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Hemicellulose plays a versatile role in plant cell wall by linking cellulose and lignin or impeding lignin removal from sustainable cellulosic fibers. Herein, hemicellulose fractions (glucuronoxylans) of Eucalyptus pulp cooked to various cooking degree were extracted by potassium hydroxide solution and purified with ethanol. The glucuronoxylans are divided into water-insoluble (GXI) and -soluble (GXS) fractions. The release or degradation behavior of glycosylated side-chain of hemicellulose in alkaline cooking was explored according to the separate discussion of GXI and GXS, and take consideration of the effect of extraction temperature on polysaccharide degradation. The GXI is constructed of basically straight xylan chain with high linearity, and GXS contains multi-branches xylan chain. The harsher cooking conditions (corresponding to H factors 317, 586 and 904) and alkaline-extraction temperature significantly influenced the composition and structure, leading more glycosyl side chains removal. More content glucuronic acid (6.04–11.26%) in GXS, which may relate to high branch on xylans and great solubility, while less of glucuronic acid (MeGlcA, 2.28–5.48%) in GXI was accounting for the poor solubility. The glycosyl analyses of the two fractions extracted from different pulp showed that the hexenuronic acid (HexA) converted from MeGlcA in GXI was retained during cooking, while that in GXS was easier to be removed in pulping process. [ABSTRACT FROM AUTHOR]

The extractability of hemicellulose from different lignocellulosics depends on the source of biomass. Differences in hemicellulose extractability are believed to be due to plant-specific hemicellulose arrangement alongside lignin within the cell wall. In this research, six biomasses were used to probe hemicellulose alkaline extractability as a function of the native lignin within the biomasses. Quantitative 2D-HSQC and 13C NMR analysis were performed to determine the S/G (S: syringyl, G: guaiacyl) and lignin-carbohydrate complex (LCC) linkages of milled wood lignin isolated from these biomasses. A strong negative correlation was observed between total lignin content and hemicellulose extractability, demonstrating that a greater presence of lignin in the original material results in lower xylan solubilization. In addition, a correlation between S/G of lignin and xylan dissolution was found within a group of hardwoods and within a group of non-woods. This suggests that monomeric constituency also influences xylan's propensity for dissolution in 10% NaOH. Although there is some uncertainty in the quantification of LCC linkages, both non-woods and hardwoods exhibited negative correlations between alkaline-stable LCC linkages content and xylan extractability. This suggests that alkaline-stable LCC structures are associated with a decrease in the alkaline extractability of hemicellulose. [ABSTRACT FROM AUTHOR]

In the corn crop industry, of all the biomass produced, about 80% are residues. The so-called corn fibers, one of the most important residues of the corn processing industry, represent about 9% of the corn kernel weight, being a low value material that could, potentially, be used for making higher added value products. This work aimed to extract the hemicelluloses present in the corn fiber via alkaline extraction, with their subsequent functionalization for production of carboxymethyl xylans in mild conditions. The corn fibers were characterized for their contents of carbohydrates, lignin, extractives, total uronic acids, acetyl groups, and ash. Their arabinoxylans were extracted by 2-18% (w/v) sodium hydroxide at room temperature, for 5 h at 10% consistency, precipitated with ethanol, washed and then vacuum dried. The resulting extract was characterized by FT-IR, viscosity, arabinoxylan content and purity. It was demonstrated that CCE treatment provides a high purity and little degraded xylan, but the extraction yields are relatively low, in the range of 4.0-23.9% wt/wt depending upon extraction conditions. The use of corn fiber arabinoxylans to obtain hemicellulosic derivatives through chemical modification reactions was also evaluated. The arabinoxylans were derivatized by carboxymethylation with sodium monochloroacetate in a 2-propanol alkaline medium using different proportions of alcohol and alkali. The product carboxymethyl xylan was characterized by degree of substitution, FT-IR, DSC, and yield, and showed high degree of substitution, yield and enthalpy of fusion. This work proved the feasibility of producing hemicellulosic derivatives from corn fibers, which excludes the use of extreme conditions of solvents and temperature. [ABSTRACT FROM AUTHOR]

