Volume 63, Issue 6

In the present study, three representative residual chromophores recently isolated from highly bleached and aged pulps, 2,5-dihydroxy-[1,4]-benzoquinone ( 1 ), 5,8-dihydroxy-[1,4]-naphthoquinone ( 2 ), and 2,6-dihydroxy-acetophenone ( 3 ), were selected to study their effects with regard to cellulose degradation under bleaching conditions, similar to those typically used in the pulp and paper industries.

A method for selective, fast, and near-quantitative methylation of carboxyl groups in the presence of aliphatic hydroxyl groups of cellulose was developed. The main advantage of the method is the complete maintenance of cellulose integrity; no degradation of cellulose whatsoever during the methylation procedure was observed, making the protocol extremely useful in advanced cellulose analytics. Trimethylsilyl diazomethane (TMS-DAM) was used as the methylation agent. The methylation conditions were pre-optimized by means of carbohydrate model compounds with low-molecular weight, such as derivatives of glucuronic acid and hexenuronic acid, and then re-optimized for methylation of cellulose. The influence of reaction parameters, such as time, temperature, solvents, and concentration, was also determined. The reaction kinetics was monitored by fluorescence labeling of the remaining carboxyl groups according to the common FDAM protocol. A general protocol for the fast methylation of carboxyl groups in pulp samples is presented. The methylation with TMS-DAM is a very fast process, both in comparison to general heterogeneous reactions on cellulosic pulps, and especially in comparison to other methylation approaches. In dissolving and paper grade pulps, methylation of xylan carboxyls proceeded faster than methylation of cellulosic carboxyls. The methylation rate and kinetics are dependent on the pulp type. As application examples, electrokinetic measurements were used to demonstrate the “blocked” reactivity of carboxyl groups in spin-coated films of methylated pulp samples, and ICP-MS was used to demonstrate the drastically decreased metal ion binding capacity of pulp after such methylation.

The difference in the effect of salts on the formation and properties of gels based on microcrystalline cellulose (MCC) and microcrystalline chitosan (MCCh) was investigated. Bleached sulphate pulp from wood and chitosan obtained from exoskeletons of crustaceans served as raw materials. These were destructed by a thermocatalytic method to the levelling-off degree of polymerisation and then dispersed in solutions of different salts. At a sufficiently high concentration, gels with a liquid crystalline structure were formed. For MCC, the gels are stronger when the dispersion solution contains polyvalent cations, which decrease the negative charge on the cellulose surface caused by the carboxyl groups present there. As a result, the mutual repulsing forces between the cellulose particles decrease and the lattice formed by them becomes stronger. For MCCh, strong gels with a great viscosity are formed when the dispersion solution contains polyvalent anions, which decrease the positive charge on the chitosan surface caused by amine groups. The effect of salts depends also on their concentration in the solution.

The identification of muconic acid type structures (MATS) in oxidised lignins employing 2D NMR spectroscopy was carried out. The primary database for MATS detection by single bond 1 H- 13 C (HSQC) and long-range 1 H- 1 H and 1 H- 13 C correlation (COSY and HMBC) NMR experiments was obtained with a series of model compounds: cis, cis - and trans, trans -muconic acids and their methylated analogues and MATS derived from monomeric lignin model compounds oxidised by ClO 2 . Additional information was obtained from the study of oxygen-organosolv lignin obtained from spent liquor after the spruce wood delignification with oxygen in an acetone-water solution. This work allowed the reliable assignment of MATS signals in the HSQC spectra of oxidised lignin and provides a methodology for detection and distinguishing of MATS from structurally similar moieties.

A trimeric β-O-4 lignin model bearing a styrene unit was polymerized in the presence of azobisisobutyronitrile as an initiator of free radical polymerization. The polymer analysis achieved by size exclusion chromatography (SEC), 1 H, 13 C, 31 P NMR, matrix-assisted laser desorption ionization combined with time-of-flight mass spectrometry (MALDI-ToF MS), differential scanning calorimetry, and thermogravimetry indicated its well-defined structure with good thermal stability at temperatures usually applied for alkaline pulping. SEC analysis proved a high degree of polymerization despite the size of the phenolic β-O-4 units in the polymer structure. MALDI-ToF spectrometry indicated that the polymer is composed of phenolic β-O-4 elements only. The chemical reactivity under alkaline conditions of the polymer was studied by both HPLC and 31 P NMR. These two methods revealed two main concurrent processes, which include an oxidation of the phenol part followed by C α -C β bond cleavage, and a formation of a quinone methide followed by its β-O-4 bond cleavage.

