Preparation of Salt-Induced Ultra-Stretchable Nanocellulose Composite Hydrogel for Self-Powered Sensors

Abstract

Hydrogels have attracted much attraction for promising flexible electronics due to the versatile tunability of the properties. However, there is still a big obstacle to balance between the multi-properties and performance of wearable electronics. Herein, we propose a salt-percolated nanocellulose composite hydrogel which was fabricated via radical polymerization with acrylic acid as polymer networks (NaCl-CNCs-PAA). CNCs were utilized as a reinforcing agent to enhance the mechanical properties of the hydrogel. Moreover, the abundant hydroxyl groups endow the hydrogel with noncovalent interactions, such as hydrogen bonding, and the robustness of the hydrogel was thus improved. NaCl incorporation induced the electrostatic interaction between CNCs and PAA polymer blocks, thus facilitating the improvement of the stretchability of the hydrogel. The as-obtained hydrogel exhibited excellent stretchability, ionic conductivity, mechanical robustness and anti-freezing properties, making it suitable for self-powered sensing applications. A single-mode triboelectric nanogenerator (C-TENG) was fabricated by utilizing the composite hydrogel as electrodes. This C-TENG could effectively convert biomechanical energy to electricity (89.2 V, 1.8 µA, 32.1 nC, and the max power density of 60.8 mW m−2 at 1.5 Hz.) Moreover, the composite hydrogel was applied for strain sensing to detect human motions. The nanocellulose composite hydrogel can achieve the application as a power supply in integrated sensing systems and as a strain sensor for human motion detection.

A Brief Review on Flexible Electronics for IoT: Solutions for Sustainability and New Perspectives for Designers

“…The biodegradability of the printed substrate is slightly lower than that of the non-printed substrate, also highlighting the importance of working on the eco-sustainability of the conductive layers. Without any doubt, the "nanopaper" technology, that is a relatively low-cost technology [124][125][126] for substrate fabrication for IoT applications, is strategic to fuel a transition toward a sustainable and green IoT, also working on the use of optimized nanocellulose with other materials and hybrid structures [127][128][129][130][131].…”

Nanotechnology Applied to Cellulosic Materials

“…This TENG allowed a voltage of 89.2 V and power density of 60.8 mW m −2 at 1.5 Hz to be obtained. Owing to its good flexibility, this TENG can be used in wearable components [118].…”

“…Responds to the possibility of fire in 5 s, can be wearable, and can trigger LED light or an electronic clock [122] With CNFs (from sugarcane bagasse), activated carbon nanoparticles, and natural rubber Power density of 2.74 W/m 2 and highest voltage output of 137 V CNFs are extracted from agricultural waste (sugarcane bagasse) [116] With CNFs (from bagasse pulp) and silica nanoparticles Superhydrophobic Can be used to transform the energy of ocean waves into electrical energy [117] With hydrogel formed by CNCs, NaCl, and acrylic acid polymeric blocks Ultra-elastic TENG that detects human bending movements (fingers, elbows, or wrists) [118] Has CNFs obtained via TEMPO-mediated oxidation and ammonium persulfate (APS)…”

Ionic hydrogels-based triboelectric nanogenerators for self-powered human–machine interfaces

“…As a synthesis material for hydrogels, CNC also possesses several advantages, including high water absorption capacity, excellent gel mechanical properties, biodegradability, and biocompatibility [150]. To enhance the robustness and stretchability of ionic hydrogels, Wang et al [72] proposed a CNC-based composite hydrogel with improved conductivity, mechanical performance, and frost resistance. Figure 4(f) demonstrates the schematic illustration of the preparation for CNC-based ionic hydrogel, where salt-permeated nanocellulose composite hydrogel was synthesized through free radical polymerization, utilizing the electrostatic interaction between salt ions and CNC as well as PAA.…”