Highly conductive Poly(L-lactic acid) composites obtained via in situ expansion of graphite

Abstract

In this work, highly electrically and thermally conductive biopolymer composites were prepared by low-temperature expandable graphite (EG) filling Poly(L-lactic acid) (PLLA) via an in situ exfoliation melt blending process. The electrical conductivity of the composites with various graphite contents was measured by a four-point probe resistivity determiner and a high value of 0.37 S/cm was obtained at 70 wt.% EG content. A hot-disk method was used to evaluate the thermal conductivity of the composites. At EG loading fraction of 70%, thermal conductivity of PLLA/EG composites reached to the highest 26.87 W/mK, which is 100 times higher than neat PLLA. The electrical percolation was observed in the vicinity of the thermal percolation threshold concentration. The expansion of EG was crucial to the overall conductivity of the blends, which was confirmed by X-ray diffraction (XRD) analysis and scanning electron microscope (SEM). Dynamic rheology analysis was applied to study the structural change by the interconnection of the exfoliated graphite flakes and the formation of the networks in the blends. Thermogravimetric analysis (TGA) was employed to determine the thermal properties of the investigated PLLA/EG composites.