<p dir="ltr">This dissertation investigates novel approaches for modifying cellulose nanofibers (CNFs) to develop sustainable alternatives to petroleum-based plastics. As plastic production continues to rise dramatically – from 2 million tons in 1950 to a projected 1231 million tons by 2060 – the need for renewable, biodegradable alternatives has become increasingly urgent. This work presents three interconnected studies exploring different aspects of CNF modification and application.</p><p dir="ltr">The first study introduces an innovative method for developing superhydrophobic (SHP) coatings using CNFs lyophilized from a 10 wt% <i>tert</i>-butyl alcohol slurry. Through solvent-free mechanochemical modification, we successfully produced oleic acid-modified CNFs (OL-CNFs), which exhibited exceptional SHP properties, demonstrating high contact angles, low hysteresis, and remarkable durability. Suspensions of OL-CNF were utilized in various spray coating applications, including moisture barriers and atmospheric water harvesting systems.</p><p dir="ltr">The second study explores the trifluoroacetylation of CNFs using trifluoroacetic anhydride (TFAA) without additional base. By employing glucopyranosides as small molecule models to guide reaction optimization, we developed a method for controlled trifluoroacetylation while preserving CNF crystallinity. Notably, we introduce a novel approach for quantifying the degree of substitution using ¹⁹F NMR spectroscopy of saponified trifluoroacetylated CNFs (TFA-CNFs) in methanol-<i>d4</i>, offering improved accuracy over traditional methods.</p><p dir="ltr">The third study examines the potential of TFA-CNFs as reinforcing materials in biodegradable polymer composites, particularly with poly(butylene adipate-co-terephthalate) (PBAT). We investigate the dispersibility of TFA-CNFs in various organic solvents and explore methods for creating PBAT/TFA-CNF blends. The research reveals promising aspects of TFA-CNFs, including their compatibility with biodegradable polymers and rapid ester hydrolysis in soil, while also identifying key challenges and opportunities for future development.</p><p dir="ltr">Together, these studies advance our understanding of sustainable CNF modification strategies and their applications in developing eco-friendly materials. This work contributes to ongoing efforts to address environmental challenges posed by conventional plastics while maintaining high performance standards for material applications.</p>