Matrix crystallization induced simultaneous enhancement of electrical conductivity and mechanical performance in poly(l-lactide)/multiwalled carbon nanotubes (PLLA/MWCNTs) nanocomposites

In this work, influence of matrix crystallization on the electrical conductivity and mechanical properties of poly(l-lactide)/multiwalled carbon nanotubes (PLLA/MWCNTs) nanocomposites has been investigated. By introducing trace amount of nucleating agent (0.15wt%) and controlling isothermal crystallization time (0.1–8min) of PLLA matrix in a hot mould (130°C), the injection molded bars of the nanocomposites with different matrix crystallinities (5–45%) were prepared. Interestingly, the electrical conductivity is found to be linearly increased with increasing matrix crystallinity for nanocomposites with low concentrations of MWCNTs (below the percolation threshold). This could be attributed to the volume exclusion effect and the straightening effect of MWCNTs provided by PLLA crystallization, as evidenced from SEM observations. However, matrix crystallization induced reconstruction of MWCNTs network cannot effectively enhance the electrical conductivity when the concentration of MWCNTs is high enough (above the percolation threshold). More interestingly, the reconstructed MWCNTs network shows a better reinforcement effect in the nanocomposites as compared with that initially formed in the amorphous matrix.