Fungal Durability Research Articles

Changes in chemical composition, crystallinity, and microstructure of wood fiber mat-reinforced composite caused by white-rot fungus Trametes versicolor and brown-rot fungus Gloeophyllum trabeum

ABSTRACT Wood fiber mat-reinforced composite (WFMRC) is a novel type of engineering wood-based polymer composite for decorative and building applications. Fungal decay strongly influences the service life of wood composites in outdoor environments. In this study, fungal durability tests were conducted to investigate how white- and brown-rot fungi (Trametes versicolor and Gloeophyllum trabeum, respectively) affect the chemical composition, crystallinity, and morphology of WFMRCs made from two different wood species (poplar and larch). The poplar WFMRC lost more mass (18.3% and 18.4% by T. versicolor and G. trabeum, respectively) than the decayed larch WFMRC (11.4% and 18.4% by T. versicolor and G. trabeum, respectively) after 12 weeks of fungal exposure. Chemical analysis and Fourier-transform infrared spectroscopy measurement revealed the degradation of holocellulose of the WFMRCs after fungal decay. X-ray diffraction analyses demonstrated that fungal decay increased the crystallinity of the poplar WFMRC but decreased the crystallinity of the larch WFMRC. Bore hole formation on the walls of wood cells, cell wall thinning, and collapsed cells were found in decayed samples, particularly in the poplar WFMRC. Although the WFMRCs could be classified as resistant to fungal decay, an appropriate protective measure should be considered to improve the outdoor durability of the WFMRC.

Combining mineralisation and thermal modification to improve the fungal durability of selected wood species

The development of non-biocidal and environmentally friendly systems to protect wood against biological decay has become a high priority in recent years. In the present study the impact of an innovative modification procedure, combining two environmentally friendly modification methods: thermal modification and mineralisation, using an aqueous solution of calcium acetoacetate as a precursor, on the fungal durability of wood was evaluated. European beechwood (Fagus sylvatica) and Norway sprucewood (Picea abies) were selected as model wood species. Wood samples were treated using either a single or combination of both methods and exposed to four different fungi: Gloeophyllum trabeum, Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus. The effect of the different modifications on moisture content, dynamic vapour sorption, contact angle and pH value was also evaluated. Overall, the highest durability against Rhodonia placenta, Trametes versicolor and Pleurotus ostreatus was achieved through thermal modification in both wood species, while the combination of mineralisation and thermal modification has a synergistic effect against degradation by Gloeophyllum trabeum. In the case of beechwood the mass loss decreased from 41% for native to 6% for combined modified samples. We proved that the effectiveness of different treatment against fungal decay of wood were in strong dependence of their moisture content, dynamic vapour sorption, contact angle and pH values. The role of fungi on the morphology of the wood and on crystal structure of formed carbonate was investigated using SEM-EDS analysis.

Physical, mechanical, and decay resistance properties of heat-treated wood by Besson® process of three European hardwood species

Description of the subject. In Europe, the heat treatment of native wood species is gradually becoming an industrial reality. It provides a promising alternative to both the use of naturally durable, essentially tropical woods and the use of chemical preservative treatments based on biocides. Objectives. The aim of this study is to quantify the effect of heat treatment on the physico-mechanical and decay resistance properties of three native hardwood species (oak, ash, beech + steamed beech). Method. The wood was heat-treated in accordance with the Besson® process. The standard physical and mechanical tests including hardness, modulus of elasticity in static bending, static bending, axial compression, splitting and impact bending strengths, have been performed on 15 treated and 15 control associated samples for each species. The standard durability test on fungi exposed 60 treated and 60 control samples to each fungus. Results. The results show a decrease in the equilibrium moisture content and an increase in dimensional stability of heat-treated wood for the three species studied. The modulus of elasticity, hardness and axial compression strength increase slightly after the heat treatment, while static and impact bending strength and splitting strength may considerably decrease. The fungal durability of oak heartwood and ash increased until class 1, beech and steamed beech until class 3. Conclusions. The global approach of this study allows a complete and precise characterization of the technological properties of three native hardwood species after heat treatment. New uses of these native species can thus be explored.

