Biological Durability Of Wood Research Articles

Enhancing water resistance and flame retardancy of wood through phytic acid catalyzed in-situ polyesterification

The treatment of wood using in-situ polyesterification with citric acid and D-sorbitol (SCA) is a novel method for enhancing wood properties. This method can effectively improve the dimensional stability and biological durability of wood. However, achieving effective fixation of polyester in wood at lower curing temperatures has not been achieved. In this study, phytic acid was used to catalyze in-situ polyesterification of SCA. The autocatalytic reaction pattern of SCA polyesterification was elucidated through an investigation of the kinetics of the curing reaction. It was also confirmed that phytic acid reduces the curing temperature and activation energy of SCA. The investigation of polyesters revealed that phytic acid catalysis enhances the esterification degree and thermal stability of the polyester. Wood treated with SCA and 2%wt phytic acid exhibited a 44% reduction in polyester leaching. Moreover, it demonstrated high water resistance and dimensional stability, with water repellency efficiency of up to 33.8% and anti-swelling efficiency of up to 46.2%. Remarkably, it exhibited excellent flame retardancy, with an oxygen index of 33.1% and a 47.5% reduction in total heat release. The outstanding flame retardancy is attributed to the dual action of phytic acid in both the solid phase and gas phase.

Statistical Analysis of Wood Durability Data and Its Effect on a Standardised Classification Scheme

The biological durability of wood is an important property for outdoor applications of wood-based products. In temperate climate zones, the most critical biological hazard is wood-destroying fungi, and the European standard EN 350 in combination with EN 113-2 provide guidance on sampling, testing, and classifying wood durability against brown and white rot fungi. However, in their latest revised versions, both standards recommend the use of probability density functions for fitting mass loss data (ML). Subsequently, the durability of wood and its variability should be further characterised. The aim of this study was to statistically analyse the ML data from laboratory agar plate tests with different European-grown wood species and to examine the effect of different statistical treatments on the standardised classification scheme of wood durability. It was concluded that more precise guidance is needed on the sampling procedure since significant differences in durability exist between stem zones. The assignment of dispersion indicators requires a revision to ensure clear, unmistakable, and reproducible durability classification of wood. Deficits in the description of the proposed statistical treatments in both standards became evident. It can be questioned whether the application of probability density functions provides additional information about the variability of wood durability.

Preparation and Characterization of Heat-Treated Douglas Fir Wood with Core–Shell Structure

Wood heat treatment has been generally accepted as an effective wood modification technology as it improves the dimensional stability and biological durability of wood. However, the property improvements are obtained at the cost of reduced mechanical properties. In this study, heat-treated Douglas fir wood with thermally modified shell and unchanged inner core was prepared by surface heating to make possible the broader applications of heat-treated wood. Colour comparison, dynamic vapor sorption and dynamic mechanical analysis were performed to characterize the physico-mechanical performance of the shell and core of the treated wood. The results reveal a darkened, hydrophobic and rigid shell and a barely changed inner core. X-ray photoelectron spectroscopy shows pronounced degradation of polysaccharides in the surface layer. In contrast, the relative contents of different carbon components in the core layer are similar to that of the untreated wood, indicating the reason for the performance difference between the shell and the core of the treated wood. The initial wood moisture content plays an important role in controlling the temperature gap between the core and the shell during treatment and can be used as a key parameter to adjust the structure and performance of the heat-treated wood.

Influences of extractives and thermal modification on the UV resistance of Albizia lebbeck wood

ABSTRACT Thermal modification is a chemical-free process for improving hydrophobicity, dimensional stability, and biological durability of wood. There are inconsistent reports on the UV resistance of thermally modified wood with the majority of studies indicating its vulnerability to UV degradation. This may be due to the natural variability of chemical constituents, particularly extractives, in different wood species. In this study, the UV resistance of sapwood and heartwood of Albizia lebbeck was evaluated to elucidate the role of extractives on photo-stabilisation. A comparison between the extractive rich untreated and heat-treated sapwood and heartwood was carried out. UV resistance was evaluated by exposing modified wood to UV light in an accelerated weathering tester. Untreated sapwood attained dark colour (photoyellowing) upon UV light exposure, whereas thermally modified sapwood showed contrasting behaviour (lightening). Untreated heartwood showed more resistance to photodegradation. Thermally modified heartwood retained its colour for a considerable extent and exhibited good UV resistance than the untreated samples. Results indicate that extractives present in the heartwood of A. lebbeck act as UV absorber to impart substantial UV stability to wood. Furthermore, the enhanced UV resistance of heat-treated heartwood could be due to the accumulation of photostable compounds evolved during the thermal modification of wood.

