Calculation of the degree of crystallinity of HDPE/GNPs nanocomposites by using various experimental techniques: a comparative study

This work is a comparative study of four different techniques to determine the crystallinity of high-density polyethylene (HDPE) nanocomposites filled with different diameter sizes (5, 15 and 25 μm) of graphene nanoplatelets (GNPs) at various amounts (0.5–5 wt%). The structure of HDPE/GNPs nanocomposites was extensively studied by using different experimental methods, such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. To further provide a complete comparison, differential scanning calorimetry measurements were utilized to calculate the crystallinity values, while temperature-modulated DSC was employed to investigate the possible mechanism of the different crystalline structures. It was found that these methods can be used to estimate the crystallinity, but the sample parameters and experimental conditions must be taken into consideration. All the techniques showed that the crystallinity depends on GNPs size and content. The distance between dispersed platelets was substantial at low concentrations of GNPs, making it comparatively easy for additional nucleation sites to incorporate the polymer matrix, and the crystal nucleus was simply formed. However, at high concentrations of GNPs, the diffusion of polymer chains to the growing crystallites was hindered by large GNPs particles, despite the formation of additional nucleation sites.