Carbon nanotubes-filled polylactic acid/polycaprolactone biodegradable blends: Effect of the polycaprolactone viscosity and carbon nanotubes addition on the microstructure, electrical and mechanical properties

Abstract

The effects of polycaprolactone (PCL) viscosity and carbon nanotubes (CNT) content on the microstructure, morphology development, tensile strength, and electrical percolation behavior of CNT/polylactic acid (PLA)/PCL blends were investigated. PLA/PCL blends with a volume ratio of 80/20 were prepared using a low viscosity PCL (PCL1) and a high viscosity PCL (PCL2). The microstructure analysis showed finer dispersion of PCL2 than PCL1 within the PLA matrix. The addition of CNT changed the PLA/PCL morphology from dispersed to co-continuous due to the localization of the nanotubes in the PCL domain (i.e. the minor domain). In addition, the introduction of CNT reduced the PCL domain size and improved the adhesion at the PLA/PCL interface. For the electrical percolation behavior, PLA/PCL2 blend exhibited a percolation threshold concentration (EPTC) of 0.5 wt.% CNT compared to 1.0 wt.% CNT for the PLA/PCL1 blend. This remarkably lower EPTC for the PCL2-based blend is in line with the microstructure analysis that indicated finer dispersion of PCL2 than PCL1 within the PLA matrix. The tensile strength analysis showed that adding up to 5 wt.% CNT does not influence the PLA/PCL blend’s tensile strength. However, remarkable adhesion and tensile strength enhancements were obtained at a CNT content of 10 wt.% and above.