Surfaces and interfaces analysis on different carboxymethylation reaction time of anionic cellulose nanoparticles derived from oil palm biomass

Abstract Recent advancements in nanotechnology have expanded the applications of cellulose nanoparticles (CNPs) isolated from various types of biomass waste like oil palm empty fruit bunches. These applications are particularly enhanced by incorporating nanoparticles or polymers. However, a significant challenge in synthesizing CNP-based nanocomposites lies in the selection of appropriate synthesis methods, as ineffective techniques can result in poor compatibility between nanoparticles. To overcome this issue, surface modification through carboxymethylation has emerged as an effective strategy. This process introduces anionic groups (−CH 2 COONa + ) onto the CNP surface, producing anionic nanocellulose particles (ACNPs) that act as capping agents to enhance nanoparticle incorporation. Despite these advancements, the optimum reaction time for isolating ACNPs from CNPs, particularly nanocrystalline cellulose, remains underexplored. This study investigates the effect of varying carboxymethylation reaction times (30 min, 2, 4, 6, and 8 h) on the synthesis of ACNPs. Characterization techniques, including Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction, transmission electron microscopy, zeta potential analysis, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), were employed. The results indicate that a reaction time of 4 h is optimal for carboxymethylation. ACNPs synthesized at this duration exhibit good dispersion, improved thermal stability, and a high zeta potential value (−41 mV) compared to CNPs (−25 mV). FTIR analysis reveals new peaks at 1,564, 1,432, and 1,321 cm⁻¹, corresponding to the carboxyl, methyl (−CH 2 ), and hydroxyl groups of the carboxymethyl group (−CH 2 –COONa), respectively. Additionally, XPS results show a high concentration of Na⁺ ions in ACNPs synthesized at 4 h. Beyond this reaction time, Na⁺ concentration decreases.