Ultrafast gelling using sulfonated lignin-Fe3+ chelates to produce dynamic crosslinked hydrogel/coating with charming stretchable, conductive, self-healing, and ultraviolet-blocking properties

Developing an ecological and economical method for fabrication and application of polymer hydrogels is important for the hydrogel/coating electronics. Here, a dynamic oxidation and coordination system composed of sulfonated lignin (SL) and Fe3+ was introduced to assemble multifunctional Fe-SL-g-polyacrylic acid (PAA) hydrogel at 20 ℃ in a time scale of minutes instead of hours. The SL-Fe3+ system can rapidly activate the ammonium persulfate (APS, initiator), and then it instantaneously provides abundant semiquinone and hydroxyl radicals to accelerate the formation of polymer chains. Moreover, the functional SL-Fe3+ chelates can also reversibly crosslink the polymer chains to form multifunctional hydrogels. Surprisingly, the resultant hydrogel obtained charming extension ratio (up to 1680%), conductivity (up to 7.0 × 10-2 S·m−1), and adhesive strength (up to 36.4 kPa). This technology was also applied to rapidly fabricate a transparent (up to 81%, thickness: 2 mm), UV-blocking (up to 99.7%, thickness: 2 mm), adhesive, and conductive hydrogel coating on substrates. Besides, the dynamic coordination inside the hydrogel imparts desirable self-healing capabilities to damaged network, with up to 98.5% recovery in conductivity and 85.7% in extension ratio. In short, this technology based on the sustainable SL-Fe3+ system greatly facilitates the rapid and low-cost preparation of multifunctional hydrogel/coatings, which have promising industrial applications in human–machine electronics.