Vibrational spectroscopy and X-ray diffraction methods to establish the differences between hardwood and softwood

FT-IR spectrometry and X-ray diffraction were applied to probe the differences between pulp fibers from Eucalyptus wood (hardwood) and Norway spruce wood (softwood). Wood processing was found to induce certain structural alterations within its components depending on the type of wood and the applied procedure. These differences were established by using techniques such as; spectral comparison of wood samples with those of individual component fractions, derivative spectroscopy, bands deconvolution, etc. FT-IR spectroscopy was shown to be an important tool that provided details about the structural characteristics of hardwood and softwood samples. Using second-derivative spectra and deconvolution processes small differences between spectra became apparent that allowed correlations to be made related to wood composition. In addition a correlation was established between the integral absorptions for the various bands and lignin content as well as the lignin/carbohydrate content. Relations between various spectral characteristics and the degree of crystallinity and sample composition were established.     

Investigation on the surface properties of chemically modified natural fibers using inverse gas chromatography

This paper presents the application of inverse gas chromatography (IGC) technique for characterization and comparison of the surface properties of the natural fibers as reinforcement fillers in wood plastic composites. The effects of chemical modification using 1% NaOH were also studied. The fibers used for this work were Iranian cultivated eucalyptus, spruce, bagasse, and wheat straw. Chemical composition of fibers was found to be modified after treatment as characterized by Fourier transform infrared spectroscopy (FTIR). The crystallinity of fibers and the specific interaction was improved by the alkaline treatment, with more relevance to the agro-fibers. The IGC shows also a general increase in the wettability of the modified fiber when compared with the raw (unmodified) samples. Alkaline treatment achieves the best overall improvement in the properties evaluated of the agro-fibers when compared to the wood fibers.     

Extraction of hemicellulosic oligosaccharides from spruce using microwave oven or steam treatment

This paper describes the extraction of hemicellulosic oligosaccharides from spruce, using microwave or steam treatment that can be used for the production of polymers, replacing fossil-based polymers, e.g., hydrogels. The highest yield of oligosaccharides, measured as mannan, was 70% obtained with treatment in the microwave oven at 200 degrees C for 5 min. The amount of oligosaccharides extracted was 12.5 g per 100 g of dry wood. The molecular weights of some selected samples were analyzed using fast protein liquid chromatography and size exclusion chromatography and time-of-flight matrix-assisted laser desorption ionization. Recovered oligosaccharides following steam treatment at 200 degrees C for 2 min had a mean molecular weight of 3400 g/mol with a maximum weight of 12000 g/mol. Higher severity, i.e., increased temperature (>200 degrees C) and residence time, resulted in lower mean molecular weights and yield. Oligosaccharides with higher mean molecular weights were obtained at lower severity, but the yield was considerably lower. The feasibility of using the extracted hemicellulosic oligosaccharides from spruce for the synthesis of hydrogels was demonstrated.     

In situ FT-IR microscopic study on enzymatic treatment of poplar wood cross-sections

The feasibility of Fourier transform infrared (FT-IR) microscopy to monitor in situ the enzymatic degradation of wood was investigated. Cross-sections of poplar wood were treated with cellulase Onozuka RS within a custom-built fluidic cell. Light-optical micrographs and FT-IR spectra were acquired in situ from normal and tension wood fibers. Light-optical micrographs showed almost complete removal of the gelatinous (G) layer in tension wood. No structural and spectral changes were observed in the lignified cell walls. The accessibility of cellulose within the lignified cell wall was found to be the main limiting factor, whereas the depletion of the enzyme due to lignin adsorption could be ruled out. The fast, selective hydrolysis of the crystalline cellulose in the G-layer, even at room temperature, might be explained by the gel-like structure and the highly porous surface. Young plantation grown hardwood trees with a high proportion of G-fibers thus represent an interesting resource for bioconversion to fermentable sugars in the process to bioethanol.     

