_Applied_  
_sciences_  
_Article_  
**Effects of Graphene Nanoplatelets and Multiwall Carbon Nanotubes on the Structure and Mechanical Properties of Poly(lactic acid) Composites:**  
**A Comparative Study**  
**[PERSON] 1,*2, [PERSON] 1, [PERSON] 1, [PERSON] 2, [PERSON] 1,2,2, [PERSON] 1, [PERSON] 3, [PERSON] 4, [PERSON] 4, [PERSON] 3,4 and [PERSON] 3,3**  
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information on the existence of GNPs in the form of individual graphene sheets in epoxidized palm oil blends [18], to disclose the effect of sonication time on the dispersion ability of graphene in the PLA matrix [19], to confirm intactness and reliable distribution of reduced graphene oxide (rGO) as graphene sheet layers into a polymer composite [20], and to study the influence of carbon nanofiller on the semi-crystalline structure of PLA and PBAT [21]. [PERSON] et al. [22] reported that PLA and nanocomposites containing different CNT concentrations exhibited nearly the same diffraction peaks at slightly different locations. Raman spectroscopy provides molecular morphology analysis, giving information on the composite material structure by evaluation of relevant vibrational features and could be used to characterize the degree of graphene or nanotube dispersion. [PERSON] et al. [23] investigated MWCNT loading, excitation laser power and temperature as parameters affecting the frequency of the Raman bands and their intensity. They reported that in the specific case of isotactic polypropylene (iPP), any interaction of the carbon nanotubes with the polymeric host has minimal effect on the frequency of the MWCNT's G band (\(\sim\)1584 cm\({}^{-1}\)); the same holds for the influence of residual stresses acting on the MWCNTs. The parameter that primarily altered the CNT's Raman bands frequency was temperature, determined by the excitation laser intensity, the MWCNTs concentration and the thermal properties of the polymer matrix. This was demonstrated by confocal micro-Raman spectra collected from agglomerates and from micro-Raman spectra of samples containing either poorly or well dispersed MWCNTs. Raman confocal spectroscopy has been used for characterization of MWCNTs embedded in PLA fibers in the absence of a chemical interaction between them [24]. By means of confocal images, agglomerates of carbon nanotubes have been noticed, even after solution ultrasound sonication. The Raman spectrum of MWCNTs, as expected, showed the graphitic D, G and G\({}^{\prime}\) bands at 1362, 1590 and 2683 cm\({}^{-1}\), respectively. The structure and properties of MWCNT-grafted silica nanohybrids were established by means of diverse physical methods, including Raman spectroscopy [25]. In this study, Raman spectroscopy was used to detect amorphous and crystalline phases in MWCNT samples with various degrees of graphitization. The characteristic peaks of the MWCNTs at 1326 cm\({}^{-1}\) (D-band) and 1580 cm\({}^{-1}\) (G-band) were attributed to amorphous carbon and well-graphitized MWCNTs, respectively. Notably, the broad peak registered at 1326 cm\({}^{-1}\) was related to the presence of a defective graphitic layer or carbon particles. In a recent article [26], the influence of filler size on the properties of poly(lactic acid) (PLA)/graphene nanoplatelets (GNP) nanocomposites were investigated. Morphological, thermal, mechanical, and electrical properties were studied to reveal the influence of particle size. Electron microscopy and X-ray diffraction showed well dispersed small GNP (GNP-S) particles up to 10 wt% loading, while large GNP (GNP-L) particles started to agglomerate at loadings \(\geq\)7 wt%. Notably, composites with GNP-L demonstrated a much stronger peak than those with GNP-S at the same loading, indicating that large GNP-L fillers induce higher polymer crystallinity than small GNP-S in the composites. The XRD results also demonstrated that there is no significant change in PLA crystallinity with the incorporation of both GNP types, regardless of their size.