## 3 Results and Discussions
### Thermal Properties Analysis of Untreated and Treated PLA/WSP Biocomposites
On the one hand, after NaSi treatment, the surface compatibility was enhanced, resulting in an increasing of crystalline. On the other hand, some oligomer or biopolymer produced by the auto polymerization of siloxane served as a lubricant of PLA, leading to the improvement of PLA molecular mobility and the decline of crystalline. The thermal stability of the PLA/WSP biocomposites was investigated while using TG analysis and it is shown in Figure 9. It can be seen that all types of composites embodied a similar trend (single step degradation) during the whole temperature range. PLA possessed the highest onset temperature of degradation (T1) of 291.04 \({}^{\circ}\)C and the temperature at maximum degradation rate (T2) of 353.5 \({}^{\circ}\)C.  
Figure 8: (a) The Differential Scanning Calorimeter (DSC) curves; 8 (b) the crystalline of PLA/WSP biocomposites: 1 PLA; 2 PLA/untreated WSP;3 PLA/2%NaSi treated WSP; 4 PLA/4%NaSi treated WSP; 5 PLA/6%NaSi treated WSP; and, 6 PLA/8%NaSi treated WSP. The incorporation of the WSP into the PLA matrix dramatically reduced the T1 and T2 to 239.87 \({}^{\circ}\)C and 304.9 \({}^{\circ}\)C. Biocomposites with NaOH/KH550 treated WSP behaved better with a higher thermal stability with T1 of 264.87-276.37 \({}^{\circ}\)C and T2 of 306.8-327.3 \({}^{\circ}\)C as compared to the PLA biocomposites with the untreated WSP. Among those, T1 and T2 of biocomposites with 8 wt.% silane treated WSP reached their highest value. The WSP consisted of 13.21% of cellulose, 55.24% of hemicellulose, and 26.79% of lignin and 5% of other impurities [46]. During the thermal degradation, the temperature of mass loss of hemicelluloses, cellulose, and lignin was at a range of 220-315, 315-400, and 160-900 \({}^{\circ}\)C, respectively [46]. Therefore, the thermal stability of hemicelluloses and lignin containing WSP/PLA composites became lower than that of neat PLA. The NaOH removed a certain amount of lower thermally-stable substances, such as hemicellulose, oil, and waxes from the surface of WSP (Figure 6), leading to the increase of the degradation temperature. However, the lignin still consisted more than 50% of the WSP, so that the degradation temperature of the PLA composites with the treated WSP was lower than that of PLA. Chemical reaction between the silane and the WSP, and the physical deposition of the silane on the WSP limited the molecular mobility and enhanced the molecular stability of PLA, leading to a more stable thermal property. However, when the content of KH550 continuously increased, the number of free molecular chains of siloxane was increasing, as a result of the drop in thermal stability. After the maximum degradation, the pure PLA and the PLA/WSP biocomposites had no almost residue. Biocomposites with the treated WSP possessed 22.3-28.1% of the residual mass. The 2 wt.% silane treated WSP composites had the highest residual mass. The main components of the WSP were cellulose and lignin after the alkali/silane treatment. The treatment of WSP with the silane slowed down the degradation of lignin, which continued to degrade under higher temperatures. The thermal properties indicated that silane treatment can enhance the thermal properties of PLA/WSP biocomposites. The similar effect of silane on natural fibers happened on polyester/coconut fiber composites (0.5 wt.% silane) [24], PLA/coir fiber composites (0.5-1 wt.% silane) [47], and PLA/corn composites (2-3 wt.% silane) [48].