The widespread use of synthetic plastics in packaging has raised critical environmental concerns due to their persistence, poor degradability, and accumulation in ecosystems. As the demand for sustainable alternatives grows, cellulose, a primary structural component of plant biomass, emerges as a promising bio-based substitute owing to its renewability, biodegradability, and low environmental footprint. However, its inherent hydrophilicity limits its application in moisture-sensitive packaging systems. This study evaluates supercritical impregnation (SCI) of ethyl oleate, a GRAS-designated and functional additive, as a method to enhance the hydrophobicity of cellulose substrates. SCI was implemented at varying temperatures (40 - 160 °C), pressures (80 - 200 bar), and durations (10 - 90 minutes), with both polar and non-polar cosolvents evaluated for their effect on cellulose swelling and additive uptake. Gravimetric analysis quantified additive loadings of up to 0.9 g per gram of cellulose. TGA indicated improved thermal stability in modified samples and confirmed low residual moisture content (~2.7 percent) in the unmodified substrate. FTIR revealed the integration of ethyl oleate through the emergence of its characteristic vibrational modes, notably the ester carbonyl (C=O) stretching at 1738 cm⁻¹ and asymmetric/symmetric methylene (C–H) stretching bands at 2921 and 2856 cm⁻¹, respectively, which intensified with additive loading, especially in acetone-treated samples. Alongside this, a substantial decrease in the broad O–H stretching envelope (3600 – 3100 cm⁻¹) was observed, indicative of disrupted intermolecular hydrogen bonding within the native cellulose supramolecular architecture, consistent with the formation of hydrogen-bonded complexes and partial substitution or steric hindrance at hydroxyl binding sites. XRD analysis showed decreased internal crystallinity, indicating interference with fibrillar order. SEM imaging revealed surface smoothing and partial pore filling, suggesting initial additive accumulation at the fiber surface prior to matrix diffusion. Vapor sorption analysis demonstrated reduced moisture uptake in modified samples, and kinetic modeling revealed faster sorption equilibrium. Contact angle measurements reached up to ~109o, confirming significantly enhanced hydrophobicity. These findings demonstrate the potential of SCI for fabricating cellulose-based materials with improved moisture resistance, advancing their suitability for sustainable packaging applications.
