Poly(L-lactide)/Four-Armed Star Poly(L-lactide)-Grafted Multiwalled Carbon Nanotubes Nanocomposites: Preparation, Rheology, Crystallization, and Mechanical properties

Four-armed star poly(L-lactide)-grafted multiwalled carbon nanotubes (CNTs-g-4PLLA) were synthesized through the nucleophilic substitution reaction between 4PLLA and acryl chloride of CNTs and then characterized by transmission electron microscope, X-ray photoelectron spectroscopy, thermal gravimetric analysis (TGA), and ultraviolet visible spectrophotometer. The results indicated that 4PLLA was successfully grafted onto CNTs, and CNTs-g-4PLLA contained 37.7 wt% of 4PLLA. PLLA/CNTs-g-4PLLA nanocomposites were prepared by solution casting with different CNTs-g4PLLA content. Rheological behavior of PLLA/CNTs-g4PLLA nanocomposites was measured using a rheometer. The result showed that CNTs-g-4PLLA formed a network structure at percolation concentration, which improves obviously rheological properties of PLLA in the molten state. The crystallization behavior and crystal structure of the nanocomposites were comprehensive evaluated through differential scanning calorimetry, X-ray diffraction, and polarizing optical microscope. The results found that CNTs-g-4PLLA played two roles in PLLA crystallization. The addition of CNTs-g-4PLLA acted as nucleating agent and obviously accelerated the spherulites growth under percolation concentration, while it inhibited the movement of PLLA chains at above percolation concentration, resulting in the decrease of crystallinity. Thermal stability and mechanical properties of the nanocomposites were also investigated using TGA, dynamic mechanical analysis, and tensile test. These results indicated that the incorporation of CNT-g-4PLLA into the PLLA matrix improved the thermal stability, storage modulus, and tensile strength of the nanocomposites. (C) 2015 Society of Plastics Engineers