Twin-screw extrusion (TSE) is a recent strategy used to prepare nanocelluloses at high solid contents. However, various aspects of the mechanism of disintegration and the role of fiber pretreatment remain to be elucidated. Oxidized cellulose fibers with carboxyl contents between 300 and 700 µmol.g-1 were extruded in the presence of polyvinyl alcohol (PVA) at a 80/20 (w/w) ratio, to produce high-consistency nanocellulose gels at 15 wt% solid content, ready for use in multiple applications. The influence of the origin of the pulps and the oxidation treatment on the efficiency of fiber disintegration was evaluated by porosity measurement. The rheological properties of the nanocellulose-PVA gels and the mechanical properties and transparency of the resulting nanopapers were studied as well. Combining TSE and rotor-stator dispersion or short sonication homogenization contributed to enhancing the fibrillation during extrusion, providing a method to increase the fraction of nanocellulose in a much less energy-consuming manner.