Comparative study of three lignin fractions isolated from mild ball‐milled Tamarix austromogoliac and Caragana sepium

Six lignin fractions from mild ball‐milled Tamarix austromogoliac (TA) and Caragana sepium (CS) were sequentially isolated with 80% dioxane containing 0.05M HCl at 75°C for 4 h, 50% aqueous ethanol containing 1M triethylamine at 70°C for 4 h, and 8% aqueous NaOH at 45°C for 3 h. The results showed that the successive treatments made it possible to isolate lignin from wood with a high yield and purity, in which 89.4 and 90.6% of the original lignin from TA and CS were released, respectively. The lignin fractions isolated with the three‐step method were analyzed with Fourier transform infrared, ¹H‐ and ¹³C‐NMR, alkaline nitrobenzene oxidation, and gel permeation chromatography. It was found that the three lignin fractions isolated from TA were rich in syringyl units, and the molar ratio of the relatively total moles of vanillin, vanillic acid, and acetovanillin to the relatively total moles of syringaldehyde, syringic acid, and acetosyringone decreased from 1: 2.6 to 1 : 3.2 to 1: 3.6 in the lignin preparations, whereas this ratio in the corresponding lignin fractions isolated from CS was found to be 1.4 : 1, 1.1 : 1, and 1 : 1.4, respectively. More importantly, the results revealed that the sequential extractions of the mild ball‐milled TA and CS with 80% acidic dioxane, 50% alkaline ethanol, and 8% aqueous NaOH under the conditions used did not significantly cleave the β–O‐4 and α–O‐4 linkages in lignin macromolecules. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Comparative study of lignins from ultrasonic irradiated sugar‐cane bagasse

After ultrasonic irradiation of sugar‐cane bagasse (SCB) in distilled water at 55 °C for 40 min and continuing stirring for 80 min, the irradiated SCB was sequentially treated with 0.5 M NaOH, 0.5 %, 1.0 %, 1.5 %, 2.0 % and 3.0 % H₂O₂ at pH 11.5, and 2 M NaOH at 55 °C for 2 h, which solubilized 3.3, 59.7, 15.5, 4.4, 5.5, 1.7, 0.6 and 0.6 % of the original lignin, and 13.4, 38.2, 11.9, 4.5, 9.0, 2.4, 1.2, and 11.3 % of the original hemicelluloses, respectively. In total, the sequential extractions resulted in a release of 91.2 % of the original lignin and 91.9 % of the original hemicelluloses, which were higher than in the case of corresponding extractions without ultrasound pre‐treatment. The eight lignin fractions were comparatively characterized by chemical composition, structural features, molecular weights, and thermal stability using alkaline nitrobenzene oxidation, acid hydrolysis, UV, FT‐IR, ¹H and ¹³CNMR spectroscopy, GPC, and thermal analysis. Compared to the lignins obtained without ultrasound, the lignin fractions prepared with the assistance of ultrasound had the same primary structure, composition, and similar or slightly higher purity. Copyright © 2004 Society of Chemical Industry     

Fractional Separation and Structural Characterization of Chlorophyll and Lignin from Perennial Ryegrass (L. perenne) and Cocksfoot Grass (D. glomerata)

Abstract

One chlorophyll rich fraction and two lignin preparations were separated from perennial grass and cocksfoot grass by sequential three‐stage treatments with 80% ethanol containing 0.2% NaOH, 2.5% H₂O₂?0.2% EDTA containing 1.5% NaOH, and 2.5% H₂O₂?0.2% TAED containing 1.0% NaOH at 75°C for 3 h, respectively, which released 4.6 and 3.6% chlorophyll rich fraction, 2.3 and 5.8%, and 0.9 and 1.0% lignin preparations, except for releasing 8.0 and 10.4%, 79.1 and 77.0%, and 12.9 and 12.5% of the original hemicelluloses, respectively. The lignin fractions obtained from the two different grasses had very similar molecular weights and structural composition. The NMR spectra of the lignin preparations revealed the presence of p‐hydroxyphenyl, guaiacyl, and syringyl structures, and the lignin in chlorophyll rich fraction contained more guaiacyl and syringyl units than p‐hydroxyphenyl unit, whereas the reverse trend was found in the two lignin preparations. The lignin preparations are distinguished with straw and wood lignins by relatively higher contents of p‐hydroxyphenyl unit and lower amounts of condensed units (β‐5 and 5‐5′) and resinol units (β‐β). This difference in distribution of structural units indicated some structural heterogeneity between grass and straw/or wood lignin.     

