Enhanced thermo-mechanical properties of poly(L-lactic acid)/single-wall carbon nanotube composites

The preparation condition of poly(L-lactic acid) (PLLA)/single-wall carbon nanotube (SWNT) composite films with highly dispersed SWNTs from solutions was examined and the thermo-mechanical properties of the resultant composite films were evaluated by tensile tests, DSC measurements and dynamic mechanical analyses. The dispersion of SWNTs in PLLA/SWNT composites significantly affected by the solvents used and the polymer concentrations. The PLLA/SWNT composite with the highest dispersion of SWNTs was obtained from a 5 wt% PLLA solution in chloroform. The tensile modulus and strength increased with increasing the SWNT content. The glass transition temperature shifted higher and the heat resistance remarkably improved with increasing the SWNT content. The PLLA/SWNT composite (PLLA-5) added with 5 wt% SWNT showed a glass transition temperature of 81 degrees C and a storage modulus of 0.91 GPa at 100 degrees C, which were 14 degrees C and 3.3 times higher, respectively, than those pure PLLA film (PLLA-0). It is important to note that the rigid-amorphous fraction determined from the DSC thermogram increased with increasing the SWNT content suggesting the specific interaction between PLLA chains and SWNTs. The tensile modulus of 9.2 GPa for a PLLA-5 film drawn to an EDR of 9 was significantly higher than that of 7.2 GPa for the PLLA-0 drawn to the maximum achieved EDR of 12. These results indicate that the mixing of small amounts of SWNT (<5 wt%) into a PLLA significantly improves the thermal stability and thermo-mechanical properties of PLLA films.