The use of thermoplastic elastomers with conductive fillers enables one to produce strain sensors in a variety of shapes and forms using thermoplastic processing routes. However, some methods of thermoplastic processing are costly and require long production times. Filament printing, an additive manufacturing route that still exhibits a high annual growth rate, is a cost- and time-efficient method of additive processing. In this study a commercial conductive thermoplastic polyurethane (TPU) based fused deposition modelling (FDM) filament and a styrenic block copolymer (TPS) compound were extruded through two different FDM-based nozzle sizes, using an FDM 3D printer. The TPU material could only be extruded through a 0.5 mm orifice; using a lower nozzle diameter resulted in a non-elastic brittle filament. For the TPS material it was possible to produce filaments with diameters of 0.3 mm and 0.5 mm. In all dynamic tests, the extruded commercial piezoresistive TPU filament either showed plastic deformation at higher elongation, which resulted in resistance uncertainty at low strain, or a secondary peak in the resistivity measurement. For the TPS material, mainly the relaxation of the material resulted in lagging of the resistive value at low strain, because of the buckling of the fiber. Using combined dynamic and static measurements, a reproducible signal could be achieved with the TPS-based material, while the TPU-based material could not be used as a sensor in this area of strains.

Piezoelectric composites with 3-3 connectivity gathered attraction due to their potential application as an acoustic transducer in medical imaging, non-destructive testing, etc. In this contribution, piezoelectric composites were fabricated with a material extrusion-based additive manufacturing process (MEX), also well-known under the names fused deposition modeling (FDM), fused filament fabrication (FFF) or fused deposition ceramics (FDC). Thermoplastic filaments were used to achieve open and offset printed piezoelectric scaffold structures. Both scaffold structures were printed, debinded and sintered successfully using commercial PZT and BaTiO₃ powder. For the first time, it could be demonstrated, that using the MEX processing method, closed pore ferroelectric structure can be achieved without pore-former additive. After ceramic processing, the PZT scaffold structures were impregnated with epoxy resin to convert them into composites with 3-3 connectivity. A series of composites with varying ceramic content were achieved by changing the infill parameter during the 3D printing process systematically, and their electromechanical properties were investigated using the electromechanical aix PES device. Also, the Figure of merit (FOM) of these composites was calculated to assess the potential of this material as a candidate for transducer applications. A maximum for the FOM at 25 vol.% of PZT could be observed in this study.

Piezoelectric fibers are widely used in composites for actuator and sensor applications due to its ability to convert electrical pulses into mechanical vibrations and transform the returned mechanical vibrations back into electrical signal. They are beneficial for the fabrication of composites especially 1–3 composites, active fiber composites (unidirectional axially aligned PZT fibers sandwiched between interdigitated electrodes and embedded in a polymer matrix) etc, with potential applications in medical imaging, structural health monitoring, energy harvesting, vibration and noise control. However, due to the brittle nature of PZT fibers, maximum strain is limited to 0.2% and cannot be integrated into flexible sensor applications. In this contribution, a new approach to develop flexible ferroelectric hybrid fibers for soft body shape sensing is investigated. Piezoelectric particles incorporated in a polymer matrix and extruded as fiber, 0–3 composite in fibrous form is studied. Commercially obtained calcined PZT and calcined BaTiO ₃ powders were used in the unsintered form to obtain flexible soft condensed matter ferroelectric hybrid fibers. The extruded fibers were subjected to investigation for their electromechanical behavior as a function of electric field. The hybrid fibers reached 10% of the maximum polarization of their sintered counterpart.