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

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Poly(lactic acid) (PLA) composites are explored for enhanced properties.
• Carbon black (CB) is a common conductive filler, but achieving optimal dispersion and percolation is challenging.
• Poly(caprolactone) (PCL) as a secondary phase can influence filler behavior in polymer blends.

Purpose of the Study:

• To investigate the role of PCL in inducing carbon black (CB) self-aggregation and percolation in PLA/PCL/CB ternary composites.
• To enhance the electrical conductivity of PLA-based composites by controlling the percolation network structure.
• To explore the effect of different mixing strategies (single-step vs. two-step) on the composite's microstructure and properties.

Main Methods:

• Fabrication of ternary composites using poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB).
• Comparative analysis of single-step versus two-step mixing processes to control PCL phase dispersion and CB aggregation.
• Characterization of the composite's microstructure, including CB aggregate size and morphology.
• Electrical conductivity measurements to quantify the enhancement achieved through controlled percolation.

Main Results:

• PCL induces CB self-aggregation and percolation, even at low PCL concentrations.
• Smaller PCL phase droplet size leads to higher-order percolation structures and significantly enhanced electrical conductivity (~4 × 10^-2 S/m with 4 wt.% CB).
• A two-step mixing process, by pre-dispersing PCL, promotes larger CB aggregates and a more expanded percolation network compared to single-step mixing.

Conclusions:

• The PCL phase plays a crucial role in directing CB aggregation and forming conductive pathways in PLA composites.
• Controlled PCL dispersion and mixing protocols are effective strategies for achieving high electrical conductivity in ternary composites.
• The enhanced electrical properties are linked to the formation of a high-order percolation structure, evidenced by mechanical and dielectric properties.