## 3 Results and Discussion
### XRD Analysis  
Pristine graphene exhibits a basal reflection (002) sharp peak at 20 = 27.0\({}^{\circ}\) corresponding to a d spacing of 3.370 A in graphite layer structure (Figure 5). The graphene showed a more intensive peak than the carbon nanotubes pattern at 20 = 26.26\({}^{\circ}\), indicating a more crystalline structure for GNP. Considering the spectral profile of MWCNT, the weak broad XRD peak at 20 = 43.54\({}^{\circ}\) is assigned to graphitic (100) crystalline lattice. A broad amorphous peak was observed as result of neat PLA XRD analysis at around 20.0\({}^{\circ}\) combined with a weak sharp peak appearing at 17.2\({}^{\circ}\) (Figure 6). This is an indication of scattering in the polymer matrix and confirms that the neat PLA has a partially pseudo orthorhombic \(\alpha\) crystalline structure with a left handed 10/3 helices chain conformation but predominantly it is a biodegradable polymer possessing an amorphous microstructure. The analysis of the patterns in Figure 6 is evidence that the intensity of the GNPs (002) peak increases with increasing GNPs loading in PLA, as expected. Regarding the XRD analysis of the 9 wt% GNP/PLA composite, a distinct diffraction is observed at 27.2\({}^{\circ}\), relating to an interlayer spacing of 0.33 nm, based on the Bragg's law, which is associated with the graphitic (002) plane. On the other hand, the position change indicates that the spacing between graphene nanoplatelets in the composites shortened (from an interlayer spacing of 0.34 nm of 6 wt% GNP/PLA to 0.33 nm for 9 wt% GNP/PLA based on Bragg's law). The addition of SNPs affects the semi-crystalline structure of the polymer: the crystalline PLA peak at 20-17.2\({}^{\circ}\) in PLA/GNP nanocomposites is absent. Figure 5: XRD patterns of pure graphene and carbon nanotubes. The high intensity recorded at 9 wt% GNP loading could be attributed to a relatively intense number of graphene layers organized in stacks. The X-ray diffraction of 6 wt% GNP/PLA nanocomposites revealed a less intensive graphite (002) pattern and weak feature of the broad PLA peak. The disappearance of PLA crystallinity with growing graphene content can be explained as a result of interfacial effects influencing the PLA semi-crystalline structural order. The XRD technique could provide information about the stacking thickness of the GNP crystallites. The average pristine nanoplatelet thickness as well as the size of the incorporated graphene was calculated by using the Scherrer equation. It was found that pure GNP has a thickness of about \(\sim\)80 nm. This dimension remains roughly the same in the composite having 9 wt% GNP (-82 nm). The influence of the carbon nanotubes loading on the polymer crystallinity is prominent in Figure 7. The improvement of the sharp PLA peak at about 17.0\({}^{\circ}\) is more significant for the compound  
Figure 6: X–ray diffraction of nanocomposites with rising graphene concentration and neat PLA as a reference. Figure 7: X–ray diffraction of nanocomposites with rising carbon nanotubes concentration and neat PLA as a reference. loaded with 9 wt% MWCNT and less intense for the composite possessing 3 wt% MWCNT. Both composite diffraction patterns are an indication of more crystalline structure compared to the neat PLA. Graphitic (002) and (100) patterns are visible mostly for the 9 wt% MWCNT/PLA composite, which could be a sign of good carbon nanotube dispersion in the polymer matrix. This behavior, which shows a different trend compared to that of GNP, can be attributed to the dimensionality of the nanoparticles and probably also to the different degree of functionalization of the nanocarbons, where carboxyl groups can act as crystallinity centers in the polymer matrix. Indeed, nanofillers are reported to act in nucleating in nanocomposites [49], with crystalline layers covering the filler [50]. On the other hand, functional groups can improve crystallization [51], indeed only one nucleating site is needed, for the polymer, to start crystallization.