Physicochemical characterization of lignins from rice straw by hydrogen peroxide treatment

Extraction of the dewaxed rice straw with 1% NaOH at 55°C for 2 h and following treatment without and with 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0% hydrogen peroxide (H₂O₂) at 45°C for 12 h at pH 11.5 resulted in a dissolution of 68.3, 85.4, 89.4, 92.3, 92.3, 94.3, and 95.1% of the original lignin, respectively. Meanwhile, the two‐stage treatment together solubilized 67.2, 77.2, 78.7, 83.7, 85.5, 87.3, and 88.5% of the original hemicelluloses and degraded 2.5, 9.8, 11.8, 12.1, 15.6, 16.4, and 17.8% of the original cellulose under the conditions given, respectively. Analyses of these lignins revealed that alkali‐soluble lignin fractions did not suffer sever oxidation, but nearly 60% of the original lignin was dissolved out during the first stage of alkali treatment. In the second stage of alkaline peroxide treatment, the residual lignins were substantially released and enriched in oxidized carbonyl and carboxyl groups. In comparison, the isolated eight pure lignin samples were further characterized by both destructive methods such as alkaline nitrobenzene oxidation and nondestructive techniques such as ultraviolet (UV), Fourier transform infrared (FTIR), and carbon‐13 magnetic resonance spectroscopy (¹³C‐NMR) as well as gel permeation chromatography (GPC), and the results are reported. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 719–732, 2001     

Structural characterization of residual lignins isolated with cyanamide-activated hydrogen peroxide from various organosolvs pretreated wheat straw

The posttreatment of various organosolvs pretreated wheat straw with cyanamide-activated hydrogen peroxide was studied. About 44–80% of the total residual lignin and 38–85% of the total residual hemicelluloses were released or degraded during the posttreatment with 1.8% H₂O₂–0.18% cyanamide at 50°C under pH 10.0 for 4 h from different aqueous organic acids or alcohols pretreated straw. The seven degraded residual lignin preparations were subjected to a comprehensive physicochemical and structural characterization by UV, FTIR, and ¹H and ¹³NMR spectroscopy, and GPC. The nitrobenzene oxidation method was also applied to the in situ lignins. It was found that the seven residual lignin preparations contained large amounts of noncondensed syringyl and guaiacyl units, together with fewer noncondensed p-hydroxyphenyl units, esterified p-coumaric acid, and mainly etherified ferulic acid. All of the lignin fractions are free of associated polysaccharides and had molecular-average weights ranging between 2980 and 3820 g mol⁻¹. Analysis of these low molecular weight degradation products revealed an oxidation of residual lignin had occurred. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Isolation of highly purity cellulose from wheat straw using a modified aqueous biphasic system

Cellulose samples with molecular weights ranging from 8.39 × 10⁴ to 11.00 × 10⁴ g/mol were obtained from wheat straw. The dewaxed wheat straw was pretreated with aqueous hydrochloric acid followed by delignification using an environmentally benign poly(ethyleneglycol)/salt aqueous biphasic system. The yield of cellulose was in the range of 48.9%–55.5% and the cellulose contained 1.2%–3.2% hemicelluloses, and 0.97%–3.47% lignin. All the isolated cellulose samples could be directly dissolved in a 6 wt-% NaOH/4 wt-% urea aqueous solution through a precooling-thawing process to form a homogenous solution. The separation process was investigated and the obtained cellulose and its solution were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray apparatus, and X-ray diffraction. The results revealed that aqueous soluble cellulose can be directly prepared from wheat straw by this method and this study opens a novel pathway to prepare cellulosic materials from agricultural waste.     

