Fig. 6

FTIR spectra of untreated and pretreated RS and lignin samples. a FTIR spectra of RS samples. The broad bands in the 3400–3300 cm⁻¹ region, the band at 2920 and 897 cm⁻¹ were cellulose characteristic peaks. The shoulder peak at 1736 cm⁻¹ which associated with the carbonyl band (C=O) in lignin and/or hemicelluloses. The peaks at 1648, 1512 and 1427 cm⁻¹ representing the lignin aromatic ring structure. b FTIR spectra of isolated lignin from RS samples. The shoulder peak at 3396 cm⁻¹ derived from the O–H stretching. The absorption peaks at 2919 and 2848 cm⁻¹ were the structure of the side chain in lignin. The peak at 1659 cm⁻¹ derived from conjugated carbonyl (C=O). The characteristic peaks of the benzene ring skeleton appeared at 1593, 1507 and 1421 cm⁻¹. The absorption peaks of S units and condensed G units at 1329 cm⁻¹. G units C=O stretch at 1270 cm⁻¹