The present work is focused on alkaline extraction of xylans from bleached Kraft pulp of Eucalyptus globulus, and its isolation from the alkaline extract, aiming high purity product and yields. Alkaline extraction was optimized, through the stirring speed and extraction time. A higher stirring speed increased extraction yields which varied between 65 and 85%. However, extraction time did not have influence on extraction yields. Xylans isolation was performed by precipitation with diluted acids and with various alcohol concentrations. Washing of the precipitates, to remove impurities, was performed either with water and/or with methanol. Water washing yielded xylans with purity values up to 99%, while with methanol those values were lower, in the range of 36-84%. Xylans characterization indicated average molecular weights of 16.8-22.7 kDa. The isolated xylan yields varied between 43 and 97%. Nitric acid showed to be the most adequate solvent to get pure xylan. On the other hand, in alcohol experiments lower yields were obtained due to the losses in the subsequent water washing process. [ABSTRACT FROM AUTHOR]

Abstract: Residual hemicellulose in dissolving pulp is known as a reason for deterioration of final product quality and processability problems during cellulose derivative production. However, the issue caused by the residual hemicellulose is not fully understood and is primarily based on industrial experience. To better understand the effect of hemicellulose on cellulose derivative process, hemicellulose in prehydrolysis kraft hardwood dissolving pulp was extracted and its glycosidic linkage structure was thoroughly analysed. Two-stage alkaline extraction, consisting of 24 wt% KOH solution and 18 wt% NaOH with 4 wt% H3BO3 solution, was found effective for the sequential extraction of high purity xylan and glucomannan from the dissolving pulp. Considering the purity and yield of extracted xylan, room temperature for Stage-1 KOH extraction condition was preferred, while 1 °C was preferred for Stage-2 NaOH extraction. Mechanical refining treatment at a mild condition improved the extraction yield of hemicellulose, although the molecular weight of the cellulose was reduced with severe refining condition. Glycosidic linkage analysis showed that native 4-O-methylglucuronic acid side groups were removed during pulping process, resulting in a linearized xylan structure, while a high amount of glucuronic acid was detected in commercial beechwood xylan. The extracted hemicellulose from the second stage showed relatively high number of branched backbone unit e.g., 1,4,6-linked mannose and 1,4,6-linked glucose. The protocol developed in this study should be useful for hemicellulose-related applications.Graphical abstract: [ABSTRACT FROM AUTHOR]

Abstract: The levelling-off degree of polymerization (LODP) is typically considered an apodictic number of each cellulosic source that relates to the length of its cellulose crystallites. In this study, we have performed hydrothermal and alkaline treatments on bleached birch kraft pulp to adjust the xylan content, and the resulting pulps have been subjected to acid hydrolysis to determine their LODP. The results show that hydrothermal treatments promote longitudinal alterations in the supramolecular structure of cellulose, represented by a linear decrease in the LODP with lowering the xylan content in the pulp. Moreover, a decrease in LODP is also observed after alkaline extraction of the birch kraft pulp, but the decrease as a function of xylan content differs from that observed after hydrothermal treatments. The results appear to indicate that the LODP is rather an artifact introduced during processing of the material than a true measure of the length of the crystallites in the native cellulose source.Graphical abstract: [ABSTRACT FROM AUTHOR]

Wheat straw was respectively pretreated by water, dilute sulfuric acid, and sodium hydroxide solution at elevated temperature. Among the pretreatments, hydrothermal process was carried out with different severities. Hydrothermal pretreated sample and dilute acid pretreated sample were subsequently extracted by sodium hydroxide solution at room temperature which was applied as post-treatment. The pretreated samples were then enzymatically hydrolyzed to evaluate reducing sugar recovery. The result indicated that alkaline pretreatment removed a significant amount of lignin. While hydrothermal pretreatment and dilute acid pretreatment solubilized a significant amount of hemicellulose. And the hydrothermal pretreatment severity affected the solubilization of hemicellulose. The alkaline pretreated sample achieved the highest reducing sugar recovery e.g. 38.5 g sugar/100 g wheat straw. The alkaline post-treatment enhanced the enzymatic hydrolysis of acidic pretreated samples by removing additional hemicellulose and lignin. The best reducing sugar recovery was obtained at 43.6 g sugar/100 g wheat straw which indicated that the combination of hydrothermal pretreatment and alkaline extraction is a promising method in terms of reducing sugar production. [ABSTRACT FROM AUTHOR]

