Volume 65, Issue 2

No abstract available

To better understand adhesive interactions with wood, reactions between model compounds of wood and a model compound of polymeric methylene diphenyl diisocyanate (pMDI) were characterized by solution-state NMR spectroscopy. For comparison, finely ground loblolly pine sapwood, milled-wood lignin and holocellulose from the same wood were isolated and derivatized with the pMDI model compound. One-bond 13 C– 1 H correlation (HSQC) experiments on derivatized and dissolved ball-milled wood revealed which hydroxyl group positions of the cell wall polymers reacted with the pMDI model compound to form carbamates. The chemical shifts of the derivatized model compounds correspond precisely to the chemical shifts of derivatized wood polymers. These model experiments will be taken as a basis in the next phase of our research (Part 2), in which the reactions of pMDI model compounds will be studied with intact wood cell walls under conditions similar to those used in oriented strand-board production.

Solution-state NMR provides a powerful tool to observe the presence or absence of covalent bonds between wood and adhesives. Finely ground wood can be dissolved in an NMR-compatible solvent system containing dimethylsulfoxide- d 6 and N -methylimidazole- d 6 , in which the wood polymers remain largely intact. High-resolution solution-state two-dimensional NMR correlation experiments, based on 13 C– 1 H one-bond heteronuclear single quantum coherence, allow structural analysis of the major cell wall components. This technique was applied to loblolly pine that was treated with polymeric methylene diphenyl diisocyanate (pMDI) related model compounds under controlled moisture and temperature conditions. Chemical shifts of carbamates formed between the pMDI model compounds and loblolly pine were determined. The results show that: (a) under dry conditions and a high concentration of isocyanate, carbamates will form preferentially with side-chain hydroxyl groups on β-aryl ether and phenylcoumaran-linked lignin units in a swelling solvent; (b) phenyl isocyanate is more capable of derivatization in the cell wall than the bulkier 4-benzylphenyl isocyanate; (c) at 5% and 14% moisture content, detectable carbamates on lignin side-chains dramatically decrease; and (d) under typical conditions of industrial oriented strand-board production in a hot press at 5% and 14% moisture content, no carbamate formation was detected.

Development of eco-friendly binders with no harmful emission during its complete life cycle is of high interest for the wood-based industry. In this paper, a fully renewable binder based on activated lignin and poly-furfuryl alcohol and a partly renewable lignin based phenol-formaldehyde (PF) binder were evaluated. Activation of kraft and soda lignins, isolated respectively from softwood and non-woods, by periodate oxidation was performed to improve lignin reactivity and application in wood adhesives. Periodate oxidation of lignin leads to higher lignin acidity, formation of quinonoid groups under more severe conditions, higher molar mass and higher reactivity towards the curing of furfuryl alcohol within a temperature range currently used in industry. Comparison of a 100% furan-based glue with a furan-based glue substituted by 10% lignin yields comparable product properties. However, periodate-activated lignin leads to lower wood failure, which might be caused by incompletely solubilised lignin particles in the acidic formulation disturbing crosslinking of the furan resin. Unmodified softwood kraft lignin performs well in a PF resin formulation at substitution levels up to 30% (w/w). Periodate oxidation of soda lignins enhances the glue performance because higher wood failure is attained. The higher molar mass after periodate treatment could be an important parameter for development of a stronger wood binder.

Bambusa dolichoclada Hayata (long-shoot bamboo) was liquefied in phenol with H 2 SO 4 as a catalyst. The phenol-liquefied bamboo was then used as a raw material to prepare spherical phenol-formaldehyde (PF) resin beads by a suspension polymerization in a two-step process. The influence of the stirring speed (300, 350 and 400 rpm), the stabilizer dosage (3%, 4% and 5%) and the total molar ratio of formaldehyde to free phenol (F/P) (3.0/1, 3.5/1 and 4.0/1) on the properties of spherical PF beads was investigated. The results show that the yield, diameter and dimensional distribution of prepared PF beads were influenced by reaction conditions. The diameter of beads decreased as the stabilizer dosage increased. It had a more uniform dimensional distribution when stirred with a speed of 400 rpm. Differential scanning calorimetry analysis shows that PF beads obtained were not completely cured and the post-curing reaction took place at temperatures exceeded 150°C. As revealed by thermal gravimetric analysis, the char yield was over 60% after heating to 800°C.

