Cationic modified lignin: Regulation of synthetic microspheres for achieving anti-photolysis and sustained release of the abscisic acid

Lignin is an abundant, renewable natural resource that shows UV resistance and whose amphiphilicity can be modified, which means that it could potentially encapsulate photo-sensitive agrichemicals. However, current technical lignins, e.g., alkaline lignin (AL), tend to form large aggregates, which severely limits its encapsulation performance. In this study, three cationic surfactants were selected for hydrophobic modification of AL, and to produce AL microspheres (AL-MPs) encapsulating abscisic acid (ABA). The surfactants tested were dodecyl tetramethyl ammonium bromide DTAB (single C12 chain), dimethyl behenyl ammonium bromide DDAB (two C12 chains) and cetylpyridinium chloride CPC (single C16 chain). The particle sizes, zeta-potentials, and encapsulation efficiencies of the AL-MPs were modified by changing the type of the surfactant and the weight percentage (wt%) of AL. The range of particle sizes, zeta potentials and encapsulation efficiencies were 232-1226 nm, -56.1-18.7 mV, and 62-78%, respectively. Fourier transform infrared spectroscopy (FTIR) was used to characterize the MPs. The photolysis protection and release of ABA from ABA-loaded MPs (e.g., ABA@AL-DDAB) were studied and a release kinetics model was built to probe the release behaviour. The effects of ABA@AL-MPs on the salt tolerance of rice seedlings under salinity stress were studied, and the mechanism is discussed. ABA@AL-MPs effectively protected the seedlings from growth inhibition by salinity stress. ABA@AL-DDAB was the most effective formulation, outperforming ABA@AL-CTAB and even the no-salt control. DDAB is less cytotoxic than CTAB and has the potential, when combine with lignin to encapsulate ABA and other agrichemicals to produce formulations with photolysis resistance and sustained-release properties.

Automated summary

Lignin, a renewable natural resource with UV resistance, was modified by cationic surfactants to produce microspheres encapsulating abscisic acid (ABA). The study showed that the type of surfactant and the weight percentage of lignin played a significant role in modifying the particle size, zeta potential and encapsulation efficiency of the microspheres. Among the surfactants tested, dodecyl tetramethyl ammonium bromide (DTAB) was the most effective in encapsulating ABA.