Nitrobenzene Oxidation Products Research Articles

Characterization and Comparison of Some Kraft Lignins Isolated from Different Sources

Lignin characteristics are significantly affected by kraft processing and isolation conditions. In the studies carried out in this context, commercial lignins or isolated lignins from industrial black solutions are generally preferred. In this study, in order to conduct more comprehensive research, three lignin samples were isolated from kraft black liquor obtained from laboratory cooking trials of pine, poplar, and wheat straw chips, representing softwoods, hardwoods, and annual plants, respectively, according to efficient pulping studies. In addition, another lignin-containing industrial waste was provided from a pulp mill (OBL). The acidification method was applied for isolating lignin from black liquor samples. After isolating the lignin samples from different sources, they were characterized and compared with the commercially available kraft lignin sample (Indulin AT). Total phenolic groups, carboxyl groups, purity, functional groups, nitrobenzene oxidation products, molecular weight, thermal stability, and element contents were analyzed. The isolated lignin samples (except wheat straw) were as pure as commercial lignin. Since the wheat straw was agricultural waste and an annual plant, inorganic elements such as P, K, and Si were more abundant than in the other samples. However, the polydispersity and molecular weight of all of the isolated lignin samples were higher than those of commercial lignin. Because the ash contents of the lignin samples for pine, poplar, OBL, and indulin AT were between 1 and 3%, they can be used for high-value applications. In particular, despite some disadvantages, wheat straw lignin has greater potential for use in extruders than softwood lignins due to their syringyl content.

Syringyl ratio and its relation to the erythro ratio of β-O-4-structure in leaf cell walls

In case of wood cell walls, there is a very clear relationship between the aromatic structure of lignin and the stereo configuration of β-O-4-structures; the syringyl ratio (S ratio, syringyl/(syringyl + guaiacyl)) obtained by the nitrobenzene oxidation method is linearly correlated to the erythro ratio (E ratio) of β-O-4 structure (erythro/(erythro + threo)) obtained by the ozonation method. In this study, 21 leaf samples and 9 stem samples were analyzed to examine whether such relationships can be found in the lignin of leaf and stem cell wall samples. Although some correlation between the S and E ratios was found in leaf and stem cell wall samples, the correlation was not as clear as in the case of woods (correlation coefficient, R2= 0.988 for 21woods and R2= 0.653 for all the leaf, stem and wood samples). In addition, the E ratios of some leaf samples were lower than 0.5, which is the lowest limit of the E-ratio for wood lignin. It was demonstrated that wood, stem and leaf samples are roughly distinguished by the yield of ozonation and nitrobenzene oxidation products from the sample (not from lignin), but not by the apparent lignin content obtained by the Klason method. The presence of syringyl nuclei in the leaves of Ginkgo, which is classified as gymnosperm, was confirmed by nitrobenzene oxidation.

Root Lignin Composition and Content in Oil Palm (Elaeis guineensis Jacq.) Genotypes with Different Defense Responses to Ganoderma boninense

Basal stem rot of oil palms (OPs) is caused by Ganoderma boninense, a white-rot fungus. Root tissues are the primary route for G. boninense penetration and subsequent pathogenesis on OPs. Little is known on the host lignin biochemistry and selectivity for G. boninense degradation. Oil palm genotypes with different defense responses to G. boninense (highly tolerant, intermediately tolerant, and susceptible) were assessed for root lignin biochemistry (lignin content and composition), plant functional traits (height, fresh weight, girth), chlorophyll content, and root elemental nutrient content. One-year-old seedlings and five-year-old trees were screened for root thioglycolic acid lignin (TGA) content, lignin composition, and elemental nutrient depositions, while plant functional traits were evaluated in the one-year-old seedlings only. The TGA lignin in all the oil palm seedlings and trees ranged from 6.37 to 23.72 pM µg−1, whereas the nitrobenzene oxidation products showed a syringyl (S)-to-guaiacyl (G) ratios of 0.18–0.48. Tolerant genotypes showed significantly lower lignin content compared to the intermediately tolerant and susceptible genotypes. Likewise, the S/G ratio was higher in genotypes with lower lignin content. The depositions of root Fe, Si, Ti, S, and Cu were significantly different among the oil palm genotypes with the susceptible genotypes showing greater content than the tolerant genotypes.

The Phenylpropanoid Pathway and Lignin in Defense against Ganoderma boninense Colonized Root Tissues in Oil Palm (Elaeis guineensis Jacq.).

