## 3 Results and Discussions
### Thermal Properties Analysis of Untreated and Treated PLA/WSP Biocomposites  
Figure 8a shows the DSC curves of PLA/WSP biocomposites and Figure 8b gives their crystalline values. It can be seen that all of the PLA/WSP composites experienced two endothermic and one exothermic phase transformation. The first endothermic inflection (black arrows) corresponds to the glass transition temperature (Tg, \({}^{\circ}\)C), while the second one represents the melting temperature (Tm, \({}^{\circ}\)C). The exothermic peak refers to the cold crystallization temperature (Tcc, \({}^{\circ}\)C) of PLA chains. Although changes of these transition temperatures are small, the effects of the WSP and the treatment on the thermal property of PLA/WSP biocomposites are obvious. The area of fusion and the area of crystallization become almost equal to each other, which causes the crystallinity (Xc) of the PLA/WSP biocomposites to become smaller (see the Equation (1)). With the addition of WSP, the Tcc of the PLA/WSP biocomposite (sample 2, 115.2 \({}^{\circ}\)C) is higher than that of the pure PLA (sample 1, 113.1 \({}^{\circ}\)C). Whereas Tg, Xc, and Tm show opposite results with lower values of 59.6 \({}^{\circ}\)C, 1.46%, and 149 \({}^{\circ}\)C, when compared to pure PLA (61.9 \({}^{\circ}\)C, 1.8%, and 155.4 \({}^{\circ}\)C). This result indicated that the walnut shell did not effectively play the role of nucleating agent and it decelerated the crystallisation process of PLA, thus slowing down its crystal growth rate and decreasing  
Figure 7: The relationship between Melt Flow Index (MFI) values and: (**a**), screen size and (**b**), weight ratio of KH550. the Tcc. The WSP has a high amount of ash, oil, wax, and other impurities [43]. Under this situation, the molecular chain of WSP was loose-packing and had more mobility. The loose-packing WSP resulted in loose-packing composites when compounded into the PLA matrix. These impurities led the WSP particles to partially aggregate and hamper the interaction between cellulosic hydroxyl groups of the WSP and the PLA matrix, leading to the poor interfacial compatibility. Meanwhile, WSP particles with lightweight molecules might lubricate the PLA matrix [44], which enhances the mobility of PLA molecular chains and increasing the free volume of molecular chains, which contributed to the lower Tg, Xc and Tm. The incorporation of the alkali and the silane increased the Tg and Tm, but decreased the Tcc of PLA/WSP biocomposites. With the increase of the KH550 concentration, the Tcc of PLA/WSP biocomposite showed a downward trend and slowly dropped to 113.3 \({}^{\circ}\)C (sample 6); while its Tg and Tm climbed steadily and reached the high points of 61.2 \({}^{\circ}\)C and 154.2 \({}^{\circ}\)C (sample 5), they then kept the level, regardless of the increase of the silane content. Firstly, alkali effectively removed the hemicelluloses and impurities from the WSP surface (Figure 6), which resulted in a better packing of cellulosic chains in the WSP. Secondly, the chemical bond -Si-C- between the WSP and silane acted as a bridge between the PLA matrix and the WSP fillers [24], resulting in a better surface compatibility. The deposition of auto polymerized siloxane on the micro pores and surface of WSP further functioned as the a mechanical interlock and enhanced the surface compatibility [45]. The chemical reaction and physical deposition both densified the molecules of PLA and limited the molecular mobility, speeding up the crystal growth rate, and accelerating the crystallisation process of PLA. This implied a lower crystal temperature and higher Tg and Tm, indicating that the NaOH/KH550 apparently improved the interfacial compatibility between PLA and WSP. The Xc of PLA/WSP composites performed in a little complex but more dramatic way: it rocketed sharply to 2.84% at 4 wt.% silane (sample 4), then dived to 1.55% abruptly at 6 wt.% silane (sample 5), and finally decreased gently to 1.25% at 8 wt.% silane (sample 6).