Morphological features and crystallization behavior of the conductive composites of poly(trimethylene terephthalate)/graphene nanosheets

Poly(trimethylene terephthalate) (PTT) composites filled with well-dispersed graphene nanosheets (GNSs) were prepared through a coagulation method. The effects of increased GNS concentration on variations in the structure and properties of the PTT matrix, such as its electrical conductivity, crystallization kinetics, melting behavior, and crystal morphology, were investigated. Several analytical techniques were used, including electrical conductivity measurement, differential scanning calorimetry, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, polarized light microscopy, transmission electron microscopy (TEM), and thermo-gravimetric analysis (TGA). Electrical conductivity increased from 1.8 x 10(-17) S/cm for neat PTT to 0.33 +/- 0.23 S/cm for PTT/GNS composites with 2.97 vol % GNS content. Percolation scaling laws were applied, and then threshold concentration and exponent were determined. In the case wherein liquid nitrogen was used to quench the melt, a mesomorphic phase was formed despite the extremely short crystallization time after adding high GNS contents. PTT crystallization rate increased with the gradual addition of GNSs. The enhanced crystallization kinetics was attributed to the high nucleation ability of GNSs to induce epitaxially grown lamellae on their surfaces, as revealed by TEM. PTT nuclei were randomly developed on the GNS surface to form the lamellae. However, crystallinity reached its maximum value near the electrical percolation threshold because the PTT chain mobility was confined after the GNS-GNS network formed. The growth of PTT banded spherulites in the bulk was still observed for composites with high GNS content, and TGA results revealed that the GNS-filled PTT composites had excellent thermal stability. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43419.