Volume 63, Issue 5

The mechanical and physical properties of wood fibres depend to a large extent on the orientation of the polymers, mainly the cellulose microfibrils, within the supramolecular structure of the cell wall. Under moist conditions, the arrangement within the polymer matrix may play a dominant role for mechanical properties in general and, especially, in the transverse direction. In this context, it is of special interest to determine the orientation of glucomannan and xylan, being the essential components of softwood hemicelluloses, and of lignin in wood fibres. Fourier transform infrared (FTIR) microscopy was used to examine the orientation of the main wood polymers in transversal and longitudinal direction of spruce fibres. We investigated fibres made from a thermomechanical pulp, in which the outer fibre wall layers were removed by mechanical action, and chemically delignified fibres. The polarised FTIR measurements indicated that glucomannan and xylan appear to have a parallel orientation with regard to the orientation of cellulose and, in all probability, an almost parallel orientation with regard to the fibre axis. Lignin was found to be less oriented in the fibre wall, although its arrangement is not fully isotropic. In the longitudinal direction of the fibres, there were no significant changes in the molecular orientation of the studied polymers.

Annual plant pulping is faced with serious challenges. Traditional pulping processes with bleaching in chlorine based sequences and without appropriate chemical recovery system cannot be tolerated anymore. Alternative pulping processes with non-conventional chemicals, such as organic solvents, e.g., monoethanolamine (MEA), might be suited for an environmentally sound process with a closed mill system. Thus, pulping of wheat straw with MEA as the main delignifying agent was investigated in comparison to soda and soda/AQ pulps as references. The main focus was placed on reduction of the cooking temperature in order to avoid heat-induced MEA degradation. The temperature was reduced stepwise from 165°C to 130°C. At 150°C, a sufficient delignification was achieved. MEA was partly substituted by water and the resulting decrease of the delignification rate could be compensated by addition of anthraquinone (AQ). After optimization of the process, a pulp with a kappa number of 17 was obtained at a total yield of 56% based on o.d. straw. This pulp was selected for bleaching. Both, O/Q/OP/DQ/P (“ECF light”) and O/Q/OP/ZQ/P (TCF Z ) bleaching were applied. NaOH was substituted by MEA as alkali source in the oxygen delignification stage. Up to 50% delignification rate was achieved under these moderate conditions. In the ECF light bleaching sequence, a brightness of 80% ISO was reached at a kappa number level below 3. In TCF Z bleaching, an even somewhat higher brightness was achieved at a kappa number level below 1. A yield of fully bleached screened pulp of around 50% (based on o.d. straw) was obtained. The strength properties of the MEA pulp were improved after bleaching. ECF bleaching resulted in slightly better pulp strengths than the TCF Z alternative. MEA forms in combination with water and AQ a very selective pulping system providing effective delignification and maintaining extremely high yields. MEA/water/AQ pulping should be regarded as a serious, environmentally friendly alternative to soda or soda/AQ pulping to produce high-quality pulp from wheat straw.

The production of ethanol based on lignocellulosic materials will bring about the coproduction of significant amounts of under-utilized lignin. This study examines the potential of conventional heterogeneous and novel homogeneous catalysts for the selective cleavage of the aryl-O-aryl and aryl-O-aliphatic linkages of ethanol organosolv lignin to convert it from a low grade fuel to potential fuel precursors or other value added chemicals. The development of hydrogenolysis conditions that effectively increase the solubility of lignin were initially examined with Ru(Cl) 2 (PPh 3 ) 3 and demonstrated the ability to decrease the molecular weight and enhance the solubility of the lignin polymer. Later studies examined several heterogeneous and homogeneous hydrogenation catalysts at optimized reaction conditions resulting in 96.4% solubility with Ru(Cl) 2 (PPh 3 ) 3 , increase in H/C ratio with Raney-Ni, Pt/C and extensive monomer formation with NaBH 4 /I 2 . The changes in molecular structure of lignin were followed by size exclusion chromatography, qualitative and quantitative NMR spectroscopy and elemental analysis. These studies demonstrated that aryl-O-aryl and aryl-O-aliphatic linkages could be cleaved and the hydrogenated lignin had a decrease in oxygen functionality and the formation of products with lower oxygen content.

