Mechanical properties of nanocellulose based materials, such as films, hydrogels, aerogels, and macrofibers, are closely associated with their building blocks. Cellulose nanofibers (CNFs) with long length and small diameter are preferable when aiming for high mechanical performances. While current CNFs preparation processes can severely damage the natural structure of cellulose, leading to low aspect ratio and low degree of polymerization (DP).  Herein, we demonstrate a mild process for fabrication of CNFs with high DP, long length and small diameter. The DP of wood pulps was nearly 2500, which is 250% higher than commercial pulps, and the DP of final CNFs are higher than 1000, which is similar to conventional cellulose microfiber. The diameter of CNFs is only ~4 nm, and the aspect ratio reached ~1000. The mechanical properties of both CNF films and macrofibers are significantly improved by building blocks optimization. This work provides a mild process of making CNFs with high DP and large length-diameter ratio for high performance nanocellulose-based materials.

Cellulose nanofibers,degree of polymerization,delignification,mechanical property