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Ionic liquids (ILs) have been widely investigated for the pretreatment and deconstruction of lignocellulosic feedstocks. However, the modes of interaction between IL-anions and cations, and plant cell wall polymers, namely, cellulose, hemicellulose, and lignin, as well as the resulting ultrastructural changes are still unclear. In this study, we investigated the atomic level and suprastructural interactions of microcrystalline cellulose, birchwood xylan, and organosolv lignin with 1,3-dialkylimidazolium ILs having varying sizes of carboxylate anions. Analysis by 13 C NMR spectroscopy indicated that cellulose and lignin exhibited stronger hydrogen bonding with acetate ions than with formate ions, as evidenced by greater chemical shift changes. Small-angle X-ray scattering analysis showed that while both cellulose and xylan adopted a single-stranded conformation in acetate-ILs, twice as many acetate ions were bound to one anhydroglucose unit than to an anhydroxylose unit. We also determined that a minimum of seven representative carbohydrate units must interact with an anion for that IL to effectively dissolve cellulose or xylan. Lignin is associated as groups of four polymer molecules in formate-ILs and dispersed as single molecules in acetate-ILs, which indicates that it is highly soluble in the latter. In summary, our study demonstrated that 1,3-dialkylimidazolium acetates displayed stronger binding interactions with cellulose and lignin, as compared to formates, and thus have superior potential to fractionate these polymers from lignocellulosic feedstocks.

Synthesizing lignin-based copolymers would valorize a major coproduct stream from pulp and paper mills and biorefineries as well as reduce the dependence on petrochemical-based consumer goods. In this study, we used organosolv lignin isolated from hybrid poplar ( Populus trichocarpa × P. deltoides) to generate lignin-containing methacrylate hydrogels. The copolymer hydrogels were synthesized by first grafting 2-hydroxyethyl methacrylate (HEMA) onto lignin (OSLH) via esterification and then by free radical polymerization of OSLH with excess HEMA. The copolymer hydrogels were prepared with different stoichiometric ratios of OSLH (e.g., 0, 10, 20, and 40 wt %) with respect to HEMA. Copolymerization with OSLH led to an increase in cross-linking density, which in turn enhanced the hydrogel's material properties; we report up to 39% improvement in water retention, 20% increase in thermostability, and up to a 3 order increase in magnitude of the storage modulus ( G'). The copolymer's properties, such as water retention and glass transition temperature, could be tuned by altering the percent functionalization of lignin OH groups and the ratio of OSLH to HEMA.

Fractionation of lignocellulosic biomass is an attractive solution to develop an economically viable biorefinery by providing a saccharide fraction to produce fuels and a lignin stream that can be converted into high value products such as carbon fibers. In this study, the analysis of ionic liquid-activated biomass demonstrates that in addition of decreasing crystallinity, the selected ILs (1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate) deacetylate Yellow poplar under mild conditions (dissolution at 60-80 °C), and lower the degradation temperature of each biomass polymeric component, thereby reducing the recalcitrance of biomass. Among the three tested ILs, 1-ethyl-3-methylimidazolium acetate performed the best, providing a strong linear relationship between the level of deacetylation and the rate of enzymatic saccharification for Yellow poplar., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Ionic liquids (ILs) have been increasingly recognized as novel solvents for dissolution and pretreatment of cellulose. However, cellulases are inactivated in the presence of ILs, even when present at low concentrations. To more fully exploit the benefits of ILs it is critical to develop a compatible IL-cellulases system in which the IL is able to effectively solubilize and activate the lignocellulosic biomass, and the cellulases possess high stability and activity. In this study, we investigated the stability and activity of a commercially available cellulases mixture in the presence of different concentrations of 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]). A mixture of cellulases and β-glucosidase (Celluclast1.5L, from Trichoderma reesei, and Novozyme188, from Aspergillus niger, respectively) retained 77% and 65% of its original activity after being pre-incubated in 15% and 20% (w/v) IL solutions, respectively, at 50°C for 3 h. The cellulases mixture also retained high activity in 15% [Emim][OAc] to hydrolyze Avicel, a model substrate for cellulose analysis, with conversion efficiency of approximately 91%. Notably, the presence of different amounts of yellow poplar lignin did not interfere significantly with the enzymatic hydrolysis of Avicel. Using this IL-cellulase system (15% [Emim][OAc]), the saccharification of yellow poplar biomass was also significantly improved (33%) compared to the untreated control (3%) during the first hour of enzymatic hydrolysis. Together, these findings provide compelling evidence that [Emim][OAc] was compatible with the cellulase mixture, and this compatible IL-cellulases system is promising for efficient activation and hydrolysis of native biomass to produce biofuels and co-products from the individual biomass components., (Copyright © 2010 Wiley Periodicals, Inc.)

