Fungal resistance of rubber wood modified by fatty acid chlorides

Decay resistance of Rubber wood (Hevea brasiliensis) esterified with three fatty acid chlorides (hexanoyl chloride (C6), decanoyl chloride (C10) and tetra-decanoyl chloride (C14)) was evaluated. Unmodified and modified wood samples were exposed to a brown rot (Polyporus meliae) and a white rot (Coriolus versicolor) fungus for 12 weeks. Unmodified rubber wood was severely decayed by P. meliae and C. versicolor, which was indicated by significant weight loss. The rate of decay by brown rot was higher than white rot. Modified wood samples exhibited very good resistant to brown and white-rot fungi. The degree of protection increased with increase in degree of modification. P. meliae, a brown rot fungus, removed structural carbohydrate component in unmodified wood selectively whereas, C. vesicolor showed preference to lignin. The FTIR spectra of modified wood exposed to fungi show no significant changes in relative peak intensities of lignin/carbohydrates indicating effectiveness of chemically modified wood in restricting chemical degradation. Chemical modification occurred more efficiently at carbohydrate portion of the wood. Therefore, it is more effective in retarding decay due to P. meliae.     

The resistance of wood chemically modified with isocyanates: the role of moisture content in decay suppression

This paper discusses the moisture content of sound and decayed Corsican pine (Pinus nigra) after modification with isocyanates {n-butyl isocyanate (BuNCO) and 1,6-diisocyanatehexane (HDI)} at specified intervals of weight percent gain (WPG). The main effects of decay fungi (brown and white rot) and levels of modification (WPG) on moisture contents of modified samples are also examined. Corsican pine reacted with isocyanates enhanced the hydrophobic (restrained water) nature of wood. The equilibrium moisture content of chemically modified wood decreases progressively with increasing WPG. Basidiomycete decay tests demonstrated protection by chemical modification. Wood moisture contents after soil block testing are significantly influenced by decay fungi and by the extent of reaction (WPG). Moisture uptake and susceptibility to decay of modified wood are higher when exposed to Coniophora puteana than other decay fungi. Corsican pine cross-linked by reaction with HDI is less susceptible to decay and is more hydrophobic than samples reacted with the single-site reactant BuNCO at comparable WPG.     

Modification of wood with isopropyl glycidyl ether and its effects on decay resistance and light stability

China fir (Cunninghamia lanceolata var. lanceolata) and maple (Acer sp.) wood were etherified with isopropyl glycidyl ether and the decay resistance and light stability of the modified wood were assessed. CP/MAS (13)C NMR and FT-IR analyses indicated that new ether bonds containing isopropyl groups formed after reacting wood with isopropyl glycidyl ether. Modified wood samples were very resistant to decay when exposed to brown-rot fungus Laetiporus sulphureus or white-rot fungus Lenzites betulina for 60 days in the soil-block test. The isopropyl glycidyl ether treatment of wood was effective in decreasing formation of phenoxyl radicals upon UV irradiation and thus protecting wood from photodiscoloration.     

Improvement of decay resistance of wood via combination treatment on wood cell wall: Swell-bonding with maleic anhydride and graft copolymerization with glycidyl methacrylate and methyl methacrylate

Poplar wood (Populus ussuriensis Kom) was modified by a novel combined two-step treatment to improve its decay resistance. Maleic Anhydride (MAN) was first employed to swell and bond to wood cell wall, and then mixed monomers of glycidyl methacrylate/methyl methacrylate (GMA/MMA) were used to graft copolymerization within wood cell lumen. The swelling and bonding of cell wall by MAN, interfacial compatibility between resultant polymer from GMA/MMA monomers and wood cell wall, and decay resistance of all composites were tested and analyzed by Scanning electron microscopy–Energy dispersive X-ray (SEM–EDX), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) apparatus. The results indicate that the volume of poplar wood treated by MAN swells about 9% with about 15% of weight percent gain, and MAN chemically bonds to the cell wall through substitution reaction with hydroxyl group, and the grafting adduct mainly remains as an amorphous form. The resultant Poplar-MAN shows improved decay resistance of 69.79% against brown fungus (Gloeophyllum trabeum (Pers. ex Fr.) Murr.) and 81.42% against white fungus (Phanerochaete chrysosporium Burdsall.) over those of untreated Poplar, respectively. After the combined two-step treatment, GMA and MMA are copolymerized within wood cell lumen, and the resultant polymer is also grafted onto wood cell wall, resulting in the improvement of interfacial compatibility between polymer and wood substance without obvious gaps. The decay resistance of the resultant composite from the combined two-step treatment against the brown decay fungus and the white decay fungus is improved by 97.64% and 99.17%, respectively, compared with those of untreated poplar wood; and also more excellent than those of MMA treated wood, GMA/MMA monomers treated wood, organic 3-Iodo-2-Propynyl Butyl Carbamate (IPBC) treated wood and inorganic boron compounds treated wood, respectively.     

