Thermoelectric behaviour of melt processed carbon nanotube/graphite/poly(lactic acid) conductive biopolymer nanocomposites (CPC)

The aim of the study was to examine the possible use of conductive polymer composites (CPC) as thermoelectrical material for energy harvesting from temperature gradient. Their ease of processing, low cost and environmental impact compared to typical thermoelectric semiconductor materials were found to be strong advantages for large scale production. Our results show that eGR-CNT hybrid fillers are the most effective to enhance the CPC electrical conductivity up to σ = 4123 S.m− 1, but that eGR is more effective to improve both thermal conductivity (λc = 5.5 W.m− 1.K− 1) and seebeck coefficient (S = 17 μV.K− 1), whereas finally CNT give the best compromise to reach the highest ZT = 7 × 10− 5 at room temperature. This finding is attributed to the ability of CNT network to allow electron circulation by tunnelling, when junctions are separated by an insulating polymer film (even of some nm thick), whereas phonon scattering at nanointerfaces will prevent their effective transmission through the CPC. Although the intrinsic individual physical properties obtained (σ, λc, S) with the different kinds of carbon filler were good, it was not possible to completely uncouple them to maximise ZT. We believe that this value of ZT, too low for commercial application, can be enhanced by increasing the confinement of conducting fillers with exclusion volumes and by decreasing the thermal conductivity of the matrix with voids.