Evaluation of the selectivity of white rot isolates using near infrared spectroscopic techniques

Seventeen isolates from white rotted beech wood and six strains from a local culture collection were evaluated for their capability to delignify beech and spruce wood selectively. Six peroxidase-positive isolates were found using a colorimetric agar plate test (Poly R-478), and genetically identified by their internal transcribed spacer (ITS1) or 28S rDNA sequences. Colonised on beech and spruce wood veneers, some of the peroxidase-positive isolates caused selective white rot on both wood species. Weight loss and lignin content of the degraded veneers were estimated from FT-NIR spectra with established linear regression models and multivariate models based on partial least squares regression (PLSR). Weight loss of the samples was also determined gravimetrically. A measure for the relative selectivity of the strains for lignin degradation was formulated and the values were calculated. Two strains that were identified as Oxyporus latemarginatus and Trametes cervina exhibited high selectivity on spruce wood, but the lignin content of the decayed wood was higher than that degraded by the reference strain Ceriporiopsis subvermispora. One strain – identified as Phlebia tremellosa – led to a lower lignin content of beech wood but caused also comparably high weight loss and thus exhibited an overall lower selectivity. The NIR spectroscopic method proved to be convenient for the quick screening of selective white rot fungi. Furthermore, the results revealed that high selectivity for lignin degradation is much more pronounced in early degradation stages.     

Selective extraction of hemicelluloses from spruce using switchable ionic liquids

Switchable ionic liquids (SILs) made from alcohols, either hexanol or butanol, and CO₂ together with an amidine (1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU)) were investigated as dissolution/fractionation solvents for wood material. Both native spruce (Picea abies), and pre-extracted spruce were treated with either butanol SIL (SIL1) or hexanol SIL (SIL2) for 5 days at 55 °C under normal pressure. The SILs were formed by bubbling CO₂ through an equimolar mixture of either 1-hexanol or 1-butanol and DBU. The viscosity of the mixture increased from 7.1 mPa s to 2980 mPa s for SIL2 and 5.1 to 1600 mPa s for SIL1. Melting points of the SILs 1 and 2 were at 8 and 14 °C, respectively. After the treatment time (5 days), the undissolved fraction contained 38 wt.% less hemicelluloses compared to native spruce. There was an increase in the glucose content of the milled spruce treated with both SILs, since the milling step reduced the cellulose crystallinity of the wood and facilitated an easier SIL access into the wood. The solvents were very neutral in terms of lignin removal. Consequently, only about 2% of the lignin was removed from native wood. Moreover, a priori removal of the wood extractives did not influence the lignin removal.     

Oligolignans in the wood of <Emphasis Type="Italic">Picea obovata</Emphasis> Ledeb.

We studied the chemical composition of the phenolic complex and the structure of oligomeric lignans in Siberian spruce (Picea obovata Ledeb.). We used the wood of Siberian spruce collected near the city of Irkutsk. The extractives were isolated from ground wood (particle size: 10–15 mm; humidity: 5.9%) by three-stage acetone extraction. The extract was separated by consecutive treatment with the solvents with increasing polarity: hexane, ethyl acetate and n-butanol. The main amount of phenolic compounds (lignans) was concentrated in the ethyl acetate fraction and it was 0.7% in absolutely dry wood (adw).The ethyl acetate fraction of spruce wood extract was separated by silica gel column; a chloroform-acetone mixture was used as the eluent (the concentration of acetone in the mixture was increased from 0 to 100%). Monomeric lignans (~60–65% of the ethyl acetate fraction of spruce wood extract), oligomeric lignans (~20–25%), and polymer lignans (~12–15%) were isolated.We also obtained ¹³C nuclear magnetic resonance (NMR) spectra for the main monomeric, oligomeric and polymeric lignan compounds of phenolic complexes. It was found that oligomeric and polymeric fractions contain monomeric lignan units with the butyrolactone cycle, primarily, the fragments with hydroxymatairesinol structure. Oligomeric lignans contain the fragments with a pinoresinol and lariciresinol structure. All the monomeric structural units are characterized by the guaiacyl substitution type of the aromatic cycles.A preliminary study has been performed on the antiviral and antioxidant activity of the ethyl acetate fraction of acetone extract of Siberian spruce wood. It was found that the lignan complex is active against Coxsackie B4 virus in cell culture and in the pancreatitis model in white mice, reducing the activity of enteroviruses in the cell culture approximately 100 times. The antioxidant activity rate of polyphenol complex of Siberian spruce wood is comparable to that of a known antioxidant dihydroquercetin.     

