Morphology evolution to form double percolation polylactide/polycaprolactone/MWCNTs nanocomposites with ultralow percolation threshold and excellent EMI shielding

Abstract

Morphological transformation only occurs in polymer blends via changing their components, which can be utilized to form double percolation structures. However, the weight percentage of either polymer in the blend generally ranges from 40 wt% to 60 wt%, which does not favor the construction of a densely conductive path. Herein, a double percolation structure had been successfully constructed in a polylactide-polycaprolactone (PLA/PCL) blend with only 30 wt% PCL by adding silicon dioxide (SiO2) to the PLA phase. The added SiO2 effectively strengthens the viscosity and elasticity of the PLA phase, which results in the morphological transformation of the PCL phase from segregated to continuous. In the blend, multi-wall carbon nanotubes (MWCNTs) were selectively distributed in the PCL phase to construct a more efficient conductive network, which brings about an enormous increase in conductivity for the nanocomposites. The electrical conductivity of PLA/PCL nanocomposite increases from 1.19 × 10−14 S/m to 4.57 × 10−4 S/m with the addition of 1.0 wt% MWCNTs and 6.0 wt% SiO2. The percolation threshold of the MWCNTs in the nanocomposite (0.11 wt%, i.e. 0.06 vol%) is 125% lower than that without SiO2 (0.28 wt%, i.e. 0.14 vol%). Furthermore, the nanocomposites with SiO2 were found to exhibit an electromagnetic interference (EMI) of approximately 26 dB with only 3.0 wt% MWCNTs, which means it can block 99.997% of microwaves. This study would provide a critical method to design eco-friendly nanocomposites with ultralow percolate threshold and excellent EMI shielding.