Band 64, Heft 2

Manganese peroxidase (MnP) is the main enzyme implicated in the biobleaching of kraft pulps by white-rot fungi. However, potential commercial applications of this enzyme have been limited by its availability in large quantities. Advances have been made to produce high-yield concentrated recombinant MnP (rMnP). The objective of this study was to evaluate the ability of rMnP to delignify and brighten kraft pulps. The rMnP, produced from the yeast Pichia pastoris – in high-cell density and in fed-batch fermentations – was found to be effective in lignin removal in both hardwood and softwood unbleached kraft pulps. The rMnP applied at 30 U g -1 pulp for 24 h followed by alkali extraction caused significant kappa number reductions for all the pulps tested with different initial lignin contents and structures. Softwood and hardwood pulps showed similar delignification rates during rMnP treatments. Highly delignified pulps with kappa number less than 10 are less susceptible to delignification by rMnP compared with the pulps with higher lignin content. The rMnP-treated pulp was also shown to be more susceptible to subsequent peroxide bleaching compared with the control pulp. More than 60% of the kappa number reduction was achieved by sequential rMnP treatments combined with alkaline extraction. Sequential treatment with xylanase and rMnP also resulted in more extensive delignification than in each enzyme treatment alone or in the case of simultaneous application of the enzymes.

The recombinant manganese peroxidase (rMnP) produced from the yeast Pichia pastoris has been investigated in totally chlorine free (TCF) and elemental chlorine free (ECF) bleaching sequences for improving the bleachability of kraft pulps. In TCF bleaching, oxygen delignified hardwood kraft pulp was treated with rMnP, followed by a sequence combining a chelating and alkaline peroxide bleaching stage. The inclusion of the enzymatic treatment significantly improved the pulp brightness to a level that is difficult to obtain by chemical bleaching alone. Furthermore, the treatment with rMnP resulted in energy savings during pulp refining with PFI mill with a slight improvement in pulp strength properties such as tensile index and burst index. In ECF bleaching, a significant reduction in chlorine dioxide consumption was obtained. A three-stage rMnP treatment combined with alkaline extraction, followed by DED bleaching sequence for hardwood kraft pulp (HWKP) or DEDED bleaching sequence for softwood kraft pulp (SWKP), reduced the total effective chlorine by 41% and 32% for HWKP and SWKP, respectively, compared with the conventional bleaching sequences without enzymatic treatment. The strength properties of the enzyme-treated pulp were also slightly better than that of the control pulp. Further reductions in the consumption of total effective chlorine were obtained when a xylanase pretreatment was incorporated into the bleaching sequence before the repeated rMnP treatment.

The concentration of the hydroxyl radical generated during oxygen delignification was measured with a radical trapping agent. The N,N′-(5-nitro-1,3-phenylene)-bisglutaramide (NPG) was found to be effective but the experiments revealed that at pH higher than 11.5 the anionic form of hydroxyl radical – the oxyl anion radical – causes up to four times more chain cleavage than the hydroxyl radical. It was also found that the effect of both radicals in the pulp moderated at higher partial oxygen pressure and in the presence of hemicelluloses. The implications are that selectivity can be improved by maintaining a moderate alkaline pH profile, increasing the oxygen partial pressure, and retaining hemicelluloses in the brownstock.

The thermal degradation products of 1-alkyl-3-methyl-imidazolium-type ionic liquids (e.g., BMIM, EMIM), which are commonly used in cellulose chemistry, were identified. Imidazole ( 5 ), N -methylimidazole ( 6 ), and N -alkylimidazoles ( 7 , 8 ) are the main products. Moreover, dimeric substituted imidazoles ( 9 – 11 ) were found carrying a methylene bridge formed from the N -methyl structure. The former 1-alkyl group (butyl or ethyl) was not present in any of the dimeric compounds. The N -methylene intermediate (12) acts as a precursor for the substituted imidazoles linked by a methylene group. All thermal degradation products are bases and catalyze the previously described reaction between the reducing end of celluloses and 1-alkyl-3-imidazolium cations. To minimize this side reaction, ionic liquids have to be liberated from such basic compounds prior to application as cellulose solvents. In this regard, the usage of “recycled” (and unpurified) ionic liquids has to be treated with caution.