Evaluation of the selectivity of white rot isolates using near infrared spectroscopic techniques

Seventeen isolates from white rotted beech wood and six strains from a local culture collection were evaluated for their capability to delignify beech and spruce wood selectively. Six peroxidase-positive isolates were found using a colorimetric agar plate test (Poly R-478), and genetically identified by their internal transcribed spacer (ITS1) or 28S rDNA sequences. Colonised on beech and spruce wood veneers, some of the peroxidase-positive isolates caused selective white rot on both wood species. Weight loss and lignin content of the degraded veneers were estimated from FT-NIR spectra with established linear regression models and multivariate models based on partial least squares regression (PLSR). Weight loss of the samples was also determined gravimetrically. A measure for the relative selectivity of the strains for lignin degradation was formulated and the values were calculated. Two strains that were identified as Oxyporus latemarginatus and Trametes cervina exhibited high selectivity on spruce wood, but the lignin content of the decayed wood was higher than that degraded by the reference strain Ceriporiopsis subvermispora. One strain – identified as Phlebia tremellosa – led to a lower lignin content of beech wood but caused also comparably high weight loss and thus exhibited an overall lower selectivity. The NIR spectroscopic method proved to be convenient for the quick screening of selective white rot fungi. Furthermore, the results revealed that high selectivity for lignin degradation is much more pronounced in early degradation stages.     

Cell-specific chemotyping and multivariate imaging by combined FT-IR microspectroscopy and orthogonal projections to latent structures (OPLS) analysis reveals the chemical landscape of secondary xylem

Fourier‐transform infrared (FT‐IR) spectroscopy combined with microscopy enables chemical information to be acquired from native plant cell walls with high spatial resolution. Combined with a 64 × 64 focal plane array (FPA) detector, 4096 spectra can be simultaneously obtained from a 0.3 × 0.3 mm image; each spectrum represents a compositional and structural ‘fingerprint’ of all cell wall components. For optimal use and analysis of such a large amount of information, multivariate approaches are preferred. Here, FT‐IR microspectroscopy with FPA detection is combined with orthogonal projections to latent structures discriminant analysis (OPLS‐DA). This allows for: (i) the extraction of spectra from single cell types, (ii) identification and characterization of different chemotypes using the full spectral information, and (iii) further visualization of the pattern of identified chemotypes by multivariate imaging. As proof of concept, the chemotypes of Populus tremula xylem cell types are described. The approach revealed unknown features about chemical plasticity and patterns of lignin composition in wood fibers that would have remained hidden in the dataset with traditional data analysis. The applicability of the method to Arabidopsis xylem and its usefulness in mutant chemotyping is also demonstrated. The methodological approach is not limited to xylem tissues but can be applied to any plant organ/tissue also using other techniques such as Raman and UV microspectroscopy.     

Probing DNA quaternary ordering with circular dichroism spectroscopy: Studies of equine sperm chromosomal fibers

Studies are described which strongly support a cholesteric liquid crystal-like quaternary structure for the DNA molecules of a biologically native chromosomal preparation from equine sperm cells. Discrete chromosomal fibers released from the head pieces of equine spermatozoon cells were prepared intact and probed for liquid crystalline ordering using reflectance and linear dichroism spectroscopy. Assuming cholesteric liquid crystalline order for the DNA molecules within the chromatin fibers, parameters measured experimentally were used to calculate the circular dichroism (CD) of the fibers. The calculated results compare remarkably well with the experimentally measured CD of the sperm chromosomal fibers and suggest a specific cholesteric liquid crystal-like quanternary structural ordering of DNA molecules in equine sperm chromatin fibers. The potential of CD spectroscopy as a tool for the study of long-range ordering of macromolecules is discussed.     

