Synthesis, stereocomplex crystallization and properties of poly(<scp>l</scp>-lactide)/four-armed star poly(<scp>d</scp>-lactide) functionalized carbon nanotubes nanocomposites

Functionalized carbon nanotubes (F-CNTs) were synthesized through the nucleophilic substitution reaction between four-armed star poly(d-lactide) (4PDLA) and acryl chloride of carbon nanotubes and were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results indicated that the 4PDLA was successfully grafted onto carbon nanotubes, and it contained 45.5 wt% of 4PDLA. Poly(l-lactide) (PLLA) nanocomposites with different F-CNTs content were prepared by solution casting. Optical microscopy and scanning electron microscopy results showed that F-CNTs were uniformly dispersed in the nanocomposites. Crystallization behavior and crystal structure of PLLA nanocomposites were investigated using differential scanning calorimetry, polarizing microscope and X-ray diffraction. The results found that poly(lactide) stereocomplex crystal could be formed between PLLA and F-CNTs. F-CNTs played different roles in the process of solution casting and melting crystallization. Polarizing microscope also revealed that crystallization temperature had a significant effect on the nucleation and spherulites growth of PLLA. Thermal stability and mechanical properties of the nanocomposites were also investigated by thermogravimetric analysis, dynamic mechanical analysis and tensile testing. These results demonstrated that the addition of F-CNTs obviously improved thermal stability and tensile strength of PLLA. The results showed that PLLA/F-CNTs would have potential values in engineering fields. Copyright © 2015 John Wiley & Sons, Ltd.