The thermal expansion behavior of tension wood cellulose obtained from Populus maximowiczii A. Henry was investigated by synchrotron X-ray fiber diffraction at temperatures ranging from 100 to 300 K. Three equatorial and one meridional d -spacings indexed as , 110, 200, and 004 showed a gradual linear increase with increasing temperature. Unit-cell parameters calculated from the changes in these d -spacings showed anisotropic thermal expansion behavior in the three axial directions related to the crystal structure and hydrogen-bonding system of cellulose I β . The linear thermal expansion coefficients (TECs) of the a -, b -, and c -axes were: α a =5.2×10 -5  K -1 , α b =2.1×10 -5  K -1 , and α c =0.4×10 -5  K -1 , respectively. The volume TEC was β =7.8×10 -5  K -1 , which was approximately 70% of previously reported values in the high-temperature region from room temperature to 250°C.

Horseradish peroxidase (HRP)-catalyzed dehydrogenative polymerization of guaiacyl (G) and syringyl (S)-type monolignol γ- O -glucosides, isoconiferin (iso-G) and isosyringin (iso-S), which contain a hydrophilic glucosyl unit on γ-position of coniferyl alcohol and sinapyl alcohol, respectively, was monitored by gel permeation chromatography coupled with photodiode array detection (GPC-PDA). Contrary to the conventional dehydrogenative polymerization of monolignols, the polymerization of the glycosides produces water-soluble synthetic lignins (DHPs) in a homogeneous aqueous phase. Taking advantage of this unique reaction system, the method was developed to follow the changes of molecular weights in the course of DHP formations. Moreover, PDA detection permits determination of oligomeric S-type quinone methide intermediates (QMs) formed as stable transient compounds during polymerization of iso-S. A detailed comparison of the polymerization profiles revealed entirely different behaviors of G- and S-type monomers. The data strongly support the view that the low reactivity of oligomeric S-type QMs impedes the formation of DHPs from S-type monomers. In copolymerization of G- and S-type monomers, it is conceivable that G-type phenolic hydroxyl groups serve as good nucleophilic reactants to scavenge S-type QMs resulting in efficient production of DHPs. As a consequence, the present approach can be a powerful tool to study the in vitro dehydrogenative polymerization providing further mechanistic insights into lignin polymerization in vivo .

The solvent pH effect in the horseradish peroxidase (HRP)-catalyzed polymerization of sinapyl alcohol (S-alc) and analogously, sinapyl alcohol γ- O -glucoside (isosyringin, iso-S) was investigated particularly focusing on the behavior of syringyl-type quinone methide intermediates (S-type QMs) under acidic conditions. At first, the HRP-catalyzed polymerization of iso-S at pH 6.5–2.5, which produces water-soluble dehydrogenation polymer (DHP) intermediates in a homogeneous phase, was monitored by UV spectroscopy and gel permeation chromatography with photodiode array detection (GPC-PDA). Under acidic conditions at pH below 4.5, unstablilized S-type QMs from iso-S are rapidly quenched resulting in efficient productions of DHPs, although substantial loss of HRP activity and the resulting insufficient polymerization were inevitable at pH below 3.5. In addition, it was found that a small addition of guaiacyl-type comonomer (isoconiferin, iso-G) effectively promotes the polymerization of iso-S under acidic conditions, in which the comonomer serves as a radical mediator to facilitate the HRP-catalyzed oxidations of iso-S. Next, the HRP-catalyzed polymerization of S-alc at various pH values was conducted and the resulting DHPs were characterized by GPC and NMR measurements. The yields of isolated DHPs significantly increased as solvent pH decreased below 4.5. The structural analyses of the DHPs demonstrated that reaction selectivity of S-type QMs during the polymerization drastically changed at pH below 4.5: they react efficiently with water molecules as solvent leading to the formation of benzyl alcohol type β-O-4 substructures preferentially to the formation of α-O-aryl type substructures. Consequently, the data in this study demonstrated that acidic conditions at pH below 4.5 are favored in the dehydrogenative polymerization of S-alc from the viewpoint of the reactivity of S-type QMs.

Functional properties of technical lignins need to be characterized in more detail to become a higher added value renewable raw material for the chemical industry. The suitability of a lignin from different plants or trees obtained by different technical processes can only be predicted for selected applications, such as binders, if reliable analytical data are available. In the present paper, structure dependent properties of four industrial lignins were analyzed before and after successive organic solvent extractions. The lignins have been fractionated according to their molar mass by these solvents extractions. Kraft and soda lignins were shown to have different molar mass distributions and chemical compositions. Lignin carbohydrate complexes are most recalcitrant for extraction with organic solvents. These poorly soluble complexes can consist of up to 34% of carbohydrates in soda lignins. Modeling by principle component analysis (PCA) was performed aiming at prediction of the application potential of different lignins for binder production. The lignins and their fractions could be classified in different clusters based on their properties, which are structure dependent. Kraft softwood lignins show the highest potential for plywood binder application followed by hardwood soda lignin and the fractions of Sarkanda grass soda lignin with medium molar mass. Expectedly, the softwood lignins contain the highest number of reactive sites in ortho positions to the phenolic OH group. Moreover, these lignins have a low level of impurities and medium molar mass.

