High-Throughput Synthesis of Lignin Particles (∼30 nm to ∼2 μm) via Aerosol Flow Reactor: Size Fractionation and Utilization in Pickering Emulsions

Abstract

An aerosol flow reactor was used for the first time for high-throughput, high yield synthesis of spherical lignin particles with given inherent hydrophilicity, depending on the precursor biomolecule. In situ fractionation via Berner type impactor afforded populations with characteristic sizes ranging from ∼30 nm to 2 μm. The as-produced, dry lignin particles displayed excellent mechanical integrity, even after redispersion under high shear in either mineral oil or water. They were effective in the stabilization of oil-in-water (O/W) Pickering emulsions with tunable droplet size, depending on the dimension of the lignin particles used for emulsification. The emulsion stability correlated with particle concentration as well as the respective lignin type. For the O/W emulsions stabilized with the more hydrophilic lignin particles, negligible changes in phase separation via Ostwald ripening and coalescence were observed over a period of time of more than two months. Together with the fact that the lignin particle concentrations used in emulsification were as low as 0.1%, our results reveal a remarkable ability to endow emulsified systems with high colloidal stability. Overall, we offer a new, high-yield, scalable nanomanufacturing approach to producing dry spherical lignin particles with size control and high production capacity. A number of emerging applications for these organic particles can be envisioned and, as a proof-of-concept, we illustrate here surfactant-free emulsification.

Pickering emulsions: Preparation processes, key parameters governing their properties and potential for pharmaceutical applications

“…For Pickering emulsion stabilization, lignins were used as nanoparticles [213][214][215][216] (see Table 3).…”

“…Lignin nanoparticles can be prepared by numerous preparation methods such as precipitation, emulsification-polymerization [214] and aerosol flow [213]. Lignin can also be modified chemically by, for example, alkylation, acetylation, esterification or polymer grafting.…”

Lignin from Micro- to Nanosize: Production Methods

“…Ago et al [114] used an aerosol reactor (see Figure 12) for the synthesis of lignin particles in the size range of 30 nm to 2 µm including a fractionation step. The process is comprised of a continuous atomizer, which forms an aerosol out of the lignin precursor solution, a heating tube passed by the aerosol with the aid of a gas carrier and a Berner-type low-pressure impactor for the collection and fractionation of the dry particles [115].…”

“…Generally, the particle size distribution became broader when the mean particle size shifted to lower values. SEM and TEM images showed solid spherical particles with smooth surfaces (see Figure 13) for all three kinds of lignin and the particles’ morphology particles was preserved after redispersion in different media under heating or shear [114]. …”

“…F1-10 indicates fraction and the scale bar is 2 µm Reprinted with permission from Ago et al [114]. Copyright 2016 American Chemical Society.…”