Controlled length and number of thermal conduction pathways for copper wire/poly(lactic acid) composites via 3D printing

Thermal conduction pathways play crucial roles in comprehending thermal transport in thermally conductive polymer composites. However, there is a lack of in-depth investigation on how the thermal conduction pathways (length and number) influence the thermal conductivity coefficients (λ) of the composites. In this work, three-dimensional (3D) printing is performed to fabricate the thermally conductive 1D copper wire/poly(lactic acid) (1D-Cw/PLA) composites, allowing for controlling the length and number of Cw thermal conduction pathways. And one thermal conduction model is also proposed and established for polymer composites with 1D thermal conduction pathways, elucidating the quantitative relationship between thermal conduction pathways and thermal conductivity. For composites with the same amount of Cw, the in-plane λ (λ//) of thermally conductive 1D-Cw/PLA composites is positively correlated with the number and length of Cw thermal conduction pathways. Specifically, when the volume fraction of Cw is 25.1 vol%, the λ// of 1D-Cw/PLA composites, containing 20 intact Cw thermal conduction pathways, can reach up to 4.23 W m−1 K−1, which is 87.2% higher than that of 1D-Cw/PLA composites without intact Cw thermal conduction pathways (2.26 W m−1 K−1), 72.0% higher than that of 1D-Cw/PLA composites with short Cw (2 intact Cw and 18 Cw broken at the half, 2.46 W m−1 K−1), and 1527% higher than that of the pure PLA matrix (0.26 W m−1 K−1). Furthermore, the predicted λ values from our established thermal conduction model and empirical equation show no significant difference from the measured λ at a 95% confidence level.