The activation parameter developed is based on the fiber wall thickness distribution, fiber curl distribution, and water retention value of the unrefined fibers. The mechanical properties of paper that contain chemical pulp depend, among other things, on the free fiber segment activation between fiber-fiber crossings that is created during drying. Experimental data revealed that the degree of fiber swelling is responsible together with the fiber shape factor (curl) and fiber wall thickness for the extent of fiber network activation. The amount of bonding between fibers also affects fiber segment activation. Based on the experimental data, it was deduced that interfiber bonding ability of fibers, characterized as the water retention value, was mainly responsible for the development of handsheet density. Tensile index development was more affected by the morphology of fibers, which was the main determinant for high activation potential of fibers. Factor analysis was used to identify the main causes of variation for a refining data set of 20 Eucalyptus grandis samples. Three independent descriptors were found to be responsible for the majority of the variation: the bonding and activation factor, the factor of microcompressions, and the factor of fiber wall thickness and fiber curl. The activation parameter developed in this study can be used to determine the effect of fiber segment activation and inter-fiber bonding on the inplane mechanical properties of paper.

Wallaba ( Eperua falcata ) is a tropical wood that is known to have naturally high moisture related dimensional stability. Samples of wallaba heartwood were subjected to differential solvent extraction. Wood pieces that were extracted with methanol showed significantly greater swelling following rehydration from oven dry to 96% relative humidity than non-extracted samples and samples extracted with other solvents. Methanol soluble wallaba heartwood extract was purified by HPLC and the compounds present were characterized by NMR spectroscopy. The structure of 13 compounds in methanol extract was identified. The relative proportion of polar compounds in methanol extract was found to be high. The compounds identified are proposed to bind to the polymeric cell wall by means of multiple hydrogen bonds restricting the association of water and therefore act as natural anti-swelling agents.

The insulation corkboard production generates black condensate (BC), a paste-like solid waste. It is hydrophobic and has the potential to be used as protective coating. To evaluate this potential, coatings were prepared from BC extracts and their surface behavior was evaluated by contact angle (CA) measurements. The CA dynamics were recorded as a function of time; advancing CAs were also registered; the approaches were applied according to Fowkes, Owens-Wendt-Rabel-Kaelble (OWRK), and Van Oss to determine the surface energy (SE) for each coating. Depending on the liquid probe, three phenomena were observed: water evaporation, diiodomethane diffusion into the coating, and rearrangement of the chemical groups on the coating surface, when glycerol was dropped onto the surface. Based on the results from the CA dynamics, the applicability of the coatings against hydrophobic environments was limited owing to its affinity to apolar compounds. The results show that the coating prepared by the toluene BC extract was the best coating. The key data were: water CA of 99.3°, total SE (between 37.4 mN m -1 and 40.1 mN m -1 ), SE polar component (0.1 mN m -1 ), and the acidic and basic characters were negligible. It can be concluded that the BC extracts have potential for coatings.

The effects of helium dielectric barrier discharge (He-DBD) plasma treatment has been studied aiming at the preparation of wood for profitable dye covering and impregnation with an antibacterial oil. Electrical and optical emission spectroscopy measurements were performed to characterise the He-DBD discharge. The hydrophilic/hydrophobic properties of the modified surfaces were studied by dynamic contact angle measurements. The spreading area of the wet spots was also evaluated as a function of wetting time. After He-DBD plasma exposure, the adhesion properties are substantially improved and the hydrophilic character of wood surface is enhanced. The behaviour of linseed oil drops on the modified surfaces confirmed the utility of He-DBD treatment.

Thermoplastic molding has been prepared from beech wood flour steamed at 180°C or at higher temperatures without any additives. It exhibited a smooth and lustrous surface and had a high density of approximately 1.45 g cm -3 . The internal structure of molding revealed that the flour particles were completely surrounded by black resin-like substance which was thermoplasticized by heat and pressure during the molding process. The chemical composition of the steamed flour and physical properties of molding were examined as a function of steaming temperature. Maximum bending strength and Young's modulus of molding reached 63 MPa and 11 GPa, respectively, at 180°C of steaming, which were much higher than those of a hardboard. The water absorption of the molding was 8% or less and decreased with the steaming temperature.

