Facile Preparation of Eco-Friendly, Flexible Starch-Based Materials with Ionic Conductivity and Strain-Responsiveness

Abstract

This work demonstrates a facile and "green" method to prepare eco-friendly, flexible, transparent, and ionically conductive starch-based materials, which have great potential for personal health-monitoring applications such as disposable electrodes. This method relies on the use of the CaCl 2 solution and enables both the efficient disorganization and amorphization of high-amylose starch granules with low energy consumption and the reinforcement of the starch chain network by starch−metal cation complexation. Specifically, the method involves a simple mixing of a high-amylose starch with the CaCl 2 solution followed by heating the mixture at 80 °C for 5 min. The whole process is completely environmentally benign, without any waste liquid or bioproducts generated. These resulting materials displayed tunable mechanical strength (500−1300 kPa), elongation at break (15−32%), Young's modulus (4−9 MPa), toughness (0.05−0.26 MJ/m 3 ), and suitable electrical resistivity (3.7−9.2 Ω•m). Moreover, the developed materials were responsive to external stimuli such as strain and liquids, satisfying the requirements for wearable sensor applications. Besides, composed of only starch, CaCl 2 , and water, the materials are much cheaper and eco-friendly (can be consumed by fish) compared with other polymer-based conductive hydrogels.

Green flexible electronics based on starch

“…The linear chain of amylose makes it more resistant to processing and may show better mechanical performance and less water sensitivity 150 . Liu et al 153 prepared flexible, transparent, ionically conductive hydrogel by simply mixing high-amylose starch with CaCl 2 solution. This material shown adjustable mechanical strength (500-1300 kPa), elongation at break (15-32%), Young's modulus (4-9 MPa), toughness (0.05-0.26 MJ/m 3 ) and suitable resistivity (3.7-9.2 Ω•m).…”

A multifunctional sustainable ionohydrogel with excellent low-hysteresis-driven mechanical performance, environmental tolerance, multimodal stimuli-responsiveness, and power generation ability for wearable electronics

“…[34][35][36][37] Among these, starch is considered as the favorite candidate for reducing internal friction in hydrogels using a glycerol/water binary solvent system due to its outstanding gelatinization abilities both in water and glycerol. [38][39][40][41][42] Establishing stiff starch networks in the entire solvent system can not only address the above-mentioned problems to some degree, but it can also allow a homogeneous gel matrix, avoiding further separation in the gel matrix. However, starch-based gels insuf-ciently improve the mechanical performances of hydrogels, as the hydrogen bonds in starch gels deteriorate signicantly and cannot dissipate external energy.…”

A stretchable, compressible and anti‐freezing ionic gel based on a natural deep eutectic solvent applied as a strain sensor

“…Starch was the most common natural polymer and the second most abundant carbohydrate in nature after cellulose. It had the characteristics of easy access to raw materials, renewable, low price and green 19 . Then, starch was composed of amylose and amylopectin, and its molecular chain contained a large number of hydroxyl groups (‐OH), which could form a hydrogen bond network with the polymer matrix 20 .…”

“…It had the characteristics of easy access to raw materials, renewable, low price and green. 19 Then, starch was composed of amylose and amylopectin, and its molecular chain contained a large number of hydroxyl groups (-OH), which could form a hydrogen bond network with the polymer matrix. 20 So, starch could be used as an eco-friendly material to enhance the mechanical properties of ionic gel.…”