Thomas Ters

Laccase-catalyzed functionalization with 4-hydroxy-3-methoxybenzylurea significantly improves internal bond of particle boards

Abstract Enzymatic functionalization is an attractive tool to provide a reactive interface for further processing of lignocellulosic materials, such as wood particles and fibers. Here, spruce wood particles have been functionalized by fungal laccase combined with 4-hydroxy-3-methoxy-benzylamine (HMBA) or 4-hydroxy-3-methoxybenzylurea (HMBU). The expectation was crosslinking with resins in subsequent glueing processes, which should improve strength properties of particle boards. Essential process parameters, such as liquid to solid mass ratio and treatment time, were optimized on a laboratory scale resulting in HMBA and HMBU binding yields of 90% and above as determined by radiochemical mass balance analysis. We employed a multifactorial experimental design for board production from treated wood particles and urea/formaldehyde resin. Mechanical testing and multivariate data analysis revealed, for the first time, an increase of internal bond (IB) as a result of functionalization with HMBU. HMBA was not successful. Variance analysis of relevant parameters and their interactions demonstrated a highly significant difference (P>99.99%) between boards treated with laccase/HMBU versus untreated wood particles. Due to positive interactions, functionalization was most effective at high bulk density (750 kg m-3) and high resin content (10%) resulting in a calculated IB improvement of 0.12 N m-2 (21%).

Effect of surface modification of beech wood flour on mechanical and thermal properties of poly (3-hydroxybutyrate)/wood flour composites

Abstract 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.

Macro- and micro-mechanical properties of red oak wood (Quercus rubra L.) treated with hemicellulases

Abstract Red oak wood (Quercus rubra L.) samples were submitted to an enzymatic treatment with a commercial mixture of hemicellulases aiming at the selective depolymerization and removal of the hemicelluloses. Mechanical properties of treated samples were characterized and compared with untreated samples at two hierarchical levels. At the macrolevel, tensile properties revealed to be less sensitive to degradation of the cell wall matrix compared to compression and hardness properties. Results obtained through indentation at the microlevel indicated that hardness and the so-called reduced modulus of treated wood were significantly lowered. Accordingly, hardness and reduced elastic modulus have proven to be most sensitive to modification of the cell wall matrix by reducing the content of hemicelluloses. It is proposed that transversal and shear stresses, which are mainly carried by the cell wall matrix, are additional parameters having strong effects on elastic modulus obtained by nanoindentation. Micromechanical modeling was employed to confirm the observed changes. There is consistency between the measured and the modeled properties, obtained at both the microlevel and the macrolevel of wood.

FT-IR imaging microscopy to localise and characterise simultaneous and selective white-rot decay within spruce wood cells

Abstract Spruce wood that had been degraded by white-rot fungi (Trametes versicolor or Ceriporiopsis subvermispora) and suffered mass losses up to 17% was investigated by transmission Fourier transform infrared (FT-IR) imaging microscopy. A significant marker during incipient simultaneous white-rot (T. versicolor) was the cleavage of glycosidic bonds of polysaccharides that preceded their metabolisation. Simultaneous white-rot processes were also characterised by a relative decrease of the overall lignin content and a relative accumulation of wood polysaccharides. No early marker was found for selective white-rot (C. subvermispora) that removes mainly lignin by an oxidative process. This feature was detected only in wood samples exhibiting mass losses higher than 12%. Furthermore, it was shown, that simultaneous and selective white-rot processes were unevenly distributed within the wood samples but quite evenly distributed within single tracheids.

Fungal pretreatment of pine wood to reduce the emission of volatile organic compounds

Abstract Sterilized pine wood strands were treated with the ascomycete Ophiostoma piliferum (Cartapip 97™) in an attempt to reduce aldehyde emissions through degradation of aldehyde-forming precursors. Wooden boards were then produced from the treated strands by means of a laboratory press. VOC emissions of these boards were characterized and the concentrations of seven major substances were followed for a period of 28 days in Markes μ-CTE micro-chambers employing Tenax-TDAS/GC/MS analytics. Boards made from treated strands showed a highly significant (P<0.001) reduction in aldehyde emissions by 70% compared to the control boards, while differences in the monoterpene emissions were not significant (P>0.05). Wood extractives from treated and untreated strands were also analyzed by GC/MS after milling and acetone/water extraction. A marked decrease of C18 unsaturated fatty acids was detected in agreement with the reduction of aldehyde emissions, and the monosaccharides as indicators of fungal growth were depleted and stilbenes and lignans were partially degraded.

