Improved Decay Resistance Research Articles

Effect of pressurized hot water extraction and esterification on the moisture properties and decay resistance of Scots pine (Pinus sylvestris L.) sapwood

Abstract Pressurized hot water extraction (HWE) treatment has the benefit of simultaneous extraction of hemicellulose-based carbohydrates and modification of the solid phase, but it does not drastically improve wood durability. However, removing hemicelluloses from the wood by HWE treatment creates water-filled spaces in the cell walls which could be filled with modification agent in order to improve the properties of the wood. Without drying, modification agent can be added into the saturated wood via diffusion. The esterification of wood with citric acid (CA) improves resistance to biological deterioration but increases brittleness. However, combining CA esterification with additional chemicals that form links with CA can mitigate brittleness. This study investigated esterification as a method for modifying HWE treated wood. HWE treatment with CA solution (4% w/v) was applied at 120 °C for 3 h to Scots pine (Pinus sylvestris L.) sapwood specimens. The specimens were further modified by diffusion with CA and starch derivatives followed by curing. The applied method changed the moisture properties and chemical composition of the wood. The results showed successful wood bulking. The investigated method slightly improved decay resistance to Coniophora puteana and Trametes versicolor but did not change resistance to Rhodonia placenta.

Pseudo lignin formed from hygrothermally treated holocellulose and its effect on fungal degradation

Hygrothermal processes are widely used in modification of wood or other lignocellulosic materials to improve their decay resistance and dimensional stability. However, the mechanism behind the improved decay resistance is still unclear. In this study, hygrothermal modification of holocellulose was carried out at different temperature (℃) -duration (min) combinations (180−60, 220−60, 220−180), and the formation of pseudo lignin in modified holocellulose was verified. Its yield, as indicated by the acid insoluble substance, increased with the intensity of the hygrothermal modification from 0.11% for untreated holocellulose to 3.85%, 24.13%, and 65.86% for 180–60, 220–60, 220–180, respectively. According to the results of HPLC, FTIR, solid 13C NMR, 31P NMR, XRD and Py-GC-MS, the formed pseudo lignin contains polyfuran, aromatic, carbonyl and aliphatic structures. The formation pathway of pseudo lignin was proposed. It exhibited a significant inhibition effect against Gloeophyllum trabeum (brown rot fungus) with reduced mass losses from 6.89% for untreated holocellulose to 6.43%, 1.09% and 0.03% for 180–60, 220–60, 220–180, respectively; however, the inhibition effect against Coriolus versicolor (white rot fungus) was much less obvious. This provides an innovative point of view to explain the fungal degradation behavior of thermally modified wood or other carbohydrate materials.

Small Angle Neutron Scattering Reveals Wood Nanostructural Features in Decay Resistant Chemically Modified Wood

While it is known that modifying the hydroxyls in wood can improve the decay resistance; what is often missing in the literature is whether these modifications alter wood nanostructure, and how these changes correlate to the improved decay resistance. Here, we used small angle neutron scattering (SANS) to probe the effects of alkylene oxide modifications on wood nanostructure. Southern pine wood samples were chemically modified to various weight percentage gains (WPG) using four different alkylene oxides: propylene oxide (PO), butylene oxide (BO), epichlorohydrin (EpH), and epoxybutene (EpB). After modification, the samples were water leached for 2 weeks to remove any unreacted reagents or homopolymers and then equilibrium moisture content (EMC) was determined at 90% relative humidity (RH) and 27°C. Laboratory soil block decay evaluations against the brown rot fungus Gloeophyllum trabeum were performed to determine weight loss and biological efficacy of the modifications. To assist in understanding the mechanism, SANS was used to study samples that were fully immersed in deuterium oxide (D2O). These measurements revealed that the modifications altered the water distribution inside the cell wall, and the most effective modifications reduced the microfibril swelling and preserved the microfibril structure even after being subject to 12 weeks of brown rot exposure.

