Search

For the transition towards greener biorefineries with reduced waste, valorization of lignin to drop‐in chemicals instead of their combustion for energy purposes is a key issue for future processes. In this context, lignin should be extracted from lignocellulosic biomass (LCB) and fragmented into smaller units, followed by catalytic funneling to fine chemicals. In this review, we report on the classical approaches for lignin valorization from LCB: thermal treatments, solvolytic valorization, acid‐catalyzed process, and base‐catalyzed process. We also provide the reader with the modern approach of lignin valorization that led to an integrated LCB biorefinery. The performance of different solid catalysts in lignin‐first approach via reductive or oxidative catalytic fractionation at different conditions is discussed in detail. [ABSTRACT FROM AUTHOR]

Lignins are the most important aromatic renewable natural resource today, serving as a sustainable, environmentally acceptable alternative feedstock to fossil‐derived chemicals and polymers in a vast scope of value‐added applications. Lignin is a biopolymeric molecule that, together with cellulose, is a fundamental component of higher vascular plants structural cell walls. It can be extracted from by‐products of the pulp and paper industries, agricultural waste and residues, and biorefinery products. Lignin properties may vary depending on source and extraction method with carbon and aromatic as the main compositions in lignin structure. These rich compositions make lignin more valuable, allowing for the creation of high‐value‐added green composites. However, the complex structure of lignin creates low reactivity to interact with crosslinker, and hence chemical modification is substantial to overcome this problem. This review aimed to present and discuss lignin structure, variation of lignin chemical properties regarding its source and extraction process, recent advances in chemical modification of lignin to enhance its reactivity, and potential applications of modified lignin for manufacturing value‐added biocomposites with enhanced properties and lower environmental impact, such as food handling/packaging, seed coating, automotive devices, 3D printing, rubber industry, and wood adhesives. [ABSTRACT FROM AUTHOR]

Eucalyptus globulusis one of the most important hardwood species used by the pulp and paper industry due to its high pulp yield, high wood density, excellent fibre quality and good handsheet properties. However, the wood is a highly variable and complex material that has different chemical, physical and anatomical properties that influence its commercial value. Therefore, based on the wide variability betweenEucalyptustrees and their economic importance, different studies have been focused on the amount, structure and behaviour of xylem components and their influence during pulping procedures. This review explores the most recent results on the chemical and anatomical variation in trees contrasting in wood density and pulp yield that explains the pulpability ofE. globulus.In particular, the lignin chemistry, xylans features and fibre biometric properties of contrastingE. globulustrees are discussed in order to understand the remarkable performance ofE. globulusduring pulping procedures and paper manufacture. In addition, a genetic approach is made using the main results on the relationship between transcript abundance of genes associated with wood formation and the chemical properties of contrastingE. globulusgenotypes. [ABSTRACT FROM PUBLISHER]

Switchgrass was pretreated with sodium hydroxide (NaOH) at various concentrations and pretreatment times to investigate how delignification caused by NaOH affects its lignin chemistry. NaOH resulted in significant delignification ranging from 44.0 to 84.6% depending on pretreatment intensity. While there was no significant glucan loss due to NaOH pretreatment, higher NaOH concentrations removed xylan by up to 28.3%. Nitrobenzene oxidation (NBO) was used to study changes in lignin chemistry, and indicated that at higher NaOH concentrations, the amount of 4-hydroxygenzaldehyde (Hy) degraded from p-hydroxyphenyl propanol (H) lignin units was significantly reduced (p < 0.05). However, amounts of syringic (SA) and vanillic (VA) acids generated from syringyl (S) and guaiacyl (G) degradation were greater at higher NaOH concentration. S/G ratio (=0.62 raw switchgrass) did not significantly (p > 0.05) change with 15 min pretreatment, but it increased to 0.75 and 0.72, respectively, with 30 and 60 min pretreatments (p < 0.05). Increase in NaOH concentration did not significantly (p > 0.05) change S/G ratio, but H/G ratio (=0.48 raw switchgrass) decreased significantly to 0.14 regardless of pretreatment times. Overall, the H unit was found to be more susceptible to NaOH than S and G unit monolignols. Though changes in lignin chemistry due to NaOH concentration were observed, their impact on cellulolytic enzyme action during hydrolysis could not be fully understood. Further studies on lignin isolation may help to determine how these changes in lignin chemistry by NaOH impact cellulolytic enzymes. [ABSTRACT FROM AUTHOR]

