Alkali-soluble Lignin Research Articles

Fractionation of carbohydrate polymers from Indonesian sorghum by-products

Extraction of cellulose and hemicellulose from natural resources has attracted considerable interest. In comparison to other cereals, there is relatively little knowledge on the cellulose, hemicellulose and lignin content of sorghum by-products. As such, the aims of this study were to develop a multi-step process for sorghum by-products (bran, stalk and panicles) fractionation and characterise them with regards to their physicochemical properties. In terms of chemical composition, sorghum panicles were found similar to bran, featuring a significant presence of arabinoxylans as well. A sequential alkaline extraction with varying concentrations of NaOH was applied, resulting in the generation of three fractions (residue, hemicellulose and alkali soluble lignin). Fractionation of sorghum stalks with 1.0 M NaOH at 50 °C for 3 h obtained ~64 % (w/w) cellulose rich fraction and 52 % (w/w) of xylose, predominant in the hemicellulose fraction. In the bran, the fractionation with 0.75 M NaOH at 50 °C for 3 h obtained ~40 % (w/w) cellulose rich fraction. Approximately 76 % of the glucose was in hemicellulose fraction reflecting starch solubilisation in the case of bran, while nearly 2 % (w/w) alkaline-soluble lignin was extracted. Overall, this study demonstrated an effective approach for the fractionation and the recovery of key components in sorghum by-products.

Response surface methodology (RSM) and artificial neural network (ANN) approach to optimize the photocatalytic conversion of rice straw hydrolysis residue (RSHR) into vanillin and 4-hydroxybenzaldehyde

Abstract Effective use of waste lignin is always a challenging task, technologies have been applied in the past to get value-added compounds from waste lignin. However, the existing technologies are not economical and efficient to produce the value-added chemicals. Alkali soluble lignin from rice straw hydrolysis residue (RSHR) is subjected to photocatalytic conversion into value-added compounds. Photocatalysis is one of the multifarious advanced oxidation processes (AOPs), carried out with TiO2 nanoparticles under a 125 W UV bulb. Gas chromatography mass spectroscopy (GCMS) confirmed the formation of vanillin and 4-hydroxybenzaldehyde. RSM and ANN techniques are adopted to optimize the process conditions for the maximization of the products. The response one (Y 1) vanillin (24.61 mg) and second response (Y 2) 4-hydroxybenzaldehyde (19.51 mg) is obtained at the optimal conditions as 7.0 h irradiation time, 2.763 g/L catalyst dose, 15 g/L lignin concentration, and 14.26 g/L NaOH dose for alkali treatment, suggested by face-centered central composite design (CCD). RSM and ANN models are statistically analyzed in terms of RMSE, R 2 and AAD. For RSM the R 2 0.9864 and 0.9787 while for ANN 0.9875 and 0.9847, closer to one warrant the good fitting of the models. Therefore, in terms of higher precision and predictive ability of both models the ANN model showed excellence for both responses as compared to the RSM model.

Kinetics of producing vanillin and 4-hydroxy benzaldehyde from the hydrolysis residue of rice straw by photocatalysis

Alkali soluble lignin present in rice straw hydrolysis residue (RSHR) is subjected to photocatalytic treatment to study its degradation rates and production of different value-added oxygenated organic compounds. TiO2 and ZnO are used as photocatalysts. ZnO could degrade lignin faster than TiO2 in pseudo-first order photocatalytic degradation. The maximum observed photocatalytic lignin degradation is 83.4% using 2 g/L ZnO dose with pseudo-first order rate constant 0.1386 h−1. Vanillin and 4-hydroxy benzaldehyde are the two important value-added products formed during photocatalysis. Both these compounds, themselves, are susceptible to photocatalytic degradation. Vanillin degradation followed pseudo-first order kinetics and the highest rate constant of 0.1415 h−1 is achieved using 2 g/L ZnO as photocatalyst. While the degradation kinetics of 4-hydroxy benzaldehyde is pseudo-first order with TiO2 and ZnO as a photocatalyst. Higher catalyst doses increased the reaction rate constant. With multiple reactions in operation, the concentration of both vanillin and 4-hydroxy benzaldehyde in the reaction mixture first increased, attained their maxima, and thereafter decreased. With 1 g/L TiO2 as a photocatalyst, the maximum attained vanillin concentration is 22.4 mg/L after 7 h photocatalysis. Maximum attained vanillin concentration, after 8 h photocatalysis, is significantly higher at 51.2 mg/L when 2 g/L ZnO is used as a catalyst. 4-Hydroxy benzaldehyde is produced in lesser amounts. Its maximum observed concentration in the reaction mixture is 20.4 mg/L, obtained with 1.5 g/L TiO2 after 10 h photocatalysis.