An increase in moisture during printing can lead to movement of fibres, such as puffing (return of a fibre to its uncollapsed state), twisting, and lifting of fibres out of the paper web. Spruce fibres are especially subject to these movements, contributing to weak bonding and increased surface roughness. The aim of the present study was to treat spruce pulp with enzymes to improve fibre bonding and stability. Spruce chemi-thermo-mechanical pulp was prepared in the laboratory and treated with mannanase, endoglucanase, and with a combination of these enzymes. Strength properties were evaluated before and after wetting of handsheets and their transverse sections were examined by scanning electron microscopy. Handsheet properties before and after rewetting as well as measurement of lumen area of fibres proved to be effective in evaluating fibre movement and puffing. The treatment of pulp with mannanase or endoglucanase improved fibre stability; however, endoglucanase treatment resulted in a loss of strength. Mannanase appeared to modify the cell walls, making them more susceptible to beating and resulting in improved fibre development and inter-fibre bonding. Endoglucanase possibly damaged fibrils, and fibre degradation instead of fibre development occurred during beating. Stability of thin-walled fibres improved more than thick-walled fibres after enzyme treatment.

A softwood thermomechanical pulp (TMP) was suspended in water and oxidized with sodium hypochlorite and catalytic amounts of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) at pH 10. When the NaClO addition levels were 20–26 mmol g -1 of the TMP, the yields of water-insoluble TEMPO-oxidized TMPs fractions were approximately 40%. Sugar composition and other analyses revealed that most of the lignin and hemicellulose components in the TMP were removed as water-soluble fractions by the oxidation. Thus, almost pure TEMPO-oxidized celluloses can also be prepared from TMP, although the addition levels of NaClO are much higher than for the TEMPO-mediated oxidation of pure celluloses. The water-soluble fractions were analyzed by NMR, showing that polyuronic acids formed from glucomannan and cellulose by oxidation were the main compounds. The water-insoluble fractions of TEMPO-oxidized TMPs prepared with NaClO of 20–26 mmol g -1 had carboxylate contents of approximately 1.2 mmol g -1 , and had the same cellulose I allomorph and the same crystal widths as in the original TMP. Transparent and highly viscous gels were obtained by disintegration of these TEMPO-oxidized TMPs in water, and the gels consisted of individual nanofibers 4–6 nm in width. Thus, TEMPO-oxidized cellulose nanofibers can also be prepared from TMP.

In order to utilize lignocellulosic biomass as a feedstock for bioethanol, ozone pretreatment was conducted on Japanese cedar sawdust and three other lignocellulosic wastes. Successful lignin degradation was accomplished by ozone pretreatment of the Japanese cedar sawdust and over 90% of polysaccharides were converted to monomeric sugars by enzymatic saccharification. This ozone pretreatment was also effective with other lignocellulosics, such as Hinoki cypress sawdust, lumber and board wastes. Ethanol production by simultaneous saccharification and fermentation of the ozone pretreated Japanese cedar sawdust was also successful. It was shown that ozone pretreatment increases enzymatic susceptibility and enables the production of ethanol from lignocellulosic biomass.

A gluing method for fiberboard based on laccase-activated tannin and wood fibers was investigated on a laboratory scale. Oxygen consumption measurements showed that hydrolyzable tannins (tannic acid and chestnut tannin) were more reactive toward laccase than condensed tannins from mimosa and quebracho. Wet-process hardboard prepared with laccase and the most reactive tannin, tannic acid, had superior mechanical strength compared to controls and boards made with laccase alone or laccase and other tannins. The other tannins did not improve mechanical properties more than laccase treatment alone. The addition of wax to the tannic acid-laccase formulation improved the dimensional stability of the boards enough for them to comply with industrial standards, although wax had a negative impact on the mechanical properties. The results cannot be directly applied to dry-process medium-density fiberboard (MDF) production; however, the positive effects of tannin and laccase on hardboard properties also warrant investigations on the green chemistry of MDF production.

