In situ preparation of monodisperse lignin-poly (lactic acid) microspheres for efficient encapsulation of 2,4-dichlorophenoxyacetic acid and controlled release

Pesticide-controlled release systems play a key role in reducing the use of pesticides and extending the lifetime of active ingredients and are therefore essential for environmental protection. Herein, composite microspheres (2,4-D@AL-PLA) loaded with 2,4-dichlorophenoxyacetic acid (2,4-D) were prepared in situ by emulsification-solvent volatilization using lignin-modified poly (lactic acid) as the precursor materials (AL-PLA). The rigid characteristics and three-dimensional structure of lignin macromolecules not only make the surface of 2,4-D@AL-PLA smooth, round and monodisperse but also endow them with a distinct porous skeleton and typical cavities. Accordingly, the 2,4-D@AL-PLA exhibited high efficiency in pesticide loading (45.43 wt%) and encapsulation (87.87%). Hydrogen bonding between lignin and PLA played a key role in controlling the release of 2,4-D from microsphere and imparted pH/temperature-responsive release properties to the model molecules. Kinetic studies showed that the release of 2,4-D followed a first-order kinetic model and the release mechanism was Fick diffusion, i.e., where the 2,4-D molecule achieved diffusion from the porous backbone of the microspheres. Moreover, the bioactivity test showed that the 2,4-D-loaded microspheres could effectively inhibit the growth of dicotyledonous weeds. This work provides a new way for designing environmentally friendly pesticide controlled-release systems and opens up new possibilities for applications in pesticide delivery.