Using transgenic poplars to elucidate the relationship between the structure and the thermal properties of lignins

Modification of a Marine Pine Kraft Lignin Sample by Enzymatic Treatment with a Pycnoporus cinnabarinus Laccase

Here, we report work on developing an enzymatic process to improve the functionalities of industrial lignin. A kraft lignin sample prepared from marine pine was treated with the high-redox-potential laccase from the basidiomycete fungus Pycnoporus cinnabarinus at three different concentrations and pH conditions, and with and without the chemical mediator 1-hydroxybenzotriazole (HBT). Laccase activity was tested in the presence and absence of kraft lignin. The optimum pH of PciLac was initially 4.0 in the presence and absence of lignin, but at incubation times over 6 h, higher activities were found at pH 4.5 in the presence of lignin. Structural changes in lignin were investigated by Fourier-transform infrared spectroscopy (FTIR) with differential scanning calorimetry (DSC), and solvent-extractable fractions were analyzed using high-performance size-exclusion chromatography (HPSEC) and gas chromatography-mass spectrometry (GC-MS). The FTIR spectral data were analyzed with two successive multivariate series using principal component analysis (PCA) and ANOVA statistical analysis to identify the best conditions for the largest range of chemical modifications. DSC combined with modulated DSC (MDSC) revealed that the greatest effect on glass transition temperature (Tg) was obtained at 130 U g cm^-1 and pH 4.5, with the laccase alone or combined with HBT. HPSEC data suggested that the laccase treatments led to concomitant phenomena of oligomerization and depolymerization, and GC-MS revealed that the reactivity of the extractable phenolic monomers depended on the conditions tested. This study demonstrates that P. cinnabarinus laccase can be used to modify marine pine kraft lignin, and that the set of analytical methods implemented here provides a valuable tool for screening enzymatic treatment conditions.

Towards producing high-quality lignin-based carbon fibers: A review of crucial factors affecting lignin properties and conversion techniques

The production of low-cost and high-quality carbon fibers (CFs) from biorenewable lignin precursors has been of worldwide interest for decades. Although numerous works have been reported and the proposed "1.72 GPa/172 GPa" target set by the Department of Energy (DOE) has been closely met in a few studies, most lignin-based CFs (LCFs) have poor strength properties compared to industrial PAN (polyacrylonitrile)-based CFs. The production of LCFs involves several steps, and the final quality of LCFs is governed by both lignin's properties and the manufacturing processes. Therefore, understanding the key factors of producing high quality LCF is of high importance. In this review, we firstly outlined several lignin's properties (e.g., impurities, thermal properties, molecular structure) that may play important role in determining its processability and suitability as carbon fiber precursor. Secondly, conversion strategies include spinning, stabilization and carbonization, and corresponding parameters influencing the final quality of LCF are comprehensively analyzed. Last, additional characterization methods are proposed as a means to facilitate analyzing of lignin and LCF. This review attempts to provide insights towards high-quality LCF production from both material and manufacturing aspects.

The Impact of Biomass and Acid Loading on Methanolysis during Two-Step Lignin-First Processing of Birchwood

We optimized the solvolysis step in methanol for two-step lignin-first upgrading of woody biomass. Birchwood was first converted via sulfuric acid methanolysis to cellulose pulp and a lignin oil intermediate, which comprises a mixture of lignin oligomers and C5 sugars in the methanol solvent. The impact of reaction temperature (140–200 °C), acid loading (0.24–0.81 wt%, dry biomass), methanol/biomass ratio (2.3/1–15.8/1 w/w) and reaction time (2 h and 0.5 h) was investigated. At high biomass loadings (ratio < 6.3/1 w/w), operation at elevated pressure facilitates delignification by keeping methanol in the liquid phase. A high degree of delignification goes together to a large extent with C5 sugar release, mostly in the form of methyl xylosides. Gel permeation chromatography and heteronuclear single quantum coherence NMR of lignin fractions obtained at high acid (0.81 wt%) and low biomass (15.8/1 w/w) loading revealed extensive cleavage of β-O-4′ bonds during acidolysis at 180 °C for 2 h. At an optimized methanol/biomass ratio of 2.3/1 w/w and acid loading (0.24 wt%), more β-O-4′ bonds could be preserved, i.e., about 33% after 2 h and 47% after 0.5 h. The high reactivity of the extracted lignin fragments was confirmed by a second hydrogenolysis step. Reductive treatment with Pd/C under mild conditions led to disappearance of ether linkages and molecular weight reduction in the hydrotreated lignin oil.

