Assembly of lignin-based colloidal particles: effects of cationic surfactants, molecular weight, and solvent on morphology

Sodium lignosulfonate (LS) is a lignin derivative, which has abundant resources and is an environmentally friendly raw material. In this study, cetyltrimethylammonium bromide (CTAB) and stearyltrimethylammonium bromide (STAB) were combined with LS at the isoelectric point for hydrophobic self-assembly. Transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) spectroscopy, and static contact angle data proved that LS/CTAB could form colloidal spheres, while LS/STAB could not form such spheres. The impact of the molecular weight of LS on the self-assembly of LS/CTAB was investigated by using the TEM, FTIR, and static contact angle data. The obtained results showed that LS/CTAB with 10 000-50 000 Da of LS could form colloidal spheres, while LS/CTAB with 3000-5000 Da of LS could not. In addition, the TEM images revealed that the solvent plays an important role in the morphology of LS/CTAB colloidal spheres. Finally, LS/CTAB colloidal spheres were used for the encapsulation of ibuprofen (IBU). The in vitro release behavior of IBU was proven to be pH-sensitive and exhibited controlled release properties. More than 85% IBU could be preserved in simulated gastric fluid, and over 75% could be released in simulated intestinal fluid. This work provides a theoretical basis for the preparation of LS/CTAB colloidal spheres and facilitates the expansion of its applications as a drug carrier.