Basal stem rot, caused by the basidiomycete fungus, Ganoderma boninense, is an economically devastating disease in Malaysia. Our study investigated the changes in lignin content and composition along with activity and expression of the phenylpropanoid pathway enzymes and genes in oil palm root tissues during G. boninense infection. We sampled control (non-inoculated) and infected (inoculated) seedlings at seven time points [1, 2, 3, 4, 8, and 12 weeks post-inoculation (wpi)] in a randomized design. The expression profiles of phenylalanine ammonia lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), and peroxidase (POD) genes were monitored at 1, 2, and 3 wpi using real-time quantitative polymerase chain reaction. Seedlings at 4, 8, and 12 wpi were screened for lignin content, lignin composition, enzyme activities (PAL, CAD, and POD), growth (weight and height), and disease severity (DS). Gene expression analysis demonstrated up-regulation of PAL, CAD, and POD genes in the infected seedlings, relative to the control seedlings at 1, 2, and 3 wpi. At 2 and 3 wpi, CAD showed highest transcript levels compared to PAL and POD. DS increased progressively throughout sampling, with 5, 34, and 69% at 4, 8, and 12 wpi, respectively. Fresh weight and height of the infected seedlings were significantly lower compared to the control seedlings at 8 and 12 wpi. Lignin content of the infected seedlings at 4 wpi was significantly higher than the control seedlings, remained elicited with no change at 8 wpi, and then collapsed with a significant reduction at 12 wpi. The nitrobenzene oxidation products of oil palm root lignin yielded both syringyl and guaiacyl monomers. Accumulation of lignin in the infected seedlings was in parallel to increased syringyl monomers, at 4 and 8 wpi. The activities of PAL and CAD enzymes in the infected seedlings at DS = 5–34% were significantly higher than the control seedlings and thereafter collapsed at DS = 69%.

Complete Dissolution of Ball-Milled Masson Pine Using an Aqueous Sodium Hydroxide Solvent

An inorganic sodium hydroxide aqueous solution was developed for the dissolution of ball-milled softwood. Extractive-free Masson pine powder was prepared from the wood meal by planetary ball milling for various lengths of time. The effects of ball milling on the dissolution and regeneration of Masson pine powder were investigated. After 4 h of ball milling, the wood powder was completely dissolved in 6 wt% NaOH aqueous solution under vigorous magnetic stirring for 10 to 20 min at room temperature. The alkaline nitrobenzene oxidation products yield of 4 h ball-milled wood was very close to that of coarse wood meal without ball milling. Regeneration of the lignin fraction was easier than cellulose during the acid neutralization process, and the dialysis regeneration yield of total biomass was 91.1%. Therefore, the complete dissolution of the Masson pine in sodium hydroxide solution is of great potential for enhancing lignin isolation with a very little structural change.

Characterization of Lignin before and after Exposure to the Gastrointestinal Tract of Ruminants

The aim of this study was to investigate the structural composition of lignin (LIPE®) extracted from Eucalyptus grandis, before and after exposure to the gastrointestinal tract of ruminants. For this study lignin was isolated, purified and characterized using 1H and 13C Nuclear Magnetic Resonance Spectroscopy, nitrobenzene oxidation, functional groups analysis and gas chromatography with mass spectroscopy. To have a better understanding of lignin morphology and of its ultra structure, electron microscopy in wood cell wall was utilized. The lignin fecal samples showed similar 1H NMR spectrums and nitrobenzene oxidation products compared with LIPE®. The result of the microanalysis of LIPE® was similar to data shown in the literature. The ultra structure of lignin was similar to that of Bamboo (hard wood). The lignin isolated from feces of sheep was identical to the original LIPE®, which means that this product can be used as an external marker in protein digestibility in sheep.

Comparison of the substrate enzymatic digestibility and lignin structure of wheat straw stems and leaves pretreated by green liquor

In this work, the substrate enzymatic digestibility (SED) and the lignin structure of green liquor (GL) pretreated wheat straw stems and leaves were investigated. Compared with wheat straw stems, leaves showed higher delignification selectivity in GL pretreatment and higher SED in enzymatic hydrolysis. Wet chemical analysis indicated that, characterized with lower content of syringyl units and less β-O-4 linkages, leaf lignin is structurally different from stem lignin. After GL pretreatment, the drops of both nitrobenzene oxidation and ozonation products yield of leaves were obviously higher than those of stems, which means that more β-O-4 linkages of leaf lignin were broken than that of stem lignin. The SED of total sugar in GL-pretreated leaves was about 50% higher than that in GL-pretreated stems. The less content and lower S/G ratio of lignin are suggested to be the important factors for the better SED of GL-pretreated leaves.

