Synthesis and structural characterization of lignin/silica hybrid nanoparticles functionalized with sulfonic acid-terminated polyamidoamine

Abstract

Lignin nanoparticles (LNPs) with an average diameter ($\overline{d}_{n}$) of 78.2 nm were prepared via rapid pH decrease of alkaline solution to acidic state. Two lignin/silica hybrid (LSH) nanoparticles, i.e., LSH1 ($\overline{d}_{n}$ = 80.9 nm) and LSH2 ($\overline{d}_{n}$ = 83.0 nm), with different lignin contents were synthesized using LNP via sol–gel method and then aminated using 3-aminopropyltriethoxysilane. Polyamidoamine (PAMAM) was then grafted onto the aminated LSHs, resulting in LSHx-PAMAM G1.0 (x = 1 or 2). Firstly, methyl acrylate was reacted with aminated LSHs. Then, methyl ester groups in the 0.5th generation were reacted with ethylenediamine (EDA), resulting in the LSHx-PAMAM G1.0. Structure and functional groups of the bio-based nanoparticles were characterized quantitatively using adequate techniques. In addition, LSH1-PAMAM G1.0 was kept for a long time in EDA (pH 13), so that the physically bonded LNP was dissolved and S-PAMAM G1.0 was obtained. LSH1-PAMAM G1.0 and S-PAMAM G1.0 were sulfonated using 1,3-propanesultone and a high degree of sulfonation, i.e., 99.93% and 99.34%, respectively, was obtained.