Lignin Moieties Research Articles

Soda/AQ Pulping of a Hardwood with Trapping of the Generated Coniferyl Alcohol

Coniferyl alcohol is generated from the cleavage of β-O-4 bonds during alkaline pulping of hardwoods and softwoods. Once formed, some of the coniferyl alcohol (CA) is transformed into vinylguaiacol (VG) and isoeugenol (IE). All three of these compounds (CA, VG, and IE) can rearrange to quinone methides (QMs) under alkaline conditions and become involved in condensation reactions with lignin and carbohydrate moieties. The aim of this investigation was to see if ethylguaiacol (EG) addition to soda-AQ (SAQ) pulping systems would lead to its reaction with the QMs from CA, VG, and IE to form dimers that are unreactive towards further condensation. Sugar maple wood meal was delignified by the SAQ process with EG added at 5.0 wt% on wood meal. Three dimers were detected in the pulping effluent and identified as a combination of EG with CA, VG, and IE. The total yield of the three dimers corresponded to ∼80% of the estimated CA that would have been generated. Conventional kraft, SAQ, and SAQ+EG pulping of the maple chips were then performed. The bleachability of the SAQ+EG pulp was significantly improved as compared to the SAQ pulp and it was estimated to be superior to the kraft pulp as well.

Minimizing the effect of undesirable reactions in ECF bleaching

Abstract One undesirable reaction during ECF bleaching is the formation of resistant quinones during the oxidation of lignin phenolic rings by ClO2. Occurrence of this side reaction was confirmed by the implementation of a new in situ method for quinone detection. It is based on the selective reaction of free-phenol groups in pulp with ClO2 at low temperature (0°C) and on the reduction of quinones into free phenols by sodium dithionite. Although not absolutely quantitative, it gives valuable information on the quinone content without any need of lignin extraction. It is proposed to apply a hydrogen peroxide treatment after each ClO2 (D) stage to solve this problem. Another undesirable reaction is the consumption of ClO2 by the muconic acid type structures which are the primary oxidation products of lignin during a D stage. Experiments with Z,Z-2, 5-dimethyl muconic acid, a model for lignin oxidized units, indicated that this reaction is most probable. Although phenolic moieties in lignin are more reactive than the muconic acid structures, the use of high ClO2 charges respective to lignin may favour its consumption by the muconic acid structures. One solution to this problem is to apply lower charges of ClO2 in each D treatment. The relevance of these findings was demonstrated by the high efficiency of (DEP)(DEP) sequences, where DEP stands for a ClO2 stage at low charge of chlorine dioxide immediately followed by an alkaline hydrogen peroxide treatment.

Structural elucidation of humic acids extracted from Pakistani lignite using spectroscopic and thermal degradative techniques

The present paper describes the characterization of Pakistan lignite coal, derived humic acids (HAL) and nitrohumic acids (NHA) along with the standard leonardite humic acids (LHA). The study utilized chromatographic and spectroscopic techniques to characterize the structure of coal and derived materials. Pyrolysis coupled to gc/ms was conducted with and without methylating agent (tetramethyl ammonium hydroxide). The pyrolysis study resulted in releasing mainly fatty acid methyl esters, different series of hydrocarbons and α, ω-dicarboxylic acid methyl esters. Triterpenoids, syringic and ρ-coumaric compounds and aromatic compounds derived from lignin moieties were also detected. Fourier transform infrared (FT-IR) and NMR data helped to evaluate the influence of coal rank on regeneration and nitration processes with respect to chemical structural composition of coal and derived materials. FT-IR spectra of four materials were similar except that NHA showed an absorption band at 1532cm−1, thus confirming the presence of -NO2 groups. 13C NMR indicated higher aromaticity and less hydroxylalkyl material in HAL than NHA. The elemental composition and acid functional group content of four materials were also reported.The combination of results from different analytical techniques gives an improved understanding of the Pakistan coal nature and helpful for its future utilization.