Effect of Thermo-Treatment on the Physical and Mechanical, Color, Fungal Durability of Wood of Tectona Grandis and Gmelina Arborea from Forest Plantations

This study evaluated the effect of thermo-treatment (THT) at 4 temperatures on the density, shrinking, mass loss, moisture absorption, color, durability in terms of resistance to decay, flexural strength, tensile adhesion of glue line and the infrared spectrum of the wood of Tectona grandis and Gmelina arborea. Sapwood, heartwood and radial and tangential grain patterns were studied. The results showed that the THT temperature decreases the density, the percentage of moisture absorption, the modulus of elasticity and modulus of rupture in the flexure test and the tensile adhesion of glue line. The percentage of shrinking and durability presented irregular behavior relative to the THT temperature. The percentage of mass loss increased with increasing THT temperature in both species. The total color change (∆E*) of thermo-treated wood (THTwood) also increased with increasing THT temperature. Sapwood of T. grandis and G. arborea, having clearer shades, showed a more noticeable color change compared to hardwood; however, no significant differences were obtained between some of the THT temperatures.DOI: http://dx.doi.org/10.5755/j01.ms.24.1.17545

Combined effect of acetylation and heat treatment on the physical, mechanical and biological behavior of jack pine (Pinus banksiana) wood

A comparative study on the combined effect of heat treatment and acetylation on jack pine wood properties was undertaken and the results were compared with those of each treatment carried out individually. The dimensional stability and mechanical property of wood with different treatments were examined and statistically analyzed. The results demonstrated that combined acetylation of jack pine wood with acetic anhydride and heat treatment at 190 °C has a positive effect on the dimensional stability. Results also suggested that the dimensional stability was affected more than the modulus of rupture (MOR) and modulus of elasticity (MOE) by both heat and acetylation treatments under the experimental conditions used. In addition, the hardness increases after high temperature modification but decreases slightly after acetylation. A comprehensive investigation of the effects of heat treatment and acetylation separately and together (combination treatment) on the fungal durability of jack pine wood against a brown rot fungus, Poria placenta (pp), and a white rot fungus, Trametes versicolor (tv) has also been performed. The results indicated that the weight loss caused by fungi is reduced by both modifications. It was also found that combination of heat treatment and acetylation offers additional bioprotection. FTIR results indicated that the heat and acetylation treatments have a significant influence on the chemical properties, but less influence on their structures.

DIMENSIONAL STABILITY AND FUNGAL DURABILITY OF ACETYLATED WOOD

DIMENSIONAL STABILITY AND FUNGAL DURABILITY OF ACETYLATED WOOD

Glassy state of wood polymers in native and thermally modified wood: effects on long-term material performance in service

This research analyses the effect of a glassy state of wood polymers, as found in some dense naturally durable wood species and in thermally modified wood (TMW), on their equilibrium moisture content, mechanical and fungal resistance (durability) performance. In the EN350-class I durability range, moisture and fungal durability are argued to become controlled by the physical state of wood polymers rather than their chemical composition. Glassy polymers may assist the dimensional stability and fungal resistance of wood, as characterised by standardised accelerated laboratory tests. However, for long-term mechanical performance and fungal resistance in service, strong cross-links must prevent the natural (aging) relaxation of the glassy state. Physical aging is expected to occur in TMW, as opposed to naturally durable wood species. The current test methodology for dimensional and fungal stability does not take physical aging effects in wood polymers into account.

Decay resistance of softwoods and hardwoods thermally modified by the Thermovouto type thermo-vacuum process to brown rot and white rot fungi

AbstractSoftwoods (SW, spruce and fir) and hardwoods (HW, ash and beech) were thermally modified by the thermo-vacuum (Termovuoto) process for 3–4 h in the temperature range 160–220°C (TMW160–220°C) and their fungal durability were examined in soil-block tests with two brown rot (BR,Postia placenta, Gloeophyllum trabeum) and two white rot (WR,Pycnoporus sanguineus, Phlebia radiata) fungi. SW-TMW160–220°Cwere exposed toP. placentaandP. sanguineusand HW-TMW190–220°Cto all fungal species. Considerable improvement (durability class 1–3) in decay resistance was only achieved for SW- and HW-TMW220°C. Thermal modification (TM) below 200°C influenced decay resistance negatively in case of some fungal species applied for both SW and HW. Judged by the durability class, decay resistance was higher in HW- than in SW-TMW at high TM temperature. Behavior of TM differed significantly between ash (ring-porous HW) and beech (diffuse-porous HW). A comparison between results of soil- and agar-block tests on Termovouoto wood demonstrated that the influence of testing method in terms of assignment to durability classes is not significant.