Reactive paper sizing agents, such as alkenyl succinic anhydride (ASA), provide hydrophobicity to paper. The reactive anhydride group of these reagents is highly susceptible to reaction with water and thus resistance against hydrolysis is of primary importance for their practical application. This study describes different application-relevant properties of recently developed sizing agents that are based on renewable vegetable oils including hydrolysis behavior, time-dependent sizing efficiency, and tendency to form deposits or foam. The novel sizing agents – maleated high oleic sunflower oil (MSOHO) and maleated rapeseed oil (MRSO) – are compared to conventional ASA as the state-of-the-art sizing agent. Although the reactive group is the same in all reagents, there are pronounced differences between the three reagents, with MSOHO showing the best performance, i.e., the slowest hydrolysis. This oil has a higher ratio of hydrophobic side chains that impede the water attack at the anhydride group. Also, the higher viscosity of MSOHO plays an important role in performance, because diffusion of water molecules into a MSOHO emulsion droplet is much slower than in the case of conventional ASA.

Olive tree pruning biomass is one of the main agricultural residues available in Mediterranean countries and is currently lacking commercial applications. To take advantage of its sugar content, a pretreatment is necessary to enhance enzyme accessibility of the cellulose fraction of the residue. This paper describes for the first time the use of organosolv pretreatment in this regard. The main process variables such as pretreatment temperature, residence time, and solvent composition (aqueous ethanol) are studied. Results show that organosolv pretreatment causes delignification and hydrolysis of hemicelluloses and improves the enzymatic digestibility of olive tree pruning biomass. A higher pretreatment severity and ethanol content of the solvent were found to increase delignification (up to 64% at 66% w/w aqueous ethanol, 210°C, 60 min). By contrast, xylan hydrolysis was promoted by a lower ethanol content (maximum 92%). The highest enzymatic hydrolysis yield (90% of the structural glucan present in the raw material) has been obtained after pretreatment with 43% w/w aqueous ethanol at 210°C for 15 min. Organosolv pretreatment was found to be the most effective pretreatment for enzymatic hydrolysis of olive tree pruning biomass.

White oak is commonly used for cooperage and the heartwood extractives are important for this application because of their impact on the flavor and color of wine and spirits aged in white oak barrels. White oak extractives comprise a complex mixture of compounds and the composition of the mixture can change within trees over time. The ability to monitor the extractives component of white oak heartwood could be helpful for assessments of barrels and their contents. Wood from five American white oak stave logs was sampled. NIR-based models could provide reasonable predictions of the concentration of individual extractives components. However, these extractives were highly correlated to one another and to radial location suggesting that segregation of white oak material based on distance from the pith could be an efficient method for selecting samples that are relatively rich in flavor-associated chemicals. The relatively poor near infrared-based prediction ability for total extractives content could be due to age-related changes in the composition of the mixture of extractives across the radius.

To search for novel therapeutic compounds with higher activity, a series of novel dehydroabietic acid derivatives bearing 1,3,4-oxadiazole moieties were designed and synthesized. Ten title compounds 5-dehydroabietyl-2-alkyl thio-1,3,4-oxadiazoles were synthesized by the reaction of 5-dehydroabietyl-2-mercapto-1,3,4-oxadiazole with alkyl halide or substituted benzyl halide in ethanolic KOH. All the title compounds were analyzed and characterized by means of IR, UV-vis, EI-MS, 1 H-NMR, 13 C-NMR, and elemental analysis. The preliminary herbicidal assay showed that almost all of the compounds exhibited an excellent growth inhibition to rape ( Brassica campestris ) and a certain inhibition to barnyard grass ( Echinochloa crusgalli L.) at a concentration of 100 μg ml -1 .

The common use of wood together with traditional chemical polymers opens new possibilities in the field of sustainable product development. Wood plastic composites (WPCs) are an ideal combination of these raw materials, which can be produced with standard plastic technology such as extrusion or injection moulding. Wood to plastic ratio in a WPC influences quality and price, thus adaptation of analytical tools for material testing and quality assurance is required. In this study, the suitability of analytical pyrolysis (Py) and differential scanning calorimetry (DSC) was investigated to quantify the amount of polypropylene (PP) in WPCs. The reliability of these methods was tested by analysing WPCs with different ratios of wood and PP. The amount of PP can be determined with DSC based on its melting point as the influence of wood is negligible in this context. The increment of typical PP markers and decrement of wood markers was observed and quantified in the pyrograms if the PP content in WPCs was elevated. Thus, the ratio of PP and wood can be reliably quantified by means of online and offline analytical pyrolysis.

