Search

In the present study, lignin from eucalyptus was extracted with 80% alkaline dioxane (0.05 M NaOH) from ball-milled wood and subsequently fractionated by gradient acid precipitation from the filtrate. Meanwhile, the residual lignin was prepared by a double enzymatic hydrolysis process. The yield of the lignin extracted by alkaline dioxane (L A-2 ) was 29.5%. The carbohydrate contents and molecular weights of the gradient acid precipitated lignin fractions gradually decreased from 4.90 to 1.36% and from 7770 to 5510 g/mol, respectively, with the decline of the pH value from 6 to 2. Results from two-dimensional heteronuclear single quantum coherence nuclear magnetic resonance (NMR) and 31 P NMR spectroscopy showed an evident reduction of β- O-4 ' linkages with the pH value decrease, while the contents of aliphatic -OH, phenolic -OH, and carboxylic groups displayed an increasing trend. Moreover, the residual lignin exhibited the highest molecular weight (11690 g/mol), the most abundant β- O-4 ' linkages (71.1%), and the highest S/G ratio (4.68).

The generation of pseudo-lignin as byproduct during the lignocellulose acidic pretreatment has been proposed for many years. However, the detailed formation mechanism is still unclear. Moreover, there is a lack of understanding in the initial reaction during the formation of humins (byproducts in furfural production) and acid-induced hydrothermal carbon (carbon material). In this work, the initial formation of these three substances were investigated. We first found the common feature of their formation process was that carbohydrate-hydrolyzed compounds could form black polymers by condensing in acidic media, but the difference was dependent on the reaction degree. Furthermore, the results revealed that oxidation was an accelerator for condensations during producing black polymers because oxidized compounds could enhance the acidity of the reaction system. However, condensations of oxidized compounds were more difficult to proceed. Meanwhile, during the initial stage, the dominating pathway was that furfural condensed with itself and isomerized xylose via aldol-condensation.

Eucommia ulmoides Oliver (EUO), a traditional Chinese herb, contains a variety of bioactive chemicals, including lignans, iridoids, phenolics, steroids, terpenoids, flavonoids, etc. These bioactive chemicals possess the effective function in nourishing the liver and kidneys and regulating blood pressure. The composition of bioactive chemicals extracted from EUO vary in the different functional parts (leaves, seeds, bark, and staminate flower) and planting models. The bioactive parts of EUO are widely used as raw materials for medicine and food, powdery extracts, herbal formulations, and tinctures. These capabilities hold potential for future development and commercial exploitation of the bioactive products from EUO.

Eucalyptus grandis fibers were treated with hot-compressed water (HCW) and laccase mediator to enhance the fiber characteristics and to produce an active lignin substrate for binderless fiberboard production. The composition, morphology, and crystallinity index (CrI) analysis of fibers showed that the HCW treatment increased the CrI and lignin content of the treated fibers through partial removal of hemicelluloses. Simultaneously, the HCW treatment produced some granules and holes on the surface of the fibers, which possibly facilitated the accessibility of the laccase mediator. Milled wood lignins and enzymatic hydrolysis lignins isolated from the control and treated fibers were comparatively characterized. A reduction of molecular weight was observed, which indicated that a preferential degradation of lignin occurred after exposure to the laccase mediator. Quantitative (13)C, 2D-HSQC and (31)P NMR characterization revealed that the integrated treatment resulted in the cleavage of β-O-4' linkages, removal of G' (oxidized α-ketone) substructures, and an increase in the S/G ratio and free phenolic hydroxyls.

An integrated process based on hydrothermal pretreatment (HTP) (i.e., 110-230 °C, 0.5-2.0 h) and alkaline post-treatment (2% NaOH at 90 °C for 2.0 h) has been performed for the production of xylooligosaccharide, lignin, and digestible substrate from sweet sorghum stems. The yield, purity, dissociation mechanisms, structural features, and structural transformations of alkali lignins obtained from the integrated process were investigated. It was found that the HTP process facilitated the subsequent alkaline delignification, releasing lignin with the highest yield (79.3%) and purity from the HTP residue obtained at 190 °C for 0.5 h. All of the results indicated that the cleavage of the β-O-4 linkages and degradation of β-β and β-5 linkages occurred under the harsh HTP conditions. Depolymerization and condensation reactions simultaneously occurred at higher temperatures (≥ 170 °C). Moreover, the thermostability of lignin was positively related to its molecular weight, but was also affected by the inherent structures, such as β-O-4 linkages and condensed units. These findings will enhance the understanding of structural transformations of the lignins during the integrated process and maximize the potential utilizations of the lignins in a current biorefinery process.

An environmentally friendly steam explosion process of bamboo, followed by alkali and alkaline ethanol delignification, was developed to fractionate lignins. Results showed that after steam explosion the lignins isolated showed relatively low carbohydrate contents (0.55-1.76%) and molecular weights (780-1050 g/mol). For each steam-exploded sample, alkali-extracted lignins presented higher phenolic OH values (1.41-1.82 mmol/g), p-coumaric acid to ferulic acid ratios (pCA/FA ratios 4.5-14.1), and syringyl to guaiacyl ratios (S/G ratios 5.0-8.5) than those from alkaline ethanol-extracted lignins (phenolic OH 0.85-1.35 mmol/g, pCA/FA ratios 1.6-5.2, and S/G ratios 3.5-4.8). The lignins obtained consisted mainly of β-O-4' linkages combined with small amounts of β-β', β-5', and α-O-4/β-O-4 linkages. Antioxidant activities of the lignins obtained were tested by the 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azobis(3-ethylbenzothiazoline-6-sulfonic acid), and ferric reducing activity power methods. It was found that alkali-extracted lignins obtained during the initial extraction process had higher antioxidant activities than alkaline ethanol-extracted lignins obtained during the second extraction process.

Cellulose acetylation was investigated in dimethyl sulfoxide (DMSO) with isopropenyl acetate (IPA) as acetylating reagent and 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU) as catalyst at 70-130 °C for 3-12 h. The degree of substitution (DS) of acetylated cellulose was comparatively determined by titration and ¹H NMR and confirmed by FT-IR analysis. The results indicated that per-O-acetylation was achieved at >90 °C for a relatively long duration. The three well-resolved peaks of carbonyl carbons in ¹³C NMR spectra also provided evidence of per-O-acetylation. The solubility of cellulose acetates in common organic solvents was examined, and the result showed that chloroform can be an alternative choice as a solvent for fully acetylated cellulose formed in this study besides DMSO. The intrinsic viscosity of acetylated cellulose solution implied almost no degradation of cellulose during acetylation in DMSO except at higher temperature (130 °C) for a long time.

