Biomass‐Derived <scp> SiO ₂ </scp> ‐Grafted Nanocellulose Fibers: Interfacial Architecture for Multiscale Reinforcement in Oil Well Cementitious Matrices

ABSTRACT To address the inherent brittleness of cement stone, this study synthesized cellulose nanofibers (CNF) from wheat straw via the TEMPO oxidation method. These CNF were then surface‐modified with tetraethyl orthosilicate to produce silica‐modified cellulose nanofibers (MCNF). MCNF demonstrated excellent thermal stability and dispersibility, effectively improving the microstructure and mechanical properties of cement paste. Mercury intrusion porosimetry (MIP) results indicated that compared to CNF‐modified cement paste, MCNF‐modified cement paste exhibited a 24.6% reduction in porosity and a 43.7% decrease in average pore size. The 28‐day flexural strength of cement paste incorporating 0.1% MCNF increased by 16.2% and 30.6% compared to CNF‐modified cement paste and unmodified cement paste, respectively. Fracture toughness testing revealed a 48.4% improvement in the maximum load‐bearing capacity of the cement paste. During early hydration, the nano‐SiO 2 on the MCNF surface undergoes pozzolanic reactions with Ca(OH) 2 , thereby accelerating hydration. In later stages, MCNF further promotes hydration by acting as a “water transport channel” for cement hydration. Additionally, nano‐SiO 2 enhances interlocking between MCNF and the cement matrix. Increased hydration products around MCNF strengthen its bridging effect and stress‐dispersing capacity. The synergistic action of these two mechanisms collectively enhances the mechanical properties of oil well cement.