Synergistic benefits from a lignin-first biorefinery of poplar via coupling acesulfamate ionic liquid followed by mild alkaline extraction

A novel mind-set, termed lignin-first biorefinery, is bewitching to synchronously boost lignin output for entirely lignocellulosic utilization. A lignin-first fractionation, using a food-additive derived ionic liquid (1-ethyl-3-methylimidazolium acesulfamate, emimAce) and mild alkaline pretreatments, was formed for the purposely isolating poplar lignin, whilst delivering a cellulose-rich substrate that can be easily available for enzymatic digestion. The emimAce-driven lignin, alkali-soluble lignin and hemicellulose, and accessible cellulose were sequentially gained. We introduce a lignin-first approach to extract the amorphous fractions, destroy the robust architecture, and reform cellulose-I to II, thereby advancing the cellulose bioconversion from 15.4 to 90.5%. A harvest of 70.7% lignin, 52.1% hemicellulose, and 330.1 mg/g glucose was fulfilled from raw poplar. A structural ‘‘beginning-to-end’’ analysis of lignin inferred that emimAce ions are expected to interact with lignin β-aryl-ether due to their aromatic character. It was reasonable to derive benefits from lignin-first technique that can substantially augment the domain of biorefinering.

Determination of lignin concentration in bleaching effluent via Coomassie brilliant blue G-250 method

Kraft pulp and alkali peroxide mechanical pulp were prepared with aspen and wheat straw and bleached with chlorine dioxide, an alkali extraction strengthened by hydrogen peroxide, hydrogen peroxide, or peroxyacetic acid. Eight different bleaching effluents were obtained, and a Coomassie brilliant blue G-250 method was applied to determine the lignin content in each of the bleaching effluents. The visible light spectra indicated that the alkali-soluble lignin and the alkali bleaching effluent could increase the absorbance of Coomassie brilliant blue G-250 at 640 nm, but the acidic soluble lignin and the acidic bleaching effluent did not increase absorbance. Thus, the Coomassie brilliant blue G-250 method applied to alkali bleaching effluents but did not apply to acidic bleaching effluents. An analysis of the pH, particle size, zeta potential, and visible light spectra determination showed the Coomassie brilliant blue G-250 absorbed on lignin particles, which caused the absorbance increase at 640 nm. With the actual measured value of the lignin content obtained via the Klason lignin method, the relative error of the results obtained via the Coomassie brilliant blue G-250 method was less than or equal to 3.8%.

Correction to: 'The effect of alkali-soluble lignin on purified core cellulase and hemicellulase activities during hydrolysis of extractive ammonia-pretreated lignocellulosic biomass'.

[This corrects the article DOI: 10.1098/rsos.171529.].

The effect of alkali-soluble lignin on purified core cellulase and hemicellulase activities during hydrolysis of extractive ammonia-pretreated lignocellulosic biomass.