Comparative studies on the durability and moisture performance of wood modified with cyclic N-methylol and N-methyl compounds

Glyoxal-based condensation resins like 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) have been used to modify wood and improve its resistance against decaying fungi. High biological durability of DMDHEU-treated wood has already been confirmed in laboratory and field tests in the past. However, the modes of protective action behind an improved decay resistance are not fully understood yet. Furthermore, it is questionable how the use of formaldehyde-poor N-methylol and formaldehyde-free N-methyl compounds instead of DMDHEU affects the moisture behavior and durability, respectively. In this study, wood blocks were treated with N-methylol (DMDHEU, methylated DMDHEU) and N-methyl compounds (1,3-dimethyl-4,5-dihydroxyethyleneurea; DMeDHEU). Untreated and modified specimens were exposed to different moisture regimes and wood-destroying fungi in order to study the indicators that control changes in the wetting ability and decay resistance. Both N-methylol and N-methyl compounds decreased the water uptake and release and increased the durability of Scots pine sapwood from ‘not durable’ (DC 5) to ‘very durable to durable’ (DC 1–2). However, high fluctuations were observed in water uptake and release as well as mass loss (ML) caused by fungal decay, when modified specimens were tested without passing through a cold-water leaching. Consequently, a significant effect of the leaching procedure according to EN 84 on the durability classification could be established. The latter appeared more pronounced for treatments with N-methyl compounds compared to N-methylol compounds. Finally, wetting ability (kwa) and resistance indicating factors (kinh) enabled a forecast of high biological durability for both treatments with N-methylol and N-methyl compounds under real service life conditions.

Dynamic strength properties and structural integrity of wood modified with cyclic N-methylol and N-methyl compounds

Abstract Cyclic N-methylol compounds have been used for cell wall impregnation modifications of wood. Besides an improved decay resistance and dimensional stability, the modifications resulted in a decrease of wood’s dynamic strength properties. However, the mechanisms behind a significant loss in dynamic strength are not fully understood yet. In this study, wood blocks were treated with the N-methylol compounds 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and methylated DMDHEU (mDMDHEU) and the N-methyl compound 1,3-dimethyl-4,5-dihydroxy-ethyleneurea (DMeDHEU). In order to study the factors that control the changes of wood performance under dynamic loads, single (impact bending strength, IBS) and multiple dynamic impact (resistance to impact milling, RIM) tests were applied. It became evident, that reductions in IBS and RIM increased with increasing solid content, formaldehyde content and catalyst concentration of the impregnation solutions, but were not affected by a cold-water leaching. Differences in structural integrity of wood modified with N-methylol and N-methyl compounds were more pronounced than those of IBS. Therefore, RIM appeared more sensitive to changes on cellular level, as a higher degree of co-condensation of the N-methylol compounds with cell wall polymers was expected in comparison with the N-methyl compound.

Effect of tallow impregnation on moisture behavior and decay resistance of various wood species

ABSTRACT Beef tallow is a by-product of rendering of fats from meat production. While tallow can be used for a variety of applications including biodiesel production, it might also be useful for enhancing the water resistance of wood to improve durability. The effects of differing retentions of tallow on wood performance were evaluated in scots pine, beech and poplar. Tallow slowed but did not completely limit water uptake nor did it completely inhibit swelling. Fourier transform infrared spectroscopic analysis indicated that tallow did not appreciably alter the wood chemistry and TGA analysis suggested that it had only minor thermal effects. Fungal exposures suggested that tallow treatment improved decay resistance slightly but would not function as a stand-alone wood protectant. The results suggest that tallow might be a useful additive for bulking the wood to enhance water repellency of an existing preservative.

