(726d) Lignin Nanoparticles (LNPs) Fabrication through Tailored Lignin Reactivity By Innovative Sequential Organosolv Fragmentation Approach (iSOFA)

Sustainable biorefinery of lignocellulosic biomass to usable platform molecules for producing a broad and multifunctional array of value-added products are key to achieving a green biobased economy. Recently, lignin valorization has been considered as an essential process for the sustainability of biorefineries. Despite various efforts, lignin valorization is still hindered by the poor fractionation performance due to its inherent heterogeneity and low reactivity, which is highly sensitive to the fractionation approach employed. To address these challenges, four sequential organosolv fragmentation approach (SOFA) configurations were developed to deconstruct biomass, fractionate the lignin and tailor its chemistry and reactivity. In a biorefinery concept, carbohydrate output in each SOFA at different stages was taken into consideration. Upon the process, the glucose and xylose yield increased in the order: stage 3>stage 2>stage 1, suggesting the improved monomer sugar release from biomass at the later stage of SOFA.

The lignin with specific reactivity fractionated from each SOFA was subsequently used to fabricate lignin nanoparticles (LNPs) via self-assembly. Results showed that the effective diameter of LNPs from each SOFA followed the order stage 2 > stage 3 > stage 1, and the smallest effective diameter was 130 nm obtained from SOFA using ethanol plus sulfuric acid. The half width, polydisperity index (PDI), and zeta potential of these LNPs were less than 50 nm, 0.08, and -50 mV, respectively, suggesting the uniform distribution and good stability of LNPs. As observed, no specific aggradation occurred during long time storage, suggesting that the LNPs dispersion was very stable in pure water. These LNPs also presented good stability at a broad range of pH values and ionic strength. Taken together, LNPs produced from SOFA were more uniform and stable due to relatively small particles size, PDI, and low zeta potential. 2D HSQC and ³¹P NMR analysis revealed that SOFA using ethanol plus sulfuric acid enriched G-type lignin, reduced S-type lignin, and thus decreased the S/G ratio. It decreased more β-O-4 and β–β linkage groups, indicating the de-polymerization of lignin. Most importantly, SOFA using ethanol plus sulfuric acid exposed more phenolic hydroxyl groups and less carboxylic hydroxyls groups, which was beneficial to the formation of uniformed and stable LNPs. As a result, high-quality LNPs with round shape, narrow size distribution, reduced polydispersity, and good stability have been fabricated through tailoring the lignin reactivity by SOFA. Fabrication of LNPs will open up a green and sustainable pathway for upgrading the lignin stream and thus contribute to the economic feasibility of biorefineries.