Surface Functionalization of Expandable Graphite With Carboxymethyl Cellulose for Enhanced Dispersion and Flame‐Retardant Performance in Waterborne Coatings

Expandable graphite (EG) is a widely used halogen‐free flame‐retardant additive; however, its poor hydrophilicity and tendency to agglomerate in aqueous media significantly hinder its dispersion and performance in waterborne intumescent flame‐retardant (IFR) coatings. To address these limitations, this study presents a sustainable surface modification strategy that enhances both the dispersibility and flame‐retardant functionality of EG. EG was chemically oxidized and subsequently functionalized with sodium carboxymethyl cellulose (CMC) via an epoxy‐mediated grafting reaction using phenol novolac epoxy resin as a coupling agent. The resulting CMC‐modified EG (CMC‐ m ‐EG) exhibited improved hydrophilicity, as confirmed by a decrease in water contact angle from 79.7° to 52.7°, and retained substantial thermal expansion capability (160 mL/g) despite surface coating. X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) analyses confirmed successful intercalation and covalent functionalization without significant structural disruption. Incorporation of CMC‐ m ‐EG into an acrylic binder resulted in enhanced dispersion, smoother coating morphology, and improved interfacial adhesion. Compared to unmodified EG, CMC‐ m ‐EG‐containing coatings demonstrated superior mechanical properties and flame retardancy, including an increased limiting oxygen index (LOI) of 25%, and a reduced peak heat release rate (HRR) of 364.4 kW/m 2 , compared to 793.8 and 941.5 kW/m 2 for the EG and neat coatings, respectively. These results highlight the potential of CMC‐ m ‐EG as a high‐performance additive for waterborne IFR systems.