Effect of Melt-Compounding Protocol on Self-Aggregation and Percolation in a Ternary Composite

Abstract

A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 × 10−2 S/m with 4 wt.% CB). To further control the percolation structure, the composite fabrication is controlled by splitting a typical single-step mixing process into two steps, focusing on the dispersion of the secondary PCL phase and the CB particles separately. Under the single-step mixing protocol, the ternary composite shows a structure with greater CB aggregation in the form of a high aspect ratio and large aggregates (aggregate perimeter~aggregate size 0.7). Meanwhile, the two-step mixing process causes the CB aggregates to expand and create a higher structure (aggregate perimeter~aggregate size 0.8). The reduced size of the secondary phase under a mixing condition with high shear force prior to the addition of CB provides a larger interfacial area for CB to diffuse into the PCL phase during the subsequent mixing step, resulting in a further expansion of CB aggregation throughout the composite. The particle percolation of such a high order structure is attributed to high storage modulus (G′), high Young’s modulus, high dielectric loss (ε″), and negative–positive switching of dielectric constant at high frequency (of 103 Hz) of composite.

Investigating the Electromechanical Properties of Carbon Black-Based Conductive Polymer Composites via Stochastic Modeling

“…Numerous manufacturing methods for creating carbon-based CPC transducers have been demonstrated in the literature, including injection/compression molding [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], extrusion [ 18 , 19 ], melt-spinning [ 20 ], 3D-printing and ink-jetting [ 15 , 21 , 22 , 23 , 24 , 25 , 26 ], fumigation coating [ 27 , 28 ], spray-layer-by-layer (sLBL) [ 5 , 29 ], and hot pressing [ 13 , 30 , 31 , 32 ] among others [ 33 , 34 , 35 ]. While various manufacturing methods have been reported in the literature, the results of studies of CPCs with similar constituent materials reveal significant variation in nominal electromechanical properties, as shown in Figure 1 .…”

“…For external surface probing, researchers have demonstrated measurement repeatability by deploying custom surface clamped electrodes [ 7 , 8 , 10 , 33 , 41 ], while others have deployed commercial volume resistivity test fixtures, such as the Keithley 8009 [ 13 , 15 , 30 ]. Instead of deploying mechanically reinforced contacts, researchers have also demonstrated the effectiveness of applying conductive surface coatings, such as sputtered gold or conductive silver paste, to create electrical contacts [ 9 , 11 , 12 , 16 , 19 , 23 , 26 , 31 , 32 ]. Other researchers have utilized the inherent adhesive properties of the CPC constituents to adhere CPC films to metallic structures with exposed contacts [ 21 , 24 , 27 , 28 ].…”