## 3 Results and Discussions  
The tensile test was conducted for all the samples; that is, ABS and 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, and 4 wt% MWCNT samples. Figure 3a presents images of the samples, showing fractures after the tensile tests. Additionally, the stress-strain curves are illustrated in Figure 3b. Generally, the tensile strength of the samples improved along with the addition of MWCNTs as filler (0.5 wt% to 2.0 wt%), compared to the pure ABS sample. Specifically, the 0.5 wt% samples showed a tensile strength value of 38.85 MPa, higher than the value of 31.43 MPa for the reference sample. This improvement revealed the reinforcement effect of MWCNTs, in terms of enhancing the mechanical properties of the ABS matrix, even with a small amount such as 0.5 wt%. The positive pattern was the same with the loading content increasing up to 2.0 wt%, for which the tensile strength was 41.81% and achieved a value of 44.57 MPa. However, there was no change in tensile strength as the MWCNT concentration reached 3.0 wt%, but was slightly reduced in the 4.0 wt% MWCNT sample, compared to the pure ABS condition. Thus, the strengthening effect of MWCNTs depends on the arrangement and distribution of the filler within the matrix. Interestingly, low content MWCNT loading delivered the best homogeneous and alignment mixing between the reinforcer and ABS substrate; therefore, all components could be adhesively bonded, giving an optimum recipe for the highest strength and stiffness properties. In addition, the MWCNT particles tended to locally agglomerate under higher content, resulting in their poor dispersion, non-uniform alignment, and a weak interaction between the MWCNTs and ABS matrix. The elongation investigations of samples are further included in Figure 3b. The percentage of tensile elongation at the breakpoint was more significant in cases of \(\geq\)1.5 wt% MWCNT samples, while the pieces with 0.5 wt% and 1 wt% exhibited a slightly higher extension, compared to pure ABS. This phenomenon was observed at the non-uniform plastic deformation region of the stress-strain curves (Figure 3b), illustrating the greater brittleness with a high concentration of MWCNTs (1.5, 2, 3 and 4 wt%) incorporated into  
Figure 2: Schematic representation for the fabrication of the ABS–MWCNT composite filaments. (**1**) Extruder machine; (**2**) cooling fan; (**3**) water cooling system; (**4**) motor of cooling box; (**5**) motor of filament extruder; (**6**) pulling system; (**7**) guiding system; (**8**) coiling system. the ABS. Notably, at 2.0 wt%, the sample elongation and tensile strength properties were inversely proportional. The DSC and MFI measurements were carried out to confirm the effect of MWCNTs on the thermal behavior of the as-synthesized nanocomposites. Figure 4 shows the thermogram profiles of the samples during the heating process, in which the temperature increased from 50 to 350 \({}^{\circ}\)C. The glass transition temperature (Tg) and melting point (Tm) for the different ABS-MWCNT composites were determined at around 90 \({}^{\circ}\)C and 240 \({}^{\circ}\)C, respectively. This observation indicated a minor effect of MWCNTs, as a filler, on the thermal properties of the ABS matrix. The peaks at about 230-240 \({}^{\circ}\)C in the DSC thermogram (Figure 3) correspond to the melting temperature T\({}_{\text{m}}\) of the composites, which was the same as that of pure ABS matrix, even with the presence of the MWCNT filler. Figure 5 presents the relationship between the MWCNT content and the melt flow index of the samples. The MFI value reached 6.3 g/10 min and 5.6 g/10 min in the blank ABS and 0.5 wt% MWCNT samples, respectively. These values were significantly reduced under higher loading of MWCNT contents, approaching 0.9 g/10 min for the 2.0 wt%  
Figure 4: DSC thermogram of ABS and ABS–MWCNT composites. Figure 3: Image of tensile test samples (**a**) and the tensile testing results (**b**). MWCNT sample. Meanwhile, the 3.0 wt% and 4.0 wt% MWCNT samples presented low MFI values.