Hydrothermal base catalysed treatment of Kraft Lignin for the preparation of a sustainable carbon fibre precursor

Industrial Kraft Lignin (KL) prepared by LignoBoost® technology was treated via hydrothermal base catalysed depolymerisation (HBCD). KL was dried and divided into methanol soluble and insoluble fractions. The insoluble fraction was treated in 1 M NaOH (aq) at 300 °C. After precipitation with HCl (aq), the solids yield was ca. 60 wt%. These solids demonstrated improved thermal stability and carbon content, increased solubility in MeOH and reduction in polydispersity. With a view to the use of the product in the preparation of carbon-based materials (e.g. carbon fibres (CF)), thermal analysis was undertaken, revealing a lack of a glass transition below the decomposition temperature, excluding melt pinning. However, a high solubility in organic solvents renders the product a suitable candidate for solvent spinning and for the production of renewable low-cost CFs. Additionally, the process generated an oily liquid phase with yields of ca. 10 wt% containing valuable catechol and methylated derivatives.