The preparation of xylan-graft-poly(ε-caprolactone) (xylan-g-PCL) copolymers was investigated by homogeneous ring-opening polymerization (ROP) in a dual-component system containing Lewis base LiCl and strong polar aprotic solvent dimethyl sulfoxide (DMSO). DMSO/LiCl acted as solvent, base, and catalyst for the ROP reaction. The effects of the parameters, including the reaction temperature, molar ratio of ε-caprolactone (ε-CL) to anhydroxylose units (AXU) in xylan, and reaction time, on the degree of substitution (DS) and weight percent of PCL side chain (WPCL) were investigated. The results showed that xylan-g-PCL copolymers with low DS in the range of 0.03-0.39 were obtained under the given conditions. The Fourier transform infrared spectroscopy (FTIR), (1)H nuclear magnetic resonance (NMR), (13)C NMR, (1)H-(1)H correlation spectroscopy (COSY), and (1)H-(13)C correlation two-dimensional (2D) NMR [heteronuclear single-quantum coherence (HSQC)] characterization provided more evidence of the attachment of side chains onto xylan. Only one ε-CL was confirmed to be attached onto xylan with each side chain. Integration of resonances assigned to the substituted C2 and C3 in the HSQC spectrum also indicated 69.23 and 30.77% of PCL side chains attached to AXU at C3 and C2 positions, respectively. Although the attachment of PCL onto xylan led to the decreased thermal stability of xylan, the loss of unrecovered xylan fractions with low molecular weight because of the high solubility of xylan in DMSO/LiCl resulted in the increased thermal stability of the samples. This kind of xylan derivative has potential application in environmentally friendly and biodegradable materials considering the good biodegradability of xylan and PCL.

Effective delignification of lignocelluloses is a very important to guarantee the economic feasibility of organosolv-based biorefinery. Eucalyptus chips were successively subjected to organosolv pretreatment (AEOP) and extended delignification (ED) process in the present study. The effects of delignification processes were scientifically evaluated by component analysis, SEM, and CP-MAS NMR techniques. It was found that the integrated process of organosolv pretreatment and subsequent delignification resulted in an effective delignification. The fundamental chemistry of the lignin obtained after these processes was thoroughly investigated by FT-IR, multidimensional NMR ((31)P-, (13)C-, and 2D-HSQC NMR), and GPC techniques. It was observed that an extensive cleavage of aryl ether linkages, ethoxylation, and some condensation reactions occurred in AEOP process, while α-oxidation mainly took place in alkaline hydrogen peroxide (AHP) process. It is believed that better understanding the fundamental chemistry of lignin facilitates the optimization of the delignification process. More importantly, well-defined of lignin polymers will facilitate their value-added applications in current and future biorefineries.

To investigate the inhomogeneity of the lignin from sweet sorghum stem, successive alkali treatments were applied to extract lignin fragments in the present study. The successive treatments released 80.3% of the original lignin from the sorghum stem. The chemical structural inhomogeneity of the isolated lignins was comparatively and comprehensively investigated by UV, FT-IR, and NMR spectra. The lignins were found to be predominantly composed of β-O-4' aryl ether linkages, together with minor amounts of β-β', β-5', β-1', and α,β-diaryl ether linkages. In addition, hydroxycinnamic acid (mainly p-coumaric acid), which was found to be attached to lignin, was released and co-precipitated in the lignin fractions isolated in the initial extracting steps, whereas hydroxycinnamic acids (p-coumaric and ferulic acids) were not detected in the subsequently extracted lignin fractions. Moreover, the high proportion of carbon-carbon structures was potentially related to the high amounts of guaiacyl units in the lignin investigated. Thermogravimetric analysis revealed that the higher molecular weights of lignins resulted in relatively higher thermal stability, and the higher content of C-C structures in the lignin probably led to a higher "char residue". These findings suggested that the lignin fractions extracted from sweet sorghum stem by successive alkali extractions had inhomogeneous features in both chemical composition and structure.

Xylan, which is a widely abundant plant polymer, has been considered as an alternative for film preparation. Up to now, however, xylan films have suffered from brittleness, low mechanical strength, and humidity sensitivity. This paper describes a new and effective strategy to prepare xylan films with high mechanical strength and less moisture-sensitive properties by introducing long carbon chains into the xylan backbone. Furthermore, this work revealed some important details on the relationships between structure (molecular structure, aggregation behaviors, and surface morphology) and properties (film-forming performance, flexibility, tensile strength, and hydrophilicity) of xylan film. It was found that the hydrophobic carbon chains (2-octenylsuccinic anhydride half-ester groups) in the xylan backbone acted as steric hindrance and could effectively prevent xylan chains from aggregation. 2-Octenylsuccinic anhydride (2-OSA) modified xylan (2-OSA-X) demonstrated amorphous structure and had better film-forming performance than the unmodified xylan. 2-OSA-X films were smooth, flexible, and less moisture-sensitive and showed significantly increasing tensile strength at a low degree of substitution.

The use of ionic liquid (IL) in biomass pretreatment has received considerable attention recently because of its effectiveness in decreasing biomass recalcitrance to subsequent enzymatic hydrolysis. To understand the structural changes of lignin after pretreatment and enzymatic hydrolysis process, ionic liquid lignin (ILL) and subsequent residual lignin (RL) were sequentially isolated from ball-milled birch wood. The quantitative structural features of ILL and RL were compared with the corresponding cellulolytic enzyme lignin (CEL) by nondestructive techniques (e.g., FTIR, GPC, quantitative (13)C, 2D and (31)P NMR). The IL pretreatment caused structural modifications of lignin (cleavage of β-O-4 ether linkages and formation of condensed structures). In addition, lignin fragments with lower S/G ratios were initially extracted, whereas the subsequently extracted lignin is rich in syringyl unit. Moreover, the maximum decomposition temperature (T(M)) was increased in the order ILL < RL < CEL, which was related to the corresponding β-O-4 ether linkage content and molecular weight (M(w)). On the basis of the results observed, a possible separation mechanism of IL lignin was proposed.

Pretreatment is the key to unlock the recalcitrance of lignocellulosic biomass for the productions of biofuels. Ionic liquid pretreatment has drawn increased attention because of its numerous advantages over conventional methods. In this study, corncob was submitted to pretreatments with 1-ethyl-3-methylimadazolium acetate (EMIMAc) and/or H(2)O/dimethyl sulfoxide (DMSO) followed by alkaline extraction to isolate hemicelluloses. The hemicellulosic fractions obtained were comprehensively characterized with a series of chemical and spectroscopic technologies, including gel permeation chromatography (GPC), thermogravimetric analysis (TGA), high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared (FTIR) spectroscopy, and one- and two-dimensional nuclear magnetic resonance (NMR). The results showed that the fractions prepared with ionic liquid pretreatments exhibited relatively higher average molecular weights (196,230-349,480 g/mol) than the fraction prepared without pretreatment (M(w), 96,260 g/mol). Furthermore, the pretreated fractions demonstrated higher thermal stability compared to the fractions without pretreatment. Structural characterization indicated that all of the fractions had similar structures, which are composed of a (1 → 4)-linked β-D-xylopyranosyl backbone substituted with arabinofuranosyls attached to O-2 and O-3 and with 4-O-methyl-α-D-glucuronic acid also linked to O-2.

