# A Green Approach for Preparing High-Loaded Sepiolite/Polymer Biocomposites
## 3 Results and Discussion
### Thermal, Spectroscopic and Morphological Characterization of Sep/NR Biocomposites
A deeper investigation of both filler/polymer interactions and morphological features of Sep/NR biocomposites was achieved by exploiting a multi-technique SEM, TEM and SAXS approach. SEM micrographs (Figure S5 of SI) revealed that SepX/NR biocomposites are homogeneous materials, without any phase separation. In particular, a uniform distribution of Sep fibers through the whole rubber matrix and the absence of fiber agglomerates were assessed by Si elemental mapping. The possible interactions occurring between SepX fibers and NRL particles were inspected by following the flocculation process with TEM. TEM images of SepX/NR colloidal systems collected during the initial steps of mixing, i.e., before the flocculation starting, are reported in Figure 4.  
Figure 4: Transmission electron microscopy (TEM) images at different magnifications of dilute dispersions of SepX in NRL allowed to dry on a carbon-coated TEM grid: (**a,b**) SepS9/NR and (**c,d**) SepB5/NR colloidal systems. In the case of SepS9/NR sample, filler aggregates lie among or in the periphery of the rubber micelles, indicating poor surface-mediated interactions between SepS9 and NRL (Figure 4a,b). Instead SepB5/NR appears constituted by homo-aggregated spherical NRL micelles [41] embedding some Sep fibers, some of which organized in bundles (Figure 4c,d). This suggests the existence of weak attractive interactions between SepB5 and NRL (short-distance forces), which may favour the adsorption of polymer chains onto Sep surfaces, thus supporting FTIR findings. TEM images collected on SepX/NR biocomposites, i.e., after the flocculation process, are shown in Figure 5.  
For both SepX/NR biocomposites, the presence of an extended filler network structures, distributed through the whole material volume is observable, suggesting that percolation occurs (Figure 5a,b). The network appears constituted by large domains composed of self-assembled and partially oriented Sep fibers. This alignment can be attributed to large interface interaction of the anisotropic Sep fibers, forming differently oriented domains of rods preferentially aligned along the main axis. In particular, SepS9/NR display poorly compact filler aggregates with cross-section of \(\sim\)100 nm, in which Sep fibers appear separated by small NR regions (Figure 5a'). Conversely, SepB5 domains are larger (cross-section \(\sim\)400 nm) and constituted by highly interconnected Sep  
Figure 5: TEM images at different magnifications of (**a**,**a**^) SepS9/NR and (**b**,**b**^) SepB5/NR biocomposites. particles bridged by thin rubber layers (Figure 5b'). These results seem to confirm the occurrence of weak attractive interactions between SepB5 and NRL, which appear instead less pronounced in the SepS9/NR system. In summary, TEM investigation reveals that the high SepX content guarantees for both SepX/NR biocomposites the formation of a percolative network, as demonstrated by the absence of wide regions constituted by pure NR. Hence, improved mechanical properties are expected (vide infra). The SepX/NR biocomposites morphology was studied also by SAXS, in order to investigate more in depth the nanostructure of NR, SepX, and their composite assembly. Scattering curves obtained are shown in Figure 6. In the SAXS pattern of NR (Figure 6a) at high scattering vectors (q \(>\) 10\({}^{-1}\) A\({}^{-1}\)) the typical reflections of the orthorhombic unit cell of NR are observed [42]. As already proposed by [PERSON] and coworkers [43], the remaining part of the curve could be described combining the scattering from aggregates [44] with the [PERSON] approximation [45]. The shoulder centered at q values around 10\({}^{-2}\) A\({}^{-1}\) indicates the presence of scattering bodies of 19 nm, most probably ascribable to the crystalline domains in the rubber, whereas at lower q the power law decay of \(-\)3.8 refers to interparticle scattering originated by micrometer sized particles with rough surface. The SAXS curves of the SepX fillers look both very similar (dark gray lines in Figure 6a,b).