"Waste to Wealth": Lignin as a Renewable Building Block for Energy Harvesting/Storage and Environmental Remediation

Lignin is the second most earth-abundant biopolymer having aromatic unit structures, but it has received less attention than other natural biomaterials. Recent advances in the development of lignin-based materials, such as mesoporous carbon, flexible thin films, and fiber matrix, have found their way into applications to photovoltaic devices, energy-storage systems, mechanical energy harvesters, and catalytic components. In this Review, we summarize and suggest another dimension of lignin valorization as a building block for the synthesis of functional materials in the fields of energy and environmental applications. We cover lignin-based materials in the photovoltaic and artificial photosynthesis for solar energy conversion applications. The most recent technological evolution in lignin-based triboelectric nanogenerators is summarized from its fundamental properties to practical implementations. Lignin-derived catalysts for solar-to-heat conversion and oxygen reduction are discussed. For energy-storage applications, we describe the utilization of lignin-based materials in lithium-ion rechargeable batteries and supercapacitors (e.g., electrodes, binders, and separators). We also summarize the use of lignin-based materials as heavy-metal adsorbents for environmental remediation. This Review paves the way to future potentials and opportunities of lignin as a renewable material for energy and environmental applications.

Improving Processing and Performance of Pure Lignin Carbon Fibers through Hardwood and Herbaceous Lignin Blends

Lignin/lignin blends were used to improve fiber spinning, stabilization rates, and properties of lignin-based carbon fibers. Organosolv lignin from Alamo switchgrass (Panicum virgatum) and yellow poplar (Liriodendron tulipifera) were used as blends for making lignin-based carbon fibers. Different ratios of yellow poplar:switchgrass lignin blends were prepared (50:50, 75:25, and 85:15 w/w). Chemical composition and thermal properties of lignin samples were determined. Thermal properties of lignins were analyzed using thermogravimetric analysis and differential scanning calorimetry. Thermal analysis confirmed switchgrass and yellow poplar lignin form miscible blends, as a single glass transition was observed. Lignin fibers were produced via melt-spinning by twin-screw extrusion. Lignin fibers were thermostabilized at different rates and subsequently carbonized. Spinnability of switchgrass lignin markedly improved by blending with yellow poplar lignin. On the other hand, switchgrass lignin significantly improved thermostabilization performance of yellow poplar fibers, preventing fusion of fibers during fast stabilization and improving mechanical properties of fibers. These results suggest a route towards a 100% renewable carbon fiber with significant decrease in production time and improved mechanical performance.

Preparation, characterization and the adsorption characteristics of lignin/silica nanocomposites from cellulosic ethanol residue

The synthesis lignin/silica nanocomposites by in situ co-precipitation method.

Characterization and Physicochemical Properties of Condensed Tannins from Acacia catechu

Condensed tannins from Acacia catechu were carefully studied to determine their chemical structure and physicochemical properties. The combined use of MALDI-TOF-MS and (13)C NMR revealed that catechin and epicatechin are the predominant monomers. Most of the compounds were dimers, as confirmed by size exclusion chromatography measurements. To evaluate their potential as aromatic building block in polymer synthesis, special care was given to the characterization and quantification of the different OH groups. A detailed (31)P NMR analysis showed the predominance of catechin, with a catechin/epicatechin ratio of 4.2:1. Two distinct (1)H NMR measurements confirmed the quantification. The thermal properties were also determined: the tannins showed a high temperature of degradation (ca. 190 °C) and a high glass transition temperature (ca. 140 °C), allowing for thermal processing or chemical reactions at relatively high temperature. A. catechu tannins thus present interesting features to be used as aromatic building blocks in polymer materials.

Characterization of the last step of lignin biosynthesis in Zinnia elegans suspension cell cultures

The last step of lignin biosynthesis in Zinnia elegans suspension cell cultures (SCCs) catalyzed by peroxidase (ZePrx) has been characterized. The k(3) values shown by ZePrx for the three monolignols revealed that sinapyl alcohol was the best substrate, and were proportional to their oxido/reduction potentials, signifying that these reactions are driven exclusively by redox thermodynamic forces. Feeding experiments demonstrate that cell wall lignification in SCCs is controlled by the rate of supply of H(2)O(2). The results also showed that sites for monolignol beta-O-4 cross-coupling in cell walls may be saturated, suggesting that the growth of the lineal lignin macromolecule is not infinite.

Signatures of cinnamyl alcohol dehydrogenase deficiency in poplar lignins

A series of transgenic poplars down-regulated for cinnamyl alcohol dehydrogenase (CAD) was analyzed by thioacidolysis. Among the lignin-derived monomers, the indene compounds that were recently shown to originate from sinapaldehyde incorporated into lignins through 8-O-4-cross-coupling, were found to increase as a function of CAD deficiency level. While these syringyl markers were recovered in substantial amounts in the most severely depressed lines, the markers for coniferaldehyde incorporation were recovered in only low amounts. In conjunction with these additional sinapaldehyde units and relative to the control samples, lignins in CAD-deficient poplar lines had less conventional syringyl-units and beta-O-4-bonds and more free phenolic groups. We found that almost half of the polymers in the most deficient lines could be solubilized in alkali and at room temperature. This unusual behavior suggests that lignins in CAD-deficient poplars occur as small, alkali-leachable lignin domains. That mainly sinapaldehyde incorporates into the lignins of CAD-deficient poplars suggests that the recently identified sinapyl alcohol dehydrogenase (SAD), which is structurally distinct from the CAD enzyme targeted herein, does not play any substantial role in constitutive lignification in poplar.