Effect of Graphene Nanoplatelets Presence on the Morphology, Structure, and Thermal Properties of Polypropylene in Fiber Melt-Spinning Process

Melt spinning of graphene nanoplatelets (GnPs)-polypropylene (PP) nanocomposite fibers are reported for the first time. PP/GnPs fibers were spun with a pilot-plant spinning machine with varying concentration of GnPs by mixing PP/GnPs masterbatch with PP. The effect of inclusion of GnPs on the morphology and crystalline structure of PP fibers was investigated. The thermal stability of the fibers was also evaluated by thermogravimetric analysis. The light microscopy images showed that the GnPs are uniformly distributed over the PP matrix. The differential scanning calorimetry (DSC) results revealed that presence of GnPs affects both the melting and crystallization behaviors. The melting peaks of PP/GnPs nanocomposite fibers were broader than that of neat PP fibers, indicating a broader crystal size distribution in PP/GnPs nanocomposite fibers as compared to the neat PP fibers. Besides, an obvious increment in the crystallization peak temperature was observed in GnPs-PP nanocomposite fibers. The wide-angle X-ray diffraction spectra (WAXD) results showed that the crystal type of nanocomposite fibers did not change and was still the -monoclinic crystal form. Moreover, the morphology of spherulites demonstrated that GnPs increased the nucleation sites in the nanocomposite fibers which in turn restricted the crystal growth of PP chains. This finding supported the DSC and WAXD results. Activation energies were calculated by Horowitz and Metzger's method as 77.87 and 105.41 kJ/mol for neat PP and PP/0.2 wt% GnPs fibers, respectively, suggesting an increase in the thermal stability of GnPs-PP nanocomposite fibers. POLYM. COMPOS., 36:367-375, 2015. (c) 2014 Society of Plastics Engineers