The aim of the present investigation was to evaluate the influence of a thermal modification on the kinetics of the water vapour sorption of maple ( Acer pseudoplatanus L.) and spruce [ Picea abies (L.) Karst.] based on the assumption that the Fickian equation can be applied in this regard in the first approximation. The unsteady-state sorption process between two equilibria of humidity was modelled as a diffusion process. The rate of sorption was recorded by the gravimetric method, and then the diffusion coefficient was determined through inverse parameter identification. The thermal modification leads to an alteration of the unsteady sorption behaviour of both wood species. Transport of water vapour decreases with increasing degree of modification. Depending on wood moisture, the trends of diffusion coefficients include all three levels of modification. Furthermore, the diffusion coefficients decrease when the thickness of specimens decreases. The calculated diffusion coefficients showed a length dependency both for unmodified and thermally modified spruce and maple. Accordingly, the results clearly show that these woods have a non-Fickian moisture transport behaviour. The results are nevertheless useful for comparative purposes.

To prevent deformation and cracking of waterlogged archaeological wood, polyethylene glycol (PEG) as a bulk impregnation agent is commonly applied. PEG maintains the wood in a swollen state during drying. However, swelling of wood can reduce its mechanical properties. In this study, the cellular structure of oak and cell wall swelling was characterized by scanning electron microscopy (SEM) of transverse cross-sections, and the microfibril angle of oak fibers was determined by wide angle X-ray scattering (WAXS). Samples of recent European oak ( Quercus robur L) impregnated with PEG (molecular weight of 600) were tested in axial tension and radial compression. Mechanical tests showed that axial tensile modulus and strength were only slightly affected by PEG, whereas radial compressive modulus and yield strength were reduced by up to 50%. This behavior can be explained by the microstructure and deformation mechanisms of the material. Microfibril angles in tensile test samples were close to zero. This implies tensile loading of cellulose microfibrils within the fiber cell walls without almost any shear in the adjacent amorphous matrix. These results are important because they can help separate the impact of PEG on mechanical properties from that of chemical degradation in archaeological artifacts, which display only small to moderate biological degradation.

Optical appearance is an important aesthetic property of wood, and this unique visual characteristic needs to be described quantitatively for many industrial applications. The objective of this study is to demonstrate the change in appearance of lumber surfaces from the viewpoint of human observation. Ten different specimens of coated and uncoated fancy veneer overlaid plywood of four species and solid and print Sugi (Japanese cedar) boards were prepared. For observation purposes, a simple goniophotometric device was constructed. A series of digital images of each specimen was taken, whereas the surface was illuminated from various lighting azimuths. The images were evaluated by subtraction, correlation, and multiresolution contrast analyses. The first two methods detect reflection anisotropy on the specimen surface through comparison of two images. Subtraction analysis also distinguishes between the coated and uncoated surfaces. However, it is difficult to determine the difference between the solid and print Sugi specimens based on these techniques. By contrast, multiresolution contrast analysis renders possible evaluation of the size and degree of the change in the surface appearances by contrast values. By comparing the contrast values for every lighting azimuth and filter size, this analysis clearly determines the change in appearance peculiar to wood, such as reflection anisotropy, improvement in reflectiveness conferred by coating, and the difference between the solid and print Sugi specimens.

Two-dimensional T 1 - T 2 1 H NMR relaxation correlation spectra and T 2 - T 2 relaxation exchange spectra for samples of spruce wood across the full moisture content range from 0% to >100% are presented. The T 1 - T 2 spectra unambiguously identify water in different environments within the wood that overlap in the corresponding and more traditional one-dimensional T 1 or T 2 experiment. The T 2 - T 2 spectra unambiguously reveal the presence of water exchange between the lumen and cell wall above the fibre saturation point in sapwood. An estimate is made of the exchange rate: 1/30 to 1/3 ms -1 .

When a log is sawn along the length, an outward bending or deflection of two half rounds arises from the release of growth stresses in the log. The relationship between this outward bending and the peripheral longitudinal growth strain in logs from a 10-year-old Eucalyptus nitens plantation was investigated. In total, 63 trees were felled and two logs (one bottom and an upper log) were cut from each felled tree. A strong association was observed between the measured longitudinal growth strain and the outward bending produced by splitting the log along its axis. A mathematical model was developed that enables calculation of the relationship between the surface axial growth stress and the opening of the split log. This involves calculation of the lateral deflection of a tapered cantilever beam of semi-circular cross-section under a known bending moment. The relationship between the opening of the slit log and the surface axial stress showed good agreement with the measured data on 126 logs. The model equation is effective in predicting the growth stress from the magnitude of the log distortion. This log sawing or splitting method is quick and reliable for assessing the surface growth stresses in small diameter trees. It could have potential in breeding programs for identifying families or clones for low-growth stresses of superior eucalypts for sawn timber production.

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