The bonding quality test is one of the most important of all tests performed on plywood, because it determines the suitability of boards for use in the type of exposure they are intended for. Because this test involves aging pretreatment, results are not available in <24–97 h after manufacture, depending on the type of board, and therefore any error in the manufacturing process is not detected until 1–4 days later. To solve this time problem, an artificial neural network was developed as a predictive method to determine the suitability of board bonding through other properties that can be determined in less testing time: thickness, moisture content, density, bending strength, and modulus of elasticity. The network designed WAS a feedforward multilayer perceptron trained by supervised learning after normalization of the input data, and allowed the bonding test result to be predicted with 93% accuracy.

In recent years, there has been increased interest in the use of inorganic UV blocking nanoparticles for photostabilization of wood surfaces. Photostability and moisture uptake properties of wood veneers coated with a combination of hybrid inorganic-organic thin sol-gel films and organic light stabilizers was investigated. The light stabilizers were applied by brushing, and the thin sol-gel films were deposi-ted on the wood surface by dipping in a sol prepared from a mixture of methyltrimethoxysilane, hexadecyltrimethoxysilane, and aluminum isopropoxide precursors. Although the sol-gel film improved the moisture resistance of the wood veneers, it showed mixed results on photostability. Under light and spray conditions in a Weather-Ometer™, specimens treated with a combination of sol-gel thin film and a UV absorber, tris-resorcinol triazine and an acrylic self-crosslink-ing binder, or treated with lignin stabilizer/tris-resorcinol triazine/acrylic self-crosslinking binder showed good overall weathering performance. Under permanent light conditions in the Weather-Ometer™, specimens treated with a combination of sol-gel thin film, a lignin stabilizer, and a water soluble UV absorber – namely: (2-hydroxyphenyl)-benzotriazole – revealed a good overall weathering performance. This study has demonstrated the feasibility of using a combination of organic light stabilizers and sol-gel deposits of hybrid inorganic-organic thin films to improve weathering resistance of softwood substrates.

Wood and wood-based composites are being used extensi-vely in single-family residential dwellings. Therefore, it is important to categorize their response when exposed to elevated temperatures for a sustained period of time. In fire-resistant design for wood structures, the main goal is to ensure that enough structural integrity is maintained, during and after a fire, to prevent collapse and to maintain means of egress. Another goal is an ability to assess post-fire structural integrity and residual strength of an existing structure. The objectives of this study are: (a) to study the effect of temperature and exposure time on bending strength (MOR) and stiffness (MOE) of solid sawn lumber (SSL), laminated veneer lumber (LVL), oriented strand board (OSB) and plywood; and (b) to develop predictive relations between different temperatures and times of exposure and the thermal degradation of strength. A total of 1080 samples were tested in static bending under various heat treatments. The results indicated that exposure to elevated temperature caused significant degradation of bending strength and stiffness. A statistical regression-based model and a kinetics-based model were developed and evaluated for predicting the strength loss of wood and wood-based composites as a function of thermal exposure temperature and exposure time. The kinetics-based model fit the data better and predictions consistently matched the observed values, making the model preferred over the regression approach.

The time-dependent mechanical behaviour (TDMB) of softwood is relevant, e.g., when wood is used as building material where the mechanical properties must be predicted for decades ahead. The established mathematical models should be able to predict the time-dependent behaviour. However, these models are not always based on the actual physical processes causing time-dependent behaviour and the physical interpretation of their input parameters is difficult. The present study describes the TDMB of a softwood tissue and its individual tracheids. A model is constructed with a local coordinate system that follows the microfibril orientation in the S2 layer of the cell wall. The inclination of the local system to the global coordinate system reflects the microfibril angle of the tracheid. Normal excitations in the local system perform linear elastically, whereas shearing excitation in the local system produces both elastic and inelastic responses. The results of the model are compared with experimental results of different types. It was observed that the model is able to describe the results. Moreover, to some surprise, the introduction of only elastic and viscous properties on the microscopic scale leads to an apparent macroscopic viscoelasticity, i.e., the time-dependent processes are to a significant degree reversible.