Molecular changes during tensile deformation of single wood fibers followed by Raman microscopy

Raman spectra were acquired in situ during tensile straining of mechanically isolated fibers of spruce latewood. Stress-strain curves were evaluated along with band positions and intensities to monitor molecular changes due to deformation. Strong correlations (r = 0.99) were found between the shift of the band at 1097 cm(-1) corresponding to the stretching of the cellulose ring structure and the applied stress and strain. High overall shifts (-6.5 cm(-1)) and shift rates (-6.1 cm(-1)/GPa) were observed. After the fiber failed, the band was found on its original position again, proving the elastic nature of the deformation. Additionally, a decrease in the band height ratio of the 1127 and 1097 cm(-1) bands was observed to go hand in hand with the straining of the fiber. This is assumed to reflect a widening of the torsion angle of the glycosidic C-O-C bonding. Thus, the 1097 cm(-1) band shift and the band height ratio enable one to follow the stretching of the cellulose at a molecular level, while the lignin bands are shown to be unaffected. Observed changes in the OH region are shown and interpreted as a weakening of the hydrogen-bonding network during straining. Future experiments on different native wood fibers with variable chemical composition and cellulose orientation and on chemically and enzymatically modified fibers will help to deepen the micromechanical understanding of plant cell walls and the associated macromolecules.     

On the Lamellar Structure of the Tracheid Cell Wall

Abstract: It is clear that cross sections of wood cells show a lamellar structure. This paper investigates the orientation of this lamellar structure of spruce (Picea abies) tracheids using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross sections of spruce wood were produced through fracturing in longitudinal bending and tensile testing. When investigated with SEM, the fracture surfaces show a structure of mostly larger radial lamellae, in the order of 30 - 100 nm, i.e., agglomerations of a few cellulose aggregates. Thin transverse sections of the fracture zones investigated with atomic force microscopy show concentric lamellae with a width in the order of a single cellulose aggregate, i.e., 15 - 25 nm. No structural connection to the splinters in the radial direction can be seen. It is suggested that the radial lamellar structure is a consequence of the energy released during fracturing of the wood samples and that the undistorted wood has a concentric lamellar structure on a smaller structural level.     

Use of NIR and pyrolysis-MBMS coupled with multivariate analysis for detecting the chemical changes associated with brown-rot biodegradation of spruce wood

Near infrared (NIR) spectroscopy and pyrolysis-molecular beam mass spectrometry (py-MBMS) analysis can be used in conjunction with multivariate regression and principal components analysis to differentiate brown-rot-degraded wood from non-degraded spruce and to follow the temporal changes in wood undergoing brown-rot degradation. Regression of NIR test results vs. percent weight loss for Postia placenta- and Gloeophyllum trabeum-infected spruce wood blocks yielded a correlation coefficient of 0.96. Regression of MBMS test results for the same samples yielded a correlation coefficient of 0.96. Principle components analysis was used to differentiate non-infected wood and P. placenta- and G. trabeum-infected wood. These techniques may be used to detect different types of biodegradation and to develop a better understanding of the chemical changes that the wood undergoes when it is subjected to brown-rot biodegradation.     

Analysis of the surfaces of wood tissues and pulp fibers using carbohydrate-binding modules specific for crystalline cellulose and mannan

Carbohydrate binding modules (CBMs) are noncatalytic substrate binding domains of many enzymes involved in carbohydrate metabolism. Here we used fluorescent labeled recombinant CBMs specific for crystalline cellulose (CBM1(HjCel7A)) and mannans (CBM27(TmMan5) and CBM35(CjMan5C)) to analyze the complex surfaces of wood tissues and pulp fibers. The crystalline cellulose CBM1(HjCel7A) was found as a reliable marker of both bacterially produced and plant G-layer cellulose, and labeling of spruce pulp fibers with CBM1(HjCel7A) revealed a signal that increased with degree of fiber damage. The mannan-specific CBM27(TmMan5) and CBM35(CjMan5C) CBMs were found to be more specific reagents than a monoclonal antibody specific for (1-->4)-beta-mannan/galacto-(1-->4)-beta-mannan for mapping carbohydrates on native substrates. We have developed a quantitative fluorometric method for analysis of crystalline cellulose accumulation on fiber surfaces and shown a quantitative difference in crystalline cellulose binding sites in differently processed pulp fibers. Our results indicated that CBMs provide useful, novel tools for monitoring changes in carbohydrate content of nonuniform substrate surfaces, for example, during wood or pulping processes and possibly fiber biosynthesis.     