A combined view on composition, molecular structure, and micromechanics of fungal degraded softwood

Abstract Fungal decay alters the composition, microstructure, and mechanical properties of wood cell walls. To understand better the structure-function relationships during fungal decay, selected annual rings of fungal deteriorated Scots pine sapwood were analyzed in terms of their composition, microstructure, and micromechanical properties. The datasets were acquired separately for earlywood and latewood concerning the S2 cell wall layer and the cell corner middle lamella (CCML) and analyzed by means of principal component analysis and partial least squares regression analysis. Links between cell wall stiffness and hardness and the composition and microstructure could be established. Increased mechanical properties in the CCML, as obtained by nanoindentation, were correlated to the degradation of pectins. In the S2 layer, the altered data were related to the degradation of hemicelluloses and lignin modification during fungal decay.

Extractives of mechanically wounded wood and knots in beech

Abstract Various types of wound-associated wood, such as discoloured wood including knots of living and dead branches, were sampled from common beech trees (Fagus sylvatica L.), extracted, and the extracts have been analysed by GC and colourimetry assay. Sequential pressurised solvent extraction was applied with cyclohexane and aqueous methanol. The yield of hydrophilic compounds was three to five times higher than that of lipophilic extractives. The fractions differed mainly in their hydrophilic moieties. The lipophilic extractives consisted mainly of free fatty acids, fatty alcohols and free sterols. The yield of fatty acids was slightly higher in reaction zones and knots. The content of free sterols was highest in the reaction zones and in the discoloured wood. The hydrophilic extractives consisted of soluble sugars, various acids and phenolic compounds with catechin as the dominant one. Expectedly, the yield of phenolic extractives and catechin (proanthocyanidins) was highest in knots and wound-wood. Discoloured wood gave rise to lower amounts of catechin.

Reduction of aldehydes and terpenes within pine wood by microbial activity

Abstract Aldehydes and terpenes are the most frequently emitted volatile organic compounds (VOCs) in the wood-processing industry. These emissions are classified as injurious to health and hazardous to the environment. To address this problem, the growth conditions have been identified under which bacteria extensively degrade both aldehydes and particularly terpenes in pine wood particles as a raw material for the production of particle boards. In this study, the focus was on pentanal and hexanal (aldehydes) as well as α- and β-pinene (terpenes). Bacterial strains were selected for their ability to metabolize α-pinene as single carbon source in liquid culture medium. α-Pinene degradation was then determined by gas chromatography (GC) analysis. Strains belonging to the genus Pseudomonas showed the best results (98% degradation after 72 h). Comparably good results were also achieved with the thermophilic strain Bacillus pallidus (90% degradation) at 55°C. Furthermore, an adapted mixed culture of Pseudomonas species was inoculated onto wood particles and incubated at room temperature for 3 days. Solid-phase microextraction (SPME) measurements of emitted volatiles and subsequent gas chromatography-mass spectrometry (GC-MS) analysis indicated a complete removal (100%) of aldehydes and, even more importantly, α- and β-pinene. Pre-treatment of unsterile pine wood particles with Pseudomonas species may have potential for industrial application.

Biological control of sapstain fungi: From laboratory experiments to field trials 10th EWLP, Stockholm, Sweden, August 25–28, 2008

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

Within-process and seasonal changes during industrial production of high-density fibreboard. Part 1: Influence of wood species composition on polyoses in the products

Abstract Industrially produced high-density fibreboard fibres are inhomogeneous in structure and chemical composition. Changes in polysaccharide chemistry during processing have an impact on strength loss, fibre separation and structural alterations. In the present study, carbohydrate composition of extracted wood chips and refiner fibres was monitored for a year at an industrial HDF plant. The polysaccharides were analysed via methanolysis and quantification of the monomeric sugars released. Significant reductions of arabinose, xylose, rhamnose and galacturonic acid were observed. The amount of glucose and extractable substances increased. The depletion of galacturonic acid and rhamnose indicates a degradation of pectin located in the compound middle lamella. The diminishing amounts of the other sugars and elevated extractive contents are a result of hemicellulose degradation. A pronounced seasonal variability of the data was observed depending on the processed wood species and degree of chemical degradation.