The aim of this study was to determine the effect of removing extractives from the woody core of hemp (chènevotte) on the chain mobility of hemicelluloses and lignins, which can react during technological transformation such as de-fibering and/or composite materials production. Extractives are molecules with low molecular weight, which are present in the cell wall matrix and can be readily removed by solvents. In the present paper, the nature and amounts of extractives, removed under different conditions and with solvents of different polarities, were determined. The mobility and structural relaxations of lignins and hemicelluloses were stu-died in situ by dynamic mechanical analysis and dielectric analysis under controlled moisture content. Extractions at low temperature led to rigidification of lignins and plasticizing of hemicelluloses, probably due to local changes by the selective removal of molecules interacting with the polymers. Probably, the accessibility of hemicelluloses to plasticizing water was increased at controlled humidity. In contrast, hot extractions including water induced rigidification of the hemi-celluloses and plasticizing of lignins. This could be related to a combination of molecule extractions and chemical modi-fications of both polymers. This interpretation is supported by the variation of activation energy for relaxation of hemi-celluloses. It can be concluded that each type of extraction has a clear specific effect on the relaxation properties of the amorphous cell wall polymers.

The dependence of the deformation change on the location and number of cells during water adsorption was examined by microscopy combined with a “charged-coupled device” camera and image analysis based on the digital image correlation method. The deformation change ratio (DCR) vs. moisture content (MC) in the radial direction approached linearity with MC with increasing in number of cells between measurement points in earlywood, whereas its relation in latewood was various such as swelling, swelling after shrinking, or remaining constant with MC. The number of cells between observation points clearly affected the DCR vs. MC, i.e., its relationship had the so-called “scale effect” that a certain physical property appears clearly with increasing scale. The mechanism of the scale effect differed in the radial and tangential directions.

The genus Trichoderma Persoon is a cosmopolitan genus consisting of more than 104 species and is commonly found on wood surfaces as a mold where it affects the appearance. Little attention has been given to wood-colonizing Trichoderma species and few studies are dedicated for identification of Trichoderma at the level of species. In the present study, up to 142 isolates were obtained from various wood samples. One Gliocladium and ten Trichoderma species were identified by morphological and molecular analysis. T. atroviride (30.3%) was the most abundant species followed by T. citrinoviride (26.8%) and T. harzianum (23.9%). The ability of Trichoderma species to discolor wood was also examined on sapwood blocks made of the commercially important radiata pine ( Pinus radiata ). T. pleuroticola caused the greatest discoloration of the wood surface.

In this study, the diversity of wood inhabiting Penicillium species in Korea was investigated through the analysis of their phenotypic traits and phylogeny. Moreover, the discoloration and growth patterns of these species on the surfaces of two commercially important conifers were examined. From a collection of 137 Penicillium isolates from various wood species, 37 Penicillium species have been identified including six unknown Penicillium species. The occurrence of six Penicillium species in Korea was demonstrated for the first time: P. biourgeianum , P. decaturense , P. kloeckeri , P. meleagrinum var. viridiflavum , P. ochrochloron , and P. sumatrense . P. funiculosum was the most prevalent species (15.4%). Sapwood blocks of Japanese red pine ( Pinus densiflora ) and radiata pine ( Pinus radiata ) were exposed to each Penicillium species to examine their discoloration and growth patterns on these woods. The blocks of Japanese red pine were more susceptible to Penicillium growth, and the highest discoloration rate on both sapwood blocks was achieved by one of the recently described species P. decaturense .

Biological deterioration is the most important issue facing the use of bamboo as a bioresource. To identify the fungi responsible for bamboo degradation, isolates were obtained from three decaying bamboo species and evaluated. A total of 16 genera and 18 species of fungi were isolated and identified. The major fungi causing serious damage are Trametes versicolor and Arthrinium arundinis , which caused the largest weight losses in tests, of approximately 21.6% and 17.9%, respectively. This investigation confirms that the natural durability of bamboo in outdoor utilization is low.

Port-Orford cedar ( Chamaecyparis lawsoniana ), Alaska yellow cedar ( Chamaecyparis nootkatensis ), and Eastern red cedar ( Juniperus virginiana ) were submitted to supercritical fluid extraction with CO 2 (SCC) and Soxhlet extracted (SE) with hexane. The components in the extracted oils were identified by GC-MS. The oils were evaluated against two common wood decay fungi, brown-rot fungus ( Gloeophyllum trabeum ) and white-rot fungus ( Trametes versicolor ). The SCC extraction yields of J. virginiana , C. nootkatensis , and C. lawsoniana were 3.27%, 3.22%, and 3.29%, respectively. The SE yields of J. virginiana , C. nootkatensis , and C. lawsoniana were 0.80%, 0.71%, and 1.52%, respectively. The statistical analysis showed that SCC extracted cedar oils had higher antifungal activities than SE cedar oils against both fungi. In vitro studies showed that C. nootkatensis oils have the strongest antifungal activity, followed by C. lawsoniana, and J. virginiana oil.

No abstract available

No abstract available