# Modified Kapok Fibers (_Ceiba pentandra_ ([PERSON]) for Oil Spill Remediation
## 3 Results and Discussion
### Characterization of Natural and Treated Materials
#### 3.2.2 SEM  
The SEM analysis (Figure 5b) indicated that at 60 \({}^{\circ}\)C kapok fibers took a flatter form when compared to the in nature material (Figure 5a), which turns the geometry of the lumen elliptical, with a minor axis of 12.7 \(\upmu\)m. The same image shows, at a 5000-fold zoom, that surface roughness apparently does not suffer alterations compared to the untreated material, concluding that treating the material at 60 \({}^{\circ}\)C exclusively reduces the water and volatile compound content, corroborating the assessment discussed in the FTIR analysis. Figure 5c, related to the material treated at 90 \({}^{\circ}\)C, shows (5000\(\times\) zoom, right-hand side) a qualitative rise in surface rugosity. Previous work attributed the roughness to an elevated surface area and, consequently, to greater oil sorption; nevertheless, at 90 \({}^{\circ}\)C, a reduction in the sorption capacity during the tests involving thermal treatment was observed [22]. Hence, the root of the sorption drawback can be connected to the flattening of the tubular structure, which reduces the lumen entrance diameter (8.98 \(\upmu\)m) and hampers the inward oil flow to the interstice of the material during the established contact time. Another obstacle observed was that the partial closure (or even more flattening) of the fibers caused bents in several points, reducing the tubular length to be filled even further. Figure 5d shows the micrographs of samples treated at 120 \({}^{\circ}\)C, which, in the sorption test, demonstrated a rise in the sorptive potential; this effect can be justified by the new tenacity of the tubular structure. At this temperature, the fibers once again have taken the near-cylindrical tubular form, with lumen diameters ranging from 13 to 19 \(\upmu\)m, allowing more room for oil insertion. The previously seen bents are no longer present, and this treatment may indicate that the material suffers volumetric dilation with a plastic deformation, returning to the conventional morphology. The qualitative analysis of roughness, under a magnification of 5000-fold, shows a smoother surface, stressing the idea that internal wax layers are propelled to the top. Therefore, although the thermal treatments appear to be an economical idea, due to their low cost and the feasible industrial implementation of kapok fibers to the productive sector, they are not a viable option when one aims to increase the sorptive potential of the natural material, because, by enhancing structural deformations and reducing the non-polar surface content, they in fact diminish the sorption capacity of the fiber. After acid treatment, the micrographs show that many fibers, which previously presented narrower entrances, were, after the acid treatment, opened, with diameters around 26.2 and 15.3 \(\upmu\)m when treated with 0.1 and 2.0 mol/L HCl, respectively, as can be seen in Figure 6a,c, suggesting the removal of the waxy layer present at this region. The strongest acidic condition, 2.0 mol/L (Figure 6d), leads to an upsurge in surface roughness, with grooves oriented in the same direction of the fiber length, when compared to the least acidic medium, at 0.1 mol/L (Figure 6b). In the literature ([PERSON], [PERSON], and [PERSON], 2012), such changes in morphology are related to greater hydrophobicity and, therefore, lipophilicity, although herein it is demonstrated these are signs of degradation and exposure of the cellulosic material with a consequent reduction in diesel sorptive properties; therefore, this is the opposite of what was found in the work cited [22]. Higher rugosity, on the other hand, helps to explain why, although HCl at 2.0 mol/L leads to the loss of functional groups on the surface, the harsher condition yielded a better sorption capacity than the treatment with 0.1 mol/L. [PERSON] et al.