A novel porous bioadsorbent for metal ion binding (Pd(2+) and Cd(2+)) was successfully prepared from lignocellulosic biomass in ionic liquid by homogeneous succinoylation and sequent chemical cross-linking. The morphology of the bioadsorbent and the interaction between bioadsorbent and metal ions was revealed by scanning electron microscopy and Fourier transform infrared spectroscopy. Results showed that the adsorption mechanism of the bioadsorbent was an ion exchange. A lower dose of cross-linker or higher carboxyl content increased the adsorption capacities of Pd(2+) and Cd(2+). The adsorption capacities of Pd(2+) and Cd(2+) remarkably increased as the pH of metal ion solutions increased. The pores in the bioadsorbent greatly favored the diffusion and adsorption of metal ions, and the adsorption equilibrium time was about 50 min. The adsorption of metal ions could be well explained by the Langmuir model, and the maximum adsorption capacities of Pd(2+) and Cd(2+) were 381.7 and 278.6 mg/g.

Delignified Arundo donax was sequentially extracted with DMSO, saturated barium hydroxide, and 1.0 M aqueous NaOH solution. The yields of the soluble fractions were 10.2, 6.7, and 10.0% (w/w), respectively, of the dry Arundo donax materials. The DMSO-, Ba(OH)(2)- and NaOH-soluble hemicellulosic fractions were further fractionated into two subfractions by gradient 50% and 80% saturation ammonium sulfate precipitation, respectively. Monosaccharide, molecular weight, FT-IR, and 1D ((1)H and (13)C) and 2D (HSQC) NMR analysis revealed the differences in structural characteristics and physicochemical properties among the subfractions. The subfractions precipitated with 50% saturation ammonium sulfate had lower arabinose/xylose and glucuronic acid/xylose ratios but had higher molecular weight than those of the subfractions precipitated by 80% saturation ammonium sulfate. FT-IR and NMR analysis revealed that the highly acetylated DMSO-soluble hemicellulosic subfraction (H(D50)) could be precipitated with a relatively lower concentration of 50% saturated ammonium sulfate, and thus the gradient ammonium sulfate precipitation technique could discriminate acetyl and non-acetyl hemicelluloses. It was found that the DMSO-soluble subfraction H(D50) precipitated by 50% saturated ammonium sulfate mainly consisted of poorly substituted O-acetyl arabino-4-O-methylglucurono xylan with terminal units of arabinose linked on position 3 of xylose, 4-O-methylglucuronic acid residues linked on position 2 of the xylan bone, and the acetyl groups (degree of acetylation, 37%) linked on position 2 or 3. The DMSO-soluble subfraction H(D80) precipitated by 80% saturated ammonium sulfate was mainly composed of highly substituted arabino-4-O-methylglucurono xylan and β-d-glucan.

Xylan-rich hemicelluloses-based hydrogel was developed as a novel porous bioadsorbent by graft co-polymerization of acrylic acid (AA) and xylan-rich hemicelluloses for adsorption of heavy metal ions (Pd(2+), Cd(2+), and Zn(2+)) from aqueous solutions. The chemical structure, the interaction between the hydrogel and metal ions, and the porous structure of xylan-rich hemicelluloses-g-AA hydrogel were revealed by Fourier transform infrared spectroscopy and scanning electron microscopy. The effects of AA and cross-linker dosage, pH value, contacting time, and initial concentration of metal ion on the adsorption capacity were studied. The adsorption equilibrium time was about 60 min from the adsorption kinetics study. The maximum adsorption capacities of Pd(2+), Cd(2+), and Zn(2+) were 859, 495, and 274 mg/g, respectively. Furthermore, xylan-rich hemicelluloses-g-AA hydrogel also exhibited highly efficient regeneration and metal ion recovery efficiency and can be reused without noticeable loss of adsorption capacity for Pd(2+), Cd(2+), and Zn(2+) after quite a number of repeated adsorption/desorption cycles.

A series of amiphiphilic cellulose-based graft copolymers (MCC-g-PLA) with various molecular factors were synthesized in ionic liquid BmimCl and characterized by FT-IR, (1)H NMR, (13)C NMR, XRD, and TGA. Their solubility in a variety of solvents was compared. The prepared MCC-g-PLA copolymers can self-assemble into spherical nanomicelles (10-50 nm) in aqueous solution. The self-assembly behaviors of the MCC-g-PLA copolymers were systematically investigated by fluorescence probe. Furthermore, the hydrophobic antitumor drug paclitaxel (PTX) was successfully encapsulated into the MCC-g-PLA micelles. The drug encapsulation efficiency and loading content were found to be as high as 89.30% (w/w) and 4.97%, respectively. Results in this study not only suggest a promising cellulose-based antitumor drug carrier but also provide information for property-directed synthesis of the cellulose graft PLA copolymers.

In this study, a novel amphoteric macromolecule was synthesized by sequential incorporation of carboxymethyl and quaternary ammonium groups into the backbone of xylan-type hemicelluloses under microwave irradiation. The reaction parameters such as the molar ratio of reagent (NaOH or 3-epoxypropyltrimethylammonium chloride)/anhydroxylose unit in hemicelluloses, the temperature, and the reaction time were investigated to optimize the reaction condition. The maximum degrees of substitution (DS) of carboxymethyl and quaternary ammonium groups under the optimum reaction condition were 0.90 and 0.52, respectively, exhibiting a higher efficiency as compared to the conventional heating method. Moreover, the thermal stability and weight-average molecular weight of amphoteric hemicellulosic derivatives decreased as compared to the native hemicelluloses. The viscosity, elastic modulus, and loss modulus of the amphoteric biomacromolecules increased with the increasing DS of quaternary ammonium groups in aqueous solution due to stronger electrostatic attraction. This study provides an efficient and rapid method to prepare amphoteric biomacromolecules.

