Molecular Dynamics Study of Thermophysical and Mechanical Properties in Hydrated Lignin with Compositions Close to Softwood

Abstract

The hydrogen bonding network analysis of softwood lignin is relevant to designing novel technologies to overcome the recalcitrance of plant biomass in the industrial deconstruction and manufacturing of ligninbased carbon fibers. In this work, we examine, by atomistic simulations, the hydrogen bonding network in guaiacyl-rich lignin and guaiacyl-type lignin over a wide range of temperatures. We determine the formation of stable water-bridged dimeric complexes by the interaction of phenolic and aliphatic hydroxyl groups and π−π stacking between phenol rings, causing a slow dynamic of lignin with temperature. The interaction strength between water oxygen and hydrogen of hydroxyl groups in these lignin complexes is established. The formation of the ice crystal structure at low temperatures in the complexes explains the anti-plasticizing action of water, increasing the Young's modulus (E) of lignin systems at high hydration. Glass-transition temperature and E were successfully predicted by CHARMM force field for lignin at different hydrations.

Effect of Molecular Organization on the Properties of Fractionated Lignin-Based Thiol–Ene Thermoset Materials

“…Previous studies on lignin structures have revealed the presence of short distance ordering in the range of 4.0–4.2 and 5.3–6.1 Å considered to be related to sandwiched and T-shaped π–π stacking interactions, respectively. , Six predominant distances/sizes ( D 1 , D 2 , D 3 , D 4 , D II order3 , and D II order4 ) were observed in lignin samples by WAXS, as shown in Table and Figures S19–S24. Based on the distance within these repeating features, D 2 and D 3 can be attributed to T-shaped and sandwich π–π stacking (combined parallel displaced and cofacial parallel stacked) interactions between the abundant lignin aromatic rings. ,− This should however be considered a simplification due to the highly complex three-dimensional lignin network structures. These π–π stacking interactions between aromatic rings normally play an important role in the stability of the systems and their properties. ,, It is however not clear how these internal stacking interactions scale when being imbedded into a larger structural ordering.…”

A density functional theory study on interactions in water-bridged dimeric complexes of lignin

“…It is important to stress that the aim of this work is not to derive new structures for WBDCs starting from randomly different configurations but rather to corroborate that there may be structures whose geometries are like those estimated with MD simulations 26 trapped in a nearby local minimum of energy landscapes estimated with DFT calculations.…”

“…2 by removing -OCH 3 groups). 26 Thus, to obtain the methoxylated complexes SÁ Á ÁG and SÁ Á ÁS, one and two -OCH 3 groups were introduced into G units, respectively. This study was performed for simple lignin complexes having a high content of -OCH 3 in their units because the S-unit shows less crosslinking in the native lignin's network.…”

“…2. 25–27 In fact, the existence of WBDCs: G⋯S and S⋯S in native lignin is a consequence of the association of monolignols and its radicals in aqueous solution during their (bio)polymerization 2,28–31 rendering lignols in folded and extended-chain structures mediated by hydrogen bonding interactions between close HO4–O4 and HO7–O7 hydroxyl groups (Fig. 2a), 8 which participate in “coiled” structures found in the xylem tissue of tracheary elements of wood.…”

Atomistic Modeling of Lignocellulosic and Carbonaceous Fuels and Their Pyrolysis Reactions: A Review

“…Lignin Builder is another robust tool that can be used to construct lignin structures and study interaction with other components (Figure b) . Many authors have used this software to model lignin structures and understand their properties and behavior. − …”