Dual‐Functional Inorganic Polymer‐Starch Composite for High‐Temperature Eco‐Drilling Fluids: Synergistic Enhancement of Thermal Stability and Clay Hydration Inhibition

ABSTRACT This study addresses the critical challenge of insufficient thermal stability in conventional starch‐based drilling fluid additives by developing an innovative inorganic polymer‐starch composite (polymerized ferrous sulfate‐potato starch, PFTS). Through optimized material synergy, PFTS significantly enhances high‐temperature resistance (up to 150°C) and hydration inhibition in eco‐friendly drilling fluids. Performance evaluations demonstrated a 29.3% reduction in fluid loss (from 12.6 to 8.9 mL) and improved rheological stability, with apparent viscosity decreasing from 7.0 to 4.9 mPa·s after 150°C aging. Multi‐scale characterization (TGA, XRD, FTIR) revealed that inorganic polymers form chemically cross‐linked networks with starch via metal ion coordination, restricting starch chain mobility and delaying thermal degradation. The composite further inhibited clay hydration by adsorbing onto clay surfaces, reducing interlayer spacing from 0.3353 nm (hydrated) to 0.3329 nm through synergistic physical barrier and charge modulation effects. Particle size analysis confirmed enhanced clay aggregation (median size increased from 6.1 to 11.0 µm), validated by mud ball experiments showing superior structural integrity under hydration stress. PFTS exhibited excellent compatibility with polyacrylamide and heteropolysaccharide systems, maintaining stable rheology and low friction coefficients under thermal aging. These results establish PFTS as a sustainable, dual‐functional solution for high‐temperature drilling operations, offering mechanistic insights for designing starch‐inorganic hybrids to overcome temperature limitations in water‐based drilling fluids. The composite's eco‐friendly profile and scalable synthesis further underscore its industrial viability.