Mechanical reinforcement was also effective in the rubbery state of PLA and increased the tensile modulus of the rubbery plateau providing thereby thermal resistance to the polymer. Oxygen barrier properties did not change significantly upon the inclusion of CNW-ICN, even when the quantity of CNW-ICN was increased to 15 wt%. More interestingly, the water vapour permeability of the CNW-ICN nanocomposite was always lower than the one of ungrafted CNW composites, which led to the conclusion that the hydrophobic surface graft and improved compatibility could counteract the effect of inclusion of hydrophilic structures in the matrix on water vapour transport. In conclusion, the surface grafting of CNW with isocyanates might be an easy and versatile tool for designing fully organic bionanocomposites with tailored properties.