Quantitative Examination of Pre-Extraction Treatment on the Determination of Lignin Content in Leaves

It has been suggested that the Klason method overestimates the lignin content of non-wood tissues of plants. To evaluate the effect of pre-extraction treatments on lignin determination in leaves, nine kinds of pre-extraction treatment were applied to ginkgo leaves and zelkova leaves. The apparent lignin contents (lignin determination by the Klason method) of ginkgo and zelkova leaves without pre-extraction treatments were 30.7% and 42.6%, respectively. After the various pre-extraction treatments, the apparent lignin contents were still high. On the other hand, the yield of nitrobenzene oxidation products (NPs) per apparent lignin content was maintained at a very low level before and after pre-extraction treatments (maximum value was 6% for ginkgo leaf and 11% for zelkova leaf after extraction treatment) compared with the value from wood (25 to 60%). These results suggested that the Klason method overestimates the lignin content of leaves even after the pre-extraction treatments examined in this study. In addition, a considerable part of the sample from which NPs or neutral sugars originate was lost during these pre-extraction stages. These results implied that some parts of the cell wall components were also removed by these pre-extraction treatments.

Fractionation and Characterization of Wood Cell Wall Components of Fagus crenata Blume Using LiCl/DMSO Solvent System

The fractionation of wood cell wall components was achieved by the application of the LiCl/DMSO solvent system developed in our previous study. Various soluble and insoluble fractions were prepared from beech milled wood by extractions with DMSO containing different amounts of lithium chloride (LiCl) for the study of a lignin-carbohydrate complex (LCC). Nitrobenzene oxidation (NO) analyses demonstrated that the lignin in the soluble fractions always has lower yields of NO products consisting of syringaldehyde + syringic acid (Sy) and vanillin + vanillic acid (Va). The syringyl ratios, Sy/(Sy+Va), were also lower than in insoluble fractions. Accordingly, lignins with lower syringyl ratios are better soluble than those with higher syringyl ratios. The former is typical in the primary wall and the latter in the secondary wall. Solubilization of glucan is significantly dependent on the LiCl concentration in DMSO. In the absence of LiCl, only about 6% of glucan was found in the soluble fraction, but about 40% of lignin and xylan were solubilized. The additional 40% of lignin and xylan became soluble together with glucan solubilization, which increased at 3% LiCl concentration. However, a fraction amounting to 13% (based on the whole wood) still remained as a residue under these conditions. Glucan solubilization could not be the reason for this observation as ball-milled cellulose is soluble in 3% LiCl/DMSO. It is likely that strong interactions between lignin and carbohydrates prevent solubilization of this fraction, which has never been isolated and analyzed in previous studies.

Characterization of lignin-derived products from Japanese beech wood as treated by two-step semi-flow hot-compressed water

Japanese beech (Fagus crenata) wood was treated by two-step semi-flow hot-compressed water (the first stage: 230 °C/10 MPa/15 min, the second stage: 270 °C/10 MPa/15 min), and produced lignin-derived products in the hot-compressed water-soluble portions at the first and second stages, and the final residue of the second stage was characterized with alkaline nitrobenzene oxidation method and gel permeation chromatographic analysis. As a result, the lignin-derived products at the first stage, where hemicellulose was also decomposed, consisted of lignin-based monomers and dimers and oligomers/polymers in the water-soluble portion. A large part of the oligomers/polymers was, however, recovered as the precipitate during 12 h setting after hot-compressed water treatment. By the analysis of nitrobenzene oxidation products, there were relatively higher contents of ether-type lignin in the precipitate at the first stage than in original beech wood. Since the ether linkages of lignin are more preferentially cleaved by this hot-compressed water, lignin-based polymeric fractions were flowed out from the porous cell walls from which hemicellulose was removed. On the other hand, at the second stage condensed-type lignin remained in the precipitate and residue. Based on these results, decomposition behavior of lignin in Japanese beech wood as treated by the two-step semi-flow hot-compressed water was discussed regarding the topochemistry of lignin structure.