The preparation of lignocellulosic aerogels from ionic liquid solutions

Nanofibrillar aerogels were prepared from cellulose, spruce wood and from mixtures of cellulose, lignin and xylan. The lignocellulosic polymers were first dissolved in an ionic liquid and coagulated from solution by adding aqueous ethanol. The obtained gel was washed with ethanol and liquid carbon dioxide and finally dried by releasing the carbon dioxide from the porous structure at supercritical temperature to obtain the aerogel. The bulk densities of the biopolymer aerogels ranged from 25 to 114 g/l and the internal surface areas (BET) from 108 to 539 m²/g depending on the biopolymer mix and on the polymer concentration in the ionic liquid solution. All aerogels were compressible and consisted of nanofibrillar biomaterial network with open-pore structure.     

MALDI-TOF mass spectrometry and PSD fragmentation as means for the analysis of condensed tannins in plant leaves and needles

MALDI-TOF mass spectrometry and 13C NMR spectroscopy were applied to unveil typical characteristics of condensed tannins of leaves and needles from willow (Salix alba), spruce (Picea abies) and beech (Fagus sylvatica) of three tree species that are ubiquitous in German forests and landscapes. For further evaluation, lime (Tilia cordata) was included. The 13C NMR spectroscopy confirmed the purity of the condensed tannin fractions and the efficiency of the procedure used for their extraction. While signals representative for procyanidin units are observable in all liquid-state 13C NMR spectra, resonance lines of prodelphinidin were only detected in those obtained from the condensed tannins of spruce needles and beech leaves. Typical signals in the chemical shift region between 70 and 90 ppm demonstrated the presence of stereoisomers (catechin/epicatechin; gallocatechin/ epigallocatechin). The MALDI-TOF mass spectra of the condensed tannins show signals of polymers of up to undecamers. Supporting the observations from the NMR spectroscopy, the mass spectra of the willow and lime leaf condensed tannins were identified as polymers with mainly procyanidin units, while the polymers of the spruce needle and beech leaves exhibit varying procyanidin/prodelphinidin ratios. Post source decay (PSD) fragmentation lead to a sequential loss of monomers and allowed a detailed characterization and sequencing of individual chains. In the case of the condensed tannins of lime this technique clearly excludes a pelargonidin terminal unit followed by a prodelphinidin unit, which would result in the same molecular masses as a polymer solely built up of procyanidin units.     

Cationic-modified PVA as a dry strength additive for rice straw fibers

Extensive research has shown that non-wood fibers are able to be substituted for wood fibers. The major shortcoming of non-fibers is their high silica content that causes some operational problems in mills, and hence silica should be kept in pulps. By keeping silica in pulps, however, the mechanical properties of papers are reduced, and a dry strength additive may be required. In this study, cationic polyvinyl alcohols (C-PVA) with two different molecular weights were prepared, and employed as dry strength additives. The adsorption of polymers on rice straw fibers obtained via soda-air-anthraquinone (AQ) pulping under various conditions was investigated thoroughly. Convincing results demonstrated that high molecular weight polymers performed more efficiently on dry strength enhancements of papers, while they adsorbed less than lower molecular weight polymers on fibers. However, the stiffness of fibers was increased to a larger extent by applying a higher molecular weight C-PVA.     

