Non-isothermal crystallization kinetics assessment of poly(lactic acid)/graphene nanocomposites

摘要

In this work, the effects of the presence and modification of graphene nanoplatelets (GNps) on the crystallization of the poly(lactic acid) (PLA) were studied. Functionalization of GNps was accomplished by acid treatment. Nanocomposite samples were prepared by solution method containing pristine and functionalized graphene. In contrast to pristine PLA, crystallization of the samples contains nano filler initiates at higher rates that showed the role of heterogeneous nucleating effects of these particles in crystallization of the PLA. Then, the effect of nano filler functionalization was comprised. Initial slope of the crystallization (Si) and full width at the half height maximum of crystallization peak are indicative of nucleation rate and spherulite size distribution, respectively; which upon the addition of the functionalized graphene nanoplatelets (FGNps), Si increased and spherulites gained normal size distribution. Non-isothermal and crystallization kinetics of the samples were studied using differential scanning calorimetry at heating rates of 2, 4, 6 and 10 degrees C/min. Performed techniques such as furrier transform infrared, dynamic-mechanical thermal analysis and visual observation of sediments confirmed the successful modification of the graphene platelets. Also, non-isothermal analysis pinpointed the fact that crystallization temperature (T-c) of the nanocomposites has increased by 11-21 degrees C, compared to the neat PLA. Upon verification of Avrami's theory, it was conducted that dominant mechanism of nucleation of the nanocomposite samples was 2D circular diffusion; wherein, Avrami's exponent (n) was determined as 2. Moreover, it was deduced from Avrami's equation that "n" have no discernible changes in nanocomposites containing GNps or FGNps. Electrical devices and shape memories can be the main application of these nanocomposites.