Viscoelasticity and thermal stability of polylactide composites with various functionalized carbon nanotubes

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (Tmax). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.