Comparisons of the Colonisation by Invertebrates of Three Species of Wood,Alder Leaves,and Plastic “Leaves” in a Temperate Stream

Small woody debris in streams is abundant, and may be a food source or may provide a substrate on which other food sources such as biofilm may develop, both of which may be significant to invertebrates in times of food scarcity. We examined patterns of invertebrate colonisation of small woody debris (veneers of red alder, Douglas‐fir, and western red cedar), red alder leaves, and plastic (as an inert substrate to mimic leaves). Invertebrate colonisation was high on alder leaves, but low on wood substrates and plastic, controlling for the available surface area. Detritivorous invertebrates had significantly higher colonisation rates of alder leaves versus the other four substrates, whereas predators and collectors did not (consistent with their use of these as substrates and not food). All wood decreased in mass by <15% and leaves by ∼50% over the 75 days of the experiment. For all taxa tested, there was no significant difference in their colonisation of the wood veneers versus the plastic sheets. These results suggest that wood was not directly used by these invertebrates as a food source, or that there could be similar biofilm development on the surfaces of these substrates. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Wood Modification on Lignin Consumption and Synthesis of Lignolytic Enzymes by the Fungus Panus (Lentinus) tigrinus

Lignin consumption and synthesis of lignolytic enzymes by the fungus Panus (Lentinus) tigrinuscultivated on solid phase (modified and unmodified birch and pine sawdusts) were studied. The fungus grew better on and consumed more readily the birch lignin than the pine wood. Peroxidase activity was higher in the case of pine sawdust; laccase and lignolytic activities, in the case of birth sawdust. Treatment with ammonia or sulfuric acid decreased lignin consumption by this fungus cultivated on either medium. Modification of sawdust by ultrasound increased lignin consumption and may be recommended for accelerating biodegradation of lignocellulose substrates.     

An investigation of cell wall micropore blocking as a possible mechanism for the decay resistance of anhydride modified wood

Corsican pine (Pinus nigra) sapwood was chemically modified with acetic, or hexanoic anhydride to a variety of weight percentage gains. The cell wall microporosity of the wood before and after chemical modification was determined using the technique of solute exclusion. The results showed that the cell wall microporosity decreased as the level of substitution increased, but the cell wall remained accessible at high levels of substitution. Values of the fibre saturation point (FSP) calculated from solute exclusion data ranged from c. 40% (for unmodified wood) to c. 20% at approx. 25% weight percentage gain, but were dependent to some degree upon the calculation method. Evidence is presented suggesting that the reduction in FSP may be attributable to bulking of the cell wall by bonded acyl adduct. It is concluded that the level of hydroxyl substitution in the cell wall is not the primary mechanism for giving decay protection in anhydride-modified wood.     

Decay resistance of ash,beech and maple wood modified with N-methylol melamine and a metal complex dye

This study evaluated the decay resistance of ash (Fraxinus excelsior L.), beech (Fagus sylvatica L.), and maple (Acer platanoides L.) wood impregnated by a full cell process with N-methylol melamine (NMM) and combined NMM-metal complex dye (NMM-BS) in aqueous solutions. Basidiomycete decay testing involved incubation with Coniophora puteana (brown rot) and Trametes versicolor (white rot) according to a modified EN 113 (1996) standard, while for the soft rot fungal resistance was evaluated following the standard ENv 807 (2001). NMM and NMM-BS modifications at a WPG range of 7–11% provided decay protection against brown rot resulting in a mass loss less than the required limit (3%). The NMM and NMM-BS modified wood showed increased resistance to white rot decay; however, a higher WPG is needed to prohibit attack from this hardwood specific fungus. The metal-complex dye alone revealed biocidal effects against basidiomycetes. An increased WPG in NMM or NMM-BS had a positive impact against soft rot decay and the lowest mass losses after 32 weeks of exposure were obtained with NMM modification at about 18–21% WPG. NMM modification at this WPG range, however, was not sufficient to protect the wood from soft rot decay. The wood of beech and maple showed slightly higher resistance to all decay types than ash, probably due to the poorer degree of modification of the latter.     

