Effect of different isolation methods on structure and properties of lignin from valonea of Quercus variabilis

Valonea of Quercus variabilis Blume, an abundant feedstock in China, can be used for tannin. However, there are little studies about lignin from this material. The present study aimed at lignin from the valonea: (1) Ethanol lignin (EL), alkali lignin (AL), milled wood lignin (MWL) and enzyme hydrolysis lignin (EHL) were prepared from the valonea of Q.variabilis Blume. (2) The effect of different isolation processes on the lignin chemical and physical features were studied by UV-vis, FT-IR, GPC, TG and (1)H NMR. (3) Antioxidant activities of four lignin preparations were evaluated by DPPH, ABTS and FRAP assays. The results showed that the valonea of Q. variabilis contained mass lignin and four lignin preparations were GSH-type with little differences. The MWL contained the least functional groups (1.75 mmol/g MeO, 0.87 mmol/g ArOH and 1.27 mmol/g AlkOH), the poorest thermostability (onset degradation temperature=111°C, maximum rate of degradation=268°C) and the highest antioxidant activity. The EHL had the highest molecular weight (Mw=1,429 g/mol; Mn=746.18 g/mol). This study provided a theoretical basis for the development and utilization of lignin from the valonea of Q. variabilis.