In situ analysis of lignin by 2D NMR of whole plant material was carried out by swelling finely ball-milled samples in deuterated dimethylsulfoxide (DMSO- d 6 ) and sonicated so that a gel was formed in the NMR analysis tube. Solution HSQC NMR spectra of different plant materials representative for hardwood ( Eucalyptus globulus ), softwood ( Picea abies ), and non-woody plants ( Agave sisalana ) are presented here. The spectra show signals corresponding to those of the main plant constituents, such as lignin and polysaccharides. The lignin signals were assigned by comparing the HSQC spectra of the whole plant materials with the HSQC spectra of their respective milled-wood lignins (MWLs). In general terms, the major lignin structural features, such as the relative abundances of the main lignin substructures, the syringyl/guaiacyl ratios and the extent of γ-acetylation of the lignin side-chain observed in the HSQC spectra of the whole plant materials, matched those obtained from the HSQC spectra of the isolated MWLs. Therefore, this technique, which needs only minor amounts of lignocellulosic material and minimal sample preparation, can be useful for the rapid screening of plant lignins without the need for tedious and time-consuming lignin isolation procedures.

The utility of simple syringyl-type phenolics of plant origin and some common synthetic compounds were compared with regard to their ability to act as laccase mediators in the oxidation of non-phenolic lignin model compounds. It was demonstrated that syringyl-type phenols, especially acetosyringone and methyl syringate, were able to mediate the oxidation of substrates of high oxidation potential by a laccase with a low redox potential. A mediator dose around 10% showed good performance compared to the equimolar quantities needed when the synthetic compounds 1-hydroxybenzotriazole or N -hydroxyacetanilide were used.

The ClO 2 titration method for in situ measurement of free phenolic groups in pulp has been improved to minimize interferences from other groups susceptible to react with ClO 2 . The method is based upon the reaction between free phenolic groups and chlorine dioxide at a temperature of 0°C, in the presence of dimethyl sulfoxide. Theoretically, one free phenolic group consumes two molecules of ClO 2 . The pH of the ClO 2 treatment was advantageously fixed at 6.7 using a phosphate buffer, and a new protocol was proposed to avoid any possible interference of quinone groups (either present in pulp or formed during the procedure) on the residual ClO 2 titration step. The results obtained on isolated lignin samples were compared to those measured by 31 P NMR spectroscopy. The ClO 2 method gave substantially higher values, for reasons which deserve further investigation.

Surface tension of kraft lignin (KL) and KL/poly(N,N-dimethylaminoethyl methacrylate) mixtures, with different composition at the air-water interface depending on pH and temperature, was measured. It was found that the surface activity of both KL and the reaction mixtures grows with decreasing pH and increasing temperature. At the same time, the surface activity of the KL/poly(N,N-dimethylaminoethyl methacrylate) reaction mixture, irrespective of its composition under the same environment conditions, considerably exceeds the surface activity of KL, indicating the synergetic effect governed by the peculiarities of the polymeric structure of the formed soluble particles of the polyelectrolyte complex.

Three types of preparations – enzyme immobilized on Eupergit C, cross-linked enzyme crystals (CLECs) and lyophilized enzyme – have been obtained from Trametes pubescens laccase. Their activity in organic solvents has been comparatively evaluated, whereby the CLECs showed a significantly higher activity compared to the immobilized and the lyophilized variant. The soluble, lyophilized laccase and the CLECs were compared for their activity in the oxidation of cellulose in the laccase/TEMPO system. The “double heterogeneous” CLEC system – both the CLECs and the cellulose substrates are solids and only the mediator is homogeneously dissolved – showed similar reactivity to the conventional enzyme system. Laccase CLECs, being a solid, robust and highly active immobilized enzyme form can be conveniently used to modify (protected) low-molecular weight carbohydrates or cellulosics also in (aqueous-)organic media, and they offer many practical advantages: operational stability and ease of recycling coupled with high volumetric productivity.

The feasibility of producing dissolving grade pulps for viscose production from different fiber raw materials, such as paper grade pulps from wood and non-woody plants, was investigated. Commercial dried bleached hardwood kraft pulps from eucalypt, and bleached non-wood soda/AQ pulps from flax, hemp, sisal, abaca, and jute, were subjected to enzymatic and chemical pre-treatments in order to improve the accessibility and reactivity of cellulose and to reduce their hemicellulose content. A commercial monocomponent endoglucanase and a commercial xylanase were employed for biochemical treatment. The chemical treatment consisted of cold alkaline extraction. The effects of these pre-treatments on pulps were studied by reactivity, according to Fock's method, and viscosity measurements, determination of hemicellulose content, and recording of molecular weight distributions. The results were compared to those of commercial bleached eucalypt dissolving pulp. Eucalypt and sisal pulps showed high improvement in reactivity, reaching levels near or even higher than that of the eucalypt dissolving pulp (65%–70%), and a low hemicellulose content (2%–4%), when both were submitted to a sequence of treatments consisting of an initial xylanase treatment followed by cold alkaline extraction, and a final endoglucanase treatment. However, the viscosity decreased considerably. A uniform and narrow molecular weight distribution was observed in both eucalypt and sisal pulps after this sequential pre-treatment.