Soil Carbon Characteristics in Two Mississippi River Deltaic Marshland Profiles

Current understanding of the soil organic matter (SOM) transformation pathways and mechanisms in coastal wetland ecosystems is limited. This study was carried out to characterize and compare chemical composition of belowground SOM from a freshwater marsh and a saline marsh in coastal Louisiana. Composite samples at three depths (0–50, 50–100, and 100–150 cm) from each site were collected and characterized by solid state 13C NMR spectroscopy. The 13C NMR spectral composition of three soil depths of the freshwater marsh was similar and dominated by contribution from polysaccharide carbon (C), followed by equal contributions from aliphatic C and total aromatic C. A steady and more pronounced drop in polysaccharide C with depth, accompanied by the de-methoxylation of lignin moieties, was observed in the profiles of the saline marsh. The δ13C signature of these marsh soils suggested that much of the C in the saline profile was likely derived from the mixed debris of previous freshwater and saline marsh vegetation rather than from the current salt-tolerant Spartina species alone. It was concluded that the chemical composition of SOM was determined more by the difference between the freshwater and the saline soil environment than by the C source in the coastal wetland ecosystems.

Fractionation and characterization of lignin-carbohydrate complexes (LCCs) from eucalyptus fibers

Abstract The effect of milling time on the structure of lignin was investigated by analyzing the quantity and molecular size distribution of thioacidolysis products obtained from wood and pulp of eucalypt (Eucalyptus globulus). After milling, the ability of three solvent systems was determined to completely dissolve the wood or pulp meal. It was found that a mixture of DMSO and 50% aqueous tetrabutylammonium hydroxide was superior to either dimethylacetamide-LiCl or DMSO-tetrabutylammonium fluoride as solvent. By applying the minimum milling time required for complete dissolution, structurally unaltered wood or pulp could be further separated into lignin-carbohydrate fractions. These were analyzed by thioacidolysis. From eucalypt pulp, two different lignin-carbohydrate fractions were obtained, one glucan- and one xylan-enriched fraction, with the latter having more syringyl units in its lignin moieties. The developed solvent system seems to be universal because spruce and flax fibers and pulps could also be dissolved in it after milling.

Valorization of an industrial organosolv–sugarcane bagasse lignin: Characterization and use as a matrix in biobased composites reinforced with sisal fibers

In the present study, the main focus was the characterization and application of the by-product lignin isolated through an industrial organosolv acid hydrolysis process from sugarcane bagasse, aiming at the production of bioethanol. The sugarcane lignin was characterized and used to prepare phenolic-type resins. The analysis confirmed that the industrial sugarcane lignin is of HGS type, with a high proportion of the less substituted aromatic ring p-hydroxyphenyl units, which favors further reaction with formaldehyde. The lignin-formaldehyde resins were used to produce biobased composites reinforced with different proportions of randomly distributed sisal fibers. The presence of lignin moieties in both the fiber and matrix increases their mutual affinity, as confirmed by SEM images, which showed good adhesion at the biocomposite fiber/matrix interface. This in turn allowed good load transference from the matrix to the fiber, leading to biobased composites with good impact strength (near 500 J m(-1) for a 40 wt% sisal fiber-reinforced composite). The study demonstrates that sugarcane bagasse lignin obtained from a bioethanol plant can be used without excessive purification in the preparation of lignocellulosic fiber-reinforced biobased composites displaying high mechanical properties.

Reactivity of long chain alkylamines to lignin moieties: Implications on hydrophobicity of lignocellulose materials

Enzymatic processes provide new perspectives for modification of lignocellulose materials. In the current study, laccase catalyzed coupling of long chain alkylamines to lignin model molecules and lignocellulose was investigated. Up to two molecules of dodecylamine (DA) and dihexylamine (DHA) were successfully coupled with lignin monomers (guaiacol, catechol and ferulic acid) while coupling onto complex lignin model compounds (syringylglycerol β-guaiacyl ether, guaiacylglycerol β-guaiacyl ether and dibenzodioxocin) yielded 1:1 coupling products. Surface analysis of beech veneers enzymatically grafted with DA showed an increase in nitrogen content of 3.18% compared to 0.71% in laccase only treated controls while the O/C ratio decreased from 0.52 to 0.46. Concomitantly the grafting of DHA or DA onto beech veneers resulted in a 53.8% and 84.2% increase in hydrophobicity, respectively when compared to simple adsorption. Therefore, laccase-mediated grafting of long chain alkylamines onto lignocellulose materials can be potentially exploited for improving their hydrophobicity.

