Hitherto, two main operating approa

Hitherto, two main operating approaches have been proposed as reported in Fig. 12. In the “direct mixing” method, the ceramic powder is first mixed with the polymer in a ball mill or in a mortar, in dry or wet conditions. Ethanol is often used as wetting agent during milling [32,67, 109,110]. Once dried, the hybrid powder is further mixed with the solvent and cold-sintered, as shown in Fig. 12a. In the case of thermosetting polymers where the organic material could be found at the liquid state prior to be cured [65], Ndayishimiye et al. [65] also followed a direct mixing route. They first mixed the ZnO powder with a 2 M acetic acid solution in an agate mortar and then added the desired amount of the polymeric mixture, obtained by low viscosity polydimethylsiloxane (PDMS) plus a crosslinking agent. After few minutes of manual mixing, cold sintering was carried out [65]. Direct mixing is the most common route for the cold sintering of hybrid composites.