In this work, the rolling process was employed to fabricate polylactic acid/multi-walled carbon nanotube (PLA/MWCNT) composites at room temperature. The effects of the rolling conditions on the mechanical and electrical properties of the fabricated composites were investigated. The evolution processes of the internal molecular structures, i.e. changes in molecular orientation and crystallinity, were examined by X-ray diffraction, differential scanning calorimetry, and density method. The results suggested that the molecular orientation improved; however, the crystallinity decreased when the rolling ratio increased. The analysis of the mechanical properties revealed that the rolled composites displayed anisotropy during the rolling process. In the rolling direction, after adding 1 wt.% MWCNTs, the tensile strength increased from 58.6 to 94.3 MPa with the rolling ratio, whereas the fracture strain sharply increased to 131.5% at the rolling ratio of 60%. In addition to the mechanical properties, electrical resistivity was also investigated; notably, this property was not significantly affected by the rolling process. Furthermore, the MWCNT dispersion and morphology were investigated by scanning electron microscopy. These findings offer a simple and effective method to fabricate conductive composites with excellent mechanical properties.
Four polycarbonate (PC)-based composites with 1, 2.5, 5, and 10 wt.% raw multiwalled carbon nanotubes (MWCNTs) were prepared using extrusion process followed by injection molding. The effects of MWCNT mass fraction (W) on composite mechanical, thermal, and electrical properties were examined. The mechanical properties suggested that the tensile strength of the composites with 2.5 wt.% raw MWCNTs exhibited an increase of ~5 MPa (~8.6%) at a particular injection condition. Besides, thermogravimetric analysis (TGA) indicated that the addition of 1 wt.% MWCNTs improved the thermal stability of PC by approximately 100°C. Aside from mechanical and thermal properties, the electrical resistivity of the 5 wt.% raw MWCNT composites was considerably decreased to 102 Ω/sq, a value approximately 15 orders of magnitude lower than that of PC. Furthermore, the effects of injection conditions on composite electrical properties were emphatically discussed, and it was found that electrical resistivity was sensitive to injection temperature and speed. Low electrical resistivity was achieved at high injection temperature and low injection speed. Scanning electron microscopy images revealed that electrical resistivity relied on the microstructure of the prepared MWCNT/PC composites.