Secondary polymer-induced particle aggregation and its rheological, electrical, and mechanical effects on PLA-based ternary composites

In order to fabricate electrically and mechanically reinforced biopolymer-based composites, we control the dispersion of the particles through the addition of a secondary polymer with high affinity to carbon black (CB) particles. The addition of a small amount of the secondary polymer induces the aggregation of CB particles beyond interfacial localization in a ternary composite. The aggregation and percolation network in poly(lactic acid) (PLA)-based ternary systems are investigated through a scaling analysis. According to rheological and geometric fractal analyses, the secondary polymer induces an aggregation of CB particles to form a percolation network because the induced-diffusion effect is stronger than the interaction between the particles, leading to a particle aggregate with a high-order structure. The modulus (G0′) of the CB/PLA binary composite has a scaling relationship with the particle volume fraction (φ), G0′∼φ1.92 (φc,G′=2.2%). In the CB/PLA binary composite, the addition of a small amount of secondary polymer having strong chemical affinity to CB changes the scaling relationship significantly depending on the type of the secondary polymer (G0′∼φ2.17∼2.53) with a lower percolation threshold (φc,G′) (φc,G′=0.96%). It also enhances the electrical percolation (electrical conductivity, σdc∼φ3.23∼3.78 φc,σ=1.50%−1.86% for ternary composites) with an increase in the exponent and a lower percolation threshold (φc,σ). The secondary polymer serves as a binder and causes the aggregates to be well dispersed, leading to a brittle-ductile transition and significant enhancement of the ductility.