Analysis of Lignin Aromatic Structure in Wood Based on the IR Spectrum

A total of 17 softwoods and 48 hardwoods were analyzed by IR spectroscopy to examine if syringyl ratio (syringyl/(syringyl+guaiacyl)) calculated from nitrobenzene oxidation products can be precisely expressed by area ratios of characteristic peaks of lignin in IR spectrum. Area ratio of two peaks is referred to as that of two wavenumber domains, represented by “wavenumber 1/ wavenumber 2.” Examined peak area ratios were 1595/1509, 1509/1460, 1275/1220, 1130/1032, and 835/(855+815). Among these ratios, log(1595/1509) and log(1275/1220) showed significant linear relationship with the syringyl ratios with a correlation coefficient of 0.98 for all 65 woods. These two ratios could also be used to distinguish all the hardwoods from the softwoods.

Lignin characteristics of bast fiber and core in kenaf, bark and wood of paper mulberry and mulberry

The structural features of bast fiber and core lignins in kenaf (Hibiscus cannabinus), bark and wood lignin of paper mulberry (Broussonetia papyrifera (L.) Vent × Broussonetia kazinoki Sieb.) and mulberry (Morus bombycis) were characterized by alkaline nitrobenzene oxidation, ozonation and methoxyl group determination. Björkman lignins were isolated from bast fiber and core, and bark and wood fractions of the plant samples, and structural characteristics were investigated by 1H NMR and 13C NMR spectroscopies. Kenaf bast fiber gave very high molar ratio of syringaldehyde to vanillin (S/V) of alkaline nitrobenzene oxidation products, while methoxyl content was about the same as that of the core fraction. Results of 1H NMR and 13C NMR of Björkman lignin suggested the presence of aliphatic fragments in lignins isolated from paper mulberry and mulberry bark, but not in kenaf bast fiber. The lower yield of alkaline nitrobenzene oxidation products from bast fiber and bark might be due to the higher content of condensed structure of lignin compared to core fraction. Total yield of erythronic (E) and threonic (T) acids of ozonation products and the molar ratio of erythronic acid to threonic acid (E/T) of the bast fibers and bark were lower than the corresponding core and wood fractions, suggesting that the contents of arylglycerol-β-aryl ether intermonomer linkages in the bast fiber and bark lignin were lower than those of the core and wood fractions. Methoxyl content of bark lignin was lower than the corresponding wood lignin. The methoxyl content of the extract-free kenaf bast fiber was similar to that of the core fraction, while the values of paper mulberry and mulberry bark were about one-half of the corresponding wood fractions, respectively. In bark lignins, the methoxyl contents of Klason lignin and Björkman lignin from bark were lower than those of the extract-free barks. This result suggests that the purity of Klason lignin and Björkman lignins of bark may be rather low.

Chemical composition of grape stalks of Vitis vinifera L. from red grape pomaces

The chemical composition and the structure of macromolecular components of grape stalks from red grape pomaces have been evaluated. These are composed mainly of cellulose (30.3%), hemicelluloses (21.0%), lignin (17.4%), tannins (15.9%) and proteins (6.1%). Among hemicelluloses the xylan was the most abundant (ca. 12%). The parameters of cellulose unitary cell, average diameter of nanofibrils and the degree of crystallinity (75.4%) were assessed by X-ray scattering analysis. The xylan was partially acetylated glucuronoxylan (DS = 0.49) possessing the Xyl p:MeGlc pA ratio of 25:1. The lignin of grape stalks was suggested to be of HGS type with H:G:S molar proportion of 3:71:26 as revealed by analysis of nitrobenzene oxidation products. Among alkali soluble condensed tannins procyanidins prevailed over prodelphinidins. The abnormal response of grape stalks to kraft pulping, leading to poorly delignified fibrous material, was attributed to a particular lignin structure and it structural association with other macromolecular components of grape stalks.

Chemical characterization of various parts of nipa palm ( Nypa fruticans)

The current study was initiated to characterize various parts of nipa palm ( Nypa fruticans) to establish whole utilization of this biomass as potential raw material for fuels and chemicals. Nipa consisting of frond, shell, husk and leaf was chemically characterized for cellulose, hemicellulose, lignin, starch, protein, extractives and inorganic constituents for its each part. The total chemical composition showed that the cellulose and hemicellulose contents were in the range of 28.9–45.6 wt% and 21.8–26.4 wt%, respectively. The hemicellulose was rich with glucuronoxylan. The lignin content was 19.4–33.8 wt% with the highest lignin content found in leaf. The alkaline nitrobenzene oxidation products showed that nipa palm lignin mainly consists of guaiacyl and syringyl propane units with a small amount of p-hydroxyphenylpropane unit. Besides the main chemical components, starch, protein and extractives were also present in significant amounts from 2 to 8 wt%. Additionally, the ash content was high from 5.1 to 11.7 wt%, consisting of the major inorganic elements being Na, K and Cl with minor inorganic elements of Mg, Ca, Si, P, S and Al. Overall, each part of the nipa palm has its individual superior characteristics and could be exploited as lignocellulosic resources for fuels and chemicals.