The amount and composition of lipophilic and hydrophilic extractives, including proanthocyanidins, has been analysed as a first screening in the bark of six Pakistani coniferous tree species, namely Pinus wallichiana , Pinus roxburghii , Pinus gerardiana , Abies pindrow , Taxus fuana and Cedrus deodara . The predominant lipophilic extractives were common fatty and resin acids, fatty alcohols and sterols. In all bark samples, short-chain fatty acids were more abundant than long-chain fatty acids. Generally, the amount of free fatty acids was also larger than the amount of triglycerides. Oleic acid was the most common fatty acid, except in C. deodara , where lignoceric acid dominated. The largest amounts of fatty acids and fatty alcohols were found in P. wallichiana and P. gerardiana . P. gerardiana contained an exceptionally large amount of resin acids, approximately 3% of the bark weight, compared to the other species. The amount of free sterols was approximately at the same level or larger than the amount of steryl esters in most samples. In addition to proanthocyanidins, different known lignans, stilbenes, ferulates and flavonoids were generally predominant amongst the hydrophilic extractives. Resveratrol glycoside was abundant in P. wallichiana , while C. deodara and P. gerardiana contained large amounts of lignans and lignan derivatives. All bark extracts contained large amounts of proanthocyanidin-related catechin and its derivatives. Furthermore, C. deodara and P. roxburghii contained quite large amounts of taxifolin. In particular, P. wallichiana and A. pindrow are potential rich sources of proanthocyanidins, representing approximately 16% and 5% of the bark weight, respectively.

Wood species resistant to biodegradation by fungi contain phenolic compounds with proven fungicidal activity. Saprophytic fungi are able to colonize wood and later begin to break down its polymeric components through metal-dependent reactions. These generate free radicals at the onset of the degradation process. Later on, extracellular enzymes are active that use metallic cofactors. Five lignans were isolated from the methanolic extracts of the Chilean heartwoods ( Austrocedrus chilensis , Fitzroya cupressoides , and Pilgerodendron uviferum ) belonging to the Cupressaceae: isotaxiresinol, secoisolariciresinol, isolariciresinol, didemethylmatairesinol, and matairesinol. Their structures were determined spectroscopically. The antioxidant activity of the methanolic extracts and the isolated compounds was determined in vitro against the radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) and their iron-chelating capacity was evaluated by the Chrome Azurol S assay. All isolated methanolic extracts and lignans exhibited antioxidant activity against DPPH and Fe-chelating capacity with values greater than 87%. This may be interpreted that the antioxidant properties and metal-chelating capacity of these compounds have a protective effect on the wood of these species when exposed to attacks by saprophytic fungi.

Poly (3-hydroxybutyrate) (PHB), a biodegradable polymer from the polyhydroxyalkanoate biopolyester class, was filled with 20% beech wood flour (WF) to form completely biodegradable films. In the present study, the influence of surface modification of wood flour was investigated on the interfacial adhesion of PHB/WF composites. In addition to a hydrothermal pretreatment, sodium hydroxide and stearic acid were used as surface modifiers. Direct measurement of interfacial adhesion was carried out by mechanical testing and dynamic mechanical analysis. Thermal properties, degree of crystallinity of PHB/WF composites were determined by differential scanning calorimetry. Effects of sodium hydroxide and stearic acid treatment on the adhesion of PHB/WF interface were feeble when no hydrothermal pretreatment was applied. Nevertheless, surface modifiers applied on hydrothermally pretreated WF significantly improved the WF/PHB interface adhesion.

Surface penetrating microwave radar is identified as a low-cost, reliable, portable, and safe means of detecting resin defects in plantation-grown pine logs. This new method of non-destructively testing logs has the potential to be applied at several intervention points in the value chain, including on standing trees, fallen stems, and merchandised logs either in the forest or in the mill. Results clearly distinguish resin-affected logs from unaffected logs, even in logs of high moisture content.

