Solvent-free manufacturing and 3D printing of ceramic-rich biopolymeric PHA-based piezocomposite for eco-friendly mechanical sensors

Similarly to the developments in green electronics, the emerging field of additive piezo-electronics increasingly focuses on more sustainable electroactive materials and cleaner production workflows. However, solution processing with hazardous solvents remains common, even for hybrid organic-inorganic piezoelectric materials (piezocomposites) made from eco-friendly biopolyesters polyhydroxyalkanoates, including ductile copolymer poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)(PHBHHx). Therefore, we investigated the solvent-free extrusion-based manufacturing and fused filament fabrication (FFF) of lead-free piezoceramic-rich PHBHHx composite with 80 wt% of barium titanate (BTO). Physicochemical characterization of filaments and prints revealed favorable melt reprocessing capability of PHBHHx as both neat and BTO-rich biopolymers retained chemical structure and thermal stability after three remelting cycles (single or double extrusion at 130 °C–140 °C and FFF at 170 °C). The re-extrusion and FFF processes were calibrated to ensure consistent printability of well-homogenized and well-fused piezocomposite (0–3 connectivity). The tensile loading of neat and BTO-rich PHBHHx structures at increasing speeds revealed complex material behavior of strain-rate-dependent strengthening, weakening, hardening and softening. Despite the high BTO fraction, the composite maintained acceptable flexibility, although the tensile strength decreased due to weaker filler-matrix interfacial bonding. The piezoelectric response and stabilization (d33 decay due to initial ferroelectric depolarization) were analyzed over a wide range of poling fields and durations. The 3D-printed piezocomposite demonstrated excellent high-field poling capability up to ∼22 kV mm−1. It provided a comparatively high maximum piezoresponse of ∼11 pC/N, matching the predictions of the Jayasundere–Smith model for two-phase particulate composites. The presented sustainable and scalable melt-based workflow is accessible to the 3D printing community, supporting democratization and further advances in the material extrusion additive manufacturing of piezoelectric sensors, energy harvesters/nanogenerators and other devices. The experimental findings are useful for the development of environmentally safe melt processing routes to produce highly filled PHBHHx-based composites.