Investigations of the Chemical Distribution in Sorbitol and Citric Acid (SorCA) Treated Wood—Development of a Quality Control Method on the Basis of Electromagnetic Radiation

Recent studies showed treatments with sorbitol and citric acid (SorCA) to significantly improve the dimensional stability and biological durability of wood. The industrialization of this process requires a quality control (QC) method to determine if the fixated chemicals are homogenously distributed within the piece of wood, which is essential for uniform material performance. Therefore, the objective of this work was to evaluate the use of common electromagnetic radiation-based methods to determine the degree of modification in SorCA-treated wood. Both Fourier transform infrared (FTIR) spectroscopy and near-infrared (NIR) spectroscopy have been used to create rough calibrations for the weight percent gain (WPG) prediction models. The FTIR measurements resulted in a high linear correlation between the band area ratio (BAR) and the WPG (R2 = 0.93). Additionally, a partial least square (PLS) regression of NIR spectroscopic data resulted in a model with a high prediction power (R2 = 0.83). Furthermore, X-ray density profiling emerged as a simple alternative for the QC by showing a gradient of modification chemicals inside the sample and differences in chemical uptake between earlywood and latewood. Overall, it can be concluded that the results from FTIR, NIR and X-ray densitometry can serve as indicators of impregnation chemical distribution in SorCA-modified wood.

Impact of different sterilization techniques and mass loss measurements on the durability of wood against wood-destroying fungi

The biological durability of wood is frequently determined in laboratory tests with monocultures of different decay fungi under ideal conditions for fungal growth. To avoid contamination with mould and inhibition of fungal growth, wood specimens need to be sterilized using different methods. To determine the mass loss of wood blocks during incubation, the initial total dry mass is needed but should be determined without oven-drying to avoid the loss of volatile compounds of the tested wood. In this study the effect of different sterilization techniques in combination with different methods of determining the oven-dry weight on mass loss (MLF) in agar plate wood block tests was investigated. No significant MLF differences were observed between sterilization through gamma radiation, steam, autoclaving, ethanol dipping and oven-drying. Solely, non-sterilized specimens showed reduced MLF, since the test fungus was inhibited by mould growth. Oven-drying of wood species that contain volatile and resistance-affecting compounds such as Scots pine (Pinus sylvestris) led to reduced biological durability and should either be avoided or adapted to kiln-drying temperatures usually applied in practice.

The effect of particle board industry waste tar on the physical and biological durability of wood

The effect of waste tar from particle board factories was investigated relative to some physical and biological resistance properties of Scots pine (Pinus sylvestris) and beech (Fagus orientalis) woods. Solutions were prepared by dissolving waste tar in ethanol:toluene (1v:1v) in concentrations of 5%, 10%, 15%, and 20%. These solutions were forced deep into the Scots pine and beech woods under vacuum and pressure (deep treatment, DT). In addition, surface coating (SC) was applied by spreading 96% waste tar on the wood surfaces after treatment. Deep-treated and surface-coated (DT+SC) wood samples were exposed to the wood-decay fungi Trametes versicolor L. and Neolentinus lepideus Fr. for 12 weeks. At the same time, sample blocks were tested against wood-destroying house borer (Hylotrupes bajulus) larvae for 16 weeks. Total phenolic content, water uptake, water-repellent efficiency, and surface contact angle were tested. Although a mean mass loss resulting from T. versicolor of 31.1% was seen in the Scots pine control samples, only 3.87% mass loss was found with a concentration of 20% (DT + SC). The H. bajulus larvae mortality rate was 80% in the Scots pine wood samples deep-treated with 20% waste tar.