β-Cyclodextrin-allyl isothiocyanate complex as a natural preservative for strand-based wood composites

Environmental concerns over chemicals used for protecting wood and wood products from biological degradation have prompted the development of natural wood preservatives with lower health risks and prolonged efficacy. In this study, an effective and environmentally friendly method is demonstrated to substantially improve the durability of a strand-based wood composite product by incorporating a natural wood preservative system. Specifically, allyl isothiocyanate (AITC), a mustard oil-based natural biocide, was encapsulated into the cavity of β-cyclodextrin (βCD) and the as-prepared βCD-AITC complex was applied in the strand-based composite manufacturing process to produce a natural-preservative-treated engineered wood panel. The formation of the βCD-AITC complex was qualitatively confirmed by attenuated total reflection-Fourier transform infrared spectroscopy, and the inclusion yield of AITC was estimated to be 71% by thermogravimetric analysis. The preservative complex was blended with southern pine strands at 0%, 5%, and 10% prior to the application of polymeric methylene diphenyl diisocyanate resin and hot-pressing. The application of the preservative system significantly improved decay resistance against brown-rot fungi, Gloeophyllum trabeum and Postia placenta, by keeping the average mass losses of the treated panels below 7%. The internal bond strengths of the treated panels were maintained above the required level for structural OSB for use in humid conditions specified in the European OSB product standard. This study suggests the βCD-AITC complex to be a promising alternative to conventional preservatives for the protection of wood composite products.

Photostability of acetylated wood coated with nano zinc oxide

Chemical modification with acetic anhydride is an effective method to stabilise wood against dimensional movement and improve decay resistance of wood. It has also been reported to retard UV light induced color darkening on wood surface. Coatings of wood surfaces with certain nano metal oxides have also shown promise as UV screening agent.In this work, we have evaluated synergistic effect of acetylation of wood and application of nano material on wood surfaces to enhance their UV stability. Photo-stability of acetylated Wrightia tinctoria wood coated with zinc oxide (ZnO) nanodispersion was evaluated by irradiating these wood specimens to UV radiation in an accelerated weathering tester. Acetylation of wood with acetic anhydride exhibited photo-bleaching and inhibited light-induced color darkening observed in unmodified wood. Coating of unmodified and modified wood surfaces with ZnO nanodispersion reduced photo-discolouration and degradation of wood polymers. The photo-bleaching observed in chemically modified wood upon light irradiation was further enhanced by application of nano coating on wood surfaces

Evaluation of dimensional stability, surface roughness, colour, flexural properties and decay resistance of thermally modified Acacia auriculiformis

This paper presents the effect of thermal modification of 14-15 year-old plantation grown Acacia auriculiformis wood in the 150-240oC temperature range under vacuum condition. Important techno-mechanical parameters of thermally modified wood such as density, dimensional stability, colour, surface roughness, decay resistance against brown and white rot fungi and flexural properties were evaluated and compared with control. Depending on severity of heat treatment, colour of modified sapwood was turned from light to dark brownish. Moreover, the change in colour was found to be uniform throughout the thickness of wood blocks. Amount of shrinkage of Acacia auriculiformis wood was observed to be decreased with increasing treatment temperatures. Maximum dimensional stability of wood thermally modified at 240oC was in the range of 60-65%. The surface roughness parameters (Ra and Rz) were reduced significantly after the treatment. The flexural strength (modulus of rupture-MOR) was observed to be reduced with increasing treatment temperatures. However, flexural stiffness (modulus of elasticity-MOE) was not found to be affected significantly up to 210oC temperature. The lower amount of weight loss of thermally modified wood compared to untreated control showed improved decay resistance against white and brown rot fungi. With desirable improvements in various esthetic and technologically important quality parameters such as enhanced dimensional stability, biological durability against fungi and certain other properties, thermally modified wood from short-rotation Acacia auriculiformis may be considered as viable alternative to scarcely available timber resource for different value-added applications.

Structural Strength Calculation & Analysis for Pressure-proof Seawater Filter in Certain Type Titanium Alloy Based on ANSYS

At present, main material of pressure-proof seawater filters for ships is copper alloy. But in order to improve decay resistance and structural strength of seawater filters, it’s proposed to use titanium alloy instead. Now use finite element analysis software ANSYS to calculate and analyze structural strength of pressure-proof seawater filter in titanium alloy, and then it’s found that the material structure and its parts both can meets the demands of strength after calculating with titanium alloy.

