Abstract This study focuses on the influence of mixing energy on the solid-state behavior and clay fraction threshold of nanocomposites. Thus, three polyamide12/clay (PA12/C30B ® ) nanocomposites exhibiting different nanostructures were prepared from three sets of processing conditions. Then, thermal and dynamical viscoelastic properties of these nanocomposites were analyzed, in relationship with the material nanostructure and processing conditions. For the first time, the solid-state properties of the nanocomposites revealed the existence of a critical specific mixing mechanical energy. Below this critical value, an increase of mechanical energy refines the structure, improving some end-use properties of the nanocomposite. Above this value, a high mixing energy supply is necessary in order to significantly modify the structure. They also highlighted that the clay fraction threshold, which is commonly attributed to the formation of a three-dimensional percolated network, decreases with increasing specific mixing energy, less significantly when this energy is superior to its critical value.