Studies on the Effect of Ball Milling on Lignin Structure Using a Modified DFRC Method

Abstract

The structures of milled wood lignin (MWL), cellulolytic enzyme lignin (CEL), and residual lignin (REL) from a loblolly pine were analyzed using a modified derivatization followed by reductive cleavage (DFRC) method developed to allow the quantitative determination of three different structural monomeric products originating in lignin: phenolic beta-O-4, alpha-O-4, and etherified beta-O-4 structures. Results show that MWL and CEL are structurally identical, with an increased phenolic beta-O-4 content compared to that of the original Wiley milled wood. These results indicate that the portion of lignin linked to carbohydrates and that not linked to carbohydrates are structurally the same. Modified DFRC analysis of the effect of ball milling on the structure of lignin in wood, MWL, CEL, and REL indicate that vibratory ball milling does not change the lignin structure provided certain precautions are taken. Specifically, dry vibratory ball milling under a nitrogen atmosphere causes substantial structural changes including condensation, whereas vibratory ball milling in toluene had little effect on the lignin structure. This indicates that the structural differences observed in MWL and CEL arise because of the extraction procedure, which preferentially extracts phenolic lignin structures. MWL and CEL are representative of the total lignin in wood; however, due primarily to the solvent extraction process, higher phenolic hydroxyl contents are observed. Nitrobenzene oxidation showed structural results similar to those from the modified DFRC method.

Determination of ethylenic residues in wood and TMP of spruce by FT-Raman spectroscopy

“…However, MWL is not represen tative of the whole lignin of a tree, because the yields are low and lignins derived from different morphological regions may be over-or under-represented (Maurer and Fengel 1992;Terashima et al 1992). Moreover, the iso lation steps -mainly the milling -involved modify lignin chemically to some degree (Ikeda et al 2002;Guerra et al 2006). In the present work, a new approach based on FTRaman spectroscopy is proposed that permits in situ quantification of the ethylenic structures in wood.…”

Biological Treatment of Poplar Wood with White-rot Fungus Trametes hirsuta C7784: Structural Elucidation of the Whole Lignin in Treated Wood

“…No H units were observed in the MWL fractions, which seemed contradictory to the results of the quantitative 31 P NMR analysis. However, it should be highlighted that the specific existing site of the H type lignin unit in plant cell walls made it hard to be isolated by ball milling (Ikeda et al 2002). Therefore, the signal belonging to H unit correlations could only be seen at the lower contour levels in the sidechain region of the spectra of MWL fractions (not shown).…”

Perdeuterated Pyridinium Ionic Liquids for Direct Biomass Dissolution and Characterization

“…Therefore, the presence of pyridinium chloride salt is crucial for the successful dissolution of the ballmilled sample. A shortcoming of using ball-milled sample is that ball-milling processing has been reported to induce some chemical changes in the structure of lignin (Kondo et al, 1995;Ikeda et al, 2002;), which will affect the accuracy of native lignin characterization. Other shortcoming includes that ball-milled process takes up to 7 days and is less efficient if a large number of samples need to be characterized.…”