Development of fiber strength properties and morphological changes on the surface of bleached hardwood kraft pulp after treatment with commercial cellobiohydrolase (CBH) was evaluated. Tensile and tear indices showed no significant effect of the treatment. The treatment resulted in reduction of wet zero-span strength, while the dry zero-span values increased. The decrease in wet zero-span values was most likely caused by preferential action of CBH on structurally irregular zones in the fiber wall coupled with greater sensitivity of wet zero-span testing towards the localized fiber defects. The fracture zone of the wet zero-span tested samples was imaged by scanning electron microscopy (SEM). Visual observation revealed differences in fiber fracture between treated and control samples. The straighter and cleaner fractures of the treated sample could be attributed to the localized hydrolytic action of CBH. Visual analysis of the treated fiber surface morphology by SEM showed an increase of more visible fiber wall dislocations, particularly on fibers of smaller diameter. The increased presence of the fiber dislocation correlates with the decrease in the wet zero-span values of treated samples.

The aim of this work was to evaluate the potential of Eucalyptus globulus hemicelluloses, mainly xylan, for bioethanol production. Hemicelluloses have been removed prior to pulping by auto-hydrolysis and an acid-catalysed hydrolysis. As the hydrolysates obtained were rich in xylose, the yeast Pichia stipitis was selected for fermentation. It was confirmed that the yeast performance is strongly dependent on pH and the presence of inhibitors, such as lignin. The addition of Ca(OH) 2 was successful for lowering the concentration of inhibitors and adjusting the pH. The strain was grown in culture media with increasing volumetric percentages of treated hydrolysates up to 100% (v/v), supplemented with nutrients other than the carbon and energy source. This methodology shortened the lag phase of fermentation and improved the performance of yeast. Maximum ethanol concentration (12 g eth l -1 ), productivity (0.22 g eth l -1 h -1 ), and yield (0.48 g eth g xyl eqs -1 ) were achieved with treated acid-hydrolysates. These results are similar to those obtained by a synthetic medium with an equivalent xylose concentration.

The changes in lignin structure of spruce thermomechanical pulp (TMP), induced by treatment with laccase of Trametes hirsuta (ThL) and laccase of Melanocarpus albomyces (MaL), has been investigated by UV-Vis, UV resonance Raman (UVRR), and Fourier transform infrared (FTIR) spectroscopy. The spectroscopic results showed that the structural changes were small; however, the changes were slightly more pronounced in the case of MaL. Nevertheless, the brightness of the pulps remained higher after treatment with MaL than after treatment with ThL. Accordingly, MaL is a promising enzyme for fiber activation and functionalization.

Sapstain fungi, which reduce the value of pine wood, were isolated from an industrial wood yard in north-eastern Germany. The predominant wood discolouring species on the industrial wood yard and in the forests of the investigated region was Sphaeropsis sapinea (syn. Diplodia pinea ), but Ophiostoma minus was also found. These fungi were challenged with antagonistic micro-organisms in laboratory trials and in field experiments. Amongst the tested microorganisms only strains of filamentous fungi ( Trichoderma sp. and Phlebiopsis gigantea ) could control the sapstain fungi on pine wood blocks efficiently. Although P. gigantea was unable to inhibit stain formation completely, the wood was bleached by this fungus in later incubation stages. In two field trials, sapstain on pine wood logs was successfully retarded for a period of 10 and 12 weeks, respectively, with a white sporulating mutant of Trichoderma harzianum . Thus, the concept using filamentous fungi as antagonists against sapstain developed under laboratory conditions also proved to be valid under natural conditions in forest eco-systems.

Hot water extraction of pine wood was carried out after 10 days of exposure to brown-rot fungi ( Gloeophyllum trabeum , Coniophora puteana and Poria placenta ) and a white-rot fungus ( Coriolus versicolor ). The microstructure of the wood cell wall was analysed by the water vapour sorption method. The content and composition of monosaccharides in the extracts were determined by high performance liquid chromatography. Despite the absence of essential mass losses at the initial stage of the contact with the fungi, slight changes in the cell wall microstructure can be observed, namely, the hydrophobisation and the change in the character of porosity in the region of 1–10 nm pore sizes. After hot water treatment, the mass decreases considerably, i.e., to 25% for the control and brown-rot treated samples and more than 30% for the white-rot treated sample. The sorption-desorption isotherms for the washed control sample and brown-rot samples were not changed practically, but the isotherm was changed clearly in the case of the white-rot treated sample. The microstructure of the white-rot sample changed after hot water washing radically and was accompanied with the formation of wide mesopores in the range of 5–9 nm width.

