Synergistic effects of filler size on thermal annealing-induced percolation in polylactic acid (PLA)/graphite nanoplatelet (GNP) nanocomposites

Abstract

Two graphene-based nanofillers of different sizes were melt mixed with polylactide acid (PLA). Composite films based on graphite nanoplatelets (GNPs) with the largest lateral size showed superior electrical conductivity and a lower percolation threshold after melt-compounding and hot-pressing at room temperature. However, upon annealing in the melt, composites based on GNPs with the smallest lateral size displayed significantly improved electrical conductivity and a decrease in percolation threshold as a result of dynamic percolation while composites based on large GNPs showed hardly any change in conductivity and percolation threshold. Hybrid filler systems based on 5 wt% GNP with variable small/large GNP filler ratios displayed synergistic effects in the formation of a conductive network during thermal annealing, and an optimum filler ratio of 50/50 was found to achieve the highest conductivity after annealing. This annealing-induced increase in particle connectivity for composites based on 5 wt.% hybrid small/large GNPs was also reflected in rheological measurements by the manifestation of a plateau in the storage modulus at low frequencies after annealing while such phenomenon was not observed for nanocomposites solely based on either small or large GNPs at similar loadings.