The wide-scale production of renewable fuels from lignocellulosic feedstocks continues to be hampered by the natural recalcitrance of biomass. Therefore, there is a need to develop robust and reliable methods to characterize and quantify components that contribute to this recalcitrance. In this study, we utilized a method that incorporates pyrolysis with successive gas chromatography and mass spectrometry (Py-GC/MS) to assess lignification in cell suspension cultures. This method was compared with other standard techniques such as acid-catalyzed hydrolysis, acetyl bromide lignin determination, and nitrobenzene oxidation for quantification of cell wall bound phenolic compounds. We found that Py-GC/MS can be conducted with about 250 µg of tissue sample and provides biologically relevant data, which constitutes a substantial advantage when compared to the 50–300 mg of tissue needed for the other methods. We show that when combined with multivariate statistical analyses, Py-GC/MS can distinguish cell wall components of switchgrass (Panicum virgatum) suspension cultures before and after inducing lignification. The deposition of lignin precursors on uninduced cell walls included predominantly guaiacyl-based units, 71% ferulic acid, and 5.3% p-coumaric acid. Formation of the primary and partial secondary cell wall was supported by the respective ~15× and ~1.7× increases in syringyl-based and guaiacyl-based precursors, respectively, in the induced cells. Ferulic acid was decreased by half after induction. These results provide the proof-of-concept for quick and reliable cell wall compositional analyses using Py-GC/MS and could be targeted for either translational genomics or for fundamental studies focused on understanding the molecular and physiological mechanisms regulating plant cell wall production and biomass recalcitrance. [ABSTRACT FROM AUTHOR]

A group of biomass-derived lignins isolated using organosolv fractionation was characterized by FT-IR spectral and thermal property analysis coupled with multivariate analysis. The principal component analysis indicated that there were significant variations between the hardwood, softwood, and grass lignins due to the differences in syringyl and guaiacyl units as well as the different processing temperatures and times used to isolate the lignins. Partial least squares regression revealed that the concentration of syringyl units was the foremost factor behind the variation in glass transition temperature (Tg) for each lignin sample. It was concluded that structural variations resulting from altering the processing time and temperature and the lignin species directly affect the thermal properties of the lignin. Therefore, by determining the thermal properties of a lignin sample, a basic understanding of its structure can be developed. [ABSTRACT FROM AUTHOR]

A new simple and safe method for quantifying lignin content in lignocellulosic biomass is described. The approach consists of measuring the absorbance of a solution of whole biomass dissolved in the ionic liquid 1-n-butyl-3-methyl imidazolium chloride, [Bmim][Cl], at 440 nm via ultraviolet- (UV-) visible spectrophotometry. An extinction coefficient for a lignin standard, highly pure lignin isolated from biomass through an organosolv process, is used in conjunction with the Beer- Lambert Law to calculate the lignin concentration. Principal component analysis (PCA) of Fourier Transform-Infrared (FTIR) spectra collected for several different lignin standards was performed to understand the differences in their chemical structure and composition (e.g., the relative amounts of syringyl and guaiacyl units). A rapid FTIR analysis of the whole biomass sample with unknown lignin content is required to assist in the proper selection of the lignin standard for the subsequent spectrophotometric analysis. The proposed method was tested and validated on two biomass types: Yellow poplar and Southern pine. The spectrophotometric approach yielded lignin contents for Yellow poplar and Southern pine of 25.7 ± 1.1% and 26.7 ± 0.7%, respectively, which are comparable to the values obtained by a standard wet chemical protocol, 25.1% ± 0.7 and 26.6 ± 0.4%, respectively. [ABSTRACT FROM AUTHOR]

Biochar pellets produced by blending switchgrass biochar, lignin and fertilizers K and P together followed by pelletization were characterized and investigated for their ability to release K and P. Pellets processed at 180°C with increasing lignin content from 10 to 30wt.% had higher density, thermal stability and durability, and produced lower pore volume and smaller pore size than pellets processed at 105°C. Fertilizer-embedded biochar pellets with 10-30wt.% lignin and processed at 180°C had a slower K and P release than pellets dried at 105°C, with release rates (53-62% in K and 49-62% in P) within the first 24h followed by gradual releases (78-87% in K and 73-78% in P) for the next 18days. Therefore, by controlling lignin content and processing temperature of the pellets, one can control the release rate of nutrients present in biochar pellets. [ABSTRACT FROM AUTHOR]

[Display omitted] • A renewable adhesive was developed from hardwood lignin biomass for joining steel substrates. • Lignin content in the compositions were varied, to alter toughness, stiffness, and surface energy. • Highest adhesive strength of 13.1 MPa was measured for an optimal composition. • This study demonstrates the viability of lignin as a valuable building block for adhesives. Adhesive bonding of metals has become increasingly relevant in recent years due to the demand for reducing weight and improving performance in structural applications such as automobiles and aerospace. We developed renewable thermoplastic adhesives from technical organosolv lignin isolated from hardwood biomass and acrylonitrile butadiene co-polymer rubber (NBR) for joining steel substrates. NBR33, NBR41 and NBR51 with acrylonitrile molar ratios of 33, 41 and 51%, respectively, were blended with lignin to form two-phase thermoplastic adhesives, and their adhesion, viscoelastic and surface properties were measured. Lignin content in the compositions were varied, ranging from 40% to 80% (w/w), to alter toughness, stiffness, and surface energy characteristics of the material. Better interaction or reactivity between the lignin and NBR phases was observed with greater nitrile content in NBR, leading to greater modulus and stiffness of the adhesive. Simultaneously, increasing the proportion of lignin reduced toughness and improved stiffness, with the highest adhesive strength of 13.1 MPa measured in a 60% lignin loading ratio with NBR51. Surface energy measurements revealed that total surface energy (sum of polar and dispersive surface energy) raised with lignin loading, suggesting that both surface energy and matrix strength play a critical role in the adhesive properties of the synthesized materials. A finite element-based cohesive zone model (CZM) was developed and implemented to study the failure strength of the adhesively bonded joint. This study demonstrates the viability of lignin as a valuable building block for adhesives, not only due to its inherent chemical structure and rigidity, but also for its surface energy characteristics. [ABSTRACT FROM AUTHOR]