Removing alkali-soluble lignin using extractive ammonia (EA) pretreatment of corn stover (CS) is known to improve biomass conversion efficiency during enzymatic hydrolysis. In this study, we investigated the effect of alkali-soluble lignin on six purified core glycosyl hydrolases and their enzyme synergies, adopting 31 enzyme combinations derived by a five-component simplex centroid model, during EA-CS hydrolysis. Hydrolysis experiment was carried out using EA-CS(−) (approx. 40% lignin removed during EA pretreatment) and EA-CS(+) (where no lignin was extracted). Enzymatic hydrolysis experiments were done at three different enzyme mass loadings (7.5, 15 and 30 mg protein g−1 glucan), using a previously developed high-throughput microplate-based protocol, and the sugar yields of glucose and xylose were detected. The optimal enzyme combinations (based on % protein mass loading) of six core glycosyl hydrolases for EA-CS(−) and EA-CS(+) were determined that gave high sugar conversion. The inhibition of lignin on optimal enzyme ratios was studied, by adding fixed amount of alkali-soluble lignin fractions to EA-CS(−), and pure Avicel, beechwood xylan and evaluating their sugar conversion. The optimal enzyme ratios that gave higher sugar conversion for EA-CS(−) were CBH I: 27.2–28.2%, CBH II: 18.2–22.2%, EG I: 29.2–34.3%, EX: 9.0–14.1%, βX: 7.2–10.2%, βG: 1.0–5.0% (at 7.5–30 mg g−1 protein mass loading). Endoglucanase was inhibited to a greater extent than other core cellulases and xylanases by lignin during enzyme hydrolysis. We also found that alkali-soluble lignin inhibits cellulase more strongly than hemicellulase during the course of enzyme hydrolysis.

Isolation of Lignin from Masson Pine by Liquid-Liquid Extraction Based on Complete Dissolution in NaOH Aqueous Solution

A method for lignin isolation from softwood based on complete dissolution in NaOH aqueous solution and liquid-liquid extraction was introduced. The structural features of milled alkali-soluble lignin (MAL) were comparatively analyzed with those of classical milled wood lignin (MWL) by means of alkaline nitrobenzene oxidation (NBO) and molecular weight, as well as Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra analyses. The results showed that the yield of crude MAL (34.2%) was about twice as much as that of MWL (16.4%). The NBO product yields of MWL and MAL were quite similar. The weight-average molecular weight of MAL (10,400 g mol-1) was much higher than for MWL (6,970 g mol-1). Both MWL and MAL displayed similar FTIR, UV, 1H NMR, and 1H-13C HSQC NMR spectra. The total OH content of MAL (4.48 mmol g-1) was higher than that of MWL (3.89 mmol g-1). Compared with MWL, MAL showed similar structural characteristics but better isolation yield and higher molecular weight.

Development of Method to Determine the Concentration of Alkali-Soluble Lignin using Coomassie Brilliant Blue G-250

A new method involving the non-covalent binding of Coomassie Brilliant Blue G-250 (CBBG) to alkali-soluble lignin was developed. The binding of the dye to alkali-soluble lignin caused an increase in visible absorption at the maximum wavelength of 630 nm or 640 nm. A linear correlation of the absorbance at their maximum absorbing peak with alkali-soluble lignin concentration was observed. Lignin estimation in black liquor showed that the result of the new method and the gravimetric methods after acidification were closer to quantitative information than that obtained from UV spectroscopy. The isothermal titration calorimetric experiments, and Fourier Transform Infrared (FTIR) spectroscopy comparative analysis of precipitates washed by water, 4% ethanol, and 95% ethanol indicated that CBBG was bound to alkali-soluble lignin, and the binding was non-covalent. This potential method is reproducible, rapid, and cheap, and there is little or no inference from carbohydrate degradation products.

Chemical and structural changes associated with Cu-catalyzed alkaline-oxidative delignification of hybrid poplar.

BackgroundAlkaline hydrogen peroxide pretreatment catalyzed by Cu(II) 2,2′-bipyridine complexes has previously been determined to substantially improve the enzymatic hydrolysis of woody plants including hybrid poplar as a consequence of moderate delignification. In the present work, cell wall morphological and lignin structural changes were characterized for this pretreatment approach to gain insights into pretreatment outcomes and, specifically, to identify the extent and nature of lignin modification.ResultsThrough TEM imaging, this catalytic oxidation process was shown to disrupt cell wall layers in hybrid poplar. Cu-containing nanoparticles, primarily in the Cu(I) oxidation state, co-localized with the disrupted regions, providing indirect evidence of catalytic activity whereby soluble Cu(II) complexes are reduced and precipitated during pretreatment. The concentration of alkali-soluble polymeric and oligomeric lignin was substantially higher for the Cu-catalyzed oxidative pretreatment. This alkali-soluble lignin content increased with time during the catalytic oxidation process, although the molecular weight distributions were unaltered. Yields of aromatic monomers (including phenolic acids and aldehydes) were found to be less than 0.2 % (wt/wt) on lignin. Oxidation of the benzylic alcohol in the lignin side-chain was evident in NMR spectra of the solubilized lignin, whereas minimal changes were observed for the pretreatment-insoluble lignin.ConclusionsThese results provide indirect evidence for catalytic activity within the cell wall. The low yields of lignin-derived aromatic monomers, together with the detailed characterization of the pretreatment-soluble and pretreatment-insoluble lignins, indicate that the majority of both lignin pools remained relatively unmodified. As such, the lignins resulting from this process retain features closely resembling native lignins and may, therefore, be amenable to subsequent valorization.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0300-5) contains supplementary material, which is available to authorized users.