Delignification and pentosan dissolution of old corrugated cardboard (OCC) pulp was carried out using formic acid (FA) followed by alkaline extraction at atmospheric pressure. The kappa number of the initial OCC pulp was 41.4, which was decreased to 18.0 after 3.5 h of formic acid treatment. At this point, the pentosan content in the formic-acid-treated pulp was 6.20 %, being further decreased to 3.92 % after alkaline extraction with 8 % NaOH for 120 min at 90 °C. The overall pulp yield after FA treatment and alkaline extraction reached 48.0 %. Alkaline-extracted pulp was bleached to 85 % brightness using a DEDED bleaching sequence, with α-cellulose content of 94.7 %. FA and alkaline extraction liquor dissolved mostly hemicellulose and lignin, which were isolated and characterized. The fractions of lignin and hemicellulosic sugars recovered from the FA spent liquor were 4.3 and 12.7 %, respectively. The lignin was characterized as having a lower amount of methoxyl but higher amount of phenolic hydroxyl groups. [ABSTRACT FROM AUTHOR]

The effects of hemicellulose removal from bleached birch kraft pulp by alkaline extraction with sodium hydroxide on the dielectric, electrical and electrostatic properties of paper material have been examined. The hemicellulose content, particularly the xylan content, of birch kraft pulp has an effect on the dielectric constant and on the dielectric loss factor. The real part of the dielectric constant increases with decreasing content of hemicellulose in papers containing the extracted birch kraft pulp. Hemicellulose removal by alkaline extraction increases the direct and alternating current electrical conductivity and changes the electrostatic properties of the paper. Dielectric relaxation spectra at different temperatures analysed using the Havriliak-Negami relaxation model revealed that the dielectric properties are determined by at least two relaxation processes which are affected by the hemicellulose content. The first relaxation process originates in the polarizable groups of cellulose and hemicellulose and the second is attributed to the water-polymer structures formed during the interaction of cellulose and hemicelluloses with moisture. Both relaxation processes are compared quantitatively. [ABSTRACT FROM AUTHOR]

In order to improve corn ethanol profitability and energy efficiency, a natural gum consisting of primarily arabinoxylan and crude protein (CP) was extracted from distillers' grains (DG), a major byproduct from the dry grind corn ethanol production. DG was fractionated into an alkali-soluble gum fraction and an alkali-insoluble residue fraction by extracting with 1-5 % NaOH at 25-75 °C for 1-5 h. The extraction conditions, which significantly affect the yields and compositions of DG gum and residue, were statistically modeled to optimize yields and compositions. DG gum had 8-22 % CP, which could all be reduced to about 8 % by purification with bentonite clay. The isolated gums (purified and unpurified) were made into emulsifying agents, whereas residues were characterized as animal feed. The results demonstrated that the purification process affects the emulsifying properties of the DG gum-derived emulsifying agents. In parallel, the DG residue was found to have increased fiber digestibility and metabolizable energy compared to the original DG. An economic analysis determined that concurrent productions and utilizations of DG gum and DG residue could improve the cost and energy balance of the current corn ethanol process. [ABSTRACT FROM AUTHOR]

Cellulose composites were produced by culturing Acetobacter aceti subsp. xylinum (ATCC 53524, agitation tolerant strain) under shaking and agitating conditions in the presence of 2% pine or beech Björkman lignin-carbohydrate complexes (LCCs) or six different types of hemicellulosic polysaccharides including glucuronoxylan, glucomannan, O-acetyl-glucuronoxylan, arabinoglucuronoxylan, arabinogalactan and xyloglucan. Hemicellulosic polysaccharide contents in cellulose composites were similar in spite of the differences in culture, shaking and agitating conditions. On the basis of hemicellulosic polysaccharide contents and X-ray diffraction patterns after extraction by dilute NaOH solution, glucomannan family polysaccharides were found to have the highest affinity to bacterial cellulose. Composites with neutral and acidic LCCs were resistant against alkali while high lability of their delignified carbohydrates against alkali indicates the importance of lignin for formation of cellulose-hemicellulose-lignin framework of plant secondary cell-walls. [ABSTRACT FROM AUTHOR]