<p>Stable nanocomposite dispersions based on pol(butyl-polymethacrylate) and cationic cellulose nanofibrils (cat-CNFs) were successfully produced through an in-situ miniemulsion polymerization process, utilizing a low amount of cationic surfactant (0.75 wt% relative to the monomer). The study investigated the influence of cat-CNFs content on the colloidal stability and rheological properties of the latex dispersion. Results indicated that the particle size dependence on cat-CNFs content, confirming the critical role of cellulose nanofibrils (CNFs) in the stabilization process during miniemulsion polymerization. Field emission scanning electron microscopy (FE-SEM) revealed the binding of cat-CNFs to polymer particles. Rheological measurements indicate that all dispersions exhibit shear-thinning behavior. The presence of yield stress in dispersions containing more than 2 wt% cat-CNFs suggests the formation of elastic network structures, emphasizing the dominant solid-like characteristics of the dispersion. The thermomechanical, melt-state rheology, and optical properties of nanocomposite films produced by casting and water evaporation were analyzed. Dynamic mechanical analysis (DMA) indicates that the incorporation of cat-CNFs enhances the strength of the films in the rubbery domain up to 4 wt%. However, further increases in CNFs content result in a decline in modulus. Additionally, nanocomposite films produced via the in-situ method demonstrate notable optical properties, highlighting effective dispersion of CNFs. Cat-CNFs-based latexes yield nanocomposite films with excellent mechanical properties and often exhibit a high transparency, making them suitable for applications where aesthetics are important, such as surface coatings and films.</p> Graphical abstract <p></p>