Comparison of decay resistance of wood and wood-polymer composite prepared by in-situ polymerization of monomers

Fast-growing plant wood Populus ussuriensis Kom, and Micheliamacclurel wood were respectively modified by formation of wood-polymer composite to improve their decay resistance. Two functional monomers, glycidyl methacrylate and ethylene glycol dimethacrylate, added with a few Azo-bis-isobutryonitrile as initiator, and maleic anhydride as catalyst, were first impregnated into wood cell lumen under a vacuum-pressure condition, and then in-situ polymerized into copolymers through a catalyst-thermal treatment. The decay resistances of untreated wood and wood-polymer composites were assessed by weight loss and compared by SEM observations. SEM and FTIR analysis indicated that the in-situ polymerized copolymers fully filled up wood cell lumen and also grafted onto wood cell walls, resulting in the blockage of passages for microorganisms and moisture to wood cell walls. Thus, the decay resistance of poplar wood-polymer composite and Micheliamacclurel wood-polymer composite against brown rot fungus and white rot fungus in terms of weight loss achieved 3.43–3.92% and 1.04–1.33%, improved 95.06–95.18% and 95.10–95.35% than those of untreated poplar wood and Micheliamacclurel wood, respectively; and also respectively higher than that of boron-treated wood. The SEM observations for the decayed poplar wood, Micheliamacclurel wood and their corresponding treated wood also showed the remarkable improvement of decay resistance of wood after such treatment, which effectively protected wood from degradation by fungi.     

Topochemical investigation of early stages of lignin modification within individual cell wall layers of Scots pine (Pinus sylvestris L.) sapwood infected by the brown-rot fungus Antrodia vaillantii (DC.: Fr.) Ryv.

The initiation and progress of wood degradation of Pinus sylvestris sapwood exposed to the brown-rot fungus Antrodia vaillantii was studied on a cellular level by scanning UV microspectrophotometry (UMSP 80, Zeiss, MSP 800 Spectralytics). This improved analytical technique enables direct imaging of lignin modification within individual cell wall layers. The topochemical analyses were supplemented by light and transmission electron microscopy (TEM) studies in order to characterize morphological changes during the first days of degradation. Small wood blocks (1.5 × 1.5 × 5 mm) of Scots pine (P. sylvestris) were exposed to fungal decay by A. vaillantii for 3, 7, 11, 16, and 22 days. No significant weight loss was determined in the initial decay periods within three up to 7 days. After three days of decay the topochemical investigation revealed that the lignin modification starts at the outermost part of the secondary wall layer, especially in the region of the latewood tracheids. During advanced degradation after exposure of 22 days, lignin modification occurs non-homogeneously throughout the tissue. Even among the significantly damaged cells, some apparently unmodified cells still exist. Knowledge about lignin modification at initial stages of wood degradation is of fundamental importance to provide more information on the progress of brown-rot decay.     

Effect of wood modification on lignin consumption and synthesis of lignolytic enzymes by the fungus Panus (Lentinus) tigrinus

Lignin consumption and synthesis of lignolytic enzymes by the fungus Panus (Lentinus) tigrinus cultivated on solid phase (modified and unmodified birch and pine sawdusts) were studied. The fungus grew better and consumed more readily the birch lignin than the pine wood. Peroxidase activity was higher in the case of pine sawdust; laccase and lignolytic activities, in the case of birth sawdust. Treatment with ammonia or sulfuric acid decreased lignin consumption by the fungus cultivated on either medium. Modification of sawdust by ultrasound increased lignin consumption and may be recommended for accelerating biodegradation of lignocellulose substrates.     

