## 3 Results and Discussions
### Mechanical Properties Analysis of Specimens Fabricated with FDM  
4.1 The Effect of Silane Treatment on the Mechanical Properties of the FDM PLA/WSP Biocomposite Samples  
Table 1 shows the average mechanical properties of FDM PLA, untreated and treated PLA/WSP biocomposite samples. All of the compression samples had a high plasticity and could not be crushed, even under a pressure of 50 KN. Accordingly, the compressive strength was recorded with a compression  
Figure 9: Thermo Gravimetric (TG) curves of PLA/WSP biocomposites. ratio of 67% for safety. From Table 1, it can be seen that the pure PLA almost possessed the highest strength and modulus at all items, except the tensile modulus. There was a decline in the mechanical properties for PLA/untreated WSP as compared to the pure PLA (sample 2). Its compressive strength and modulus dropped drastically by 59.8%. Its flexural strength considerably decreases by 36.4%. Whereas its tensile strength and flexural modulus performed more moderate with a drop from 57.3 MPa and 35.8 MPa to 48.3 MPa and the 33.5 MPa, respectively. However, the tensile modulus had a dramatic climb from 1908.7 to 3050.4 MPa, indicating that the capacity of anti-tensile deformation was enhanced. There are three factors that might affect the mechanical properties. Firstly, the WSP has a higher amount of lignin, lower amount of cellulose and hemicellulose, and a small amount of ash, oil, and other impurities. The higher amount of lignin aggravated the brittleness of composites [49], and the ash had a negative effect on the bonding [43], leading to a lower strength. Secondly, the rigid WSP particles boosted the stiffness of the PLA/WSP composite, and a small number of Nano-scale WSP particles acted as a nucleating agent of PLA [24], both resulting in the improvement of the mechanical strength and modulus. In this research, 5 wt.% content of the untreated WSP particles might be too much for the polymer matrix of PLA, because the effect of hemicelluloses and other impurities on mechanical properties was stronger than its function as a nucleating agent. Thirdly, FDM is a kind of layer-by-layer manufacturing, so the impact of the integration degree between layers on the mechanical properties cannot be ignored [35]. The manufacturing direction was identical with the compressive direction, and perpendicular to the tensile axis and the flexural center. Therefore, the bonding degree between layers played a more significant role in compressive properties than in flexural properties. It resulted in a dramatic decline of compressive property and a moderate drop of flexural property. For improving the compatibility of PLA and WSP, the WSP was modified by the NaOH and the silane (2, 4, 6, and 8 wt.% concentration). As shown in Table 1, the tensile and flexural strength of PLA/NaSi treated WSP showed a slightly rising trend with an increment of 4.2 MPa and 6.9 MPa for each, when the concentration of KH550 was increased, as compared to PLA/untreated WSP. The PLA/8%NaSi treated WSP (sample 6) gets maximum values of tensile strength (52.5 MPa) and flexural strength (51.7 MPa). However the modulus of PLA/NaSi treated WSP experienced a thoroughly negative performance and decreased slowly to 2570.5 MPa of tensile modulus (sample 6) and 28.8 MPa of flexural modulus (sample 5), respectively. The compressive strength PLA/NaSi treated WSP grew slightly to 219.9 MPa at 2 wt.% silane following a rapid rise to 252.5 MPa at 4 wt.%, and then continuously increased to the highest value of 276.6 MPa at 8 wt.% silane. The compressive modulus showed a steadily upward tendency when the silane concentration was increased, and gradually leveled off to a peak of 34.6 MPa at 8 wt.% silane. As previously analyzed, the alkali removed the hemicelluloses and impurities from the WSP, so that the molecular chains of the WSP rearranged and repacked themselves. The deposition of auto polymerized siloxane on the micro pores and the surface of WSP, which enhanced the interfacial compatibility between the PLA and the WSP.