Polycarbonate composites for material extrusion-based additive manufacturing of thermally conductive objects

Abstract

Enhanced thermally conductive polymer composites can be used in many engineering applications where either the physicochemical properties of plastics or the processing properties of plastics are required. Rapid prototyping is currently being addressed for a number of applications that require good heat transfer properties. Such applications include various types of heat exchangers containing coolant/heating fluid as well as passive heat sinks for standard heat removal from various types of heat-generating products. The present work is focused on the research of thermally conductive composites for printing such structures using additive manufacturing (AM), namely material extrusion. In this study, a number of parameters of the composites were investigated that affect the final properties of the printed structures; these include the TC (Thermal Conductivity), mechanical properties, and printability of the composites, depending on the composition, but also the printing direction. The composites studied were made up of a matrix of PC (Polycarbonate) and a mixture of different thermally conductive fillers, specifically, h-BN (Hexagonal Boron Nitride), EG (Expanded Graphite), PCFs (Pitch-based Carbon Fibers) and Al (Aluminum Particles). Different types of thermally conductive composites were studied, from binary to ternary combinations of fillers. One of the best-performing composites was achieved for the combination of all four types of filler, where thermal conductivity along the printing direction was achieved for the PC matrix with 30 wt% of the mixture of all fillers. Up to 1.56 W m−1 K−1 was achieved, which is 5-fold higher than for neat PC. Although these composites have approximately half the tensile strength only, the hardness is similar to that of the neat PC. The behavior of fillers was observed by SEM analysis. Al, EG, and PCFs behave predictably. Unusual behavior was observed in the case of PC only with h-BN, where the filler migration from the matrix to the voids between the non-fused printing paths occurred, likely caused by a larger amount of dispersion component of the overall surface energy of h-BN. Such phenomena could be used in the optimized form in the future so that segregated thermally conductive structures could be created using material extrusion-based AM and allow even higher thermal conductivity of final structures.