Upcycling Industrial Lignin Into Cationic Hydrogels With Potential for Sustainable Plant Protection

Bio-based antimicrobial materials are increasingly explored as sustainable alternatives for plant pathogen control. Here, we report a circular economy approach in which industrial kraft lignin was upcycled into cationic lignin (CL) and physically embedded within chitosan-genipin (CH-GPN) hydrogels to form CH-GPN-CL. These bioactive materials were evaluated for the in vitro inhibition of the plant pathogen Pseudomonas syringae pv. tomato DC3000. To enhance antimicrobial activity, kraft lignin was cationized with glycidyl trimethylammonium chloride (GTMAC) using different lignin/GTMAC mass ratios, producing CL samples with varying degrees of substitution (DS). Leaf infiltration-based phytotoxicity assays of CL using Nicotiana benthamiana showed no concentration- or DS-dependent phytotoxicity under buffered conditions, suggesting compatibility with infiltrated leaf tissue. Bacterial inhibition assays showed that GTMAC cationization strongly improved lignin antimicrobial activity. Based on strong activity and a lower lignin/GTMAC mass ratio, a representative CL sample was selected for incorporation into the hydrogel framework. The resulting CH-GPN-CL hydrogels retained gel-like behavior and porous morphology and showed enhanced in vitro antimicrobial activity compared to the control hydrogel without embedded CL. These findings highlight the potential of CH-GPN-CL hydrogels as sustainable bioactive materials for further plant protection evaluation.