# A Green Approach for Preparing High-Loaded Sepiolite/Polymer Biocomposites
## 3 Results and Discussion
### Thermal, Spectroscopic and Morphological Characterization of Sep/NR Biocomposites  
The loading of SepX fibers in the biocomposites was evaluated by TGA analysis (Figure S5, SI). In detail, SepX/NR biocomposites display a slight mass loss (\(\sim\)1%) at 100 \({}^{\circ}\)C attributed to physisorbed water, while a major weight loss is detectable from 300 to 500 \({}^{\circ}\)C, due to thermal degradation of the rubber components and to the Sep organo-modifiers, when present [33]. The total amount of Sep fibers in the biocomposites thus matches with the remaining weight percentages at the end of the thermal evolution and corresponds to 45 and 50 wt. % for SepS9 and SepB5, respectively. The XRD patterns of SepX/NR (Figure S6 of SI) clearly show the diffraction peaks ascribable to the SepX fibers, confirming that the flocculation process do not alter the Sep crystalline structure [34]. Figure 2: Trend of \(\zeta\)-potential vs. pH for NRL–medium ammonia (MA) (\(\bullet\), - black line), SepS9 (\(\blacksquare\), - orange line) and SepB5 (\(\blacktriangle\), - blue line). To investigate the nature of the potential interactions between Sep surfaces and NR matrix, ATR-FTIR spectra of SepX/NR biocomposites were collected and compared to those of NR, SepS9 and SepB5 (Figure 3). The NR spectrum (black line in Figure 3) shows, as expected, the bands in the 3100-2850 cm\({}^{-1}\) region due to the stretching of C-H bonds (both unsatured and satured) and those in the 1600-1350 cm\({}^{-1}\) range, attributed to the stretching of C-C bonds and bending of C-H bonds [32]. At 840 cm\({}^{-1}\), the C-H out-of-plane bending typical of the poly(1,4-cis-isoprene) chains is also detectable. Other bands can be attributed to some non-isoprene compounds, such as such as proteins and phospholipids [35], typically contained in the NR:NH groups of amines (3283 cm\({}^{-1}\)), carbonyl groups of esters (1748-1738 cm\({}^{-1}\)), carboxylic acids (1711 cm\({}^{-1}\)), and amides (1630 and 1541 cm\({}^{-1}\)). SepS9 spectrum (gray line in Figure 3a) evidences the adsorption bands at: (i) 3700-3555 cm\({}^{-1}\), attributable to the stretching vibrations of OH groups and water molecules bounded to octahedral  
Figure 3: Fourier transform infrared spectroscopy (FTIR) spectra of (**a**) NR (black line), SepS9 (gray line), SepS9/NR biocomposite (orange line), (**b**) NR (black line), SepB5 (gray line), SepB5/NR biocomposite (blue line). The light green and violet shadow areas highlight the most significant spectral regions. magnesium centers, and (ii) 692 cm\({}^{-1}\) the Mg-O-H bending vibration [36]. The band at 3754  cm\({}^{-1}\) can be assigned to the silanol hydroxyl groups, while the typical Si-O bands of Sep tetrahedral sheets are present at 1057 and 1018 cm\({}^{-1}\). SepB5 spectrum (gray line in Figure 3b) presents, in addition to the typical SepS9 absorption bands [37], the vibrations of benzyl alkyl chains at 2923, 2849, 1661 cm\({}^{-1}\), due to organic modifier. Compared to SepS9 and SepB5 spectra, the stretching vibration of Si-O-Si and hydroxyl of Sep in both SepX/NR biocomposites resulted slightly shifted to higher wavenumbers (selected green region in Figure 3a,b), suggesting a weak interfacial interaction occurring between Sep and NR [38]. This effect may be connected to the physical adsorption of polymer polar or non-polar components present in NR onto Sep surface [39]. Moreover, the intensity of amide stretching bands at 1541 cm\({}^{-1}\) were found to decrease in SepX/NR biocomposites (selected violet region in Figure 3a,b), envisaging the occurrence of intermolecular hydrogen bonds between protein molecules in NR and silanol groups of SepX [40]. These findings seem to support an interaction between non-rubber components in NR, such as lipids and proteins, and silanol functional groups on Sep surface, [40] able to promote the dispersion of the clays in the polymer matrix.