Probing native lignin macromolecular configuration in Arabidopsis thaliana in specific cell wall types: Further insights into limited substrate degeneracy and assembly of the lignins of ref8, fah 1–2 and C4H::F5H lines

The interest in renewable, plant-derived, bioenergy/biofuels has resulted in a renaissance of plant cell-wall/lignin research. Herein, effects of modulating lignin monomeric compositions in a single plant species, Arabidopsis, are described. The earliest stage of putative "AcBr/Klason lignin" deposition was apparently unaffected by modulating p-coumarate 3-hydroxylase or ferulate 5-hydroxylase activities. This finding helps account for the inability of many other studies to fully suppress the reported putative levels of lignin deposition through monolignol biosynthesis manipulation, and also underscores limitations in frequently used lignin analytical protocols. The overall putative lignin content was greatly reduced (circa 62%) in a plant line harboring an H-(p-hydroxyphenyl) enriched lignin phenotype. This slightly increased H-monomer deposition level apparently occurred in cell-wall domains normally harboring guaiacyl (G) and/or syringyl (S) lignin moieties. For G- and S-enriched lignin phenotypes, the overall lignification process appeared analogous to wild type, with only xylem fiber and interfascicular fiber cells forming the S-enriched lignins. Laser microscope dissection of vascular bundles and interfascicular fibers, followed by pyrolysis GC/MS, supported these findings. Some cell types, presumably metaxylem and possibly protoxylem, also afforded small amounts of benzodioxane (sub)structures due to limited substrate degeneracy (i.e. utilizing 5-hydroxyconiferyl alcohol rather than sinapyl alcohol). For all plant lines studied, the 8-O-4' inter-unit frequency of cleavable H, G and/or S monomers was essentially invariant of monomeric composition for a given (putative) lignin content. These data again underscore the need for determination of lignin primary structures and identification of all proteins/enzymes involved in control of lignin polymer assembly/macromolecular configuration.

Chemical Changes Induced by High-Speed Rotation Welding of Wood — Application to Two Canadian Hardwood Species

The chemical changes occurring upon rotational welding with dowels of Canadian wood species sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis) were examined by pyrolysis-GC/MS, DSC and XPS anlayses. The analyses performed separately on wood substrate (reference wood) and welded material by pyrolysis-GC/MS, DSC and XPS indicate that the differences in mechanical performances of the two welded woods are due mainly to the differences in original lignin structures as well as in the welding temperatures determined for the two wood species. The more pronounced guaiacyl character of the maple wood lignin seems to explain the preferential condensation reactions of the guaiacyl moieties in maple lignin with formaldehyde and furanic compounds released from lignin and carbohydrates during the fast pyrolysis associated with the welding process. The higher temperature determined for maple wood welding than for birch could be responsible for enhanced miscibility of wood polymers in the welding zone, explaining, therefore, the more significant presence of xylan polymer together with newly formed lignin carbohydrate complex (LCC) in the welded material. The detailed analysis of the compounds identified by pyrolysis-GC/MS, together with the results of the other two methods applied in this study, has confirmed that the S/G ratio cannot be taken as the sole criterion for the discussion of the chemical changes in lignins during welding of wood.

