Extraction and characterization of lignin from corncob residue after acid-catalyzed steam explosion pretreatment

Corncob residue after acid catalyzed steam explosion (CRSE) is rich in cellulose and lignin. However, the structure of the lignin present in the CRSE has not been studied in detail and this hinders its application. An enzymatic mild acidolysis lignin (EMAL) extraction is adopted to process the CRSE where the extraction conditions are modified to improve lignin recovery and purity. Extraction severity factor is calculated and correlations between it and lignin recovery, lignin purity and total phenolic groups are evaluated. The best extraction condition produces lignin with a purity of 99.0% and a yield of 57.3%. A comparative study between lignin samples extracted under the best condition from the CRSE and untreated corncob (CC) is conducted. The structures of extracted lignin samples are investigated by using P-31 NMR, 2D-HSQC NMR, FTIR and GPC. Although SE pretreatment caused degradation of lignin, the abundance per 100 aromatic units of beta-O-4' linkages is 46.0, which is higher than most technical lignins. The molecular weight of CRSE EMAL is found to be higher than that of CC EMAL due to condensation reactions. Antioxidant property of CC EMAL and CRSE EMAL is measured and compared. The data shows that CRSE EMAL possesses better antioxidant activity (IC50 = 128 mu g/mL) than CC EMAL (IC50 = 238 mu g/mL), which makes CRSE EMAL an ideal additive for polymer composites.