Effect of process variations of polycaprolactone modification on wood durability, dimensional stability and boron leaching

Abstract In this study, in situ graft polymerization of ε-caprolactone (CL) was studied for its potential to limit boric acid (BA) leaching from wood, and to increase the dimensional stability and biological durability of wood against Coniophora puteana and Trametes versicolor fungi. For this purpose, CL monomer with/without BA was impregnated into wood, and the monomer was polymerized in wood cell walls using various methods and combinations of reactants. It was found that biodegradable polycaprolactone (PCL) grafting at high monomer concentrations could inhibit fungal degradation of wood cell walls, as well as improve the dimensional stability of wood up to 55% and reduce water uptake (WU) by about 50%. However, inductively coupled plasma-optical emission spectrometry (ICP-OES) analysis revealed that in situ graft polymerization of CL is not an effective method to prevent BA leaching from wood.

Classification of uncoated plywood based on moisture dynamics

Moisture has a significant influence on the mechanical and physical properties and on the biological durability of wood and wood based materials. As plywood is commonly used as a building material for outdoor applications knowledge regarding its moisture behaviour is of utmost importance. The aim of this research is to model water accumulation in plywood panels in terms of their basic characteristics and in-service moisture conditions. Therefore, moisture dynamics of 29 uncoated plywood types consisting of different wood species, adhesives and layering were evaluated using a simple laboratory water floating test and an outdoor continuous moisture measurement set-up. A significant correlation was found between laboratory and field test results. By means of regression analysis the material characteristics affecting the moisture dynamics of plywood were evaluated. The most influential parameters were wood species, glue type and thickness of the top veneer. Limit values for the water left in the plywood specimen after 72 h absorption and subsequent 72 h desorption, the residual moisture content (rm72), were calculated as to develop a classification tool for plywood. Based on such a classification tool some recommendations for uncoated plywood regarding end use and service life were drafted. Enhanced performance should be obtained by means of wood preservation or by reducing its residual moisture by applying a coating or by an optimal selection of adhesive, wood species and top veneer thickness.

Wood degradation affected by process conditions during thermal modification of European beech in a high-pressure reactor system

The degradation of beech wood during a thermal modification process in a high-pressure reactor system using steam as medium was investigated. The wood was modified at different peak temperatures (150–180 °C), peak durations (1–6 h) and maximum water vapor pressures (0.14–0.79 MPa), while wood mass loss and wood moisture content as well as soluble degradation products were analyzed. Wood degradation was found to be predominantly determined by the maximum pressure, rather than the peak temperature applied. However, accumulation of degradation products, i.e., carbohydrates and furfural, in wood modified at elevated pressure had to be considered when using mass loss as a marker for wood degradation. Mass loss and mass loss rate increased with the maximum pressure until reaching saturation at mass losses above 20 %, due to the limited amount of amorphous carbohydrates within the wood. Several factors have been discussed with regard to their impact on accelerated degradation reactions at elevated water vapor pressure, such as a better heat transfer in a compressed gas atmosphere, reduced evaporative cooling, the accumulation of organic acids as well as the presence of water in the wood during the process. However, none of these individual factors were completely consistent with the observed mass loss progression, which leads to the conclusion that the impact of elevated water vapor pressure, rather, is a combination of several factors that apply simultaneously. The application of elevated pressure might enable an effective process technique to generate sufficient wood degradation to upgrade dimensional stability and biological durability of wood at a low temperature range.

Biological durability of wood in relation to end-use—Part 2: The use of an accelerated outdoor L-joint performance test

As exterior above ground testing is considered important for the assessment of treated wood intended for use in hazard class 3, reliability and reproducibility have become most relevant factors. Laboratory testing of natural durability focussing on such application has to be linked to performance, when suitability of wood species and service life are to be determined. Therefore an accelerated L-joint test has been developed to allow worst case assessment under semi-controlled outdoor circumstances. After 48 months outdoor exposure wood species could clearly be differentiated. Both, fungi isolated and mass loss figures recorded were in line with the proposed basidiomycete laboratory testing of natural durability.

Biological durability of wood in relation to end-use

Biological durability of wood in relation to end-use