A total of 28 tropical Amazon woods – many of them rarely used – from Tapajós National Forest, Pará state, Brazil, were tested for their natural resistance against the decay fungi: Ganoderma applanatum , Trametes versicolor , Pycnoporus sanguineus , Meruliporia incrassata , and Gloeophyllum trabeum . The wood resistance classification was made according to the ASTM D 2017-81 method. High variability on susceptibility to wood decay fungi was found. Their mean weight losses varied from 0.6% to 45.6%. Highly resistant species include: Astronium gracile , Bagassa guianensis , Caryocar villosum , Claricia racemosa , Diplotropis purpurea , Dipteryx odorata , Hymenaea courbaril , Manilkara huberi , Mezilaurus itauba , Sextonia rubra , Tabebuia incana, and Vatairea paraensis . The following wood species are less durable: Brosimum parinarioides , Jacaranda copaia , Laetia procera , Pouteria pachycarpa , Virola caducifolia , and Trattinnickia rhoifolia . Meruliporia incrassata caused extensive weight losses in most of the investigated Amazon wood species.

Thermal treatments of wood ( Fagus sylvatica and Fraxinus excelsior ) were examined. The temperature load on wood causes characteristic changes in the chemical composition, which were determined by means of several defined methods. The results confirm that in addition to the degradation of polyoses lignin, known as the thermally most stable compound, also shows significant thermal alterations. In addition, mechanical properties of the specimens were examined in order to correlate these results with the effects of chemical changes of thermally treated wood. It was shown, e.g., that the decomposition of the polyoses can affect the strength properties both positively and negatively.

SO 2 -ethanol-water (SEW) pulping is a promising fractionation process for lignocellulosics to produce pulp and value-added chemicals as a contribution to the concept of forest biorefinery. The presence of SO 2 leads to dissolution of hemicelluloses in high yield mostly as monomeric sugars, while lignin becomes soluble through sulfonation. After lignin removal, the dissolved sugars may be used as feedstock for fermentation to ethanol or butanol. SEW pulping may be considered a hybrid between solvent pulping (organosolv pulping by solvolysis) and acid sulfite pulping. Absence of an inorganic base leads to simplification of the recovery cycle. Furthermore, alcohol increases the impregnation rate of dissolved SO 2 into wood, so that a separate impregnation phase is not necessary. Also, the presence of SO 2 allows cooking of softwoods, while ethanol pulping is limited to hardwoods. Thus, SEW pulping may be applied to a wide variety of lignocellulosics at lower temperatures and similar cooking times than those used in kraft pulping. In the present study, SEW pulping experiments were performed on spruce chips at cooking temperatures of 135–165°C with a 12% SO 2 solution at a liquor-to-wood ratio of 6:1 l kg -1 . The effect of cooking temperature and time on kappa number, yield, and intrinsic viscosity of the pulp was determined. Based on these results, the kinetics of delignification, hemicelluloses removal, and cellulose hydrolytic destruction were established.

Chelation of thermomechanical pulp (TMP) was studied in this work. The desorption of Mn, Fe, and Mg due to their impact on peroxide bleaching was investigated. The desorption experiments were performed with EDTA, citric acid, oxalic acid, and formic acid as chelating agents at different pH. Chelation experiments with EDTA were carried out at pH 3–11. Sodium dithionite was used as the reducing agent in studying chelation with EDTA in a reducing environment. Mn was very effectively desorbed with EDTA from TMP at pH <10 and the reducing environment further improved the removal of all the studied metal ions from TMP with EDTA. Citric acid also removed Mn effectively from TMP at pH 5. The thermodynamic stability constants of different metal chelates do not present the correct picture of how strongly the metal ions are bound by the chelating agents in different conditions. But by means of the side reaction coefficients ( α M ( L ) -coefficients) it is also theoretically possible to evaluate and compare the real binding strengths between the metal ions and different chelating agents at varying pH values and other solution conditions. In this study, a theory is given for the calculation of side reaction coefficients. Values of the α M ( L ) -coefficients, for the pH range 0–14, are presented for EDTA, DTPA, and also for some other new potential environmentally friendly chelating agents.

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