小麦秸秆催化液化工艺研究

常温常压下小麦秸秆催化液化制绿色化学品。分别研究了小麦秸秆在甲醇、乙醇、丙三醇和丁醇中的液化效果,考察了甲醇和苯酚的混合体系下液化时间与不同催化剂对液化产率的影响。结果表明,常温常压下,4种醇对小麦秸秆的液化产率的高低顺序:甲醇>乙醇>丙三醇>丁醇,甲醇的液化产率最高,达到17.23%,可以作为木质素液化的有效试剂。甲醇和苯酚混合液化体系的液化产率可达到24.52%,以对甲苯磺酸作为催化剂液化产率可达到28.40%。     

Fractional and structural characterization of ball-milled and enzyme lignins from wheat straw

Ball-milled and enzyme lignins were extracted with 90 and 50% dioxane–water from 6 days ball-milled wheat straw, and subsequently cellulase-treated straw residues, respectively. The crude lignin preparations were purified using a two-step precipitation method instead of the traditional ether precipitation procedure, and fractionated into pure milled lignin (PML), pure enzyme lignin (PEL), hemicellulose-rich milled lignin (HRML), lignin-rich enzyme lignin (LREL), and solubilized lignin during enzyme treatment (SLET) fractions. The five lignin fraction were studied using spectroscopic and degradative tecyhniques. The PML and PEL fractions showed very low content of associated polysaccharides (2.36–2.86%). The PML is mainly composed of β-O-4 ether bonds in the lignin structural units. The less common β-5 and β-β carbon–carbon linkages are also present. The results obtained also indicated that the lignins in wheat straw cell walls appeared to be very closely associated to p-coumaric and ferulic acid, and glucuronic acid or 4-O-methylglucuronic acid. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1633–1641, 1998     

Acetylation of wheat straw using simplified procedure and ultrasonic irradiation

An investigation of the acetylation of wheat straw with acetic anhydride using a simplified procedure and with or without ultrasonic irradiation was undertaken. The new procedure greatly shortened the reaction time and simplified the chemical recovery. Acetylation weight gains of 15.8% can be achieved in 1 h at 120°C without ultrasound assistance. At the same reaction conditions but with ultrasound assistance at 60°C for 5 min, a weight percent gain (WPG) value of 15.0% was obtained, indicating a slightly negative effect of ultrasonic irradiation on the rate of acetylation without solvents or catalysts. However, a positive sonication effect on the solubility of low molecular materials, mainly extractives, was found in all the cases of the reactions. The characterization of acetylated wheat straw was performed by FTIR, solid‐state ¹³C‐NMR, and thermal studies, which provided evidence for acetylation. The thermal stability of acetylated straw was found to be higher than that of unmodified wheat straw. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1277–1284, 2003     

碱-氧-蒽醌蒸煮麦草脱木素

引　言木素、纤维素和半纤维素是构成麦草的主要成分 ,是自然界中较为丰富的可再生资源 .木素在制浆造纸过程中生成碱木素 ,溶于黑液 ,排入江河后 ,不仅污染了环境 ,而且浪费了大量的木素资源 ,因此寻求对可再生资源的工业化应用途径越来越受到人们的重视 .通常 ,脱木素的方法有亚硫酸盐法和碱法 ,后来许多研究者对其进行了改进 ,不过这些研究的目是为了提高纸浆得率 ,在不破坏纤维素的条件下得到白度好、易漂白、易成浆的纸浆 ,这些方法只考虑了对纤维素进行造纸的利用 ,而没有考虑对纤维素的其他利用途径以及对木素资源的利用[1～ 8] .纤…     

Removal of residual lignin of ethanol‐based organosolv pulp by an alkali extraction process

Organosolv pulps usually have high kappa number. This research investigated an alkaline extraction method prior to bleaching for reducing the kappa number of organosolv pulp. Ethanol wheat straw pulp with a kappa number of 58.2 was extracted with 1% NaOH solution. The results show that the ethanol pulp has a large amount of lignin particles on the fiber surface. After 1 min alkali extraction, the kappa number of the ethanol pulp is reduced by 60%, to 22.2, and both the number and the size of the lignin particles on the fiber surface are significantly reduced. In comparison with a further ethanol washing/extraction, the alkali extraction is much more effective in terms of lignin removal. X‐ray photoelectron spectroscopy results show that a thin layer of lignin remained on the fiber surface after alkli extraction, but this did not reduce the internal bond strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Facile fabrication of polyester filament fabric with highly and durable hydrophilic surface by microwave‐assisted glycolysis

