## 3 Results and Discussions  
### Effect of the Alkaline Treatment on the Fibers' Morphology and Microstructure  
From the diameter- and length-distribution examination, it was observed that the natural fiber diameter was uniform throughout the length, hence the average was considered (Figure 3a). The average values of the diameter distribution indicated that most fibers existed around 150 \(\upmu\)m \(\pm\) 5, whereas the length distribution showed that the average values of fiber length were 15 cm \(\pm\) 5. The natural fibers exhibited a multi-cellular structure with a very porous surface. Additionally, to the surface pores, the fibers contained some impurities, as seen in Figure 3b. By performing the alkaline treatment on the fibers, an increase in the fiber's volume and swelling was observed. The swelling resulted in a more uniform diameter along the length and a smoother fiber surface. This can be explained by the removal of cellulosic material contained in the BNF by the sodium hydroxide (NaOH) solution [53]. The treatment of the BNF by the sodium hydroxide (NaOH) solution removes hemicellulose and lignin primarily compared to other components like waves and pectins.  
Figure 3: \(Cont.\)Visual examination (in Figure 4) of the BNF at various treatment times reveals that within the first four hours of treatment, the color of the NaOH solution changes from light brown to very dark brown. The NaOH solution's dark color was noted for the treatment at 4, 24, and 48 h. After 72 h, the solution's colour usually becomes lighter again. This indicates that lignin and other impurities have been removed from the natural fiber. Lignin, a complex polymer that binds cellulose fibers together, needs to be eliminated to increase the fiber's strength [54], absorbency [55], and dyeability [56]. This visual observation serves as a preliminary sign of the alkaline treatment process's efficacy. As lignin and other impurities break down during alkaline treatment, the color lightens, making the fiber more resistant to additional manipulation. Nonetheless, the NaOH's color shift from very dark brown to light brown after 72 h would suggest that no further impurities are being removed [9]. The degree of polymerization (DP) of cellulose, or the average number of glucose units in a cellulose chain, decreases because of the alkaline treatment. Impurities can hydrolyze, cross-link, or crystallize the cellulose fibres, resulting in a decrease, increase, or change in DP. Examples of these impurities are hemicellulose, lignin, phenolic compounds, water, and acid. Thus, the fiber's absorbency and wettability are enhanced by the DP decrease, which creates a more porous and open fiber structure as seen in Figure 3. [PERSON] reported that alkali infiltrates the amorphous region, causing the cellulose fibres to swell. Subsequently, the alkali diffuses laterally down the polymer chain, forming an alkali complex. After that, the alkali reaches the crystalline area and forms Na-Cell II, an antiparallel crystalline soda complex [57]. The following equation can describe the chemical reaction occurring:  
Figure 3: (a) Chemically treated Borassus fibers (CBNF) and (b) untreated Borassus fibers (BNF).