Preparation and Properties of Heat-treated Masson Pine (Pinus massoniana) Veneer

The feasibility of heat treatment of Masson pine veneers (MPVs) was evaluated based on mass loss, tensile strength, bending strength, and water absorption of the heat-treated MPVs, and its application in plywood was explored. Fourier-transform infrared and X-ray diffraction results showed that heat-treated MPVs contained a lower amount of hydrophilic groups and had an increased crystallinity. The maximum tensile strength was 59.2 MPa when MPVs were heat-treated at 210 °C for 5.0 min. The corresponding mass loss, water absorption (384 h), and bending strength values were 1.72%, 105.44%, and 83.1 MPa, respectively. Plywood produced from heat-treated MPV (210 °C, 30 min) with the best fungal durability and the lowest shear strength (1.07 MPa) still met the requirements of the Chinese National Standard (GB/T 9846.3-2004, ≥0.80 MPa) for exterior plywood. These results indicate that products based on heat-treated MPV will have increased fungal durability.

Comparison of EMC and durability of heat treated wood from high versus low water vapour pressure reactor systems

A large number of different heating technologies has been put into use for industrial scale thermal modification of wood. A useful classification of these processes is by the level of water vapour pressure, which ranges from vacuum to high saturated steam pressures. Only high water vapour pressure systems can maintain a finite moisture content during the heat treatment, but little is known about the water vapour pressure dependence of the thermal modification chemistry and the resulting modified wood properties. It is concluded from our analysis that the thermal wood reaction chemistry at the molecular functional group level is quite independent of the process and wood species. Wood properties that are strongly determined by wood chemical composition, such as the fungal durability and the equilibrium moisture content (EMC), can hence be equally achieved by all processes and for all wood species. This finding cannot be transferred to every other thermally modified wood property.

Fungal durability of polyaniline modified wood and the impact of a low pulsed electric field

New wood protection technologies should be effective against biodeterioration and at the same time minimize environmental impact. The present study investigates the effect of polyaniline modification of wood and the effect of a pulsed electric field on fungal protection. The effect of fungi and a pulsed electric field on the conductivity of the modified wood was also measured.It was found that it is possible to polymerize polyaniline particles in-situ homogeneously throughout the wood specimens. The polyaniline particles themselves were not found to be anti-fungal, however when in contact with water they affected the pH drastically and inhibited fungal growth. The wood treatment with polyaniline and the connection to a pulsed electric field were found to be effective in protecting the wood from deterioration when exposed to Postia placenta. The unmodified samples that were connected to a pulsed electric field lost under 10 wt% due to fungal degradation. The combination of polyaniline treatment with the connection to a pulsed electric field showed a slight synergistic effect which resulted in less weight loss due to fungal degradation. However, a more brittle wood structure was observed.Leached and fungal exposed samples showed a significant drop in the conductivity, indicating that the network has broken down slightly.

Effect of extractives on conferred and natural durability of Cupressus lusitanica heartwood

• Identification of extractives present in Cupressus lusitanica heartwood has been conducted using GC-MS analyses. The chromatogram of toluene/ethanol extracts indicated the presence of large amounts of benzaldehyde and numerous terpenic compounds such as cedrol, agathadiol, epimanool, bornyl acetate, α-cedrene and β-cedrene. • The effect of these extractives on the natural durability of cypress wood was investigated on heart wood blocks exposed to pure culture of Poria placenta before or after solvent extraction. Weight losses revealed severe fungal degradations on the extracted blocks compared to unextracted ones. • Efficiency of heartwood extractives as inhibitors of the growth of Poria placenta on malt/agar test confirms their contribution to cypress natural durability. • Cypress blocks were treated at 240 ◦ C for different times to reach different levels of thermodegradation to evaluate effect of heat treatment on fungal durability. Results indicate that evaporation of volatile extractives during the first few minutes of heat treatment contribute to decreased wood durability, while longer treatment times lead to the expected improvement of durability. • This study suggests that the content of extractives, which may be modified during wood drying or weathering processes, could be the origin of the conflicting data described in the literature concerning cypress natural durability.