Poly(ethylene terephthalate) (PET) fabric with highly and durable hydrophilic surface was fabricated using microwave‐assisted glycolysis. Sodium hydroxide (NaOH) as a catalyst was proven to be suitable for PET glycolysis under assistance of microwave. The modified PET fabric (0.5% NaOH, irradiation 120 s) showed high surface hydrophilicity with a contact angle of 17.4 ° and a wicking length of 19.36 mm. The exposure of the carboxyl‐ and hydroxyl‐end groups on the surface of PET and the introduction of etches were confirmed by Methylene Blue staining and field emission scanning electron microscopy (FESEM), receptively. Although the strength of PET fabric decreased after modification, it was still high enough for textile applications. The thermal properties of the modified PET fabrics were well maintained. The high hydrophilicity and its original properties of PET could be controlled by changing the irradiation time from 60 s to 120 s and adjusting the content of sodium hydroxide from 0.2% to 0.5%. These results suggest microwave‐assisted glycolysis with sodium hydroxide is an effective method for PET hydrophilic finishing. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44069.     

Synthesis of wheat straw composite superabsorbent

A novel wheat straw composite superabsorbent was prepared by graft polymerization with acrylic acid (AA), acrylamide (AM), and maleic anhydride‐modified wheat straw in aqueous solution, using N,N‐methylene‐bis‐acrylamide (MBA) as a cross‐linker and ammonium persulfate (APS) and sodium bisulfite (SBS) as redox initiators. Factors influencing the degree of carboxylation, such as reaction time, reaction temperature, and the amount of maleic anhydride, were investigated. Morphologies and structure of the wheat straw composite superabsorbent were characterized by fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and X‐ray diffraction (XRD). Water absorption of wheat straw composite superabsorbent was rapid, requiring 13.1 min to reach 63% of equilibrium absorbency (781 g/g). FTIR spectra indicate that maleic anhydride has been reacted onto the wheat straw backbone and the structure of wheat straw graft copolymer is formed. SEM data show that the fibrous morphology of wheat straw disappears and gel aggregates with many large microporous holes are formed after wheat straw graft modification. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3404–3410, 2013     

有机-无机溶剂连续抽提巨龙竹木质素及其结构表征

为了分析巨龙竹木质素的结构特征,采用有机-无机溶剂连续抽提的方式将木质素和半纤维素进行分离,脱蜡竹粉依次用80%二氧六环、80%二氧六环-0.5% NaOH、2% NaOH、5% NaOH和8% NaOH连续抽提后,得5个木质素样品L₁~L₅,计算了木质素得率,并对抽提所得的木质素样品进行了红外光谱(FT-IR)、紫外光谱(UV)、核磁共振碳谱(¹³C NMR)和二维核磁共振(2D HSQC)分析。结果表明:在二氧六环和不同浓度碱性水溶液的连续抽提下,最终从巨龙竹原料中分离得到70.6%的原本木质素,其中木质素样品L₂的纯度最高,表明该方法是一种较为有效的竹材木质素组分分离方法。木质素的苯环骨架结构在分离过程中没有被破坏,但碱浓度的增加导致木质素中部分酯键发生断裂。巨龙竹木质素大分子主要由愈创木基单元(G)、紫丁香基单元(S)、对羟基苯基单元(H)组成,木质素大分子基本单元之间的联接键主要是β-O-4'醚键,除此之外还有β-β'、β-5'和β-1'联接。     

Recovery and characterization of lignin from alkaline straw pulping black liquor: As feedstock for bio‐oil research

Conversion of lignin derived from lignocellulosic biomass to bio‐oil has the promising potential to significantly reduce petroleum dependence. For that purpose, it is necessary to search for a low‐cost lignin source. In this study, lignin sample was separated from straw pulping black liquor by HCl‐precipitation, followed by extraction with a mixture of dioxane and water. The content of lignin in the total black liquor solid reached up to 34.8%, determined by UV spectroscopy, and the yield could account for 74.4% of the total lignin composition. The structure of lignin was investigated by various spectroscopic techniques such as FTIR, ¹H‐NMR, XRD, and XPS. The structural analysis revealed that recovered lignin preserved basic lignin structure, but had relatively lower amount of β‐O‐4 linkages. The molecular weights were studied through THF‐eluted GPC showing that separated lignin had the low M_n, which was favorable for the full degradation process during conversion of lignin to bio‐oil. Therefore, a feasible solution for effective utilization of lignin in straw pulping black liquor as feedstock for bio‐oil was proposed in the study. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42057.     