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 durability of home-garden teak against brown-rot and white-rot fungi

Natural decay resistance of teak wood grown in home-garden forestry and the factors influencing decay resistance were determined in comparison with that of a typical forest plantation. Accelerated laboratory tests were conducted on 1800 wood samples drawn from 15 trees of three planted sites. Analysis of variance based on a univariate mixed model showed that planted site, fungal species, and their interaction terms were important sources of variation in decay resistance. With increasing decay resistance from centre to periphery of the heartwood, radial position was a critical factor and the interaction effect of fungal species × radial position was significant in influencing the durability. No significant differences were found in decay resistance either between the opposite radii or due to the various possible interaction terms of radii with the site, fungal species and radial position. There were significant differences in decay resistance against brown-rot fungi between wet and dry sites of home-garden teak although differences against white-rot fungi were non-significant among the three planted sites. Polyporus palustris was the more aggressive brown-rot fungus than Gloeophyllum trabeum. The higher susceptibility of wet site home-garden teak to brown-rot decay was associated with a paler colour of the wood and lower extractive content.     

Assessment of the biocontrol potential of a Trichoderma viride isolate: Part II: Protection against soft rot and basidiomycete decay

A previous paper reported on the establishment of a field and fungal cellar trial set up to determine the biocontrol potential of a specific Trichoderma isolate against wood decay fungi. This paper reports on the analyses used to examine the protective effect of the selected isolate, and presents results indicating an initial protective effect against both basidiomycetes and soft rot fungi. The parameters assessed in the field and fungal cellar trials were soft rot decay, basidiomycete decay, Trichoderma colonisation, moisture content and nitrogen content. The results of these analyses show that the introduction of a biological control agent has had a significant effect on moisture content, decay and nitrogen content. A protective effect has been observed against soft rot and basidiomycete decay fungi in field samples.     

Changes in the Chemical Composition and Decay Resistance of Thermally-Modified Hevea brasiliensis Wood

In this study the effect of thermal treatment on the equilibrium moisture content, chemical composition and biological resistance to decay fungi of juvenile and mature Hevea brasiliensis wood (rubber wood) was evaluated. Samples were taken from a 53-year-old rubber wood plantation located in Tabapuã, Sao Paulo, Brazil. The samples were thermally-modified at 180°C, 200°C and 220°C. Results indicate that the thermal modification caused: (1) a significant increase in the extractive content and proportional increase in the lignin content at 220°C; (2) a significant decrease in the equilibrium moisture content, holocelluloses, arabinose, galactose and xylose content, but no change in glucose content; and (3) a significant increase in wood decay resistance against both Pycnoporus sanguineus (L.) Murrill and Gloeophyllum trabeum (Pers.) Murrill decay fungi. The greatest decay resistance was achieved from treatment at 220°C which resulted in a change in wood decay resistance class from moderately resistant to resistant. Finally, this study also demonstrated that the influence of thermal treatment in mature wood was lower than in juvenile wood.     

Characterization and stability investigation of Cu,Zn-superoxide dismutase covalently modified by low molecular weight heparin

Cu,Zn-superoxide dismutase (SOD) was chemically modified with low molecular weight heparin (LMWH). To characterize the conjugate, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide gel electrophoresis (native PAGE) with protein staining and polysaccharide staining were employed. The stabilities of the modified enzyme to heat, acid, alkali, and trypsin treatment were also investigated. SDS-PAGE of the conjugate presented two major bands, and native PAGE of the conjugate showed similar banding position with protein staining and polysaccharide staining, which was different from that of the unmodified SOD and LMWH/SOD mixture. Moreover, the conjugate migrated faster with increasing extent of the modification. Enhanced heat stability, acid resistance, alkali resistance, and anti-trypsin stability of the modified enzyme were observed compared with those of the unmodified enzyme. Results of the study suggest that covalent linkage in LMWH-SOD can be effectively characterized by electrophoretic techniques and the chemical modification of SOD with LMWH can enhance the stabilities of the enzyme. In addition, native PAGE with protein staining can be used to evaluate the extent of the modification.     

Characterization and stability investigation of cu,zn-superoxide dismutase covalently modified by low molecular weight heparin

Cu,Zn-superoxide dismutase (SOD) was chemically modified with low molecular weight heparin (LMWH). To characterize the conjugate, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and native polyacrylamide gel electrophoresis (native PAGE) with protein staining and polysaccharide staining were employed. The stabilities of the modified enzyme to heat, acid, alkali, and trypsin treatment were also investigated. SDS-PAGE of the conjugate presented two major bands, and native PAGE of the conjugate showed similar banding position with protein staining and polysaccharide staining, which was different from that of the unmodified SOD and LMWH/SOD mixture. Moreover, the conjugate migrated faster with increasing extent of the modification. Enhanced heat stability, acid resistance, alkali resistance, and anti-trypsin stability of the modified enzyme were observed compared with those of the unmodified enzyme. Results of the study suggest that covalent linkage in LMWH-SOD can be effectively characterized by electrophoretic techniques and the chemical modification of SOD with LMWH can enhance the stabilities of the enzyme. In addition, native PAGE with protein staining can be used to evaluate the extent of the modification.     