Enzymatic and Chemical Treatment Limits on the Controlled Solubilization of Brewers’ Spent Grain

The enzymatic hydrolysis of brewers' spent grain (BSG) has been investigated through treatment with commercial carbohydrases and proteases. Resultant residues were then chemically fractionated and delignified. Enzymatic treatments released 25-30% of the BSG mass and yielded precursors suitable for subsequent conversion to potentially value-added products. Controlled chemical fractionation selectively solubilized arabinoxylan but with no differences apparent due to prior enzyme treatment. The loss of non-polysaccharide components during alkali treatment suggests the presence of a high proportion of alkali-soluble lignin. Further delignification of the alkali-insoluble residues and further chemical fractionation released the remaining hemicellulose, to yield a residue which was >90% cellulose. Further knowledge of the properties and interaction between BSG polymers will facilitate an improved enzyme-assisted total deconstruction of BSG and hence the exploitation of its biomass.

Effect of organic bound Na groups on pyrolysis and CO2-gasification of alkali lignin

the effect of organic bound Na groups on pyrolysis and gasification behaviors of alkali lignin, an experimental study was carried out by Thermogravimetric Analyzer coupled with Fourier Transform Infrared Spectrometry (TG-FTIR). Acid precipitated lignin (APL) and Alkali soluble lignin (ASL) were selected as the testing samples, and physiochemical properties were studied by FTIR, 1H NMR, and SEM analyses. The research results showed that the pyrolysis and gasification characteristics of alkali lignin depended on phenolic sodium (-CONa) and carboxylate sodium (-COONa) groups (PCSG). In pyrolysis stage, PCSG improved the yields of alcohols and hydrocarbons but inhibited benzenes. During gasification stage, in the present of PCSG, the peak value of gasification rate increased, yet the initial gasification temperature decreased. Meanwhile, CO releasing was relatively concentrated and intensively increased from 37 min (740 oC) to 42 min (840 oC).

Nanocomposite-based lignocellulosic fibers 3: polyelectrolyte adsorption onto heterogeneous fiber surfaces

Wood and natural fibers are composed of multiple polymeric components. Lignin, one primary component, is typically removed to various degrees during paper-making, but is present on thermomechanically isolated fibers. The effect of the residual lignin on the adsorption of poly(diallyldimethylammonium) chloride (PDDA) onto lignocellulosic fibers was investigated under varying solution conditions (electrolyte concentration and pH). Using nitrogen elemental analysis it was shown for the samples containing the highest concentration of lignin, PDDA adsorption to the fibers was reduced for all solution conditions. Upon extracting the alkali-soluble lignin, the samples showed the greatest amount of PDDA adsorption, achieving ~1.6% (w/w), under neutral solution conditions without the presence of added electrolyte. Furthermore, the influence of polyelectrolyte loading and electrokinetic potential on subsequent multilayer formation of PDDA and montmorillonite clay was quantified. It was revealed that electrokinetic potential of fiber after PDDA adsorption, rather than the amount of adsorbed PDDA layer, controlled the subsequent clay adsorption. Significant mass of PDDA/clay (up to ~75% of starting dry fiber mass for only 4 bi-layers) can be adsorbed onto steam-exploded wood fibers through the multilayer assembly process. This paper provides insight into how non-covalent modification of heterogeneous fibrous substrates offers a novel route for the creation of organic/inorganic fiber materials.