Fractionation of lignocellulosic material into its constitutive components is of vital importance for the production of biofuels as well as other value-added chemicals. The conventional acetosolv processes are mainly focused on the production of pulp from woody lignocelluloses. In this study, a mild acetosolv process was developed to fractionate bamboo under atmospheric pressure to obtain cellulosic pulp, water-soluble fraction, and acetic acid lignin. The structural features of the lignins obtained under various conditions were characterized with elemental analysis, sugar analysis, alkaline nitrobenzene oxidation, gel permeation chromatography (GPC), (1)H nuclear magnetic resonance ((1)H NMR), and heteronuclear single-quantum coherence (HSQC) spectroscopy. As compared to milled wood lignin (MWL) of bamboo, acetic acid lignins had low impurities (carbohydrates 2.48-4.56%) mainly due to the cleavage of linkages between lignin and carbohydrates. In addition, acetic acid lignins showed a low proportion of syringyl (S) units. Due to the cleavage of linkages between lignin units, acetic acid lignins had weight-average molecular weights ranging from 4870 to 5210 g/mol, less than half that of MWL (13000 g/mol). In addition, acetic acid lignins showed stronger antioxidant activity mainly due to the significant increase of free phenolic hydroxyls. The lignins obtained with such low impurities, high free phenolic hydroxyls, and medium molecular weights are promising feedstocks to replace petroleum chemicals.

Analytical thioacidolysis releases diagnostic monomers from lignins by selectively cleaving alkyl aryl ether bonds. High yielding syntheses of the three thioacidolysis monomers were developed, and the compounds were used as standards for gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detector (GC-FID) quantitation of monomers released from lignocellulosics. First, syringyl, guaiacyl, and p-hydroxyphenyl glycerols were synthesized from the corresponding ethyl cinnamates and used as thioacidolysis substrates to prepare the monomers in high yields. These monomers were then used as standard compounds to measure their GC-MS and GC-FID response factors against two internal standards, 4,4'-ethylenebisphenol and tetracosane. For quantitation, it was shown that 4,4'-ethylenebisphenol is the better internal standard for GC-MS, whereas tetracosane remains the choice for GC-FID. When the obtained response factors were applied, the thioacidolysis monomer yields from white spruce, loblolly pine, poplar, bamboo, and sugar cane bagasse were determined by GC-MS. The obtained results were consistent with those reported in the literature.

Detailed chemical structural elucidation of lignin fractions from Miscanthus × giganteus was performed by several analytical techniques. Mild formosolv, basic organosolv, and cellulolytic enzyme treatments were applied to isolate three lignin fractions (AL, BL, and CL, respectively), and their structural characterization was comparatively evaluated. Both non-destructive techniques [e.g., Fourier transform infrared (FTIR) spectroscopy, size-exclusion chromatography (SEC), and two-dimensional (2D) nuclear magnetic resonance (NMR)] and degradation methods [e.g., acidic hydrolysis, derivatization followed by reductive cleavage (DFRC), and thioacidolysis] were used. The analysis revealed that a certain amount of carbohydrates (12.8%) was associated with CL and partially led to its increased molecular weight determined by SEC before acetylation. β-O-4 linkages were determined to be the predominant interunits (82%), but also, extensively acylated structures were observed. Alkaline organosolv treatment significantly improved the purity of the lignin fraction (carbohydrate content of 1.0%) and basically kept the original structure of the lignin macromolecule. Under acidic conditions, not only the portion of aryl alkyl ether bonds were cleaved but also new carbon-carbon bonds were formed by condensation reactions, resulting in an increment of the lignin molecular weights. Guaiacyl units were more reactive toward condensation than syringyl units, which was evidenced by an increasing S/G ratio from 0.7 (CL) to 1.7 (AL).

To characterize the lignin structures and lignin-carbohydrate complex (LCC) linkages, milled wood lignin (MWL) and mild acidolysis lignin (MAL) with a high content of associated carbohydrates were sequentially isolated from ball-milled poplar wood. Quantification of their structural features has been achieved by using a combination of quantitative (13)C and 2D HSQC NMR techniques. The results showed that acetylated 4-O-methylgluconoxylan is the main carbohydrate associated with lignins, and acetyl groups frequently acylate the C2 and C3 positions. MWL and MAL exhibited similar structural features. The main substructures were β-O-4' aryl ether, resinol, and phenylcoumaran, and their abundances per 100 Ar units changed from 41.5 to 43.3, from 14.6 to 12.7, and from 3.7 to 4.0, respectively. The S/G ratios were estimated to be 1.57 and 1.62 for MWL and MAL, respectively. Phenyl glycoside and benzyl ether LCC linkages were clearly quantified, whereas the amount of γ-ester LCC linkages was ambiguous for quantification.

In this study, cornstalk was pretreated by an acid-chlorite delignification procedure to enhance the conversion of cornstalk to bio-oil in hot-compressed water liquefaction. The effects of the pretreatment conditions on the compositional and structural changes of the cornstalk and bio-oil yield were investigated. It was found that acid-chlorite pretreatment changed the main components and physical structures of cornstalk and effectively enhanced the bio-oil yield. Shorter residence time favored production of the total bio-oil products, whereas longer time led to cracking of the products. A high water loading was found to be favorable for high yields of total bio-oil and water-soluble oil. GC-MS analysis showed that the water-soluble oil and heavy oil were the complicated products of C(5-10) and C(8-11) organic compounds.

Lignocellulose materials are potentially valuable resources for transformation into biofuels and bioproducts. However, their complicated structures make it difficult to fractionate them into cellulose, hemicelluloses, and lignin, which limits their utilization and economical conversion into value-added products. This study proposes a novel and feasible fractionation method based on complete dissolution of bagasse in 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) followed by precipitation in acetone/water (9:1, v/v) and extraction with 3% NaOH solution. The ionic liquid [C(4)mim]Cl was easily recycled after concentration and treatment with acetonitrile. (1)H NMR analysis confirmed that there was no obvious difference between the recycled [C(4)mim]Cl and fresh material. Bagasse was fractionated with this method to 36.78% cellulose, 26.04% hemicelluloses, and 10.51% lignin, accounting for 47.17 and 33.85% of the original polysaccharides and 54.62% of the original lignin, respectively. The physicochemical properties of the isolated fractions were characterized by chemical analysis, high-performance anion exchange chromatography (HPAEC), gel permeation chromatography (GPC), Fourier transform infrared (FT-IR), and (1)H and 2D (13)C-(1)H correlation (HSQC) nuclear magnetic resonance spectroscopy. The results showed that the acetone-soluble lignin and alkaline lignin fractions had structures similar to those of milled wood lignin (MWL). The easy extraction of the noncellulose components from homogeneous bagasse solution and amorphous regenerated materials resulted in the relatively high purity of cellulosic fraction (>92%). The hemicellulosic fraction was mainly 4-O-methyl-D-glucuronoxylans with some α-L-arabinofuranosyl units substituted at C-2 and C-3.

