Abstract
Electrically conductive and flexible thermoplastic polyurethane/graphene (TPU/GE) porous structures were successfully fabricated by selective laser sintering (SLS) technique starting from graphene (GE)-wrapped thermoplastic polyurethane (TPU) powders. Several 3D mathematically defined architectures, with porosities from 20% to 80%, were designed by using triply periodic minimal surfaces (TMPS) equations corresponding to Schwarz (S), Diamond (D), and Gyroid (G) unit cells. The resulting three-dimensional porous structures exhibit an effective conductive network due to the segregation of graphene nanoplatelets previously assembled onto the TPU powder surface. GE nanoplatelets improve the thermal stability of the TPU matrix, also increasing its glass transition temperature. Moreover, the porous structures realized by S geometry display higher elastic modulus values in comparison to D and G-based structures. Upon cyclic compression tests, all porous structures exhibit a robust negative piezoresistive behavior, regardless of their porosity and geometry, with outstanding strain sensitivity. Gauge factor (GF) values of 12.4 at 8% strain are achieved for S structures at 40 and 60% porosity, and GF values up to 60 are obtained for deformation extents lower than 5%. Thermal conductivity of the TPU/GE structures significantly decreases with increasing porosity, while the effect of the structure architecture is less relevant. The TPU/GE porous structures herein reported hold great potential as flexible, highly sensitive, and stable strain sensors in wearable or implantable devices, as well as dielectric elastomer actuators.
Highlights
Additive manufacturing, known as 3D printing (3DP), is an innovative manufacturing technology which allows one to turn complex 3D models into real objects without special tooling andAppl
thermoplastic polyurethane/graphene (TPU/GE) composite powder was used in the selective laser sintering (SLS) printing process in order to build three porous structures by using Schwarz, Diamond, and Gyroid unit cells
Porous structures, consisting of 3 × 3 × 3 unit cells, were SLS printed by using the thermoplastic polyurethane (TPU)/GE
Summary
Known as 3D printing (3DP), is an innovative manufacturing technology which allows one to turn complex 3D models into real objects without special tooling andAppl. Despite the continuous progress in the optimization of SLS technology, many critical issues still remain unsolved, including the possibility to manufacture multifunctional conductive parts able to exhibit both electrical conductivity alongside lightweight and elastic properties. In this context, it is very interesting to develop new powders made up of conductive nanoparticles dispersed in or coated onto elastomeric particles [15,16]. The mechanical deformation of the structure brings about a change in the conductive pathway by modifying the mean particle distance between the conductive nanoparticles, and the material’s resistivity [18]
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