Analysis of chemical changes in Picea abies wood decayed by different Streptomyces strains showing evidence for biopulping procedures

The present study is focused on analysing the suitability of different Streptomyces strains for biomechanical pulping purposes using spruce wood (Picea abies) as substrate. After 2 weeks of incubation, no apparent variations in lignin Klason content of treated woods were detected compared with the control. However, the increase in acid-soluble lignin fraction pointed out chemical alterations in lignin moiety. Through Py-GC/MS analysis enrichment in cellulose and lignin molecule modifications were detected in treated woods. The increase in the relative abundance of the most G-type phenol units with a higher oxidation degree suggests that some oxidation occurred in the lignin C3-alkyl chain. In addition, the decrease in the phenylmethane + phenylethane/phenylpropane (phC1 + ph C2/ph C3) ratio would indicate the ability of Streptomyces strains to breakdown the C3-alkyl chain linkages once carbons had been oxidized. From this study it could be concluded that the assayed strains are able to produce a delignification of spruce wood which may improve mechanical pulping processes.

Stability and maturity of a green waste and biowaste compost assessed on the basis of a molecular study using spectroscopy, thermal analysis, thermodesorption and thermochemolysis

The organic matter (OM) of a green waste and bio waste compost was characterised over 8 months and the observed evolution was correlated with physico-chemical parameters (temperature, pH, carbon content, C/N ratio). Thermochemolysis and thermodesorption were used to monitor bacterial activity (stability) whereas diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and thermodifferential analysis (TDA) permitted to determine the degree of OM humification (maturity). DRIFT spectroscopy and TDA provide two indicators of maturity since, with these two techniques, the signals associated with the biodegradable organic matter decrease relatively to the signals associated with refractory organic matter. This increase in R TG and R IR ratios between aromatic to aliphatic signals constitutes a proof for OM complexification. It correlates with humic acids/fulvic acids ratio known to be a maturity index. Pyrolysates are mainly constituted of lignin moieties, terpenoids, nitrogen containing compounds, carbohydrates (furanosic moiety), mono- and diacids (as methyl esters), and methoxyesters. The R branched/linear ratio between branched to linear acids traduces the evolution of the bacterial activity during composting. Moreover the R di/mono ratio between aliphatic mono to diacids correlates with the latter showing that diacids can occur from the biological oxidation of monoacids. These two ratios determined by thermochemolysis are useful to monitor the stability of compost. VOC, observed by thermodesorption are mainly constituted of terpenes, light acids, aldehydes and ketone. An unexpected result was obtained since the amount of phytol increases relatively to the isoprenoid ketone considered to originate from the latter.

Structural features of humic acids from a sedimentary sequence in the Guadiana estuary (Portugal–Spain border)

The structural characteristics of humic acids (HAs) from two different depths of a sedimentary sequence representing the last 13kyr in the valley of Guadiana river estuary (SW Portugal/Spain border) have been approached using a combination of spectroscopic techniques, wet chemical degradation methods (sequential oxidation with sodium persulfate followed by KMnO4, and oxidation with RuO4) and analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) in the presence and absence of tetramethylammonium hydroxyde (TMAH). The aim was to obtain complementary information on the sources and alteration of the organic matter (OM) provided by a previous study on the vertical distribution of terrestrial and phytoplankton biogeochemical markers in the sequence. Both the FT-IR (Fourier transformed infrared) and 13C NMR (nuclear magnetic resonance) spectra showed a close similarity with the structural characteristics of the HA samples. NMR signals in the alkyl region (0–45ppm) as well as FT-IR band patterns typical for methoxyl-substituted aromatic rings pointed to the presence of an important aliphatic domain, as well as to lignin-derived compounds. This finding was confirmed using analytical pyrolysis. In addition, the main TMAH thermochemolysis products were typical lignin-derived methoxyphenols with both guaicyl and syringyl nuclei. The detection of methoxyphenol units with three to six carbon atom (C3–C6) side chains suggests that lignin and possibly suberin were only partially degraded. Compounds arising from proteins and polysaccharides were also detected, although in lesser and varying amount. The major products from persulfate oxidation were series of n-alkanes (C16–C33 with clear odd/even predominance) and n-fatty acids, both saturated (C10–C26 with strong even/odd predominance) and unsaturated, which may arise from the above aliphatic biomacromolecules. The major products from permanganate oxidation of the persulfate residue were α,ω-diacids (C6–C11) originating from oxidation of the ether bonds linking the building blocks constituting the core of the HA structure. Aromatic compounds (phenols, methoxy-dimethoxybenzene carboxylic acid and benzene di-, tri-, tetra- and pentacarboxylic acids), most probably derived from the aromatic backbone of the HAs, that may also include lignin moieties as well as other polyphenols (flavonoids and tannins) were also detected. The RuO4 oxidation also released series of n-alkanes (C16–C33), linear saturated fatty acids (C10–C28) and α,ω-diacids (C7–C25), as well as traces of benzene polycarboxylic acids. Regarding the usefulness of the various techniques used, they provide complementary information. Indeed, spectroscopic techniques and analytical pyrolysis provide information on the backbone of the HAs, and on their origin, whereas the oxidative degradations provide different information on the structural features of the HA, particularly the nature of the linking between the building blocks. In general, the data support the idea that the HAs still contain information about the signature of aliphatic and aromatic biomacromolecules contributing to the OM deposited. The presence of lignin-derived residues suggests a large input from terrestrial carbon throughout the core.

