## 3 Results and Discussion  
Effect of Treatment Processes on the Physical and Microfabric Structure of Nonwoven Coir Geotextiles  
Before treatment, the nonwoven coir geotextiles had a dull brown color with three (3) mm thickness. Physical changes, such as the color and thickness of the nonwoven coir geotextiles, were observed after the mercerization and bleaching treatment processes. Figure 7 shows that the mercerized nonwoven coir geotextile has a more vibrant yet lighter color than that of the untreated nonwoven coir geotextile. On the other hand, the bleached nonwoven coir geotextile presents a very light color compared to both the untreated and  
Figure 6: Summary of procedures. the mercerized samples. The hydrogen peroxide in the solution caused the discoloration of the bleached geotextile [32]. When dissociated within an alkaline medium, hydrogen peroxide produces perhydroxyl ions, which make the color of the fibers lighter [28]. Figure 8 shows a comparison of the thickness of the coir geotextiles under different treatments. After treatment, the thickness of the coir geotextiles was reduced, with the bleached geotextile being the thinnest. Measurement of thickness using a Vernier caliper showed that the thickness of the untreated, mercerized, and bleached geotextiles was 3 mm, 2 mm, and 1.5 mm, respectively. One of the main causes of the reduction in thickness of the treated geotextiles was the detachment of some fibers during the treatment processes. The treatment processes caused the thinning of the samples owing to the reduction in the hemicellulose and lignin contents of the fibers. During the bleaching process, the hydrogen peroxide removed the lignin and hemicellulose surface impurities of the fibers. Similarly, mercerization makes the surface of fibers rougher and influences the extraction of lignin and hemicellulose compounds from the fiber. The surface morphology of the nonwoven coir geotextiles was investigated using a scanning electron microscope (SEM). Figure 9 shows the SEM micrographs of untreated nonwoven coir geotextiles with magnifications of 500\(\times\) and 1500\(\times\). These micrographs show that impurities are prevalent across the surfaces of the fiber. Extensive cracking along the surface can also be detected in these micrographs at higher magnification (Figure 9b). [PERSON] et al. [33] reported similar properties of untreated coir fiber, with the layer of the coir fiber covered with surface impurities. Figure 8: Nonwoven coir geotextiles showing the thickness: (**a**) untreated; (**b**) mercerized; (**c**) bleached. Figure 7: Nonwoven coir geotextiles: (**a**) untreated; (**b**) after mercerization treatment; (**c**) after bleaching treatment. Micrographs of the mercerized nonwoven coir geotextile are shown in Figure 10. After the mercerization treatment, the micrographs revealed small cracks on the surface of the coir fiber and the removal of surface contaminants; however, minimal impurities remained on the surface of the coir fiber. Alkali treatment or mercerization treatment removes the binding materials from the fiber bundles. The alkaline solution (NaOH) dissolved the surface lignin, resulting in a twofold impact [34]. In a study by [PERSON] et al. [35], residues of the impurities in the form of globular protrusions, which are fatty deposits known as tyloses, remained on the fiber surface after the removal of the surface contaminants through alkali treatment. Figure 10: Micrographs of mercerized nonwoven coir geotextiles. (**a**) at 500\(\times\) magnification. (**b**) at 1500\(\times\) magnification. Figure 9: Micrographs of untreated nonwoven coir geotextiles. (**a**) at 500\(\times\) magnification. (**b**) at 1500\(\times\) magnification. Micrographs of the bleached-treated nonwoven coir geotextile are shown in Figure 11. Similar to the mercerized specimen, the impurities on the surface of the coir fiber were reduced. However, the bleached sample shows a smoother and clean fiber surface compared to the mercerized and untreated specimens.