Citation: Wang, X.; Li, X.; Wang, B.;
Chen, J.; Zhang, L.; Zhang, K.; He, M.;
Xue, Y.; Yang, G. Preparation of
Salt-Induced Ultra-Stretchable
Nanocellulose Composite Hydrogel
for Self-Powered Sensors.
Nanomaterials 2023, 13, 157. https://
doi.org/10.3390/nano13010157
Academic Editors: Deepak Kukkar
and Ki-Hyun Kim
Received: 14 November 2022
Revised: 17 December 2022
Accepted: 23 December 2022
Published: 29 December 2022
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
Preparation of Salt-Induced Ultra-Stretchable Nanocellulose
Composite Hydrogel for Self-Powered Sensors
Xiaofa Wang
1
, Xincai Li
1
, Baobin Wang
1,2,
*, Jiachuan Chen
1,
*, Lei Zhang
1,2
, Kai Zhang
1
, Ming He
1
, Yu Xue
1
and Guihua Yang
1
1
State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology,
Shandong Academy of Sciences, Jinan 250353, China
2
Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control, College of Light Industry and
Food Engineering, Guangxi University, Nanning 530004, China
* Correspondence: baobinqlu@edu.cn (B.W.); chenjc@qlu.edu.cn (J.C.)
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
µ
A,
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.
Keywords:
cellulose nanocrystals (CNCs); hydrogel; self-powered sensor; triboelectric nanogenerator
(TENG); strain sensor
1. Introduction
The booming development of artificial intelligence and Internet of Things (IoT) in-
spires the next generation of wearable electronics [
1
–
3
]. The conventional passive sensors
integrated with power supply suffer in regard to portability and long-lasting utilization, as
they hardly meet the requirements for the current wearable devices. Triboelectric nanogen-
erators derived flexible self-powered sensors which can fulfill the power supply function,
as well as sensing applications, demonstrate a promising candidate for the next generation
of sensors [4–6].
Hydrogels are hydrophilic polymer networks infiltrated with abundant water/ionic
liquid [
7
,
8
]. The highly tunable properties, such as mechanical property, ionic conductivity,
and biocompatibility, enabled the application of hydrogels as the electrode part of TENGs.
The common single-network hydrogels are restricted by the inferior mechanical robustness
and durability [
9
,
10
]. Nanocomposite incorporation is considered to be an efficient strategy
to promote the mechanical properties of the hydrogel [
11
,
12
]. By introducing noncovalent
interactions into the hydrogel matrix [
13
,
14
], the mechanical properties, such as mechan-
ical robustness, stretchability, and durability, could thus be enhanced. Moreover, other
Nanomaterials 2023, 13, 157. https://doi.org/10.3390/nano13010157 https://www.mdpi.com/journal/nanomaterials