Laccase‐Mediated Wood Surface Functionalization

AbstractLaccase‐catalyzed grafting of functional molecules on wood surface presents an eco‐friendly opportunity to improve wood properties. In a novel stepwise approach, functional molecules were bound to an enzymatically modified wood surface containing anchor groups. As anchor groups, phenolic amines were coupled to lignin moieties of wood using the 62 kDa Trametes hirsuta laccase. The coupling reaction to lignin was mimicked using the lignin model compounds 4‐O‐methyl guaiacylglycerol β‐guaiacyl ether A, guaiacylglycerol β‐guaiacyl ether E, dehydrodivanillyl alcohol type dibenzodioxocin D and syringylglycerol β‐guaiacylether G. Using this approach it was possible to increase binding of the fungicides propiconazole and thiabendazole by 42 % and 58 %, respectively, when compared to coupling onto wood pieces which were oxidized by laccase only.

Wood solubilization and depolymerization using supercritical methanol. Part 1: Process optimization and analysis of methanol insoluble components (bio-char)

Abstract Conversion of wood into a methanol soluble liquid (bio-oil) was shown to occur under supercritical methanol treatment (SCM). The particle size of the solid material (bio-char) left after evaporating the solvent from the bio-oil was analyzed. Expectedly, the degradation of the particle size was more pronounced during a severe SCM treatment in comparison to subcritical solubilization conditions. Molecular mass was reduced by 90% under optimal conditions of SCM treatment under which the highest degree of solubilization (degradation) was obtained. The bio-char was also analyzed by pyrolysis GC-MS. The composition of the bio-char after sub- and moderate SCM treatments consisted mainly of carbohydrate derived degradation products, which was mixed with some lignin moieties. At near to optimal SCM treatment conditions, the remaining bio-char was composed mainly of modified cellulose and lignin. The optimization of the liquefaction process was performed by means of the statistical design called “response surface model with a central composite design”.

Off‐line pyrolysis and compound‐specific stable carbon isotope analysis of lignin moieties: a new method for determining the fate of lignin residues in soil

Off-line pyrolysis was used to liberate lignin moieties from dung and soil and, after trimethylsilylation, the delta(13)C values of these derivatives were determined by gas chromatography-combustion-isotope ratio mass spectrometry. Initial delta(13)C values determined for 4-vinylphenol, syringol, 4-vinylguaiacol, 4-acetylsyringol, 4-vinylsyringol, 4-(2-Z-propenyl)syringol, 4-(2-E-propenyl)syringol and 4-(2-propenone)syringol pyrolysis products of the lignin polyphenol structure from C(4) (delta(13)C(bulk) = -12.6%) and C(3) (delta(13)C(bulk) = -30.1 per thousand) dung confirmed the robust and reproducible nature of the off-line preparation technique. C(4) dung was used as a treatment in a randomised field experiment to assess the short-term sequestration of dung carbon in managed grasslands. Since lignin was on average 3.5 per thousand depleted in (13)C compared with bulk dung delta(13)C values, this may have resulted in an under-estimation of dung C incorporation based on bulk delta(13)C values. Therefore, an investigation of the compound-specific delta(13)C values of dung-derived lignin moieties extracted from soils sampled up to 372 days was undertaken. Delta(13)C values between lignin moieties extracted from treated and untreated soils showed that dung-derived lignin was not especially resistant to degradation and suggested that individual moieties of the lignin macromolecule must: (i) move into soil, (ii) be degraded, or (iii) be transformed diagenetically at different rates. This adds to a gathering body of evidence that lignin is not particularly stable in soils, which has considerable significance for the perceived role of different biochemical components in the cycling of C in soils.

