This study reports the synthesis of a stable and homogeneous nanocomposite of cellulose nanocrystals (CNCs) and vinyl acetate (VA) monomer via a semi-batch water-based emulsion polymerization technique, targeting a total solid content (TSC) of 50 wt.% to meet industrial requirements such as smaller storage volume, and easier transportation. The semi-batch approach enabled a consistent distribution of the reactants and improved scalability for industrial applications. CNCs were successfully incorporated into a polyvinyl acetate (PVAc) latex formulation at concentrations of up to 3.22 wt.% relative to VA monomer. Fourier-transform infrared spectroscopy indicated the consumption of hydroxyl groups on the CNC surfaces. The nanocomposites containing 1.93% CNC demonstrated the most promising performance, reducing the water sensitivity of pristine PVAc and lowering both the water vapor transmission rate (WVTR) and permeation. Nevertheless, the increased CNC content induced an uneven surface topography and a broader polymer particle size and distribution, as observed by polarized light and scanning electron microscopy. Mechanical testing revealed a general reduction in the tensile properties relative to neat PVAc, although the 1.93 wt. % CNC sample exhibited the least decline. The resulting nanocomposites exhibited an extended shelf life and colloidal stability, indicating their potential for industrial applications.