Hierarchical structure of juvenile hybrid aspen xylem revealed using X-ray scattering and microtomography

X-ray scattering and microtomography (μCT) are useful techniques to reveal the structure of wood at the nano- and micrometer scales. The nanostructure of xylem in greenhouse-grown 2.5- to 3.5-month-old Populus tremula L.?×?tremuloides Michx. trees was characterized using wide-angle X-ray scattering (WAXS), and the cellular structure was investigated using μCT. For comparison, the nanostructure of wood in 2-year-old silver birch, Norway spruce and Scots pine saplings was determined. Based on the μCT results, the lengths of fiber lumina of the hybrid aspen saplings were shorter than any previous results on the lengths of wood fibers. The mean microfibril angles of the hybrid aspen saplings were significantly lower (8°–14°) than those of the birch, spruce and pine saplings (27°–35°) implicating that cellulose microfibrils were oriented nearly parallel to the cell axis in the young hybrid aspen saplings. Hybrid aspen saplings were found to contain tension wood based on the histochemical analysis and μCT images. However, typical tension wood properties, i.e. larger crystallite width and higher crystallinity than in normal wood, were detected only in a few hybrid aspen samples, while in most of the hybrid aspen saplings, the crystallite widths (3.0?±?0.1?nm) and the crystallinities (30?±?5?%) corresponded to those of normal wood. The deformations of cellulose crystallites were determined using WAXS in situ upon dehydration of the never-dried samples. In all the species studied, the cellulose unit cell dimension decreased and disorder of cellulose chains increased parallel to the chains upon drying. Also, the transverse disorder of chains increased in birch, spruce and pine, while no changes were detected in this direction in hybrid aspen. The crystallite widths and drying deformation results might indicate that the gelatinous layer has not fully developed in the young hybrid aspen saplings.     

Qualitative and quantitative changes of beech wood degraded by wood-rotting basidiomycetes monitored by Fourier transform infrared spectroscopic methods and multivariate data analysis

Beech wood (Fagus sylvatica L.) veneers were cultivated with white and brown rot fungi for up to 10 weeks. Fungal wood modification was traced with Fourier transform near infrared (FT-NIR) and Fourier transform mid infrared (FT-MIR) methods. Partial least square regression (PLSR) models to predict the total lignin content before and after fungal decay in the range between 17.0% and 26.6% were developed for FT-MIR transmission spectra as well as for FT-NIR reflectance spectra. Weight loss of the decayed samples between 0% and 38.2% could be estimated from the wood surface using individual PLSR models for white rot and brown rot fungi, and from a model including samples subjected to both degradation types.     

Wood Chemical Composition in Species of Cactaceae: The Relationship between Lignification and Stem Morphology

In Cactaceae, wood anatomy is related to stem morphology in terms of the conferred support. In species of cacti with dimorphic wood, a unique process occurs in which the cambium stops producing wide-band tracheids (WBTs) and produces fibers; this is associated with the aging of individuals and increases in size. Stem support and lignification have only been studied in fibrous tree-like species, and studies in species with WBTs or dimorphic wood are lacking. In this study, we approach this process with a chemical focus, emphasizing the role of wood lignification. We hypothesized that the degree of wood lignification in Cactaceae increases with height of the species and that its chemical composition varies with wood anatomy. To test this, we studied the chemical composition (cellulose, hemicellulose, and lignin content) in 13 species (2 WBTs wood, 3 dimorphic, and 8 fibrous) with contrasting growth forms. We also analyzed lignification in dimorphic and fibrous species to determine the chemical features of WBTs and fibers and their relationship with stem support. The lignin contents were characterized by Fourier transform infrared spectroscopy and high performance liquid chromatography. We found that 11 species have a higher percentage (>35%) of lignin in their wood than other angiosperms or gymnosperms. The lignin chemical composition in fibrous species is similar to that of other dicots, but it is markedly heterogeneous in non-fibrous species where WBTs are abundant. The lignification in WBTs is associated with the resistance to high water pressure within cells rather than the contribution to mechanical support. Dimorphic wood species are usually richer in syringyl lignin, and tree-like species with lignified rays have more guaiacyl lignin. The results suggest that wood anatomy and lignin distribution play an important role in the chemical composition of wood, and further research is needed at the cellular level.