## 3 Results and Discussion
For PLA composites containing kenaf acetylated for 2 h or longer, the fractured surfaces were smoother, with fewer voids (Figure 5g,i). Also, the fibers in these composites appeared to be more evenly dispersed in the PLA matrix (depicted in Figure 5h,j). These observations collectively signify improved compatibility and adhesion, as cell wall hydroxyls were substituted with lower polar acetyl groups [29], leading to improved mechanical strength of the composites. Figure 5: Field Emission Scanning Electron Microscopy (FESEM) micrographs of flexural fractured surfaces of flexural specimens of untreated and acetylated kenaf–polymactic acid (PLA) composites. Figure 6 shows results of TGA analysis for observing thermal stability of kenaf before and after acetylation. From the residual mass curves, thermal degradation of these fibers could be divided into three stages: 50-110, 250-330, and 340-400 \({}^{\circ}\)C. The first stage of mass loss (below 110 \({}^{\circ}\)C) was due to moisture evaporation [11]. At this stage, the mass loss was higher for untreated fibers, followed by fibers that were acetylated for not longer than one hour. Little mass loss was observed for fibers that were acetylated longer (i.e., 2 and 3 h). This observation is related to moisture effects, owing to the considerable amounts of available hydroxyls (at zero or low acetylation levels), and is consistent with the trend of fiber acetyl content [30] depicted in Figure 6. At the second stage of mass loss (250-330 \({}^{\circ}\)C), the inferred degradation was observed to be higher in untreated kenaf when compared to acetylated kenaf. This degradation is mostly related to the decomposition of hemicelluloses and lignin. At the third and most prominent stage of mass loss (at 340-400 \({}^{\circ}\)C), untreated fibers were the most severely affected. This mass loss is mostly due to cellulose degradation and also the continued decomposition of lignin [24]. The consistently lower mass loss for acetylated fibers compared to untreated fibers is an indication of improved thermal stability imparted by acetylation. The increased thermal stability could also be due to the pre-removal of impurities (during acetylation, as discussed earlier), which are presumably smaller and thermally unstable. Table 1 shows the main pyrolysis temperatures. The temperature at the initial 5% pyrolysis point varies by up to 50 \({}^{\circ}\)C depending on the acetylation treatment. This can be interpreted as a result of surface foreign matter decomposition and the removal of moisture mentioned above. The 10% decomposition point also shows a large difference. The stability on the surface increases. However, the 50% decomposition temperature is not significantly different. If the temperature exceeds a certain level, then the main cellulose chain is decomposed. Figure 7 presents the TGA results of PLA composites containing either untreated or acetylated kenaf. The thermal stability of composites was altered depending on the degree of fiber acetylation, and this observation is in accordance with the findings of [PERSON] et al. [29]. The untreated kenaf-PLA composite degraded earlier than composites of acetylated kenaf. As the degree of kenaf acetylation increased, the thermal stability of composites was further enhanced. There are two possible reasons for the increased thermal stability. The first reason is the favorable improvement of interfacial adhesion \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Weight Loss Point** & \(\mathbf{T_{DS\%}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{D10\%}}\) (\({}^{\circ}\)C) & \(\mathbf{T_{DS\%}}\) (\({}^{\circ}\)C) \\ \hline
**Time of Acetylation (h)** & & & \\ \hline
0 & 270.2 & 297.4 & 373.3 \\
0.5 & 300.51 & 325.4 & 375.8 \\
1 & 315.11 & 334.7 & 378.5 \\
2 & 322.43 & 338.9 & 379.7 \\
3 & 323.41 & 339.5 & 379 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Temperature by main pyrol. Figure 6: Thermogravimetric curves of kenaf fibers at different acetylation reaction times.