Study on the preparation and characterization of biodegradable polylactide/multi-walled carbon nanotubes nanocomposites

In this study, polylactide/multi-walled carbon nanotubes (PLA/MWNTs) hybrids were prepared by means of a melt blending method. To enhance the compatibility between PLA and MWNTs, the acrylic acid grafted polylactide (PLA-g-AA) and the multihydroxyl-functionalized MWNTs (MWNTs-OH) were used to replace PLA and MWNTs, respectively. The crude MWNTs were chemically oxidized by a mixture of H2SO4 and HNO3 and then reacted with thionyl chloride to functionalize them with chlorocarbonyl groups (MWNTs-COCl). The MWNTs-OH was finally obtained by the reaction of MWNTs-COCl and 1,6-hexanediol. The resulting products have been characterized by FTIR, 13C solid-state NMR, TGA, DMA, SEM, TEM, and Instron mechanical tester. Due to the formation of ester groups through the reaction between carboxylic acid groups of PLA-g-AA and hydroxyl groups of MWNTs-OH, results demonstrated dramatic enhancement in thermal and mechanical properties of PLA, for example, 77 °C increase in initial decomposition temperature with the addition of only 1 wt%. Based on the result of thermal and mechanical examinations, it was found that the optimal amount of MWNTs-OH was 1 wt% because excess MWNTs-OH caused separation of the organic and inorganic phases and lowered their compatibility.