Etherification of hemicelluloses from sugarcane bagasse

Conditions for the preparation of etherified hemicelluloses from sugarcane bagasse with 2, 3‐epoxypropyltrimethylammonium chloride (ETA) using sodium hydroxide as a catalyst in aqueous solution were studied comparatively. The extent of the etherification was measured by yield percentage and degree of substitution. The effects of reaction time of 3–7 h, reaction temperature of 50–80°C, temperature of alkaline activation of 30–60°C, and time of alkaline activation of 0–60 min on the reaction yield and degree of substitution were investigated in detail. The overall yield and degree of substitution were varied from 35.2 to 41.9% and from 0.14 to 0.33, respectively, by changing the reaction temperature and duration as well as time and temperature of alkaline activation. The new materials were characterized by FT‐IR and 13C NMR spectroscopy, thermal analysis as well as GPC. It was found that the thermal stability of the hemicellulosic ethers decreased after chemical modification, and the molecular weights of the etherified hemicelluloses were lower than those of the native hemicelluloses. ¹³C NMR spectra gave the evidence for etherification reaction and the quaternization of hemicelluloses occurred mainly at C‐3 position. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Alkaline Pre-treatment of Hardwood Chips Prior to Delignification

Abstract

Hardwood (Betula pendula) chips were extracted having alkaline aqueous solutions with varying chemical charges (1, 2, 3, 4, 6, and 8% of NaOH on wood), treatment times (30, 60, 90, and 120 minutes), and temperatures (130°C and 150°C). The total amount of material removed was in the range 2.1–16.5% of the original dry feedstock. This fraction was characterized in terms of carbohydrates and their degradation products (mainly aliphatic carboxylic acids together with some furanoic compounds), lignin, and extractives. Low alkali charges (1–4% of NaOH) were not sufficient to neutralize all the acids formed (mainly acetic acid from the acetyl groups of xylan). In contrast, an increase in alkali charge (6% and 8% of NaOH) more intensively facilitated the alkali-catalyzed degradation reactions of polysaccharides to various hydroxy acids, which were then typically present as one of the main constituents in the dissolved organic matter, along with other aliphatic carboxylic acids (acetic and formic acids), lignin, extractives, and carbohydrates.     

Fractionnement de deux bois tropicaux (eucalyptus et wapa) par traitement thermomécanique en phase aqueuse. Partie II: Caractéristiques chimiques des résidus et considérations cinétiques sur la solubilisation des hémicelluloses

We have characterized the residual solids derived from the aqueous phase liquefaction of two tropical wood species. The liquefaction process comprises the following steps: preparation of an aqueous suspension of milled wood, preheating at 135°C, sudden decompression through an orifice (ΔP = 17.2 MPa), reaction at 80–230°C and rapid quenching. The residues have been analyzed by two methods: acid hydrolysis and elemental analysis. The quantification of the monosaccharides present in the residues allows us to follow the solubilization profiles of both hemicelluloses and cellulose. The elemental composition of the residues is related to the severity of the process and it becomes a solubilization index for the hemicelluloses and the lignin. The chromatographic analysis of the gaseous phase after liquefaction has resulted in the determination of CO₂ as the only gas produced up to 230°C. Kinetic first order models represent well the solubilization of the hemicelluloses and the CO₂ formation.     

Enzymatic hydrolysis of dissolved corn stalk hemicelluloses: reaction kinetics and modeling

The enzymatic hydrolysis of hemicelluloses as a filtrate originating from aqueous/steam pretreated corn stalks was carried out using commercial enzyme systems of several activities composed of cellulases and β‐D ‐xylosidases from Aspergillus niger. The hydrolysis was conducted using free enzymes in aqueous substrate solution at a temperature of 30 °C and a pH of 5. Saccharification corresponding to 90% of potential simple sugar release was obtained after 10 h using 0.12 activity units (U) of Cellulases_1 complex per mg of dissolved solids present in the filtrate. Synergetic action of Cellulases_1 enzyme complex and β‐D ‐xylosidases proved to be effective for the hydrolysis of plant hemicelluloses. A lumped model based on the Michaelis–Menten approach successfully described the fate of the lumped variables describing the hydrolysis of the overall kinetics of corn stalk hemicelluloses. The maximum saccharification rate evolved with the cellulases concentration as . This overall and pseudokinetic tendency was comparable to those reported in the literature for more simple systems employing a defined substrate and a pure hydrolytic enzyme. The n‐value was found to be in the range of 0.1–0.9 depending on the substrate lump involved in the reaction system. Copyright © 2003 Society of Chemical Industry     

Comparative Study of Water-soluble and Alkali-soluble Hemicelluloses Extracted by Hydrothermal Pretreatment