Exploitation of biomaterials derived from renewable resources is an important approach to address environmental and resource problems in the world today. In this paper, novel ionic hydrogels based on xylan-rich hemicelluloses were prepared by free radical graft copolymerization of acrylic acid (AA) and xylan-rich hemicelluloses (XH) by using N,N-methylene-bis(acrylamide) (MBA) as cross-linker and ammonium persulfate/N,N,N',N'-tetramethylethylenediamine (APS/TMEDA) as redox initiator system. The network characteristics of the ionic hydrogels were investigated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), as well as by determination of mechanical properties, swelling, and stimuli responses to pH, salts, and organic solvents. The results showed that an increase in the MBA/XH or AA/XH ratio resulted in higher cross-linking density of the network and thus decreased the swelling ratio. Expansion of the network hydrogels took place at high pH, whereas shrinkage occurred at low pH or in salt solutions as well as in organic solvents. The ionic hydrogels had high water adsorption capacity and showed rapid and multiple responses to pH, ions, and organic solvents, which may allow their use in several areas such as adsorption, separation, and drug release systems.

To improve yields while minimizing the extent of mechanical action (just 2 h of planetary ball-milling), the residual wood meal obtained from extraction of milled wood lignin (MWL) was sequentially treated with cellulolytic enzyme and alkali, and the yields of MWL, cellulolytic enzyme lignin (CEL), and alkaline lignin (AL) were 5.4, 23.2, and 16.3%, respectively. The chemical structures of the lignin fractions obtained were characterized by carbohydrate analysis, gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectroscopy, and various advanced NMR spectroscopic techniques. The results showed that the lignin isolated as MWL during the early part of ball milling may originate mainly from the middle lamella. This lignin fraction was less degradable and contained more linear hemicelluloses and more C═O in unconjugated groups as well as more phenolic OH groups. Both 1D and 2D NMR spectra analyses confirmed that the lignin in triploid of Populus tomentosa Carr. is GSH-type and partially acylated at the γ-carbon of the side chain. Two-dimensional heteronuclear single-quantum coherence (¹³C-¹H) NMR of MWL, CEL, and AL showed a predominance of β-O-4' aryl ether linkages (81.1-84.5% of total side chains), followed by β-β' resinol-type linkages (12.2-16.4%), and lower amounts of β-5' phenylcoumaran (2.1-2.6%) and β-1' spirodienone-type (0.4-1.4%) linkages. The syringyl (S)/guaiacyl (G) ratios were estimated to be 1.43, 2.29, and 2.83 for MWL, CEL, and AL, respectively.

In this article, a facile, rapid, and efficient method was developed for the preparation of carboxymethyl hemicelluloses using microwave-induced organic reaction enhancement chemistry. The influences of the factors including reaction time, temperature, and the amount of sodium monochloroacetate and sodium hydroxide on the degree of substitution (DS) of the products were investigated. The rheological properties and the chemical structure of the resulting polymers were also studied. It was found that microwave irradiation could significantly promote the chemical reaction efficiency and accelerate the carboxymethylation of hemicelluloses with sodium monochloroacetate. Therefore, carboxymethyl hemicelluloses with higher DS of 1.02 could be obtained in much shorter time scales as compared to the conventional heating method. Results from rheological analysis indicated that carboxymethyl hemicellulose solutions exhibited shear-thinning behavior in the range of shear rates tested and showed lower viscosity and modulus in comparison with those of the native hemicelluloses due to lower molecular weight and the role of carboxymethyl groups in reducing the entanglements between hemicelluloses chains.

A three-step sequential extraction-precipitation method was used to isolate lignin from Eucalyptus tereticornis. The ball-milled eucalyptus was extracted with 96% dioxane, 50% dioxane, and 80% dioxane containing 1% NaOH at boiling temperature, consecutively resulting in solubilization of lignin and hemicelluloses. By precipitating such solutions into 70% aqueous ethanol, the hemicelluloses were removed substantially although there were still some carbohydrates left over, especially for lignin fraction extracted by 50% dioxane. Lignins dissolved in the 70% ethanol solutions were recovered via concentration and precipitation into acidified water. About 37% of the original lignin was released following such procedure whereas only 13.5% can be isolated by traditional milled wood lignin (MWL) method. The obtained lignin fractions were analyzed by high performance anion exchange chromatography (HPAEC) following acid hydrolysis for sugar composition of the contaminating carbohydrates and characterized by quantitative (31)P NMR as well as two-dimensional heteronuclear single-quantum coherence ((13)C-(1)H) NMR. The results showed that 96% aqueous dioxane extraction of ball-milled wood under conditions used in this study resulted in lignin preparation with very similar structures and sugar composition as traditional MWL. Therefore extracting ball-milled wood with 96% aqueous dioxane produced lignin in 33.6% yield, which makes it very attractive as an alternative to the traditional MWL method. However further extraction with 50% aqueous dioxane or 80% aqueous dioxane containing 1% NaOH gave just a little more lignins with different carbohydrate compositions from those in MWL. The eucalyptus lignins obtained were syringyl and guaiacyl type units. Lignin fraction obtained from 96% dioxane extraction was found to have more phenolic hydroxyl and less aliphatic hydroxyl than the other two preparations.

Wood meal was completely dissolved under constant conditions (130 °C, 6 h) in the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl), and the various factors and potential mechanism of the homogeneous esterification of wood in this reaction medium were mainly studied. The physicochemical properties of the esterified wood were also investigated. It has been shown that highly substituted wood esters could be obtained by reacting wood dissolved in [C(4)mim]Cl with octanoyl chloride in the presence of triethylamine as a neutralizer. The weight percent gain was arranged from 121.5% to 297.4%. All reactions were performed under mild conditions, low excess of reagent, and a short reaction time compared to the heterogeneous chemical modification. Meanwhile, characterization of the derivatives confirmed that the homogeneous esterification was successfully processed. It was also found that thermal stability and morphological properties of the esterified wood were significantly different from those in previous reports. Octanoylation of wood meal in the [C(4)mim]Cl homogeneous system reduced the initial temperature of their thermal degradation and decreased the thermal stability compared to those in unmodified wood meal. Furthermore, the fibrillar appearance of wood meal changed into a relatively more homogeneous macrostructure of the esterfied wood. All these results suggested that homogeneous esterification of poplar wood in [C(4)mim]Cl would enhance the compatibility and improve the processability of wood with synthetic polymers.

