Production of Lignin-containing nanocellulose by FeCl3-catalyzed ternary deep eutectic solvent pretreatment system: Structural characteristics and emulsification capabilities

Abstract

Pretreatment method is one of the key factors to improve the quality of nanocellulose (NC) production. As a green novel solvent, ternary deep eutectic solvent (TDES) plays an important role in production of lignin-containing nanocellulose (LNC), however, higher reaction temperature would limit its industrial application. Herein, a novel strategy of FeCl3-catalyzed TDES (F-TDES) pretreatment combined microfluidization was proposed to produce LNC from poplar (PopulusL.) at lower temperature (80 °C). The TDES was composed of choline chloride, lactic acid, and p-toluenesulfonic acid in a molar ratio of 2:10:1. When the optimum dose of FeCl3 in per gram TDES system was 0.15 mmol (i.e. about 3.9% based on the weight of F-TDES), ribbon-like LNCs about 28.68 nm wide and 3.46 nm thick were obtained, which were smaller than that of lignin-free nanocellulose attained from the same preparation conditions. The LNC, lignin content 18.93%, displayed good dispersion stability in water and higher cellulose I crystallinity (57.8%) and thermal stability (Tmax=376 °C). Especially, the LNC exhibited more excellent emulsification performance and emulsion stability than NC, which was closely associated with its good amphiphilicity. Within the studied LNC concentration (0.1–0.4%) and oil/water mass ratio (20:80–50:50), increasing LNC concentration and/or oil/water mass ratio was beneficial for the stability of Pickering emulsions. The findings not only provide a milder route for producing LNC from lignocellulose, but also prove LNC would have promising prospects in emulsion systems.