Reactivity improvement of cellulolytic enzyme lignin via mild hydrothermal modification

Isolated by the cellulolytic enzyme lignin (CEL) process, water-alcohol (1:1, v/v) was introduced as co-solvent in the process of the hydrothermal treatment. The modification parameters such as reaction temperature and time, solid-to-liquid ratio, and catalysts (NaOH and NaOAlO₂) have been investigated in terms of the specific lignin properties, such as the phenolic hydroxyl content (OH_phen), DPPH free radical scavenging rate, and formaldehyde value. The CELs were also characterized by GPC, FT-IR and ¹H NMR spectroscopy, and Py-GC/MS. The key data are under optimal lignin modification conditions (solid-to-liquid ratio of 1:10 (w/v) and a temperature of 250°C for 60min) are: OH_phen content: 2.50mmol/g; half maximal inhibitory concentration (IC₅₀) towards DPPH free radicals: 88.2mg/L; formaldehyde value: 446.9g/kg). Both base catalysts decrease the residue rate, but phenol reactivities of the products were also detracted. Py-GC/MS results revealed that modified lignin had a higher phenolic composition than the CEL did, especially the modified lignin without catalyst (ML), which represented 74.51% phenolic content.