This is a manuscript originally written by Knut Lundquist and Jim Parkås in a more popular science spirit on topics in lignin chemistry where Knut and Chalmers has contributed and Knut's view on the bearing of this research on lignin chemistry. The manuscript was never published and was translated from Swedish by Ulla Westermark and Jim Parkås with a new title. The following topics are briefly addressed: stereochemistry and its implication on lignin structure and lignin biosynthesis, lignin-carbohydrate bonds, oxidative lignin degrading enzymes, reactions of β-ethers at neutral and acidic conditions. [ABSTRACT FROM PUBLISHER]

Lignin is a major component of plant litter. In this review, we found lignin comprises a complex class of organic compounds whose concentration differs greatly both between and within plant species. There are many analytical methods for detecting the composition and structure of lignins. As lignins are enormously complex compounds, chemical assay is difficult and different methods vary with the results. Lignin plays a significant role in the carbon cycle, sequestering atmospheric carbon into the living tissues of woody perennial vegetation. It has also great effects on nitrogen dynamics of forest ecosystems as well as other ecological processes. Lignin is one of the most slowly decomposing components of dead vegetation, contributing a major fraction of the material that becomes humus as it decomposes. Lignin is highly correlated with decomposition of litter. Thus, there is evidence that the lignin concentration is a more influential factor than the other chemical concentrations, in determining the rate of leaf litter decomposition of different forest ecosystems. Although a great number of researchers have addressed lignin's role in litter decomposition, still there are many aspects of lignin biogeochemistry that are not known. This lack of information hinders complete amalgam of lignin effects on litter decomposition processes and dynamics of nutrient cycling. [ABSTRACT FROM AUTHOR]

Non-permineralized or mummified ancient wood found within proglacial soil near the ad Astra Ice Cap (81°N, 76°W), Ellesmere Island, Canada was investigated to ascertain the identification of the trees, current morphological and chemical characteristics of the woods and the fungi within them. These woods, identified as Betula, Larix, Picea and Pinus, were found with varying states of physical and chemical degradation. Modern microbial decomposition caused by soft rot fungi was evident and rDNA sequencing of fungi obtained from the samples revealed several species including Cadophora sp ., Exophiala sp., Phialocephala sp., as well as others. Analytical 13C-labeled tetramethylammonium hydroxide thermochemolysis showed the lignin from the ancient wood was in a high degree of preservation with minor side chain alteration and little to no demethylation or ring hydroxylation. The exposure of these ancient woods to the young soils, where woody debris is not usually prevalent, provides carbon and nutrients into the polar environment that are captured and utilized by unique decay fungi at this Arctic site. [ABSTRACT FROM AUTHOR]

Lignin is the by-product of pulp and paper industries and bio-refining operations. It is available as the leading natural phenolic biopolymer in the market. It has chromophore functional groups and can absorb a broad spectrum of UV light in range of 250–400 nm. Using lignin as a natural ingredient in sunscreen cream, transparent film, paints, varnishes and microorganism protection has been actively investigated. Both in non-modified and modified forms, lignin provides enhancing UV protection of commercial products with less than a 10% blend with other material. In mixtures with other synthetic UV blockers, lignin indicated synergic effects and increased final UV blocking potential in compare with using only synthetic UV blocker or lignin. However, using lignin as a UV blocker is also challenging due to its complex structure, polydispersity in molecular weight, brownish color and some impurities that require more research in order to make it an ideal bio-based UV blocker. [ABSTRACT FROM AUTHOR]