Preparation and Characterization of Lignin Polymeric Nanoparticles Using the Green Solvent Ethylene Glycol: Acid Precipitation Technology

Alkali lignin (AL) was prepared by the acidification of black liquor obtained from a pulp and paper factory. The average molecular weight of the AL (2,530 g/mol) was determined using gel permeation chromatography (GPC). Alkali lignin modified by ethylene glycol and lignin nanoparticles (LN) were prepared via acid precipitation technology. Reactions in a pH range of 4 to 6 were evaluated while preparing the nanoparticles. Lignin nanoparticles were stable at pH 4 to 10. The sizes of the nanoparticles were assessed with dynamic light scattering (DLS); the average diameter of the nanoparticles at pH 4 was 52.7 nm, which was confirmed by SEM. LN has polar centers that can produce an interacting interface with the polymer matrix in which it will be dispersed. The morphologies and structures of combinations of AL and LN were investigated using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis-derivative thermogravimetric (TGA-DTG). The FTIR spectra clearly showed that the positions of the peaks in lignin nanoparticles shifted to slightly lower values due to the interaction between lignin molecules and ethylene glycol.