Fractional and structural characterization of organosolv and alkaline lignins from Tamarix austromogoliac

A comparative study was conducted on the seven lignin fractions, isolated from dewaxed Tamarix austromogoliac (TA) with DMSO, 70% ethanol containing 5% triethylamine, 70% ethanol containing 0.5% NaOH at 70°C for 5 h, and 1 M KOH, 1 M NaOH, 1 M LiOH and 1 M NH3·H2O at 50°C for 5 h, respectively. The comprehensive structural characterization of the three organic solvent-soluble and four alkali-soluble lignin isolations were examined by UV, FT-IR, TGA, 1H, 13C and 2D 13C-1H correlation (HSQC) NMR spectroscopy techniques. The results showed that the DMSO-soluble lignin fraction, which was rich in hemicelluloses, had a relatively higher molecular weight (4730 g/mol) while the other six lignin isolations had lower molecular weights ranging from 1240 - 2160 g/mol. The thermogravimetric analysis (TGA) showed a decrease of thermal stability with a decrease in the molecular weight. In addition, the HSQC spectrum of the fraction isolated with 70% ethanol containing 0.5% NaOH from TA indicated a predominance of β-O-4′ aryl ether linkages (73% of total side chains), followed by lower amounts of β-β′ resinol-type linkages (19% of total side chains), trace amounts of β-5′ phenylcoumaran (3%), β-1′ spirodienone-type (3%) substructures and cinnamyl end groups (2%). Key words: Organosolv lignins, Tamarix austromogoliac, TGA, 13C NMR, HSQC.

Fractional Separation of Hemicelluloses and Lignin in High Yield and Purity from Mild Ball-Milled Periploca sepium

A novel three-step procedure for separation of hemicelluloses and lignin with high yield and purity was proposed in this study, where wood is mildly milled and successively extracted to produce three hemicellulosic and lignin fractions representing the total hemicelluloses and lignin in wood. The sequential treatments of the mild ball-milled Periploca sepium with 80% aqueous dioxane containing 0.05 M HCl at 85°C for 4 h, DMSO at 85°C for 4 h, and 8% NaOH at 50°C for 3 h resulted in a total release of over 85% of the original hemicelluloses and 86% of the original lignin. In particular, approximately 36% of the original hemicelluloses and 50% of the original lignin were separated during the first mild acidolytic hydrolysis process after low intensity milling. The structure of the acidic dioxane-, DMSO-, and alkali-soluble hemicellulosic and lignin fractions were elucidated using wet chemical analysis, FT-IR, and solution-state 1H, 13C, and 31P NMR techniques. Results showed that both the mild ball milling and the mild acidolysis under the conditions given did not affect the separated lignin macromolecular structure. On the other hand, the mild acidolytic hydrolysis condition did cause substantial hemicellulosic depolymerization exception for a significant cleavage the ether linkages between lignin and hemicelluloses. The acidic dioxane-soluble lignin fraction was structurally different from the DMSO- and alkali-soluble lignin preparations and may originate mainly from the primary wall, while the alkali-soluble lignin preparation was mainly released from the secondary wall of Periploca sepium. Furthermore, it was found that the acidic dioxane-soluble hemicelluloses mainly contained more branched and less acidic arabinoxylans, and the 8% NaOH-soluble hemicellulosic fraction H3 was both less branched and less acidic in structure, whereas the DMSO-soluble hemicelluloses were more acidic but less branched and consisted mainly of 4-O-methylglucuronoarabinoxylan.

Determination of cell wall ferulic and p-coumaric acids in sugarcane bagasse

To completely determine ferulic and p-coumaric acids and related phenolic compounds in the cell walls of sugarcane bagasse (SCB), a second mild alkaline hydrolysis of the alkali-soluble lignin preparations and acid hydrolysis of the 90% acidic dioxane-soluble lignin fractions were performed, which released 48.8% of the total ester-linked p-CA and 43.8% of the total esterified FA from the alkali-soluble lignin fractions, and 38.8% of the total ether-linked p-CA and 38.5% of the total ether-linked FA from the 90% acidic dioxane-soluble lignin preparations, respectively. Based on the dry weight, it has been found that the SCB contained 1.76% p-CA and 1.29% FA as well as minor quantities of related phenols. Further study of the solubilized lignin samples by combining with UV and FT-IR spectroscopy, and 1H and 13C NMR spectroscopy confirmed that a predominant amount of p-CA (69.5–76.4%) is ester-linked to the cell wall components, mainly to lignin. On the other hand, about half of the FA (44.0–55.0%) is esterified to the cell wall hemicelluloses, and the remaining half of the FA is also be etherified through the phenolic oxygen to lignin component in the cell walls of SCB.