INVESTIGATION OF DECAY RESISTANCE OF ALKALINE COPPER, UREA-FORMALDEHYDE, AND PHENOL -FORMALDEHYDE RESINS

The decay resistance of modi fi ed fast-growing poplar lumber with ion-based preservative and thermosetting resins were determined in laboratory and field stake tests. Commercial alkaline copper quat-type D (ACQ-D), thermosetting phenol–formaldehyde (PF) resin with varying concentrations, and urea–formaldehyde (UF) resin were used to improve decay resistance of low-grade fastgrowing poplar. The results indicated that the concentrations of PF and weight gains of resin-modified specimens were highly correlated, and target resin retains can be achieved from resin concentration. The retention rates of ACQ of 1.1% concentration, UF of 41.5% concentration and PF of 10% concentration were 6.72, 18.43, and 7.31 kg/m3, respectively. For PF, the retention rate is linearly related to concentration. The mass losses (ML) for the untreated, ACQ-treated, and UF-treated specimens were 26.34%, 8.91%, and 11.66% after 12 wk of incubation in laboratory, respectively. The ML for the treated specimens were 9.74%, 7.32%, 3.14%, 2.38%, and 2.41% for PF impregnated wood at concentrations of 10%, 15%, 20%, 25%, and 40%, respectively, after 12 wk of incubation in the laboratory.

Effect of thermal modification on the micromorphology of decay of hardwoods and softwoods by the white rot fungusPycnoporus sanguineus

AbstractThermal modification (TM) of wood at high temperatures can lead to significantly improved decay resistance against white rot (WR) fungi, but little is known about the mechanism of this improvement at the cellular level. As a contribution to this topic, hardwoods (HWs) (ash, beech) and softwoods (SWs) (spruce, fir) were submitted to the Termovuoto®TM process at 220°C for 3–4 h (shortly TMW220°C) and were degraded by the WR fungusPycnoporus sanguineus.The results were studied using microscopy techniques. Decay occurred preferentially via cell wall delignification prior to the removal of cellulose and hemicelluloses. Concerning this effect and fungal colonization, there were no essential differences between TMW220°Cand the unmodified reference of all wood species. TMW220°C, however, showed a number of characteristic changes in decay morphology. Narrow and distinct concentric transition zones were observable in decayed fiber and tracheid cell walls, which demark the lignified and delignified regions. Moreover, cell wall separation by preferential delignification of compound middle lamellae (CML) was not seen in decayed tracheids. It can be concluded that the Termovuoto TMW220°Cprocess has an impact on the delignification process ofP. sanguineusat the cell wall level, which slows down the decay.

Layer-by-layer self-assembly of reduced graphene oxide on bamboo timber surface with improved decay resistance

Because bamboo is easily attacked by many fungi, and conventional preservatives have many disadvantages including environmental pollution and human health damage, bamboo products should be protected with environmentally friendly methods. Herein, a novel and efficient process for fabrication of antifungal bamboo timber by coating with graphene materials is presented. The crystal phase, morphology, microstructure and other physicochemical properties of the as-prepared samples were characterized by XRD, Raman, SEM, EDX, XPS and FTIR. XRD studies and Raman spectrum confirmed that graphene oxide was reduced to graphene aggregates in the one-step hydrothermal reduction process. SEM images proved that reduced graphene oxide (RGO) nanoplates were deposited on bamboo timber surface by layer-by-layer self-assembly. EDX proved the carbon element composition of RGO coating on the bamboo surface. XPS and FTIR indicated strong interaction of hydrogen bond between bamboo substrate and RGO coating. The anti-fungal activity of bamboo timber with RGO coating was improved significantly when bamboo was infected by Gloeophyllum trabeum and Panerochaete chrysosporium.