Organic matter humification in olive oil mill wastewater by abiotic catalysis with manganese(IV) oxide

The chemical changes occurring in an olive oil mill wastewater (OMW) sample digested catalytically with MnO 2 for 30 and 60 days were evaluated comparatively with those occurring in the same OMW left standing for the same time in an open-air lagoon. Both treatments increased the pH and electrical conductivity and decreased the contents of dry matter, total organic C and total N, and C/N ratio of OMW. The humic acid (HA)-like fraction isolated from the fresh OMW was characterized by a marked aliphatic character, small O and acidic functional group contents, marked presence of proteinaceous materials, partially modified lignin moieties and polysaccharides-like structures, extended molecular heterogeneity, and small degrees of aromatic ring polycondensation, polymerization and humification. With increasing the time of either lagooning or catalytic digestion, a loss of aliphatic materials and an increase of extraction yield, oxygenation, acidic functional groups, carbohydrates and aromaticity occurred in the HA-like fractions. The more evident changes measured for the HA-like fractions from catalytically-digested OMW, with respect to those from lagooned OMW, indicated that MnO 2 was able to catalyze organic matter humification in OMW.

Application of the amount of oxygen consumption to the investigation of the oxidation mechanism of lignin during oxygen-alkali treatment

The dioxygen consumption by kraft lignin and several lignin model compounds during oxygen-alkali treatments were directly analyzed using a dioxygen fl owmeter. The average dioxygen consumption by 200 g of kraft lignin was about 3 moles. Because this value was as much as those obtained for monomeric phenolic lignin model compounds, guaiacol and vanillyl alcohol, it was postulated that not only phenolic but also nonphenolic moieties in kraft lignin are extensively oxidized. The dioxygen consumption by 0.5 moles (one equivalent of aromatic units) of a dimeric lignin model compound, guaiacylglycerol-β-guaiacyl ether (GG), was also similar to that for 1 mole of guaiacol and vanillyl alcohol, regardless of the type of the aromatic moiety, which supports the above postulation. The most plausible mechanism for the oxidation of nonphenolic moieties is the oxidation of side chains of residual β-O-4 substructures by active oxygen species. By this mechanism, nonphenolic moieties in kraft lignin and GG are converted into corresponding phenolic moieties, and the oxidation by dioxygen progresses.

Relationship between molecular characteristics of soil humic fractions and glycolytic pathway and krebs cycle in maize seedlings

A humic acid (HA) isolated from a volcanic soil was separated in three fractions of decreasing molecular size (I, II and III) by preparative high performance size exclusion chromatography (HPSEC). The molecular content of the bulk soil HA and its size fractions was characterized by pyrolysis-GC-MS (thermochemolysis with tetramethylammonium hydroxide) and NMR spectroscopy. All soil humic materials were used to evaluate their effects on the enzymatic activities involved in glycolytic and respiratory processes of Zea mays (L.) seedlings. The elementary analyses and NMR spectra of the humic fractions indicated that the content of polar carbons (mainly carbohydrates) increased with decreasing molecular size of separated fractions. The products evolved by on-line thermochemolysis showed that the smallest size fraction (Fraction III) with the least rigid molecular conformation among the humic samples had the lowest content of lignin moieties and the largest amount of other non-lignin aromatic compounds. The bulk HA and the three humic fractions affected the enzyme activities related to glycolysis and tricarboxylic acid cycle (TCA) in different ways depending on molecular size, molecular characteristics and concentrations. The overall effectiveness of the four fractions in promoting the metabolic pathways was in the order: III>HA>II>I. The largest effect of Fraction III, either alone or incorporated into the bulk HA, was attributed to a flexible conformational structure that promoted a more efficient diffusion of bioactive humic components to maize cells. A better knowledge of the relationship between molecular structure of soil humic matter and plant activity may be of practical interest in increasing carbon fixation in plants and redirect atmospheric CO 2 into bio-fuel resources.

