3D Printed Polypropylene-Based Multifunctional Skin-Core Structures for Thermal Conductivity

In this work, polypropylene (PP)-based filaments for Fused Filament Fabrication (FFF) containing boron nitride (BN) and talc(T) were developed, aiming at formulating multi-material 3D printed parts showing thermal conductivity and balanced mechanical properties. Particularly, skin-core structures obtained by localizing BN in the surface layers while confining T in the core were 3D printed and characterized, and their properties were compared to those of correspondent mono-material samples. The characterization of the PP/BN mono-material samples revealed a crucial role of the FFF process in inducing higher thermal conductivity in the radial direction of the specimens as compared to the axial one, owing to the preferential alignment of the fillers along the printing direction allowing the creation of continuous conductive paths in the in-plane direction. For the multi-material structures, it was demonstrated that confining the thermally conductive fillers to the surface of the samples allows achieving higher in-plane thermal conductivity as compared to PP/BN samples; for instance, nearly doubled values were obtained by decreasing the number of BN-containing layers from 15 to 3. Most importantly, the skin-core structures exhibit tensile modulus and stress practically identical to those of PP/T mono-material samples, despite the lower content of the reinforcing filler and the presence of interfaces between the two different composites.