Water and aqueous alkali sequential treatments of delignified bamboo particles were performed to extract hemicelluloses with a high yield and weight-average molecular mass (Mw). The sequential treatment together dissolved 42% of hemicelluloses based on dry holocellulose. GPC results showed that the alkali-extractable hemicelluloses have higher Mw (35000 and 44450 g mol(-1)) than water-extractable ones (20100-28100 g mol(-1)). Structural determination based on FT-IR and (1)H, (13)C, and 2D-HSQC NMR analyses showed that both the water- and alkali-extractable hemicelluloses shared the structure composed of the (1 → 4)-linked β-D-xylopyranosyl backbone with 4-O-methyl-α-d-glucuronic acid attached to O-2 of the xylose residues and l-arabinose attached to O-3 of the xylose residues. Moreover, it revealed that the water-extractable hemicelluloses retained original structure without cleaving chemical linkages. Furthermore, it was also found that the hemicelluloses with the highest yield and Mw were obtained by the aqueous alkali treatment from the delignified bamboo. A small amount of other minor hemicelluloses (β-glucans) including xylans in the water-extractable hemicelluloses could be identified by NMR and other approaches.

The dewaxed cell walls of Populus gansuensis were delignified with NaClO(2) and then sequentially extracted with 0.25, 0.5, and 1.0 M KOH under a solid to liquid ratio of 1: 25 (g mL(-1)) at 25 degrees C for 10 h. The successive treatments together resulted in the dissolution of 83.7% of original hemicelluloses. The solubilized hemicellulosic fractions were further fractionated into six hemicellulosic subfractions by an iodine-complex precipitation technique. Their chemical and physical characteristics were determined by HPAEC, GPC, FT-IR, and (1)H and (13)C NMR spectroscopy. Neutral sugar composition and molecular weight analysis showed that, for each extract, the hemicellulosic subfractions that precipitated with aqueous potassium iodide-iodine had lower overall uronic acid/xylose (Uro/Xyl) ratios and higher molecular weights (M(w)) than those remaining in the solution. FT-IR, (1)H, and (13)C NMR spectroscopy analysis indicated that the alkali-soluble hemicelluloses of Populus gansuensis had a structure composed of the (1 --> 4)-linked beta-D-xylopyranosyl backbone with 4-O-methyl-alpha-D-glucuronic acid attached to O-2 of the xylose residues.

Attempts were made to enhance polysaccharide digestibility by crude cellulases in the isolation of cellulolytic enzyme lignin (CEL) by dissolution of ball-milled wood in a dimethyl sulfoxide (DMSO)/N-methylimidazole solvent system as a pretreatment step. Wood regenerated from the DMSO/N-methylimidazole solution was hydrolyzed with crude cellulases for 48 h, removing 73.7 and 66.9% of the original carbohydrate for basswood and loblolly pine, respectively; only 61.7 and 49.2% were hydrolyzed by the crude cellulases without pretreatment. The yields of CEL isolated from regenerated ball-milled wood samples were therefore higher than those directly from ball-milled wood material, presumably via decreasing crystallinity of cellulose. For basswood, the yields of lignin were 45.8 and 36.5% (based on Klason lignin); for loblolly pine, the yields were 35.3 and 30.5%. The isolated lignins were structurally examined using two-dimensional heteronuclear single-quantum coherence ((1)H-(13)C HSQC) NMR methods, which showed that the main structural characteristics of the lignin fractions obtained using these two methods are similar except for slightly higher amounts of carbohydrates in the solvent dissolution product.

The two hemicellulosic fractions were subsequentially extracted with 5% and 8% NaOH aqueous solution at a solid to liquid ratio of 1:25 (g mL(-1)) at 50 degrees C for 3 h from the water, 1 and 3% NaOH-treated sugar cane bagasse, and subfractionated into six preparations by a graded ethanol precipitation method at concentrations of 15%, 30% and 60% (v/v). Sugar composition and molecular weight analysis showed that, with an increasing concentration of ethanol, hemicellulosic subfractions with both higher Ara/Xyl ratios and higher molecular weights were obtained. In other words, with an increasing ethanol concentration from 15% to 60%, the Ara/Xyl ratios increased from 0.043 in H(1) to 0.088 in H(3) and from 0.040 in H(4) to 0.088 in H(6), and the weight-average molecular weights of hemicellulosic subfractions increased from 42 430 (H(1)) to 85 510 (H(3)) g mol(-1) and from 46 130 (H(4)) to 64 070 (H(6)) g mol(-1), respectively. The results obtained by the analysis of Fourier transform infrared, sugar composition, and (1)H and (13)C nuclear magnetic spectroscopy showed that the alkali-soluble hemicelluloses had a backbone of xylose residues with a beta-(1-->4)-linkage and were branched mainly through arabinofuranosyl units at C-2 and/or C-3 of the main chain, whereas the differences may occur in the distribution of branches along the xylan backbone.

The sequential treatment of dewaxed sugarcane bagasse with H(2)O and 1 and 3% NaOH at a solid to liquid ratio of 1:25 (g mL(-1)) at 50 degrees C for 3 h yielded 74.9% of the original hemicelluloses. Each of the hemicellulosic fractions was successively subfractionated by graded precipitation at ethanol concentrations of 15, 30, and 60% (v/v). Chemical composition, physicochemical properties, and structures of eight precipitated hemicellulosic fractions were elucidated by a combination of sugar analysis, nitrobenzene oxidation of bound lignin, molecular determination, Fourier transform infrared (FT-IR), (1)H and (13)C nuclear magnetic spectroscopies, and thermal analysis. The results showed that the sequential treatments and graded precipitations were very effective on the fractionation of hemicelluloses from bagasse. Comparison of these hemicelluloses indicated that the smaller sized and more branched hemicelluloses were extracted by the hot water treatment; they are rich in glucose, probably originating from alpha-glucan and pectic polysaccharides. The larger molecular size and more linear hemicelluloses were dissolved by the alkali treatment; they are rich in xylose, principally resulting from l-arabino-(4-O-methylglucurono)-d-xylans. In addition, noticeable differences in the chemical composition and molecular weights were observed among the graded hemicellulosic subfractions from the water-soluble and alkali-soluble hemicelluloses. The Ara/Xyl ratio increased with the increment of ethanol concentration from 15 to 60%, and the arabinoxylans with higher Ara/Xyl ratios had higher molecular weights. There were no significant differences in the structural features of the precipitated hemicellulosic subfractions, which are mainly constituted of l-arabino-(4-O-methyl-d-glucurono)xylan, whereas the difference may occur in the distribution of branches along the xylan backbone.

The homogeneous chemical modification of cellulose with succinic anhydride was investigated in a solvent system containing 1-butyl-3-methylimidazolium chloride ionic liquid and dimethylsulfoxide using N-bromosuccinimide (NBS) as a catalyst. The results showed that the degree of substitution of the succinylated cellulosic samples, in the range of 0.24-2.31, noticeably increased as compared with the products without any catalysts, indicating that NBS was a novel efficient catalyst for cellulose succinoylation in ionic liquids. Fourier transform infrared and solid-state cross-polarization/magic angle spinning (13)C NMR spectroscopies also provided evidence of succinoylation reaction. The results indicated that the reaction of hydroxyl groups at C-6, C-2, and C-3 positions in cellulose occurred. The thermal stability of the succinylated cellulose was found to decrease upon chemical modification.

