Photocurable Printed Piezocapacitive Pressure Sensor Based on an Acrylic Resin Modified with Polyaniline and Lignin

Abstract

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.

Lignin as a High-Value Bioaditive in 3D-DLP Printable Acrylic Resins and Polyaniline Conductive Composite

“…Low D p values have the advantage of allowing accurate control of the polymerization process and minimal over-cure, although the shortcoming of longer building times [ 36 ]. Further, the curing parameters are similar to those calculated for PANI and PANI MWCNT composites fabricated with the same acrylic matrix and photoinitiator content [ 23 , 31 , 32 ].…”

“…Preparation of Lignin. Lignin was extracted from Betula Alba bark by organosolv fractionation using as a solvent acetic acid and hydrochloric acid, as described in a previous reference [ 23 ]. The obtained lignin was lyophilized before its use.…”

“…In the field of electronics, lignin has been widely investigated [ 11 , 12 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ] for the manufacture of energy storage devices [ 22 ], electromagnetic shielding [ 16 , 17 ], organic cathodes [ 11 ], as a natural binder or even as a dopant in conductive polymers for the production of electrochemical capacitors or supercapacitors [ 12 , 18 , 19 , 20 , 21 ]. Due to the redox activity of the quinone/hydroquinone moieties, lignin derivatives effectively enhanced the capacitance of intrinsically conductive polymers, including poly(3,4-ethylenedioxythiophene), polypyrrole, and polyaniline (PANI) [ 23 ] as well as carbon-based materials such as graphene [ 19 ]. Sulfomethylated lignin has been shown to effectively dope PANI and increase the conductivity and dispersibility of lignin/PANI composites in water [ 24 ].…”

“…In a previous work, the authors developed a formulation based on the conductive filler PANI-lignin in a photocurable acrylic matrix, which proved to be valid for the manufacture of flexible wearable electronics and sensors [ 23 ]. The present research is focused on the incorporation of unmodified organosolv lignin as an additive to the photocurable resin.…”

Bio-Based Carbon Materials for High-Performance Supercapacitors

“…LS was better dispersed with polyaniline. In Figure 3 k,l,n, individual nanorods or nanoparticles can be found, the surface of which is partially covered by smaller spherical lignosulfonate particles, and the fibers became thinner after lignosulfonate incorporation, with a diameter of 50–100 nm [ 32 ]. This may be due to volume shrinkage caused by the thermal degradation of LS/PANI to charcoal [ 7 ].…”