Carbon Nanotube-Based Segregated Thermoplastic Nanocomposites Structured via Electromagnetic Melt Processing

A cutting-edge method that uses electromagnetic (EM) energy for the melt processing of thermoplastic polymer nanocomposites (TPNCs) is reported. The properties and microstructures of TPNCs produced via the proposed EM-processing method and TPNCs via conventional heat processing are contrasted. The EM-processed TPNCs prepared with EM-susceptible carbon nanotubes (CNTs) exhibited a significant enhancement in transport and mechanical properties, outperforming the conventionally processed TPNCs. Thus, the EM-processed TPNCs demonstrated an ultralow electrical percolation threshold (similar to 0.09 vol %) and a remarkable increase in volume electrical conductivity of 8 orders of magnitude (i.e., 1.1 x 10-5 S/m) at only 1.0 wt % CNT loading, compared to their hot-pressed counterparts. This highlights the superior network formation, level of segregation, and structuring enabled by EM processing. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) revealed that EM-processed TPNCs exhibited higher crystallinity (similar to 9% higher) and a predominantly alpha crystal phase compared to the hot-pressed TPNCs. Microstructural inspection by electron microscopy disclosed that EM processing led to segregated but interconnected multiscale networks of a thin and well-defined CNT interphase that encompassed from the nanoscale of the CNTs to the macroscopic scale of TPNCs. In contrast, conventional processing developed a more diffused CNT interphase with less interconnectivity. The EM-processed TPNCs developed a statistically higher stiffness (+20%) and in certain cases, even better strength (+10%) than the hot-pressed TPNCs. However, the EM-processed TPNCs displayed significantly lower ductility, owing to their higher crystallinity, more brittle crystal alpha phase, and the potential formation of microvoids in the bulk of the TPNCs inherent to the unoptimized EM processing. This work provides an understanding of an alternative and unconventional processing method capable of achieving higher structuring in nanocomposites with advanced multifunctional properties.