Effect of a lignin-degrading fungus on feeding preferences of Formosan subterranean termite (Isoptera: Rhinotermitidae) for different commercial lumber

The feeding preferences of the Formosan subterranean termite, Coptotermes formosanus Shiraki, for commercial lumber Alaska yellow cedar, Chamaecyparis nootkatensis (D. Don) Spach; yellow birch, Betula alleghaniensis Britton; northern red oak, Quercus rubra L.; redwood, Sequoia sempervirers (D. Don) Endl; and spruce (Picea spp.) were examined to determine whether the presence of the lignin-degrading basidiomycete Marasmiellus troyanus (Murrill) Singer could alter the relative preference of termites for these wood species. In paired choice tests with fungus-inoculated sawdust versus control sawdust, termites showed a strong preference for the fungus-inoculated sawdust for all wood species tested, except for Alaska yellow cedar. In a multiple-choice test using sawdust without fungus, termites showed a very strong preference for red oak sawdust over the other three species. In a paired choice test using fungus-inoculated sawdust, termites showed a preference for redwood over red oak sawdust. In a feeding test using autoclaved wood blocks without fungal decay, there was no difference in termite consumption of birch, red oak, or redwood. The relative preference of termites for redwood increased when blocks were decayed by M. troyanus for 3 and 8 wk. These results indicate that chemical modifications due to fungal decay affected the feeding preference of termites for different commercial lumber.     

Characterisation of the initial degradation stage of Scots pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) sapwood after attack by brown-rot fungus <Emphasis Type="Italic">Coniophora puteana</Emphasis>

In our study, early period degradation (10 days) of Scots pine (Pinus sylvestris L.) sapwood by the brown-rot fungus Coniophora puteana (Schum.: Fr.) Karst. (BAM Ebw.15) was followed at the wood chemical composition and ultrastructurelevel, and highlighted the generation of reactive oxygen species (ROS). An advanced decay period of 50 days was chosen for comparison of the degradation dynamics. Scanning UV microspectrophotometry (UMSP) analyses of lignin distribution in wood cells revealed that the linkages of lignin and polysaccharides were already disrupted in the early period of fungal attack. An increase in the lignin absorption A₂₈₀ value from 0.24 (control) to 0.44 in decayed wood was attributed to its oxidative modification which has been proposed to be generated by Fenton reaction derived ROS. The wood weight loss in the initial degradation period was 2%, whilst cellulose and lignin content decreased by 6.7% and 1%, respectively. Lignin methoxyl (–OCH₃) content decreased from 15.1% (control) to 14.2% in decayed wood. Diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy corroborated the moderate loss in the hemicellulose and lignin degradation accompanying degradation. Electron paramagnetic resonance spectra and spin trapping confirmed the generation of ROS, such as hydroxyl radicals (HO^∙), in the early wood degradation period. Our results showed that irreversible changes in wood structure started immediately after wood colonisation by fungal hyphae and the results generated here will assist in the understanding of the biochemical mechanisms of wood biodegradation by brown-rot fungi with the ultimate aim of developing novel wood protection methods.     

Distribution of Myxomycetes on coarse woody debris of <Emphasis Type="Italic">Pinus densiflora</Emphasis> at different decay stages in secondary forests of western Japan

The relationship between myxomycete species and the decay stage of wood of Pinus densiflora coarse woody debris was investigated in warm temperate secondary forests of western Japan. The number of species and species diversity of the myxomycete community reached the maximum on moderately decayed wood. The 25 dominant species recorded from 8 or more samples of the total 1530 samples were arranged in order of the succession index corresponding to the stage of decay. Species on slightly decayed hard pine wood were characterized by Stemonitis splendens, Enerthenema papillatum, and Physarum viride, whereas species of Cribrariaceae were found on brittle decayed soft wood increasing abundance according to the decay stages. Most of the species occurred where there was sufficient moisture preserved in the environment of the decaying wood, although S. splendens specifically emerged in low-moisture environments. Because the myxomycete species had preference to different decay stages of wood, it appears that they change sequentially during myxomycete community succession on dead pine wood according to the progression of decay.