麦草碱-氧蒸煮脱木素

用碱－氧蒸煮麦草脱木素,考察了工艺条件对麦草脱木素的影响．结果表明：适宜的麦草脱木素的条件为温度 １６０℃,碱浓度 ８％,氧压 ０．８ ＭＰａ,固液比 ０．８,保温时间 １ｈ．同时,通过 ＩＲ和 １Ｈ－ＮＭＲ对木素结构进行了分析．     

稻草和麦草绿液蒸煮过程中各组分变化规律比较

对比了相同蒸煮温度下稻草和麦草绿液蒸煮过程中各组分变化规律。结果表明,稻、麦草原料绿液蒸煮脱木素过程呈明显的两个阶段：主要脱木素阶段木素脱出率约为64%~70%,残余脱木素阶段木素脱出率约为5%~10%。主要脱木素阶段二者脱木素速率相近,残余脱木素阶段稻草脱木素速率略高于麦草;两种原料在主要脱木素阶段和残余脱木素阶段均有聚糖溶出,其中主要脱木素阶段聚糖的溶出率分别为稻草60%、麦草34%,二者脱木素选择性分别为2.1和1.1;残余脱木素阶段聚糖溶出率分别为稻草6%、麦草14%,脱木素选择性分别为0.4和1.7。稻、麦草原料绿液蒸煮过程中硅的变化规律呈现三个阶段,每一阶段稻草浆中硅的保留率都高于麦草原料。150℃保温2 h后,原料中硅的溶出率分别为稻草9.3%和麦草45%。相应地,稻草绿液蒸煮黑液中硅的浓度远低于麦草原料,黑液的临界浓度可达45%,约为麦草的3倍。     

Comparative study of cellulose isolated by totally chlorine‐free method from wood and cereal straw

Highly purified cellulose preparations were obtained by pretreatment of dewaxed barley straw, oil palm frond fiber, poplar wood, maize stems, wheat straw, rice straw, and rye straw with 2.0% H₂O₂ at 45°C and pH 11.6 for 16 h, and sequential purification with 80% acetic acid–70% nitric acid (10/1, v/v) at 120°C for 15 min. The purified cellulose obtained was relatively free of bound hemicelluloses (2.3–3.2%) and lignin (0.4–0.6%) and had a yield of 35.5% from barley straw, 39.6% from oil palm frond fiber, 40.8% from poplar wood, 36.0% from maize stems, 34.1% from wheat straw, 23.4% from rice straw, and 35.8% from rye straw. The weight‐average molecular weights of the purified cellulose ranged from 39,030 to 48,380 g/mol. The thermal stability of the purified cellulose was higher than that of the corresponding crude cellulose. In comparison, the isolated crude and purified cellulose samples were also studied by Fourier transform IR and cross‐polarization/magic‐angle spinning ¹³C‐NMR spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 322–335, 2005     

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.     

Surface modification of PVDF hollow fiber membrane to enhance hydrophobicity using organosilanes

This work investigates the membrane modification to enhance hydrophobicity aiming for applications as membrane contactors. The PVDF membranes were activated by NaOH and by plasma activation followed by grafting using three organosilanes. For the NaOH, the contact angle of original membranes (68°) was decreased from 44° to 31° with increasing NaOH concentration from 2.5M to 7.5M at 60°C for 3 h. The contact angle of NaOH treated membranes was increased to 100° after modification with 0.01M FAS‐C8 for 24 h. A needle‐like structure was observed on the membrane surface while there was no significant change in pore size and pore size distribution. Moreover, FTIR and XPS data showed Si peak and composition. The mechanical strength was improved. The surface modified membranes under helium plasma activation followed by grafting with 0.01M FAS‐C8 for 24 h showed higher contact angle, mechanical strength and surface roughness than that obtained by NaOH activation method while other physical properties did not change. The long‐term performance test for 15 days of operation was conducted. The modified membranes exhibited good stability and durability for CO₂ absorption. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013