AbstractThe utilization of sustainable feedstocks in surfactant production is crucial for reducing environmental impact, enhancing resource efficiency, and aligning with global efforts toward a circular economy and green chemistry. In this research, cellulose derivatives were synthesized by methylating cellulose fibers extracted from Guinea grass (Megathyrsus maximus) and their interfacial properties as surfactants were evaluated. The derivatives were characterized using Fourier‐transform infrared spectroscopy (FTIR), which revealed distinct stretching vibration absorption bands indicative of methyl groups. Thermogravimetric analysis (TGA) identified a dual‐stage decomposition process, consistent with reported behavior for methylcellulose. Time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) further confirmed the presence of methyl ether groups, with the H5CO+ ion detected as the characteristic fragment of the methylated samples. Functional evaluations demonstrated that double‐methylated cellulose derivatives exhibited a hydrophilic–lipophilic balance (HLB) of 12.7 and a surface tension of 55 dyne/cm when compared to mono or unmethylated fibers. Additionally, the double‐methylated derivatives displayed enhanced foaming activity, emulsion stability, and water solubility. These cellulose‐based surfactants exhibited interfacial properties comparable to their synthetic counterparts, emphasizing their potential for industrial applications and their role in advancing sustainable material development.