Decay resistance and dimensional stability improvement of wood by low melting point alloy heat treatment

Wood has no inherent natural resistance against agents of biodegradation. We evaluated the effects of metal bath heat treatment (MBHT) on decay resistance and dimensional stability of Chinese parasol (Firmiana simplex) and Chinese fir (Cunninghamia lanceolata) wood. A low melting point alloy was used as heating medium in the treatment of the wood samples at 150, 180, and 210 °C for 2, 4, and 8 h. Heat-treated and control samples were exposed to brown rot fungus (Poria placenta) and white rot fungus (Coriolus versicolor) for decay resistance testing and anti-swelling efficiency (ASE). The improved decay resistance with increase temperatures with low mass losses of 7.3 and 7.3% for F. simplex, and 3.9 and 3.6% for C. lanceolata at 210 °C for 8 h against Coriolus versicolor and Poria placenta, respectively. ASE indicated that MBHT contributed to improved dimensional stability of both wood species after treatment. Scanning electron micrograph results indicate that metal bath-treated samples showed strong decay resistance. Therefore, our approach to thermally modify wood should be explored to overcome the energy utilization by using low melting point alloy for the heat treatment of wood.

Chemical characterization and decay resistance analysis of smoke treated bamboo species

Severe human health and environmental hazards associated with commercial chemical preservatives has prompted researchers to look for alternative treatment techniques for preservation of bamboo species. In the present study, validation of traditional smoke treatment method to preserve bamboo species (D. strictus) has been performed. Physico-chemical characterization of smoke treated culms showed reduction in alkali solubility (18.8 %), starch (34.5 %) and moisture content (69 %) and considerable increase in lignin content (24.5 %). Improved decay resistance of smoke treated sample (weight loss: 12.2 %) as compared to severely degraded control samples (weight loss: 55.6 %) shows the potential of this indigenous method to preserve bamboo.

Utilization of temperature kinetics as a method to predict treatment intensity and corresponding treated wood quality: Durability and mechanical properties of thermally modified wood

Wood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. However, this improvement of durability is realized at the expense of the mechanical resistance. Decay resistance and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. However, the introduction of a fast and accurate system for measuring this mass loss on an industrial scale is very difficult. Nowadays, many studies are conducted on the determination of control parameters which could be correlated with the treatment conditions and final heat treated wood quality such as decay resistance. The aim of this study is to investigate the relations between kinetics of temperature used during thermal treatment process representing heat treatment intensity, mass losses due to thermal degradation and conferred properties to heat treated wood. It might appear that relative area of treatment temperature curves is a good indicator of treatment intensity. Heat treatment with different treatment conditions (temperature-time) have been performed under vacuum, on four wood species (one hardwood and three softwoods) in order to obtain thermal degradation mass loses of 8, 10 and 12%. For each experiment, relative areas corresponding to temperature kinetics, mass loss, decay resistance and mechanical properties have been determined. Results highlight the statement that the temperature curves’ area constitutes a good indicator in the prediction of needed treatment intensity, to obtain required wood durability and mechanical properties such as bending resistance and Brinell hardness.

Wood thermodegradation: experimental analysis and modeling of mass loss kinetics

Wood heat treatment is an attractive alternative to improve decay resistance of low natural durability of wood species. Decay resistance is strongly correlated to thermal degradation of wood cell wall components. Some recent studies proposed the use of wood mass loss during the heat treatment as a valuable marker to predict final properties of the material (Hakkou et al. 2006, Welzbacher et al. 2007). In this study, heat treatment was carried out in a relatively low temperature (230°C). Mass loss kinetics was studied using equipment, specially conceived to measure sample�s mass during the thermal treatment. Laboratory experiments were performed for heating rates of 1°C min-1. Mathematical model for kinetics of pyrolysis process was used and validated. During the pyrolysis of dry wood samples under inert atmosphere, measurements of temperature distribution and dynamic weight loss were performed. Five different wood species Fagus sylvatica (Beech), Populus nigra (Poplar), Fraxinus excelsior (Ash), Pinus sylvestris (Pine) and Abies pectinata (Silver Fir) were investigated. The unsteady-state mathematical model equations were solved numerically using the commercial package Femlab 2.0. A detailed discussion of the computational model and the solution algorithm is given. The validity of different model assumptions was analyzed. Experimental results were compared with those calculated by the model. Acceptable agreement was achieved.

