# Modified Kapok Fibers (_Ceiba pentandra_ ([PERSON]) for Oil Spill Remediation
## 2 Materials and Methods
### Characterization of Natural and Treated Materials  
Prior to and after the surface treatments, the materials were characterized via Fourier Transform Infrared spectroscopy (FTIR), using a FTIR IR PRESTIGE 21 spectrometer (Shimadzu, Kyoto, Japan), within the 4000 to 400 cm\({}^{-1}\) spectral range with a 4 cm\({}^{-1}\) resolution, operating with an Attenuated Total Reflectance (ATR) apparatus, and Scanning Electron Microscopy (SEM), using a SSX-550 Superscan microscope (Shimadzu, Kyoto, Japan) with pre-metalation in a Sanyu Electron metallizer (Quick Coater SC-701, Tokyo, Japan). The analysis was performed using augmentation, varying from 300- to 5000-fold, and a voltage of 10 kV. Twenty different regions from 10 samples were evaluated for each treatment using SEM, taking note of the main characteristics which were repeated in all of them. Lastly, the mean roughness of the surface (Ra) was determined using Atomic Force Microscopy (AFM) (Multiview 4000\({}^{\text{TM}}\), Nanonics, Jerusalem, Israel), coupled with an optical microscope (BXFM Olympus, Tokyo, Japan). The AFM system was acoustically isolated and stabilized to reduce the interference of external noise. The topography of the samples was recorded at a resolution of 256 \(\times\) 256 pixels on tapping mode, with a scanning range of 0.3 to 1.0 Hz and an area of 5 \(\times\) 5 \(\upmu\)m. The probe diameter was inferior to the 10 nm cantilever of 300 \(\upmu\)m, 30\({}^{\circ}\) inclination angle, resonance frequency of 34 kHz, and Cr coating. Fifty regions per experimental group were analyzed and the mean roughness (Ra) was calculated using WSxM 3.1 (Nanotec, Madrid, Spain) software. The mean roughness was determined as the absolute average of the irregularity's heights on the profile, according to Equation (2):  
\[R_{a}=\frac{1}{N}{\sum}_{i=1}^{N}|z_{i}-\overline{z}| \tag{2}\]  
where N is the number of datapoints in the sample; z\({}_{i}\) is the height of each datapoint; and \(\overline{z}\) is the average height of the datapoints in the sample. The statistical analysis was performed using GraphPad prism 8.0.2 software to assess the actual differences between the treatments based on roughness values. Non-parametric data were analyzed by one-way ANOVA followed by the multiple comparison [PERSON]'s test at a significance level of 95% (\(p=0.05\)). FTIR spectroscopy was applied to identify variations in the surface functional groups caused by the treatments, or even the degradation of moieties previously present in the fiber. SEM was employed to identify alterations in the fiber distribution, as well as the augmentation of the lumen diameter, and the external modification and presence of surface wax. AFM was used to discuss either the increment or reduction in roughness of the fibrous system, and to which point this effect might be beneficial to the sorption process.  
A study of the mechanical resistance of the treated fibers at the most extreme conditions (120 \({}^{\circ}\)C and 2.0 M for chemicals) was also applied in reference to natural fibers, aiming to evaluate possible changes in resistance that could impact on the performance of the materials as sorbents. A tensile test was used using two-point fixation in a Microten-sile OM100--Odeme and the maximum resistance force (kgf) was evaluated. The testwas performed in quintuplicate with standardized samples in terms of small bundles of approximately 0.01 g.