nanofibrils

With nano-dimension, high aspect ratio, and high mechanical properties, cellulose nanofibrils (CNFs) are emerging sustainable nanomaterials with potential applications in films and composites. However, their preparation often involves a series of chemical treatments such as delignification, bleaching and harsh chemical pretreatments, and treats lignin as waste. Herein, we report a sustainable method to prepare high-quality lignin-containing cellulose nanofibrils (LCNFs) from bamboo chips, using a one-step maleic anhydride esterification treatment without any toxic organic solvent or catalyst. The resultant LCNFs have high lignin content (24%), high surface charge (2.25 mmol/g), fine diameter (∼2.5 nm), and high aspect ratio (>400). These superior properties can be translated into the corresponding nanopaper films with high optical transmittance (85% at 600 nm), UV shielding (<10% transmittance at 200–350 nm), hydrophobicity (water contact angle 75°), thermal stability (maximal weight loss temperature at 338 °C), and mechanical properties. Importantly, such films show the best reported tensile strength (290 MPa) among all the LCNF films, and it still outperforms conventional CNF films after 5 rounds of recycling. Furthermore, as sustainable nanofillers, such LCNFs can be directly incorporated into a hydrophobic polyester matrix, and significantly enhances the UV shielding and mechanical properties of the final nanocomposites. Altogether, with eco-friendly production and multiple functions, these LCNFs are a new class of nanocelluloses with high industrial relevance.