Moisture dynamics of WPC and the impact on fungal testing

Wood-plastic composites (WPCs) are increasingly used in decking applications, where exterior exposure can lead to sufficient moisture for fungal deterioration. Standard tests recommended to assess fungal durability of WPC, but initially developed for wood or wood-based panels, are not applied in this study because the similarity in moisture behaviour for wood (-based panels) and WPC is questioned. The moisture dynamics of commercialised WPC versus wood-based panels were studied employing different moistening methods. The moisture sorption differences between various WPCs were minimal despite different wood contents, particle sizes, and plastics employed, but given sufficient time WPC wood particles gained sufficient water for fungal decay. To assay fungal durability of WPCs, immersion of the specimens for at least 1 week in water at 70 °C seems to be the most effective pre-treatment.

The effect of substituent distribution on the decay resistance of chemically modified wood

Fungal durability of chemically modified wood was investigated with respect to the macroscopic distribution of substituents. Sugi (Cryptomeria japonica D. Don) sapwood samples were treated with modifying chemicals, which involved acid anhydrides (benzoic and n-hexanoic anhydrides) and acid chlorides (benzoyl and n-hexanoyl chlorides), to prepare benzoylated and n-hexanoylated wood. Neutron radiography technique was applied to visualize and evaluate the distribution of the substituents in those modified wood samples. Results revealed that the reaction with acid chlorides led to the heterogeneous distribution, high content of the substituents near the cross sections but relatively low content inside, while the modification with acid anhydrides resulted in the almost homogeneous distribution. The effect of such different distribution on the decay resistance was estimated by using the brown-rot fungus Fomitopsis palustris. It was found that wood samples modified with benzoyl and n-hexanoyl anhydrides exhibited clearly higher resistance against the brown-rot decay than those modified with corresponding acid chlorides, indicating the homogeneous distribution of the substituents is more effective. These results demonstrate that the substituent distribution is one of the important factors for the decay resistance of chemically modified wood.

Investigations of the reasons for fungal durability of heat-treated beech wood

It is generally accepted that thermal treatment of wood by mild pyrolysis (retification or torrefaction) improves its durability to fungal degradation. However, this property has recently been questioned in the literature and definitely needs further investigation. The increase in durability conferred by thermal treatment is generally explained by four hypotheses: the low affinity of heat-treated wood to water; the generation of toxic compounds during heating; the chemical modification of the main wood polymers and the degradation of hemicelluloses. This study was undertaken to understand the reasons for durability of heat-treated beech wood. In order to confirm or not the above mentioned hypotheses, the durability of heat-treated beech wood towards Coriolus versicolor was evaluated according to different parameters like mass loss, wettability or chemical composition. The heat treatment was carried out in a temperature range of 20–280 °C under inert atmosphere for 10 different temperatures. The results show clearly an important correlation between the temperature of treatment and the fungal durability. At the same time, there was insufficient evidence to support the hypothesis of improved decay resistance due to generation of fungicidal compounds or due to the hydrophobic character of wood. Finally, the most plausible hypothesis to explain improvement of wood durability concerns its chemical modifications. Indeed, degradation of hemicellulose associated with other chemical modifications appearing during treatment could be the origin of improved durability. There is a good correlation between decay resistance and mass loss measurements which are directly correlated to hemicellulose degradation.

The effect of artificial ageing on the durability of wood-based board materials against basidiomycete decay fungi

In the biological testing of wood based board materials it has been demonstrated that the exposure of boards in a closed vessel system may lead to inaccurate results due to the build-up of volatile substances that inhibit the test fungi. It is assumed that this is a transitory effect of freshly manufactured boards. Our results with the European standard for testing the fungal durability of board materials, which is currently under development (ENV 12038:1996), confirm that this inhibition has a significant effect on the reliability of the durability results obtained. In the standard, a leaching procedure is used as part of a preconditioning method to remove this effect. Several factors suggest that leaching may not be the most appropriate method for this task. Therefore, a variety of alternative ageing procedures were studied, including natural weathering, leaching and evaporative procedures, to determine the most appropriate preconditioning protocol for the decay test. The results show that non leaching procedures can be more efficient, and possibly more meaningful, than leaching for use on board specimens.