Search

An integrated lignin biorefinery process was studied by chemometrics. A regime for structurally preserved lignins with tuneable properties was identified.

Studies have shown that the size of LNP depends on the molecular weight (Mw) of lignin.

Mechanical milling of lignocellulose has been used in several studies as a key pretreatment enabling the extraction of lignin from various sources for structural analysis. It is also applied as an alternative to wet chemical methods for lignin valorization. However, the changes caused to the plant cell walls at different hierarchical scales and how they relate to the molecular events are still poorly understood. In this context, we sought to gain deeper insights into molecular heterogeneity in milled cell walls, with a primary focus on lignin. A novel fractionation protocol was developed to enable the advanced analysis (1D and 2D NMR, SEC, XRD) of molecular populations in ball milled fiber walls. The methodology was applied to follow the emergence of such populations through the milling process, and in different milling environments. Lignin heterogeneity in the ball milled fibers was found to consist of distinct populations of small and large fractions of lignin carbohydrate complexes and pure lignin fractions, both with differences in lignin inter-unit abundances. Lignin-carbohydrate bonds of benzyl ester type were unequivocally demonstrated for the first time by combination of HSQC-HMBC NMR analysis. γ-Ester LCC and phenyl glycoside LCCs were also detected. Furthermore, an important branching point in lignin, previously controversial, namely the 4-O-etherified 5-5′ substructure, is unequivocally shown here by HSQC-HMBC analysis of the milled wood isolates, and supported by biomimetic lignin (DHP) to originate from the native structure. Based on the advanced characterization, the origin of lignin heterogeneity in ball milled fibers is proposed to result from the uneven distribution of the applied mechanical energy, where synergistic effects between crystalline and amorphous states play a central role. Accordingly, a plant cell wall model is proposed and a complete mechanism of its disintegration during the milling exercise is presented. The unveiled heterogeneity model of ball milled cell walls can serve as a useful guide for future studies on mechanical fractionation and valorization of lignocellulose based polymers.

Correction for ‘Protected lignin biorefining through cyclic extraction: gaining fundamental insights into the tuneable properties of lignin by chemometrics’ by Maria Karlsson et al., Green Chem., 2022, 24, 1211–1223, DOI: 10.1039/D1GC04171A.

Transforming biomass derived components to materials with controlled and predictable properties is a major challenge. Current work describes the controlled synthesis of starcopolymers with functional and degradable arms from the Lignoboost® process. Macromolecular control is achieved by combining lignin fractionation and characterization with ring-opening copolymerization (ROCP). The cyclic monomers used are e-caprolactone (eCL) and a functional carbonate monomer, 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis is performed at ambient temperature, under bulk conditions, in an open flask, and the graft composition and allyl functionality distribution are controlled by the copolymerization kinetics. Emphasis is placed on understanding the initiation efficiency, structural changes to the lignin backbone and the final macromolecular architecture. The present approach provides a green, scalable and cost effective protocol to create well-defined functional macromolecules from technical lignins.

Replacing fossil-based resources with renewable alternatives is generally acknowledged as a critical component to address several of today's environmental concerns. In this context, lignocellulosic biomass is an attractive, sustainable resource. However, the constitutional biopolymers of interest are locked in the structural complexity of the plant cell walls, which defines their properties and contributes to fractionation recalcitrance. One of the key suspects restricting fractionation of the biopolymers in high yield is the presence of lignin–carbohydrate bonds forming a matrix referred to as lignin–carbohydrate complex (LCC). Nevertheless, covalent bonds between lignin and carbohydrates, remain one of the most controversial topics in lignocellulose chemistry. This challenge can be attributed to the slow progress made in their research, which also forms the basis for this review. Herein, we will critically discuss the literature with a particular focus on the latest characterization and analytical techniques. Discussions on existing techniques and, importantly the drawbacks with them should be compelling to researchers in the area, especially at this time when crucial issues surrounding the realization of biorefineries need to be addressed.

Wood is not fully soluble in current non-derivatising direct-dissolution solvents, contrary to the many reports in the literature quoting wood 'dissolution' in ionic liquids. Herein, we demonstrate that the application of autohydrolysis, as a green and economical wood pre-treatment method, allows for a massive increase in solubility compared to untreated wood. This is demonstrated by the application of two derivitising methods (phosphitylation and acetylation), followed by NMR analysis, in the cellulose-dissolving ionic liquids 1-allyl-3-methylimidazolium chloride ([amim]Cl) and 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]. In addition, the non-derivitising tetrabutylphosphonium acetate ([P-4444][OAc]) : DMSO-d6 electrolyte also allowed for dissolution of the autohydrolysed wood samples. By combination of different particle sizes and P-factors (autohydrolysis intensity), it has been clearly demonstrated that the solubility of even wood chips can be drastically increased by application of autohydrolysis. The physiochemical factors affecting wood solubility after autohydrolysis are also discussed.