New Green Hydrogels Based on Lignin

The development of various green materials from lignin, which is most often considered as waste, is of prime interest from environmental and economic points of view. In the last years, only few studies regarding the use of lignin as a backbone component in the hydrogels have been made. The potential efficacy of lignin in hydrogels with particular emphasis on synthesis and characterization was investigated. By using steam explosion lignin from aspen wood or the corresponding epoxy-resin mixed with poly(vinyl alcohol), a series of new green hydrogels were prepared by covalent crosslinking in the presence of the epichlorohydrin. The unmodified and modified lignins were characterized by determination of functional groups content (OH _T , OH_ph, OCH₃ and epoxy groups), average particle size and zeta potential. The intermolecular interactions between lignin and poly(vinyl alcohol) was evaluated by Fourier transform infrared spectroscopy (FTIR), when the achievement of the cross-linking reaction was proved. The structural features of lignin-based hydrogels were revealed by X-ray diffraction (XRD) analysis. The scanning electron microscopy (SEM) images showed the porous nature of the hydrogels and that the pore size increase with increasing the lignin content. The yield in hydrogel showed a dependence on the structure of the lignins. In addition, it has been established that the lignin nature significantly influences the swelling process of hydrogels.