Estimation of Fiber-Fiber Interactions in Cellulose Fiber Sheets via Relationship between Fiber Network Density and Cross-Linking Point

Understanding fiber-fiber interactions in materials using cellulose nanofibril (CNF) is essential for advancing bio-based material design. This study investigates the relationship between fiber network density and crosslinking points to estimate inter-fiber interactions in CNF sheets. The sheets were prepared from CNFs obtained from bacterial cellulose pellicle and bamboo pulp dispersions, subjected to various drying and solvent exchange conditions. Atomic force microscopy (AFM) images were processed and analyzed using SOAX software to quantify crosslinking points. Tensile tests were conducted to evaluate mechanical properties, and interaction energy per crosslinking point was calculated. The results showed that solvent exchange with ethanol increased the apparent number of crosslinking points but reduced the calculated interaction energy, suggesting weaker inter-fiber bonding. The estimated interaction energies ranged from values comparable to moderate hydrogen bonds to those dipole–dipole interactions, depending on the preparation methods. This approach provides a simple and effective method to estimate fiber–fiber interaction energy from network density and mechanical data, offering valuable insights for CNF-based material development.