Comparison of mechanical properties of heat treated beech wood cured under nitrogen or vacuum

Heat treated wood has been subjected to increasing interest during the last decade. This non biocidal treatment is an attractive alternative with a low environmental impact to improve decay resistance of low natural durability wood species. Nowadays, several types of heat treatment processes exist. These treatments differ mainly by the nature of the inert atmosphere used to avoid combustion of wood: nitrogen, steam pressure, oil or more recently vacuum. We have shown in a previous study that utilization of vacuum to perform thermal treatment instead of nitrogen allows to reduce considerably degradation of wood polysaccharrides. Indeed, it appears that for a similar 12% mass loss generated by thermal degradation, thermodegradation performed under vacuum allowed to reduce degradation of sugar constitutive of hemicelluloses and formation of recondensation products within the wood structure. These results may be explain by the effect of vacuum allowing removal of volatile degradation products like organic acids, aldehydes and furans limiting therefore acidic degradation of polysaccharides and recondensation of volatile by-products. Decay durability tests, performed against different brown and white rots fungi, have shown no significant differences for vacuum and nitrogen heat treated samples, all presenting an improved decay resistance.According to these results, the aim of this short paper is to report the effect of vacuum versus nitrogen on the mechanical properties of heat treated samples making the assumption that lower degradation of wood polysaccharides during treatment performed under vacuum may reduce the weakening of mechanical properties. For this purpose, modulus of rupture (MOR) and modulus of elasticity (MOE) in bending and Brinell hardness (HB) were determined. Results show that the mechanical properties were lower degraded in the case of wood samples treated under vacuum.

Comparison of chemical composition and decay durability of heat treated wood cured under different inert atmospheres: Nitrogen or vacuum

Wood heat treatment is an attractive alternative to improve decay resistance of low natural durability wood species. Nowadays, several types of thermal treatments of wood exist. These treatments differ mainly by the nature of the inert atmosphere used to avoid wood combustion which may correspond to: nitrogen, vacuum, steam or oil. Decay resistance is strongly correlated to thermal degradation of wood cells wall components and consequently of treatment conditions from which depend chemical modifications. The aim of this study is to determine the effect of a new generation of treatment performed under vacuum on the chemical modifications occurring during treatment. For this purpose, one hardwood (beech) has been treated under different conditions (vacuum, nitrogen, steam). All treatments were performed at 220 °C for mass losses resulting from wood thermodegradation of approximately 12%. For each treatment condition extractives, Klason lignin, hemicelluloses and α-celluloses content were determined as well as monosaccharide composition. Intensity of thermodegradation was also evaluated by TD-GC-MS. Results show that extracts content were lower in the case of wood samples treated under vacuum, while lignin, hemicelluloses and α-celluloses contents were higher in the case of samples treated under steam and nitrogen, indicating lower wood degradation under vacuum treatment. These results were confirmed by chromatography analyses according to the nature and quantity of thermodegradation volatile products formed during TD-GC-MS analyses.

Decay resistance and physical properties of oil heat treated aspen wood

The decay resistance of oil-heat treated aspen wood (Populus tremula l.) against white rot fungi (Coriolus versicolor) and brown rot fungi (Coniophora puteana) was investigated. Three different temperature stages and two time levels for oil heat treatment for the selection of optimum conditions were determined. Linseed oil as a heating medium was used. The mass loss of treated samples that were exposed to both fungi was significantly lower than that of the control samples. Results also showed improvement in dimensional stability after oil heat treatment. Decay resistance and dimensional stability of aspen wood were increased significantly with temperature increasing, but time seemed to have no effect on those properties. Oil heat treatment is a suitable method to improve decay resistance of aspen wood as it reduced the mass loss by 71% and 77% against Coriolus versicolor and Coniophora puteana compared with control samples, respectively. On the other hand, oil heat treatment improved the dimensional stability by about 20.5%.