Improving the degree of polymerization of cellulose nanofibers by largely preserving native structure of wood fibers.

The degree of polymerization (DP) of cellulose plays an essential role in unlocking the superior mechanical potential of wood cellulose nanofibrils (CNFs). However, severe degradation of cellulose chains during the chemical pulping is a big challenge to obtain CNFs with high DP. In this work, we tend to improve the DP of wood CNFs by significantly preserving the native structure of wood fibers in an industrial method. Wood sticks are first pretreated with hydrothermal treatment to partially remove hemicellulose, thus leading to an increased porous structure that facilitates the penetration of cooking liquid and lignin removal during delignification, and dilute-alkali-sulfate pulping is then employed to obtain wood fibers with highest viscosity average DP (DP) of nearly 2400. After that, the as-prepared wood fibers with high DP are separated into CNFs with highest average DP of 1333. Finally, we demonstrate the potential application of wood CNFs with improved DP in the fabrication of strong and tough isotropic films and macrofibers.