A Comparative Study of Oil Palm and Japanese Beech on Their Fractionation and Characterization as Treated by Supercritical Water

Supercritical water treatment (380°C/100 MPa/8 s) was applied to extractive-free oil palm trunk and sapwood portion of Japanese beech and their fractionated products were comparatively characterized, for water-soluble portion and water-insoluble portion composed of methanol-soluble portion and methanol-insoluble residue. As a result, the water-soluble portion was determined to be composed of carbohydrate-derived products such as organic acids, sugar decomposed products and lignin-derived products, etc. for both species. The oil palm, however, shows higher yield of organic acids (12.9%) and lignin-derived products (12.2%) compared to Japanese beech, in which organic acids were 4.7% in yield and lignin-derived products 9.8%. The methanol-soluble portion was, on the other hand, mainly composed of lignin-derived products, and in oil palm, these lignin-derived products consisted of both syringyl and guaiacyl-type similar to Japanese beech. The methanol-insoluble residue, was also mainly composed of lignin to be 99.2% in its content in the oil palm, compared to Japanese beech 93.7%. Moreover, the phenolic hydroxyl content determined by aminolysis method was higher in oil palm (36.5 PhOH/100C9) compared to Japanese beech (16.9 PhOH/100C9). Furthermore, an alkaline nitrobenzene oxidation analysis indicated that, the methanol-insoluble residue of the oil palm was less in oxidation products whereas in Japanese beech nitrobenzene oxidation products completely diminished. These lines of evidence suggest that methanol-insoluble residue is composed of lignin with more condensed-type of linkages with high phenolic hydroxyl groups. In addition, the water-soluble portion could be utilized for organic acid production, whereas the methanol-soluble portion and its insoluble residue for phenolic chemical production, with oil palm showing higher potential compared to Japanese beech.

Characteristics of Lignin from Flax Shives as Affected by Extraction Conditions

Lignin, a polyphenolic molecule, is a major constituent of flax shives. This polyphenolic molecular structure renders lignin a potential source of a variety of commercially viable products such as fine chemicals. This work compares the performance of different lignin isolation methods. Lignin from flax shive was isolated using both conventional alkaline extraction method and a novel experimental pressurized low polarity water (PLPW) extraction process. The lignin yields and chemical composition of the lignin fractions were determined. The conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h, extracted 92 g lignin per kg flax shives, while lignin yields from the PLPW extracts ranged from 27 to 241 g lignin per kg flax shives. The purity and monomeric composition of the lignins obtained from the different extraction conditions was assessed via UV spectroscopy and alkaline nitrobenzene oxidation. Lignin obtained from conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h was of low purity and exhibited the lowest yields of nitrobenzene oxidation products. With respect to alkali assisted PLPW extractions, temperature created an opposing effect on lignin yield and nitrobenzene oxidation products. More lignin was extracted as temperature increased, yet the yield of nitrobenzene oxidation products decreased. The low yield of nitrobenzene oxidation products may be attributed to either the formation of condensed structures or the selective dissolution of condensed structures of lignin during the pressurized alkaline high temperature treatment. Analytical pyrolysis, using pyroprobe GC-MS, was used to investigate the molecular composition of the lignin samples. The total yield of pyrolysis lignin products was 13.3, 64.7, and 30.5% for the 1.25 M NaOH extracted lignin, alkaline assisted PLPW extracted lignin, and the unprocessed flax shives, respectively. Key lignin derived compounds such as guaiacol, 4-vinyl guaiacol, 4-methyl guaiacol, syringol, eugenol, isoeugenol, catechol, homocatechol, and vanillin were detected in all of the samples.

