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The global overabundance of electronic waste and ever‐increasing concerns regarding the energy‐and material‐intensive manufacturing processes associated with traditional electronics are driving the development of solution‐processed, degradable electronics. Of note, the industry‐dominating prevalence of harmful lead‐based materials in sensing and actuating devices drives the push for more eco‐friendly solution‐processed piezoelectric systems. Yet current ecofriendly multi‐material printing processes are limited by both the conventional challenges of multilayer processes as well as the low‐temperature thermal constraints of biodegradable materials. Herein, a novel approach for fabricating fully printed, sustainable piezoelectric transducers on paper substrates is presented. Low‐temperature screen‐printing processes are used to integrate non‐toxic KNbO3 layers with degradable carbon‐ or zinc‐based conductive inks into devices. The influence of electrode material on device characteristics is assessed, with effective piezoelectric coefficients reported as high as 4.6 pC N−1 and 5.1 pC N−1 for devices with carbon and zinc electrodes respectively. The potential of the developed technology is then demonstrated through the first‐ever instance of fully printed piezoelectric force sensors and acoustic speakers comprised entirely of green materials. By demonstrating entirely printable green piezoelectric devices compatible with various electrode materials, this work serves as a step towards developing more complex sustainable piezoelectric technologies in the future. [ABSTRACT FROM AUTHOR]

Combining recycling of paper wastes (WPs) with extrusion‐based additive manufacturing represents a sustainable route to cellular cellulose composites tailored for lightweight construction. Particularly, shear mixing of shredded WPs with an aqueous solution of a polymer binder like polyvinyl alcohol (PVA) yields aqueous pastes suitable for 3D printing. As a shear thinning additive, both WP and microfibrillated cellulose account for enhanced shear thinning and dimensional stability. Opposite to the formation of dense WP/PVA composites by melt extrusion, 3D printing of aqueous pastes produces cellular cellulose/PVA composites exhibiting hierarchical pore architectures. In spite of low densities around 0.8 g cm−3, high Young's modulus (2.0 GPa) and tensile strength (53 MPa) are achieved. Mechanical stability, water resistance, and even flame retardancy simultaneously improve by crosslinking with glyoxal and especially by mineralization. Multimaterial 3D printing combines the 3D dispensing of cellulose/PVA pastes with the simultaneous, staged, or subsequent spraying of aqueous water glass to enable mineralization of composite surface, bulk, and interlayers. Furthermore, the glyoxal‐mediated crosslinking affords thermo‐ and moisture‐responsive cellulose/PVA composites with programmable shape change induced either by heating at 100 °C or by exposure to moisture at 37 °C. [ABSTRACT FROM AUTHOR]