The purpose of this study was to explore the differences of the hemicelluloses extracted by hydrothermal pretreatment using water and alkaline solutions(Na OH or KOH). The physicochemical properties and structural characteristics of two water-soluble and four alkali-soluble hemicelluloses extracted from the triploid of Populus tomentosa Carr. through the hydrothermal pretreatment were comparatively studied. It was observed that the alkalis(Na OH and KOH) were more effective than distilled water as extractants. Sugar analysis showed that xylose(66.83%~86.49%) was the major constituent, followed by glucose(6.83%~18.49%). Mannose(1.40%~8.42%), galactose(2.17%~4.05%), and arabinose(0.21%~2.26%) were also detected in the hemicellulosic fractions. The results of gelpermeation chromatography(GPC) indicated that the hemicelluloses extracted using the alkaline solutions had relatively higher molecular weights than those solubilized in distilled water. Further, based on spectroscopic ~1Hnuclear magnetic resonance(~1H-NMR) and two-dimensional heteronuclear singular quantum correlation(2D-HSQC) analyses, it was confirmed that the hemicellulosic fractions had a major structure of(1→4)-b-D-xylan and a minor structure of(1→4)-a-D-glucan with small amounts of substituted sugars and glucuronic acid attached.     

新型溶剂体系处理对棉秆半纤维素分离效果初探

初步探究了8种新型溶剂体系处理对棉秆半纤维素的分离效果。结果表明,基于不同溶剂体系处理棉秆,再经二甲基亚砜(DMSO)抽提,可实现半纤维素组分的分离;由于处理体系性质不同,导致分离所得半纤维素的结构差异较大。其中,碱性溶剂体系分离得到的半纤维素纯度较好,主要由聚木糖组成,同时含有一定量来源于木糖聚葡萄糖的葡萄糖;而采用近中性体系,如八丁基氟化铵/二甲基亚砜、1-烯丙基-3-甲基咪唑氯盐/二甲基亚砜、1,3-二甲基丙撑脲/二甲基亚砜及N-甲基吗啉氧化物/二甲基亚砜分离得到的半纤维素中含有大量来源于纤维素的葡萄糖,表明近中性溶剂体系不适宜用于高纯半纤维素的分离。     

半纤维素功能材料——水凝胶

与各种高分子合成的水凝胶相比,半纤维素基水凝胶具有难以比拟的优势,如环境友好性、生物兼容性、无毒及可降解性等.文中从制备方法角度归纳和总结了木质纤维半纤维素基水凝胶材料近年来的研究进展以及潜在的商业应用前景,并指出了半纤维素基水凝胶在研究中存在的问题及发展方向.     

Characterization of Hemicelluloses Extracted from Populus tomentosa Carr. by the Hydrothermal Method with Ethanol

The aim of this study was to investigate the hemicelluloses extracted from Populus tomentosa Carr.by the hydrothermal method with ethanol.The influence of ethanol concentration on the hemicellulosic fractions was systematically studied.The chemical compositions and structural features of the hemicellulosic fractions were investigated by a combination of sugar analysis,gel-permeation chromatography,Fourier transform infrared spectroscopy,and one-dimensional proton and carbon-13 nuclear magnetic resonance,and two-dimensional heteronuclear single quantum coherence spectroscopy.Neutral sugar analysis of the hemicellulosic fractions revealed that a higher ethanol concentration(45%~80%) favored the isolation of hemicelluloses with more side chains and lower glucose contents.The molecular weights of these polysaccharides ranged between 2842 g/mol and 5101 g/mol.The results of this study indicate that the hydrothermal ethanol process provides a new pretreatment strategy for the isolation and extraction of biomass.     

Modification of the water-insoluble hemicelluloses via free radical copolymerization in diluted alkali aqueous medium

The synthesis of hemicelluloses-g-polyacrylamide (PAM) was carried out in diluted alkaline aqueous solution via free radical copolymerization initiated by redox initiator composed of potassium persulfate (KPS)/sodium thiosulfate (Na₂S₂O₃). The less substituted hemicelluloses, l-arabino-4-O-methyl-d-glucurono-d-Xylan (wis-AGX), are the main components of the hemicelluloses isolated from corncobs by the ultrasound-assisted diluted alkali extraction method and exhibit poor water solubility, which largely limit their applications. The factors, such as the initiator dosage, the monomer concentration, and the reaction time, which influenced both the grafting percent and the grafting efficiency, were investigated. The chemical structure and thermal and macromolecular weight properties of the graft copolymers were characterized by Fourier transform infrared spectrometer (FT-IR), ¹H nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The results indicated that the PAM moieties were successfully introduced into the side chains of the hemicelluloses, and the graft copolymers showed good solubility in water. Such modification is suggested to find a possible new way for broadening applications of water-insoluble hemicelluloses, and the resultant graft copolymers might have potential applications, such as gels, films, adsorbents, coatings, or drug delivery systems.