Size-controlled preparation of lignin nanoparticles in a continuous process, TAPPICon25

A jet mixer was designed for nanoparticle production from lignin solutions at high concentrations, i.e. above 10%. Experiments were performed with industrial lignin dissolved in alkali and with HCl or NaHCO3 as counter solvents.

A first set of experiments was performed with dissolved lignin and HCl. These experiments showed that the mixing flow rate was crucial for obtaining lignin nanoparticles. The experiments also showed that the particles obtained were quite unstable. A larger particle size was obtained when solutions were left for 72 hours.

Lignin solubility was investigated by measuring the particle size distribution at different pH. Two peaks were observed in the size distribution, one around 10 nm corresponding to dissolved lignin and one around 300 nm corresponding to lignin nanoparticles. The intensity of the second peak decreased with increasing pH, and the lignin could be considered dissolved above pH 13.

Aging experiments were performed on lignin precipitations by adding glucuronic acid (GA), lauric acid (LA) or sodium dodecyl sulphate (SDS). There were some problems of dissolving LA and SDS, while GA prevented particle growth. It was also shown that the stability was increased with addition of ultrapure water (MQ), probably due to a lower ionic strength related to the lower pH. When dissolved lignin was mixed with NaHCO3 as counter solvent, agglomeration tendencies were observed during aging of the particle dispersions.

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