Highly Anisotropic Thermal Conductivity of Three-Dimensional Printed Boron Nitride-Filled Thermoplastic Polyurethane Composites: Effects of Size, Orientation, Viscosity, and Voids

Abstract

Extrusion-based three-dimensional (3D) printing techniques usually exhibit anisotropic thermal, mechanical, and electric properties due to the shearing-induced alignment during extrusion. However, the transformation from the extrusion to stacking process is always neglected and its influence on the final properties remains ambiguous. In this work, we adopt two different sized boron nitride (BN) sheets, namely, small-sized BN (S-BN) and large-sized BN (L-BN), to explore their impact on the orientation degree, morphology, and final anisotropic thermal conductivity (TC) of thermoplastic polyurethane (TPU) composites by fused deposition modeling. The transformation from onedimensional axial alignment in the extruded filament to two-dimensional alignment (horizontal and vertical alignment) in the stacking filament of BN sheets is observed, and its impact on anisotropic TC in three directions is clarified. It is found that L-BN/ TPU composites show a high TC of 6.45 W m −1 K −1 at 60 wt % BN content along the printing direction, while at a lower content (<40 wt %), S-BN/TPU composites exhibit a higher TC than L-BN/TPU composites. Effects of orientation, viscosity, and voids are comprehensively considered to elucidate such differences. Finally, heat dissipation tests demonstrate the great potential of 3D printed BN/TPU composites to be used in thermal management applications.

Ultrahigh thermal conductive polymer composites by the 3D printing induced vertical alignment of carbon fiber

“…31 Guo et al prepared a BN/TPU composite with 6.45 W m −1 K −1 at 60 wt% filler content and studied the orientation degree, morphology, and anisotropic thermal conductivity changes of the composites with different sizes of BN fabricated by FDM. 32 Subsequently, Guo et al used the same method to fabricate up to 12 W m −1 K −1 graphene/TPU composites at 45 wt% and demonstrated the excellent performance of the composites in the field of battery thermal management. 33 However, this method is unsuitable for soft composite materials because of prefabricated filament production and unique processing technology limitations.…”

Recent progress of tree frog toe pads inspired wet adhesive materials

“…Computer-controlled layer-by-layer curing of polymer resins can produce surfaces with complex micro-/nano structures. Taking advantage of 3D printing, TPU [51,57,58] with hierarchical structures can be obtained. They can be directly used as adhesive surfaces or as templates to replicate adhesive polymer materials.…”

Improvement of “point‐plane”‐like hetero‐structured fillers on thermal conductivity of poly(vinyl alcohol) composites

“…[31] In order to take advantage of the anisotropic heat conduction of BNNSs, various strategies have been dedicated to obtaining the well-ordered arrangement of BNNSs, such as magnetic field, [32] ice template, [33] vacuum-assisted, [34] doctor blading, [35] electrospinning [36] and 3D Printing. [37] Recent research has drawn considerable attention to hetero-structured fillers due to the synergistic improvement effects of avoiding the introduction of interfacial thermal resistances between different fillers and establishing an effective thermal conduction network. [38] For example, Han et al prepared "Fungal tree"like hetero-structured fillers (AgNWs@BNNS) by in situ growth method, and the in-plane TC of AgNWs@BNNS/ aramid nanofibers composites reached 9.44 W/(mÁK) at a filler content of 50 wt%.…”