Although three-dimensional (3D) internal log images are useful to wood scientists for assessing internal log features, little work has been carried out on this subject. The aim of this paper was to demonstrate how two-dimensional (2D) log images may be combined to create 3D images of internal log features. The selected log features include heartwood, sapwood, bark, and knots in a sugar maple log and a black spruce log. The 2D cross-sectional images of the logs were acquired through computed tomography (CT) scanning. For each log, 72 successive 2D cross-sectional CT images of the log were employed to create the corresponding 3D internal log images based on the marching cubes algorithm. The results suggest that the proposed method can produce clear 3D images for each selected internal log features in sugar maple and black spruce. The accuracy analysis of the 3D reconstruction is still a huge challenge and should be fully investigated in future work.

The three-dimensional microstructure of a series of laboratory medium density fiberboard (MDF) samples with densities varying from 300 kg m -3 to 1000 kg m -3 was investigated by synchrotron microtomography (SRμCT). After reconstruction and filtering of the volume data, an adapted image analysis was used to extract the structural information about the fiber network at different densities. Information was established on the distribution of intra- and inter-fiber voids, cell-wall material, individual fibers, and fiber bundles. Calculations were performed concerning the surface area towards the ambient void spaces, the number of contacts, and the contact area between selected fibers. Furthermore, the resin distribution on the fibers was investigated and characterized by SRμCT and environmental scanning electron microscopy with stained adhesives. The results presented here allow a new approach to examine the complete wood fiber network of MDFs by automatic image analysis routines.

Diffusion processes in samples of European beech ( Fagus sylvatica L.) and Norway spruce ( Picea abies [L.] Karst.) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute in Villigen (Switzerland) using a thermal neutron spectrum. NI is a non-destructive and non-invasive testing method with a very high sensitivity for hydrogen and thus water. Within the scope of this study, diffusion processes in the longitudinal direction were ascertained for solid wood samples exposed to a differentiating climate (dry side/wet side). With NI it was possible to determine the local distribution and consequently the total amount of water absorbed by the samples. The calculated values scarcely differ from those ascertained by weighing (≤3%). The method yields profiles of the water content over the whole sample, thus allowing the local and temporal resolution of diffusion processes within the sample in the main transport direction (longitudinal). On the basis of these profiles, it was possible to calculate the diffusion coefficients along the fibre direction according to Fick's second law.

This work describes the application of end loaded split and single-leg bending tests to the mixed-mode fracture characterization of wood. Experimental tests and numerical validation analyses were performed. A new data reduction scheme based on the crack equivalent concept is proposed. The method overcomes the difficulties inherent to these tests, such as crack length monitoring during propagation and influence of clamping conditions. The single-leg bending test is simpler to execute and provided accurate results. The obtained mixed-mode fracture energy is associated with the pure mode values and the obtained trend point to a linear fracture criterion as a candidate to describe the fracture behavior of the Pinus pinaster Ait. wood.

In this research, Poisson's ratio of plywood as obtained by a tension test was examined by varying the width of the specimen. The tension tests were conducted on five-plywood of lauan ( Shorea sp.) with various widths, and Young's moduli and Poisson's ratios of the specimens were measured. Finite element calculations were independently conducted. A comparison of the experimental results with those of finite element analysis revealed that Young's modulus could be obtained properly when the width of the plywood strip varied. In contrast, the width of the plywood strip should be large enough to determine Poisson's ratio properly.

Wood-based composites, such as oriented strand board, are typically manufactured by consolidating mats of resinated wood elements under heat and pressure. During this process, the temperature and moisture content distributions within the mat greatly affect the properties of end products. To improve the fundamental understanding of mat consolidation during hot-pressing, a model is established to investigate the transverse compression behavior of aspen wood strands for a variety of combinations of temperatures (20–200°C) and moisture contents (0–15%). A regression approach is used to obtain the modulus-temperature-moisture relationship. In addition, elevated temperatures and moistures are found to influence the strain function of wood strands, which was previously assumed to be independent of these factors.

