This article reviews recent advances in conductive polymer composites from renewable resources, and introduces a number of potential applications for this material class. In order to overcome disadvantages such as poor mechanical properties of polymers from renewable resources, and give renewable polymer composites better electrical and thermal conductive properties, various filling contents and matrix polymers have been developed over the last decade. These natural or reusable filling contents, polymers, and their composites are expected to greatly reduce the tremendous pressure of industrial development on the natural environment while offering acceptable conductive properties. The unique characteristics, such as electrical/thermal conductivity, mechanical strength, biodegradability and recyclability of renewable conductive polymer composites has enabled them to be implemented in many novel and exciting applications including chemical sensors, light-emitting diode, batteries, fuel cells, heat exchangers, biosensors etc. In this article, the progress of conductive composites from natural or reusable filling contents and polymer matrices, including (1) natural polymers, such as starch and cellulose, (2) conductive filler, and (3) preparation approaches, are described, with an emphasis on potential applications of these bio-based conductive polymer composites. Moreover, several commonly-used and innovative methods for the preparation of conductive polymer composites are also introduced and compared systematically.

Thermal conductive networks (TCNs) in polymer composites are divided into high thermal dissipation TCN and low thermal dissipation TCN according to the rate of heat loss during transmission. The limited thermal conductivity (TC) enhancement in the composites prepared by traditional compounding methods was due to the high thermal dissipation of TCNs. In this study, TC enhancement based on conductive network conversion from high to low thermal dissipation was demonstrated in polydimethylsiloxane/short carbon fiber/glass bubble (PDMS/SCF/GB) composites. Two approaches, i.e., densification of the TCN by the spatial confining forced network assembly (SCFNA) method and volume exclusion by adding rigid particles, were used to realize TCN conversion from high to low thermal dissipation. Compared with the TC of PDMS/SCF (30 wt%) composites prepared by traditional compounding methods (1.053 W m⁻¹ K⁻¹), the TC (11.423 W m⁻¹ K⁻¹) of the same composites was increased by more than 9 times using the SCFNA method. The TC even presented an unexpected ∼13% enhancement to 13.004 W m⁻¹ K⁻¹ after adding 2 wt% GB with a relatively low TC of 0.15 W m⁻¹ K⁻¹. In summary, appropriate combination and optimization of these two approaches would lead to TC enhancement by one order of magnitude and more compared with traditional compounding methods.

Electrically conductive polymer composites are in high demand for modern technologies, however, the intrinsic brittleness of conducting conjugated polymers and the moderate electrical conductivity of engineering polymer/carbon composites have highly constrained their applications. In this work, super high electrical conductive polymer composites were produced by a novel hot embossing design. The polydimethylsiloxane (PDMS) composites containing short carbon fiber (SCF) exhibited an electrical percolation threshold at 0.45 wt % and reached a saturated electrical conductivity of 49 S/m at 8 wt % of SCF. When reducing the sample thickness from 1.0 to 0.1 mm by the hot embossing process, a compression-induced percolation threshold occurred at 0.3 wt %, while the electrical conductivity was further enhanced to 378 S/m at 8 wt % SCF. Furthermore, the addition of a second nanofiller of 1 wt %, such as carbon nanotube or conducting carbon black, further increased the electrical conductivity of the PDMS/SCF (8 wt %) composites to 909 S/m and 657 S/m, respectively. The synergy of the densified conducting filler network by the mechanical compression and the hierarchical micro-/nano-scale filler approach has realized super high electrically conductive, yet mechanically flexible, polymer composites for modern flexible electronics applications.

Constructing a compacted network in polymer matrices is an important method to improve the thermal conductivity (TC) of polymer composites. In this paper, a compacted network was built using the Spatial Confining Forced Network Assembly (SCFNA) method. The homogeneous compound of polymer and fillers, prepared using a conical twin-screw mixer, was placed in a compression mold with confining space to carry out two-stage compression, free compression and spatial confining compression. Aluminum oxide (Al₂O₃) was studied as filler in a polydimethylsiloxane (PDMS) matrix to illustrate the applicability of the SCFNA method. The polymer composites with an Al₂O₃ filler ranging from 10 to 80 wt% were prepared. When the filler content was 80 wt%, the TC of the PDMS/Al₂O₃ composites prepared using the SCFNA method increased by 16.35 times in comparison to the TC of pure PDMS. Observing the SEM of PDMS/Al₂O₃ composites with various thicknesses, the gap between fillers decreased with a decrease in thickness. The composite with TC up to 2.566 W (mK)⁻¹ obtained at 80 wt% filler was further employed as a heat spreader, causing a decrease of about 8.23 °C in the set-point compared with the temperature of the heat source.