Characteristics of degraded hemicellulosic polymers obtained from steam exploded wheat straw

The fractionation of wheat straw was studied using a two-stage process based on a steam explosion pre-treatment followed by alkaline peroxide post-treatment. Straw was steamed at temperatures comprised between 200 °C for 10 and 33 min and 220 °C for 3, 5, and 8 min. The steamed straw was washed with water to yield a solution rich in hemicelluloses-derived mono- and oligosaccharides (20.5–28.5%) together with small amounts of degraded hemicellulosic polymers (2.4–6.2%) and minor quantities of lignin (1.9–2.1%). The washed fibre was post-treated by 2% alkaline peroxide (pH 11.5) at 50 °C for 5 h. The alkali-soluble lignin (13.7–15.0%) and hemicelluloses (8.4–13.3%) were recovered by precipitation. The post-treatment was sufficient to remove lignin and survived hemicellulosic polymers and increase the brightness of the exploded straw significantly. The two-stage treatments together degraded 77.0–87.6 of the total original hemicelluloses and 92.3–99.4% of the total original lignin. This paper examined these two groups of six hemicellulosic polymer preparations degraded during the various steam explosion pre-treatments (H 1a–6a) and released during the sequential alkaline peroxide post-treatment (H 1b–6b). The effect of the most important variables in steam explosion pre-treatment (temperature, residence time, and water to straw ratio) on physico-chemical properties and structural features of the degraded hemicellulosic polymers were investigated. Thermoanalysis of these degraded hemicellulosic polymer fractions indicated that hemicellulose degradation products were also condensed to form more thermostable substrates during the steam explosion.

Fractionation of Eucalyptus grandis chips by dilute acid-catalysed steam explosion.

Steam explosion of Eucalyptus grandis has been carried out under various pretreatment conditions (200-210 degrees C, 2-5 min) after impregnation of the wood chips with 0.087 and 0.175% (w/w) H2SO4. This study, arranged as a 2(3) factorial design, indicated that pretreatment temperature is the most critical variable affecting the yield of steam-treated fractions. Pretreatment of 0.175% (w/w) H2SO4-impregnated chips at 210 degrees C for 2 min was the best condition for hemicellulose recovery (mostly as xylose) in the water soluble fraction, reaching almost 70% of the corresponding xylose theoretical yield. By contrast, lower pretreatment temperatures of 200 degrees C were enough to yield steam-treated substrates from which a 90% cellulose conversion was obtained in 48 h, using low enzyme loadings of a Celluclast 1.5 1 plus Novozym 188 mixture (Novo Nordisk). Release of water-soluble chromophores was monitored by UV spectroscopy and their concentration increased with pretreatment severity. The yield of alkali-soluble lignin increased at higher levels of acid impregnation and pretreatment temperatures. Thermoanalysis of these lignin fractions indicated a pattern of lignin fragmentation towards greater pretreatment severities but lignin condensation prevailed at the most drastic pretreatment conditions.

Quantitative determination of hydroxycinnamic acids in wheat, rice, rye, and barley straws, maize stems, oil palm frond fiber, and fast-growing poplar wood.

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.

Study on Alkali-Accessible Chromophores from Unbleached Kraft Pulp

Summary An approach to a chromophore composition study using the direct size-exclusion chromatography (SEC-UV) analysis of an alkaline extract of pulp fibre walls is described. Absorbance in the 290–405 nm range of 2% and 18% NaOH extract from unbleached pulps obtained by conventional and extended kraft delignification of black alder wood is compared. The effect of cooking conditions on the localisation and accessibility of chromophores is elucidated. The alkali-soluble lignin from pulp produced by extended cooking was less oxidised, less conjugated, and less coloured as compared with the conventional kraft lignin. A chromophore accessibility index is proposed. The chromogenic structures in pulps obtained by extended cooking were more resistant to alkali solutions than those in conventional kraft pulps.