The effect of chemical modification with acetic or hexanoic anhydride upon the decay resistance of wood was studied. Both sapwoods and heartwoods of the following trees were investigated: Japanese larch, Larix kaempferi (Lamb.) Carrière; Korean pine, Pinus koraiensis Siebold et Zucc. as softwoods and European beech (only sapwood), Fagus sylvatica L.; oriental white oak, Quercus aliena (Blume) as hardwoods. After chemical modification, the samples were exposed to the brown rot fungus Coniophora puteana (FPRL 11E). The study investigated whether weight percentage gain or degree of hydroxyl substitution were the main factors controlling decay resistance. It was found that decay resistance is associated primarily with cell wall bulking rather than hydroxyl substitution. However, there are differences in behaviour between the acetylated and hexanoylated wood and the possible reasons for these differences are discussed.

A novel type of chemical modification of wood was developed and applied to functionalise wood permanently with organoboron compounds. The covalent attachment of metalloid substituents via a benzotriazolyl-activated benzoic acid to wood hydroxy groups was in focus. Thus, standard modification procedures in wood chemistry – such as the acetylation – are improved by avoiding either the loss of half the reagent in the case of acid anhydrides or the release of corrosive hydrochloric acid in the case of carboxylic acid chlorides. The introduced boron moiety could be a contribution to solve a long-lasting problem in the field of wood protection: chemical fixation of an organoboron compound by means of a well-defined covalent bond. Accordingly, the hitherto insufficient long-term availability of conventionally spread boron compounds as wood protecting agents caused by leaching can now be avoided. The investigation was also extended to arylsilyl compounds, as a second type of organometal substances, which potentially allow for subsequent chemical modifications by ipso -substitution. The presented wood modification reactions yielded weight percent gain values from 14% to 31% on beech wood, spruce wood, and pine sapwood meal (approximately 500 μm in diameter) or pine sapwood veneer chips. The modified meals and chips were analysed by IR spectroscopy.

The successional diversity of basidiomycetous fungi was studied on Korean pine ( Pinus koraiensis ) and pitch pine ( Pinus rigida ) logs that were left exposed on the forest floor based on fungal surveys conducted after 18, 42, and 54 months of exposure. A total of 131 basidiomycetous isolates were recovered from the logs and grouped by their cultural morphology. Fungal identification was achieved by a BLAST search of partial nuclear large subunit ribosomal DNA sequences in GenBank. The results of the 18 month survey revealed that the isolation frequency and fungal diversity were higher for pitch pine than Korean pine. The dominant species found on Korean and pitch pine logs during the first survey were Hypochnicium karstenii and Phlebiopsis gigantea , respectively. In the 42 and 54 month surveys, the primary species were replaced by Hypochnicium eichleri , Phanerochaete velutina , Phlebia radiata , Rhizochaete sp., and Trametes versicolor . These results showed that decay fungi have host preference for woody materials that vary according to the species of tree being colonized.

Colonisation and degradation by the white rot fungi, Trametes versicolor and T. pubescens , were studied in wood of Norway spruce and beech subjected to three different treatments: (1) hygro-thermal treatment (160°C and 180°C), (2) mechanical densification, and (3) thermo-hygro-mechanical (THM) treatment including densification and post-treatment at different temperatures (140°C, 160°C and 180°C). The weight losses induced by the fungi were lowest in THM-densified woods. However, volume related numerical indicators for decay susceptibility did not show any significant improvements of THM-densified woods against both fungi. Analysis of the chemical composition of treated wood species revealed slight alterations in the content of polysaccharides and lignin. White rot fungi circumvented conditions restricting hyphal growth within the occluded tracheid lumina by hyphal tunnelling in the secondary walls of fibre tracheids in beech or by forming bore holes that transversally penetrated cell walls of earlywood tracheids in THM-densified spruce. The studies indicate that THM-densified beech and Norway spruce wood may have some potential in utility class 3 but are inappropriate for use in utility class 4.

No Abstract available