A comparative study of bamboo ( Phyllostachys incarnata Wen) milled wood lignin and the successively alkali-fractionated lignins.

The chemical composition and structural characterization of the milled wood lignin (MWL) and successively alkali-fractionated lignins from bamboo ( Phyllostachys incarnata Wen) were comparatively investigated using Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), 2D heteronuclear single quantum coherence (HSQC), and alkaline nitrobenzene oxidation. It was found that bamboo MWL (S/G ~ 1.3) is of SGH type with a considerable amount of esterified p-coumaric acid and etherified ferulic acid. Molecular weights of 3,320 g/mol for MWL and varying weights between 970 and 3,430 g/mol for the alkali-fractionated lignins were obtained. Moreover, 2D HSQC of MWL showed a predominance of β- O-4′ linkages (65%), followed by β-β′ linkages (15%) and lower amounts of β-5′ (7%), β-1′ (4%), 5-5′ (4%) linkages, and cinnamyl acetate end groups (5%). In addition, a percentage (~45%) of the lignin side chain was found to be acylated at the γ-carbon. However, the alkali-fractionated lignins lost parts of these linkages during successive alkaline fractionation processes. [ABSTRACT FROM AUTHOR]