Deconvolution and fractionation of constituents of Klason lignin extracts from switchgrass

Lignin is a complex phenolic bio-polymer with vast potential as a renewable source of bioenergy and bio-chemicals. Valorization of lignin to high value products is often challenged by limited understanding of the properties and composition of the bio-polymer its recalcitrance to depolymerization. Our knowledge of lignin depolymerization is also hampered by the availability of robust analytical tools and strategies for studying the macro-molecule. Here we report the development of a strategy for fractionating and characterizing the composition of Klason lignin extract from switchgrass. The lignin extract was fractionated by manipulating the physico-chemical properties of the moieties at ambient temperature and pressure. We observed that approximately 90% of the lignin moieties were soluble in water at high pH conditions. The residual insoluble lignin consists primarily of very high molecular weight moieties. The water-soluble lignin moieties were further fractionated and separated into soluble and insoluble fraction at neutral pH by manipulating the amphiphilic properties of the moieties. The neutral water soluble fraction was highly polydispersed, ranging in size from monomers to very high molecular moieties (≥ 100 kDa). In all, we identified 5 – 8 distinct types of lignin moieties from the lignin extracts with varying physico-chemical properties. These distinct lignin moieties were also observed in ionic-liquid pre-treated and organosolv lignin extracts. The neutral water-soluble fraction from this study is currently being utilized as a substrate for developing analytical strategies for evaluating lignin depolymerization and improving our understanding of their physico- chemical properties.