Lignin is a promising feedstock in sustainable formulations for agrochemicals not only because of its biodegradability but also because the biopolymer occurs naturally in the cell wall of plants and therefore is renewable and abundant. We used different lignin sulfonates to prepare stable aqueous dispersions of lignin nanocarriers loaded with agrochemicals by interfacial cross-linking in a direct miniemulsion. Despite the differences in structure and functionality, different lignin sulfonates were successfully methacrylated and degrees of methacrylation (>70%) were achieved. The resulting methacrylated lignin sulfonates were water-soluble and exhibited interfacial activity; they were used as reactive surfactants to stabilize oil droplets (cyclohexane or olive or rapeseed oil) loaded with a dithiol cross-linker [EDBET, 2,2'-(ethylenedioxy)bis(ethylthiol)] and a hydrophobic cargo (the fluorescent dye 1,3,5,7-tetramethyl-8-phenyl-4,4-difluoroboradiazaindacene or the commercial fungicides prothioconazole and pyraclostrobin). After the addition of a water-soluble base, the thia-Michael addition was initiated at the droplet interface and produced lignin sulfonate nanocarriers with a core-shell structure within oily core and a cross-linked shell. Nanocarriers with diameters of ca. 200-300 nm were prepared; encapsulation efficiencies between 65 and 90% were achieved depending on the cargo. When the amount of the cross-linker was varied, the resulting lignin nanocarriers allowed a controlled release of loaded cargo by diffusion over a period of several days. The strategy proves the potential of lignin sulfonates as a feedstock for delivery systems for advanced plant protection.

The delivery of agrochemicals is typically achieved by the spraying of fossil-based polymer dispersions, which might accumulate in the soil and increase microplastic pollution. A potentially sustainable alternative is the use of biodegradable nano- or micro-formulations based on biopolymers, which can be degraded selectively by fungal enzymes to release encapsulated agrochemicals. To date, no hemicellulose nanocarriers for drug delivery in plants have been reported. Xylan is a renewable and abundant feedstock occurring naturally in high amounts in hemicellulose - a major component of the plant cell wall. Herein, xylan from corncobs was used to produce the first fungicide-loaded xylan-based nanocarriers by interfacial polyaddition in an inverse miniemulsion using toluene diisocyanate (TDI) as a crosslinking agent. The nanocarriers were redispersed in water and the aqueous dispersions were proven to be active in vitro against several pathogenic fungi, which are responsible for fungal plant diseases in horticulture or agriculture. Besides, empty xylan-based nanocarriers stimulated the growth of fungal mycelium, which indicated the degradation of xylan in the presence of the fungi, and underlined the degradation as a trigger to release a loaded agrochemical. This first example of crosslinked xylan-based nanocarriers expands the library of biodegradable and biobased nanocarriers for agrochemical release and might play a crucial role for future formulations in plant protection.