Selective Localization of Multi-walled CNT in Polylactic Acid/Thermoplastic Polyurethane Blends and Its Effect on Mechanical Properties

Background: Due to excellent properties such as degradability, high strength, and biocompatibility, polylactic acid (PLA) has received enormous attention recently as a promising potential candidate material to replace petroleum-based polymers. However, PLA shows high brittleness as well as low toughness which may limit its application. Objective: In this work, PLA was melt blended with thermoplastic polyurethane (TPU) and then filled with carbon nanotubes (CNTs) to produce environmentally friendly polymeric materials with improved mechanical properties. Method: The specimens were prepared by using an internal mixer, followed by compression molding. Morphology of the matrix and particles dispersion state in the composite was investigated by using Scanning Electron Microscopy (SEM), while mechanical properties were evaluated via impact and tensile tests. Results: Observation from SEM's micrograph showed that two distinct phases were present in the blend, with selective localization of CNTs at one of the phases in the system. Thermodynamic calculation using Owen and Wendt's equation predicted that the CNTs were preferably dispersed at TPU phase. As CNTs content increased, the toughness of TPU/CNT and TPU/PLA/CNT composites increased whereas the toughness of PLA/CNT composite decreased, that might be ascribed to the phenomenon of selective localization of the CNTs. Other than that, the elongation at break of PLA/CNT, PLA/TPU/CNT and TPU/CNT also increased with the addition of CNT. The incorporation of TPU in the TPU/PLA blends also imparted ductility to the blends. Conclusion: In conclusion, the selective localization prediction is in line with the trends observed in mechanical properties of PLA/TPU/MWCNT composites.