Isothermal and nonisothermal crystallization of isotactic polypropylene/graphene oxide nanosheet nanocomposites

Isothermal and nonisothermal crystallization of isotactic polypropylene (iPP)/graphene oxide nanosheet (GONS) nanocomposites were investigated by differential scanning calorimetry, polarizing optical microscopy and synchrotron wide-angle X-ray diffraction. Nonisothermal crystallization measurement revealed that GONSs significantly elevated crystallization peak temperature of iPP. Nucleating activity of the nanocomposites containing 0.05 wt% and 0.1 wt% GONSs was 0.61 and 0.56, respectively, indicating strong nucleation ability of GONSs. Induction period and half crystallization time of nanocomposites was greatly reduced during isothermal crystallization process. Moreover, only 0.05 wt% and 0.1 wt% caused less temperature dependence of crystallization kinetics in a wide temperature range of 132-140 degrees C. A very low GONS loading provided sufficient surface area for crystallite nucleation. Polarized optical microscopy showed that nucleation density of nanocomposites was much larger than that of neat iPP, accelerating overall spherulite growth rate. Crystal structure of iPP was not affected by GONSs, confirming the alpha-nucleating ability of GONSs.