Morphology, rheology and crystallization behavior of polylactide composites prepared through addition of five-armed star polylactide grafted multiwalled carbon nanotubes

Functionalized multiwalled carbon nanotubes (F-MWNTs) were prepared by covalent grafting of five-armed star polylactide (fa-PLA), and were characterized by thermogravimetric analysis (TGA), nuclear magnetic resonance (NMR) spectroscopy and Raman spectroscopy. A series of polylactide (PLA)/F-MWNTs composites was prepared via coagulation method. Several techniques were applied to investigate the effects of F-MWNTs on the morphology, melt rheology, and crystallization and melting behaviors of the PLA composites. The optical microscope (OM), field-emission scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM) observations demonstrated that, in comparison with the case of PLA filled with pristine MWNTs, F-MWNTs case showed improved dispersion and interfacial adhesion. Oscillatory frequency sweep measurements showed that addition of about 2.0 wt% F-MWNTs led to a solidlike response where a percolated network structure formed, and the composites exhibited remarkable improvement of rheological properties in the melt state as compared with that of neat PLA. DSC measurements showed that F-MWNTs acted as a nucleating agent to enhance crystallization when below the percolation concentration, while also acted as a hindrance to retard crystallization above the percolation concentration. The double melting peaks on the DSC curves were attributed to melting of the crystals formed in the cold crystallization stage and the melting-recrystallization-remelting (mrr) event during heating, respectively.