Comparative studies of grass compost lignin and the lignin component of compost humic substances

The aim of this research was to compare the structural features of lignin and alkali-soluble humic substances isolated from grass compost at different stages of composting, and to estimate the applicability of basic analytical techniques used in lignin chemistry for characterising the lignin structures transformed during composting. Elemental, functional analyses, alkaline nitrobenzene oxidation, analytical ozonation and FT-IR techniques were applied. Compost Björkman lignins were used as reference samples. FT-IR of the compost Björkman lignins was typical for guaiacyl–syringyl lignins. The humic substances contained methoxyl groups and gave the same products as Björkman lignins by nitrobenzene oxidation and ozonation. The lignin component of humic substances, calculated on the basis of chemical markers, was lower than that for the Klason procedure and decreased in following order: methoxyl group>nitrobenzene oxidation products>ozonation products. Methoxyl groups are recommended for lignin content evaluation in compost because of their higher stability in the compost environment among the chemical markers under study. Our results showed that lignin macromolecules were already sufficiently modified at the early stage of composting to be dissolved in alkali. Modified lignin constituted a significant part of grass compost humic substances.

Studies on the macromolecular components of nonwood available in Bangladesh

The structural feature of macromolecular component of dhaincha, cotton stalks, jute fiber, rice straw and wheat straw, which are commonly used in paper pulp production in forest deficient countries, was thoroughly studied. Lignin was isolated by classical Bjorkman method and characterized by elemental and methoxyl analysis, alkaline nitrobenzene oxidation, FTIR and 1H NMR spectroscopy. The C 9 formulas for cotton stalks, jute fiber, dhaincha, rice straw and wheat straw were C 9H 8.95O 3.53(OCH 3) 1.00, C 9H 8.12O 4.03(OCH 3) 1.65, C 9H 8.10O 4.65(OCH 3) 1.32, C 9H 8.58O 3.74(OCH 3) 1.23 and C 9H 8.31O 3.54(OCH 3) 1.23, respectively. The alkaline nitrobenzene oxidation products showed that syringyl to vanilin ratio of these nonwood varied from 1.1 to 2.9. Jute fiber showed the highest syringyl to vanilin ratio that are consistent with C 9 formula. The β- O-4 units in these nonwood lignins had predominately erythro stereochemistry type. The crystalline structure of these nonwood cellulose was also studied using X-ray diffraction and FTIR spectroscopy. The proportions of crystallinity, crystal size were varied from plant to plant. Jute fiber showed the highest proportion of crystallinity (73.4%) and crystal size (4.2 nm). The degree of polymerization of these nonwoods cellulose has also been studied. Degree of polymerization of jute cellulose was also the highest (3875). FTIR spectroscopy showed that these nonwoods cellulose was monoclinic unit cell structure (I β). Carbohydrate analysis showed that the main sugar component in the hydrolyzates of these nonwoods were xylose apart from glucose.

Variations in chemical characteristics and pulpability within jute plant ( Chorcorus capsularis)

The differences in morphological and chemical characteristics and pulpability of core and bark fiber of jute at different position, top, middle and bottom were studied. The fiber length at the middle part of both bark and core was longer than the top and bottom part. With increasing height from bottom to top lignin content is decreased and α-cellulose content increased. The bark had higher α-cellulose and lower lignin than core. The bark produced nitrobenzene oxidation products with larger syringaldehyde/vanillin (S/V) ratios than the core. The yields of nitrobenzene oxidation products in bark were higher than core. The analysis of neutral sugars suggested that xylose is the predominant sugar of hemicellulose in both bark and core. The bark had higher glucose and lower xylose as compared to core. Under identical conditions of pulping, bark gave higher pulp yield and lower kappa number than core. The bark pulp showed better bleachability than core pulp. The higher tensile index in core pulp and higher tear index in bark pulp were observed.

The relationship between lignin and morphological characteristics of the tracheary elements from cacao(Theobroma cacao L.) Hulls

Tracheary elements (TEs) were physically separated from the hulls of cacao pods(Theobroma cacao L). Their morphological features were extensively investigated with scanning electron microscopy and chemical characterization. Spiral TEs were covered with a thin layer of primary wall that had a web-like structure on its outer surface. These TEs had a spiral circularity diameter of 8.2 ± 0.6 μm and an estimated secondary wall thickness of about 2.1 ± 0.2 μm. Polarized microscopy analysis revealed that the cellulose microfibrils were aligned parallel to that thickening. Lignin content was 36.1%, with a 0.13:1.00 molar ratio of syringyl to guaiacyl units and a 1.09:1.00 molar ratio of erythronic acid and threonic acid. Total yields of the alkaline nitrobenzene oxidation and ozonation products were 324.5 and 148.8 μmol g-1 of extract-free TEs, respectively. Based on these morphological and lignin characteristics, we conclude that fully ripened cacao hulls exhibit the same features of secondary wall thickening as those seen at an earlier stage.