There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.

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In this context, dielectric polymeric materials are being investigated due to their scientific and technological interest since they combine dielectric properties with appropriate mechanical flexibility and simple processability. [2,3] Such composite materials show huge opportunities to be integrated in devices such as electronics, [4][5][6] sensors and actuators. [7] Within this context, additive manufacturing emerges as a set of advanced fabrication techniques that enable the production of fully functional electronic devices in one step printing. [1,[8][9][10] However, for photopolymerization-based 3D printing techniques the number of UV curable materials suitable for the fabrication of sensors and actuators is still scarce. [1] Research in this field pursues 3D printing materials with new features but also environmentally more friendly and sustainable, as demanded by today's society. [11][12][13] Techniques as stereolithography (SLA) and digital light processing (DLP) are based on the layer-by-layer solidification of a liquid photosensitive resin via UV-light exposure. [14] This is a tailorable process where multicomponent resins provide the photo-rheological and mechanical properties necessary to ensure a successful print. [15] The design of suitable materials for the manufacture of pressure sensors with high sensitivity and flexibility in wearable electronics is still a challenge. In this study, a flexible and portable pressure sensor is developed based on a photopolymeric formulation of polyaniline (PANI)/Lignin/acrylate. The amount of photoinitiator and the presence of lignin within the filler are investigated to obtain the best printability and capacitive response. Low PANI contents drastically increase the dielectric constant and 4 wt% photoinitiator improves the signal and sensitivity. A sensitivity of 0.012 kPa -1 is achieved in a linear range (0-10 kPa) with only 3.5 wt% PANI. Lignin improves both the dispersion of the filler within the matrix and the printability of the resin, due to lower absorptivity at the UV wavelength of the 3D printer. Thus, the PANI-Lignin filler is selected for the fabrication of a piezocapacitive prototype transducer. The pressure transducer demonstrate its practical application by responding to a human footfall and transmitting its corresponding electrical signal. This study shows the enhanced properties of lignin modified PANI acrylate composites. Based on lignin, an abundant natural waste, a sustainable photocurable cost-effective polymer is proposed for the fabrication of printable, wearable electronics.