Wheat straw hemicelluloses were converted to novel bifunctional hemicellulosic derivatives by etherification using acrylamide as reactant and sodium hydroxide as catalyst. The degree of substitution can be monitored by altering the molar ratio of acrylamide to xylose unit in hemicelluloses in the range of 1.0-10.0 and the molar ratio of sodium hydroxide to xylose unit in hemicelluloses in the range of 0.5-1.6, without changing the structure of the hemicelluloses. Comparison of the reaction in different media is discussed in detail. The optimized product with a high DS value of 0.58 was obtained by varying the condition parameters. Novel hemicellulosic derivatives containing carbamoylethyl and carboxyethyl groups could be confirmed by FT-IR, (1)H NMR, and (13)C NMR spectroscopies. The behavior of hemicellulosic derivatives was monitored by means of thermogravimetry (TG) and differential thermal analysis (TGA). It was found that the product with a high DS had a lower thermal stability than the native hemicelluloses.

To reduce the cost of biodiesel production, the feasibility of Zanthoxylum bungeanum Maxim seed oil (ZBMSO) was studied to produce biodiesel. A methyl ester biodiesel was produced from ZBMSO using methanol, sulfuric acid, and potassium hydroxide in a two-stage process. The main variables that affect the process were investigated. The high level of free fatty acids in ZBMSO was reduced to < 1% by an acid-catalyzed (2% H2SO4) esterification with methanol to oil molar ratios of 20-25:1 for 1 h. A maximum yield of 96% of methyl esters in ZBMSO biodiesel was achieved using a 6.5:1 molar ratio of methanol to oil, 0.9% KOH (percent oil), and reaction time of 0.5 h at 55 degrees C. Further investigation has also been devoted to the assessment of some important fuel properties of ZBMSO biodiesel produced under the optimized conditions according to specifications for biodiesel as fuel in diesel engines. The fuel properties of the ZBMSO biodiesel obtained are similar to those of no. 0 petroleum diesel fuel, and most of the parameters comply with the limits established by specifications for biodiesel.

Lauroylation of wheat straw hemicelluloses in the N, N-dimethylformamide/lithium chloride system under microwave irradiation was studied. The parameters optimized included lauroyl chloride concentration as the molar ratio of xylose unit in hemicelluloses/lauroyl chloride (1:1-1:4), 4-dimethylaminopyridine concentration (2-10%), reaction time (1-8 min), molar ratio of xylose unit in hemicelluloses/triethylamine (1:2), and reaction temperature (78 degrees C). The reaction efficiency was measured by the yield and degree of substitution (DS). Under an optimum reaction condition (molar ratio of xylose unit in hemicelluloses/lauroyl chloride 1:3, molar ratio of xylose unit in hemicelluloses/triethylamine 1:2, 5% 4-dimethylaminopyridine, 78 degrees C, 5 min), a DS of 1.63 was obtained. Changes in the structure of hemicelluloses were verified by FT-IR and 1H and 13C NMR spectroscopy. The results showed that the lauroylation occurred preferentially at the C-3 position of the xylose unit in hemicelluloses. The behavior of the lauroylated hemicelluloses was monitored by means of thermogravimetric (TG) and differential thermogravimetric (DTG) analysis. It was found that the product with low DS had a lower thermal stability than the native hemicelluloses, whereas the lauroylated polymers with high DS showed a higher thermal stability than the unmodified hemicelluloses.

Homogeneous modification of cellulose, isolated with 10% KOH from delignified sugarcane bagasse, was performed in room-temperature ionic liquid 1-allyl-3-methylinidazolium chloride with phthalic anhydride in the absence of catalyst. The results showed the degree of substitution of phthalated cellulosic derivatives, ranging from 0.10 to 0.73, increased with the increment of reaction temperature, reaction time, and the molar ratio of phthalic anhydride/anhydroglucose units in cellulose under the conditions given. The products were characterized by FT-IR and solid-state CP/MAS 13C NMR spectroscopy as well as thermal analysis, and the results revealed that the phthalation reaction at C-6, C-2, and C-3 positions of the cellulose all occurred. The thermal stability of the phthalated cellulose was found to decrease upon chemical modification. However, this thermal stability of the phthalated cellulose over 200 degrees C is rather satisfactory.

Cell walls of sugarcane bagasse were first delignified with chlorite followed by ultrasonic irradiation and then by two-step sequential extractions at 23 degrees C with 15 and 18% KOH for 2 h, 15 and 18% NaOH for 2 h, 8 and 10% KOH for 12 h, and 8 and 10% NaOH for 12 h and by a single one-stage isolation with 10% KOH for 16 h and with 10% NaOH for 16 h, which released 79.4, 81.8, 83.6, 85.7, 61.5, and 65.6% of the original hemicelluloses, and subsequently yielded 50.7, 49.5, 48.6, 47.8, 57.2, and 55.4% of the cellulose, respectively. The six cellulosic preparations were free of bound lignin and had a purity of 77.1-90.1% with the intrinsic viscosity (eta), viscosity average degree of polymerization, and molecular weight (M(w)) ranging from 534.1 to 631.6 mL g(-1), from 1858.1 to 2238.2 mL g(-1), and from 301000 to 362600 g mol(-1), respectively. The structural features of the isolated six cellulosic samples were comparatively examined by Fourier transform infrared and cross-polarization/magic angle spinning (13)C NMR spectroscopy and X-ray diffraction, and their thermal stability was investigated by using thermogravimetric analysis. It was found that all of the cellulosic preparations have the typical cellulose I structure but the crystallinity of the SCB cellulose was lower than that of flax, cotton, and kenaf.

A sequential totally chlorine-free procedure for isolation of cellulose from wheat straw was proposed in this study. The dewaxed straw was pretreated with 0.5 M NaOH in 60% methanol at 60 degrees C for 2.5 h under ultrasonic irradiation for 0-35 min and sequentially posttreated with 2% H(2)O(2)-0.2% TAED at pH 11.8 for 12 h at 48 degrees C, which together solubilized 85.3-86.1% of the original hemicelluloses and 91.7-93.2% of the original lignin, respectively. The yield of crude cellulose ranged between 46.2 and 49.2% on a dry weight basis related to wheat straw, which contained 11.2-12.2% residual hemicelluloses and 2.5-2.9% remaining lignin. Further treatment of the corresponding crude cellulosic preparations with 80% acetic acid-70% nitric acid under the condition given yielded 36.8-37.7% of the purified cellulose, which contained minor amounts of bound hemicelluloses (2.5-2.8%) and was relatively free of associated lignin (0.1-0.2%). The isolated crude and purified cellulose samples were comparatively studied by FT-IR and CP/MAS (13)C NMR spectroscopy, and the relative crystallinity was also estimated. The final stage treatment with 80% acetic acid-70% nitric acid decreased the hemicelluloses and lignin associated in the crude cellulose but led to 3.1-5.4% degradation of the original cellulose; in addition, the purity of the obtained cellulose was high. However, it was found that the final stage treatment is not severe enough to cause decrystallization of cellulose. The thermal stability of the purified cellulose is higher than that of the corresponding crude cellulose.

