[The performance and applications of lignin based hydrogels: a review]

Lignin is the only natural aromatic polymer and the second most abundant lignocellulosic resource in nature after cellulose, and its derived high-value products can be used in a variety of fields. An efficient, highly value-added and high-quality production of lignin is critical for lignocellulose biorefinery, but the complex and variable structure of lignin macromolecules, poor activity of reactions, and redundant functional groups make it difficult to prepare polymeric materials with stable properties. With the increasing research on lignin modification, the application of lignin composite hydrogels has also received great attention. In this paper, the preparation of lignin composite hydrogels based on the basic structural composition and reaction properties of lignin was briefly outlined. The current applications of lignin composite hydrogels, including biosensors, controlled release materials, environmentally responsive materials, adsorbent materials, electrode materials, and other materials, were summarized. Moreover, future perspectives of lignin-based composite hydrogels were prospected.