Structural and Thermal Characterization of Milled Wood Lignin from Bamboo (Phyllostachys pubescens) Grown in Korea

The structural and thermal characterization of milled wood lignin (MWL) prepared from bamboo (Phyllostachys pubescens) grown in Korea was investigated, and the results were compared with bamboo MWLs from other studies. The C-9 formula of the bamboo MWL was C9H7.76O3.23N0.02 (OCH3)(1.41). The Mw and Mn of MWL were 13,000 and 4400 Da, respectively, which resulted in a polydispersity index (PDI) of 3.0. The PDI of the prepared MWL was higher than other bamboo MWLs (1.3-2.2), suggesting a broader molecular weight distribution. The structural features of MWL were elucidated using FT-IR spectroscopy and NMR techniques (H-1, C-13, HSQC, P-31 NMR), which indicate that MWL is of the HGS-type lignin. The major lignin linkages (beta-O-4, beta-beta, beta-5) were not different from other bamboo MWLs. The syringyl/guaiacyl ratio, determined from H-1 NMR, was calculated as 0.89. P-31 NMR revealed variations in hydroxyl content, with a higher aliphatic hydroxyl content in MWL compared to other bamboo MWLs. Thermal properties were investigated through TGA, DSC, and pyrolysis-GC/MS spectrometry (Py-GC/MS). The DTG(max) of MWL under inert conditions was 287 degrees C, and the T-g of MWL was 159 degrees C. Py-GC/MS at 675 degrees C revealed a syringyl, guaiacyl, p-hydroxyphenyl composition of 17:37:47.