Sequential treatments of dewaxed bagasse with distilled water, 0.5 M NaOH, 0.5, 1.0, 1.5, 2.0, and 3.0% H(2)O(2) at pH 11.5, and 2 M NaOH at 55 degrees C for 2 h solubilized 2.8, 52.5, 14.9, 3.3, 5.5, 5.0, 2.8, and 2.2% of the original lignin, respectively. The eight isolated lignin fractions were subjected to a comprehensive structural characterization by UV, FT-IR, and (1)H and (13)C NMR spectroscopies and thermal analysis. The nitrobenzene oxidation method was also applied to the in situ lignins. The seven lignin fractions, isolated successively with alkali and alkaline peroxide, were all SGH-type lignins, with a small amount of esterified p-coumaric acid and mainly etherified ferulic acid. No significant differences were found in the weight-average molecular weights (1680-2220 g/mol) of the seven alkali and alkaline peroxide dissolved lignins. However, the first four lignin fractions, isolated with 0.5 M NaOH and 0.5, 1.0, and 1.5% H(2)O(2) at pH 11.5, were rich in syringyl units and contained large amounts of noncondensed ether structures, whereas the last three lignin fractions, isolated sequentially with 2.0 and 3.0% H(2)O(2) at pH 11.5 and 2 M NaOH at 55 degrees C for 2 h, had a higher degree on condensation and were rich in guaiacyl lignins.

The cell wall material of Chinese shrubs Haloxylon ammodendron and Elaeagnus angustifolia was fractionated by successive extractions with ethanol/H(2)O (60:40, v/v) under acidic conditions (0.2 N HCl) at 70 degrees C for 4 h, and 2% H(2)O(2) at pH 11.5 for 16 h, respectively. The sequential two-step treatment resulted in the dissolution of 83.9% and 87.6% of the original hemicelluloses from dewaxed H. ammodendron and E. angustifolia, respectively. Xylose, glucose, and galactose were the major sugar constituents in the two acidic organosolv-soluble hemicellulosic preparations. The two alkaline peroxide-soluble hemicellulosic fractions were shown to be composed primarily of xylose, comprising over 80% of the total sugars. The results also showed that the two alkaline peroxide-soluble hemicellulosic fractions were more linear and acidic, and had higher molecular mass and thermal stability than the two acidic organosolv-soluble hemicellulosic preparations. The 2% H(2)O(2) posttreatment did not result in any significant changes in the macromolecular structure of the isolated hemicelluloses. It is probable that lignin protects hemicelluloses and cellulose from being attacked by peroxide.

A new method has been developed for the quantitative determination of hydroxycinnamic acids participating in ester or ether linkages to the cell wall polymers. The method is based on mild alkaline hydrolysis followed by acid hydrolysis or mild alkaline hydrolysis, which partially removed esterified phenolic acids, and high-temperature concentrated alkaline treatment, which cleaved both the ester and ether linkages. It was found that traditional mild alkaline hydrolysis and acid hydrolysis released only part of the ester- and ether-linked phenolic acids, respectively. Approximately half (44.0-47.9%) of the total ester-linked p-coumaric acid and 18.2-32.6% of the total esterified ferulic acid remained ester-linked to the mild alkali-soluble lignin polymers, and 55.0-72.0% of the total ether-linked p-coumaric acid and 37.5-53.8% of the total ether-linked ferulic acid remained ether-linked to the solubilized lignin molecules after the acid hydrolysis. To correct this, a second mild alkaline hydrolysis of the alkali-soluble lignin preparations and acid hydrolysis of the solubilized lignin fractions, obtained from the first acid hydrolysis of the cell wall materials, was investigated. On the basis of this new method, a majority of the cell wall p-coumaric acid (55.8-81.5%) was found to be ester-linked to cell wall components, mainly to lignin, and about half of the cell wall ferulic acid is etherified through its phenolic oxygen to the cell wall lignin component, whereas the remainder is esterified to the cell wall hemicelluloses and/or lignin in different plant materials.

A sequential treatment of dewaxed barley straw with sodium hydroxide, different concentrations of hydrogen peroxide, and potassium hydroxide/sodium borate degraded various proportions of the original lignin and solubilized different amounts of the original hemicelluloses. The isolated lignin fractions were subjected to comprehensive structural characterization by UV, FT-IR, and (13)C NMR spectroscopy, and their chemical compositions were analyzed by alkaline nitrobenzene oxidation. All of the lignin fractions were typical of grass lignins and had weight-average molecular weights between 1750 and 2190. It was found that the peroxide treatment at low concentrations (< or =2.0%) resulted in a slight increase in the amount of carboxyl groups, whereas the treatment at a relatively high concentration of alkaline peroxide, such as at 3.0% H(2)O(2), led to a noticeable oxidation of the lignins, as shown by an increase of carboxyl groups. Moreover, the results obtained indicated that the successive treatments with alkali and alkaline peroxide under the conditions used did not significantly affect the beta-O-4 structures of lignins. Substantial amounts of etherified ferulic acids were cleaved by the sequential treatments with alkaline peroxide, as shown in the (13)C NMR spectra. The results underscore the structural differences between alkali- and alkaline peroxide-soluble lignins from barley straw.

Water-treated maize stems were subjected to delignification with peroxymonosulfuric acid at 20 degrees C for 144 h, with peroxyformic acid at 80 degrees C for 6 h, with peracetic acid at 50 degrees C for 6 h, and with 2% hydrogen peroxide at 45 degrees C for 12 h at pH 1.5, 4.4, 9.5, 11.5, 12.0, and 12.6, respectively, which solubilized 47.1, 91.3, 33.3, 16.6, 15.9, 17.4, 86.2, 87.7, and 91. 3% of the original lignin, respectively. Substantial lignins were released during the treatment with peroxyformic acid and hydrogen peroxide at pH > or =11.5, whereas an insignificant effect on delignification was observed by using peroxymonosulfuric acid, peracetic acid, and hydrogen peroxide under acidic, natural, and weakly alkaline media conditions. The structures of the isolated lignin preparations were investigated by chemical analysis, gel permeation chromatography, and UV, FT-IR, and (13)C NMR spectroscopy.