Surface-Modified Cellulose Nanofibers for Stabilization of Barite in Water-Based Drilling Fluids Under High Temperatures

Surface modification is an effective strategy for extending the application of cellulose nanofibers (CNFs) under harsh conditions while preserving their sustainable characteristics. Herein, thermally stable modified TEMPO-oxidized cellulose nanofibers (MTCNFs) were fabricated by free-radical graft copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and acrylamide (AM) onto the CNF surface. Spectroscopic and microscopic characterizations confirmed the formation of a polymer-grafted shell enriched with sulfonic acid and amide functionalities. Surface grafting markedly enhanced the thermal stability of CNFs, while the zeta potential became more negative, indicating improved colloidal stability. The modified nanofibers effectively inhibited barite sedimentation after aging, as demonstrated by multiple light scattering and particle size analyses. Mechanistic investigations revealed that the superior suspension stability originated from the synergistic enhancement of electrostatic repulsion, steric hindrance provided by the grafted polymer chains, and the formation of a robust three-dimensional nanofiber network. When incorporated into water-based drilling fluids, MTCNFs significantly improved rheological stability, reduced filtration loss, and suppressed barite sagging under high-temperature conditions. Furthermore, the MTCNFs exhibited measurable biodegradation potential under the conditions employed. This work demonstrates that rational surface engineering of CNFs offers an effective route to simultaneously improve thermal stability and suspension performance, broadening the applicability of sustainable polysaccharide nanomaterials in high-temperature colloidal systems.