Characterization of the transformations of lignocellulosic structures upon degradation in planted soil

Analytical pyrolysis (AP) as well as chemical analysis, ESR, FTIR and UV/VIS-spectroscopy has been used to characterize effects of modification of industrial lignins (hydrolysis lignin and kraft lignin) with silicon-containing oligomers on their transformation in soil planted with timothy grass ( Phleum pratense). Using Py-GC/MS it was shown that carbohydrate-originated admixtures of non-modified hydrolysis lignin were degraded preferentially during the first vegetation season (12 weeks), whereas the degradation of lignin moieties was developed during the second vegetation season (60 weeks of incubation). The modification of both hydrolysis and kraft lignins with Si-oligomers promotes degradation of lignin from the earlier stage of incubation in soil. After the first 12 weeks of incubation the G/S ratio in products from pyrolysis of residual Si-modified hydrolysis lignin has increased almost twice, whereas for non-modified hydrolysis lignin this ratio has not changed. At the same time, Si-modification prevented oxidation of lignin during the whole incubation duration: yields of CO 2 and carbonyl-containing compounds upon pyrolysis of residues of Si-modified hydrolysis lignin were lower in comparison with those for the residues of non-modified lignin. Simultaneously with degradation, condensation of the lignins residual structure occurred, moreover in Si-modified hydrolysis lignin up to a higher extent than for non-modified lignin. For non-modified kraft lignin an aromatization and condensation of the structure was observed at earlier incubation time in comparison with hydrolysis lignin, and the effect of Si-modification in this case is not as potent as it is observed for hydrolysis lignin. Py-GC/MS data were used to define relationships between the changes in chemical structure of lignins and numbers of microorganisms in the timothy grass rhizosphere. Significant positive correlations were found between the development of humus-degrading bacteria population and the relative abundance of carbon dioxide in the lignin pyrolysis products as well as between numbers of humus-degrading fungi population and relative abundances of guaiacol and syringol.

Pyrolysis-GC/MS and TG/MS study of mediated laccase biodelignification of Eucalyptus globulus kraft pulp

Biobleaching studies using laccase mediator system (LMS) were carried out, under optimized conditions, on two unbleached Eucalyptus globulus kraft pulps, one produced by conventional way, with kappa number of 16.1, and another with kappa number of 14.5, obtained by modified kraft procedure with a high liquor/wood ratio and with black liquor replacement in the middle of the cooking. The pulp properties before and after LMS and alkaline extraction were evaluated in terms of kappa number, hexeneuronic acid content, viscosity, brightness and acid insoluble lignin content. The original milled wood sample and the kraft pulps were characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermogravimetry/mass spectrometry (TG/MS). Eucalypt wood lignin produces guaiacol and syringol derivatives during pyrolysis. These lignin products can be detected with high sensitivity using the selected ion chromatograms even in the bleached pulp of low lignin content (about 0.5%). Py-GC/MS revealed that the lignin moieties were similarly altered during biobleaching as during pulping, which is exemplified by the preferential removal of aldehyde groups from the alkyl side groups. Semi-quantitative analysis of the pyrograms indicates that the lignin content of the biobleached pulps is reduced by about half in comparison with the unbleached pulps. The TG/MS results show that the hemicellulose content of wood was strongly modified during pulping resulting in higher thermal stability.