Thermoresponsive lignin-based polyelectrolyte complexes for the preparation of spherical nanoparticles: Application in pesticide encapsulation.

Lignin-based nanoparticles hold tremendous potential for various applications. This study proposes an innovative and straightforward method for the synthesis of spherical hybrid lignin nanoparticles (hy-LNPs) with a tunable pore structure. The approach involves blending lignin with 20 wt% polyamide-epichlorohydrin, resulting in the formation of thermoresponsive lignin-based polyelectrolyte complexes. Upon heating to 80 °C, the complexes undergo self-assembly into uniform spherical nanoparticles, achieving a minimum polydispersity index (PDI) as low as 0.08. The study reveals that nanoparticle formation involves simultaneous collapse and growth. During collapse, hy-LNPs become more compact, increasing their elastic behavior and inhibiting particle coalescence, which is critical for the formation of stable, low-dispersibility nanoparticles. Contrary to the expectation that collapse would reduce pore size, the average pore size of the hy-LNPs increases from 24.9 nm to 35.8 nm, likely due to the coalescence of smaller pores into larger ones. Furthermore, this straightforward method was applied to encapsulation β-cypermethrin, achieving an encapsulation efficiency of up to 95 % and reducing the release rate in an ethanol-water solution from 90.6 % to 63.1 % over 5 h. The thermoresponsive lignin-based polyelectrolyte complexes provide a new pathway for the controlled preparation of lignin-based nanoparticles. These nanoparticles demonstrate promising potential for applications such as drug encapsulation.