# Modified Kapok Fibers (_Ceiba pentandra_ ([PERSON]) for Oil Spill Remediation
## 3 Results and Discussion  
### Sorption Assay  
After the fibers were submitted to treatments at six different temperatures for 8 h, the materials were compared through total sorption assays, according to the average values and deviations shown in Figure 3a. The sorption value obtained by [PERSON] et al. (2020) for natural kapok fibers was used as a reference, since the materials tested were collected from the same trees as the ones used in the present work. In that occasion, the authors have found a mean sorption capacity of 58.5 g/g of diesel oil [21]. It is worth noting that, when they were treated at 60 \({}^{\circ}\)C, the kapok fibers showed a sorption value of 57.8 g/g, which is almost the same as the reference number (in natura). This result indicates that at this temperature, the material solely went through the drying process, losing only moisture, whereas it did not present any appreciable difference from the crude material. When the temperature rises to 70 \({}^{\circ}\)C, a reduction in total sorption was observed, with a loss of 11.3% compared to the reference, going to 51.86 g/g. Observing this reduction, it may be inferred that at this temperature, the volatilization of the paraffins and other surface compounds start to take place, which lessens the lipophilicity. This pattern of diminishing sorption was clearly accentuated when the temperature increased to 80 \({}^{\circ}\)C and 90 \({}^{\circ}\)C, with reductions in sorption capacities to 48.85 and 47.55 g/g. Given this behavior, the hypothesis that a heat-promoted volatilization of the non-polar surface compounds (hydrocarbons, esters and fatty acids) is detrimental to the fiber inherent lipophilicity may be endorsed. When the fibers were treated at even higher temperatures, on the other hand, a slight increase compared to the sample submitted to 90 \({}^{\circ}\)C in sorption was observed; after the 100 \({}^{\circ}\)C treatment, the sorption went to 47.92 g/g and at 120 \({}^{\circ}\)C, it reached 50.29 g/g. These data suggest that, although there was a loss of functionalization, other interactive mechanisms may have taken place and contributed to boosting the sorption, for instance, the presence of a higher surface roughness, which increases the contact surface of the sorbent, or an increment in the access the oil has to the material lumen. The phenomena described are corroborated by the analyses of the samples treated at 60, 90, and 120 \({}^{\circ}\)C via the FTIR and SEM characterization, as shown in Figures 4a and 5, respectively. Figure 3: (**a**) Sorptive capacities of kapok fiber submitted to thermal treatment, (**b**) acid treatment, and (**c**) alkali treatment. The average values and deviations obtained in the sorption tests of the kapok fibers submitted to acid media are shown in Figure 3b, which shows that, when treated with a solution of HCl at 0.01 mol/L, kapok fibers presented an oil sorption of 50.96 g/g, which already represents a loss of capacity compared to the natural material. When the acid  
Figure 4: (**a**) FTIR spectra of the kapok samples treated at different temperatures. (**b**) Acid activation and (**c**) alkali activation. Figure 5: Fibers images without treatment (**a**) and treated at (**b**) 60, (**c**) 90, and (**d**) 120 \({}^{\circ}\)C.  
concentration is increased by 10-fold, 0.1 mol/L HCl, there is a much more prominent reduction in oil retention, with a sorption of merely 40.43 g/g, indicating that at this concentration, HCl drastically degrades the fiber, likely accompanied by the removal of the surface paraffin material. When the concentration rose to 1.0 mol/L, an unexpected behavior took place: the sorbent once again enhanced its sorption potential, reaching 58.57 g/g, a value similar to the in nature fibers and 30% higher than the ones treated with 0.1 mol/L of acid. Based on this observation, it is expected that the contact surface has increased due to the changes in morphology, and new fissures have been created, exposing the tubular structure to a larger volume of diesel.