Further information on the mechanical characterization of the neat epoxy resin can be found in the SI Ch. 2. As already observed in the nanoindentation tests, composites containing unmodified and non-crosslinked SPs show similar values of stiffness as the used epoxy resin with a flexural modulus (of 0.9 ± 0.5 GPa), and they fracture at relatively low stress levels of 10 ± 8 MPa (Fig. ). SEM micrographs of fracture surfaces (Fig. ) in fact reveal that the SPs-epoxy material fails at both, the NC-NC interfaces -as indicated by fractured SPsand at the SP-epoxy interface -as depicted by the spherical-shaped holes. This observation cronfirms that both, the NC-NC interface and the SP-epoxy interface lack strong interactions between them.