Spruce milled wood lignin: linear, branched or cross-linked?

Abstract

<p>Plausible up-to-date structural model of spruce MWL in agreement with the current structural and molecular weight data.</p>

Deciphering lignin heterogeneity in ball milled softwood: unravelling the synergy between the supramolecular cell wall structure and molecular events

“…The total β-O-4' was then estimated using the sum of the integrals at 70.8/4.74 ppm (β-Ο-4' α-ΟΗ), 79.5/4.46 ppm (α-etherified) and 85.3/3.9 ppm (DBDO) and found to be 35% per 100 Aromatic rings. It is worth to note that lignin-lignin benzyl ethers, as well as lignin carbohydrate benzyl ethers, both present in β-aryl ether structures, exist in milled wood 11,36 and is therefore critical to keep in mind that the etherification with solvent achieved here will result in a signal that overlaps with the original benzyl ethers. The discussed region was also heavily overlapped with carbohydrate signals in the original sample and not included in the β-O-4' evaluation of the original WWE fraction.…”

“…Furthermore, lignin-lignin benzyl ethers also resonate in this region. 11 The total β-O-4' content in lignin can be approximated by HSQC after setting the signals of C2-Ar to 100 and using the integrals of the HSQC signals in the following equation: In Figure 10, the β-O-4' content for the populations obtained when milling was performed in the two atmospheres is presented as a function of milling time. It is clear that the β-O-4' is significantly lower in the WWE than in the alkaline and IL/EtOH, H + samples.…”

“…8,9 Recent work by Balakshin and co-workers revisited this debate of linearity in MWL and based on combined NMR analyses and size exclusion chromatography studies concluded that MWL is a highly branched and crosslinked polymer. 11 All aforementioned protocols of MWL extraction and study have extensively utilized ball milling as a necessary, mechanical pretreatment. Ball milling reduces the particle size and increases the surface area of the material, which also increases accessibility to the fibers, hence expedite the extraction.…”

“…12,13 It has also been shown, that the structural changes induced are related to the milling time and intensity. 11,14 During ball milling, the wood particles are introduced to a jar and grinding balls are added. Through collisions with the grinding balls and jar, a combination of compression and shear stress forces create cracks to the substrate.…”

Hardwood versus softwood Kraft lignin – precursor-product relationships in the manufacture of porous carbon nanofibers for supercapacitors

“…It can be described as a polymer with a crosslinked, complex and three-dimensional structure of phenylpropanoid units bonded through various ether bonds (C-O-C) or carbon-carbon (C-C) linkages. 4 Together with its high degree of aromaticity and its high carbon content (>60%) lignin is an ideal candidate for the preparation of porous carbons with good yield, which is a distinct difference to other biopolymers, such as cellulose, hemicellulose or chitosan. 5 The reactions during the Kra process yielding new structural arrangements (building units and linkages) and chemical compositions of Kra lignins have been the focus of several research works in the past.…”