Fuente: Journal of applied polymer Lugar: RESEARCH ARTICLE Using agricultural waste-wheat straw-as raw material, cellulose nanofibers (CNF) were prepared via the TEMPO oxidation method. Subsequently, nano-SiO2 was grafted onto the CNF surface using tetraethyl orthosilicate (TEOS) as the silicon source, yielding modified cellulose nanofibers (MCNF). These were then applied to oil well cement. The surface-branched nano-SiO2 on MCNF reacts with the initial hydration products of cement to form calcium silicate hydrate (CSH), enhancing the interfacial bonding between cellulose nanofibers and cement. Furthermore, the water-conducting channels and pozzolanic effect of MCNF promote cement hydration, thereby further improving the mechanical properties of the cement paste.

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-SiO2 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-SiO2 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.