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Abstract

This paper deals with an original and non-biocidal chemical treatment consisting of a vacuum/pressure impregnation step of beech wood with a water-borne mixture made from heat-activated condensation of succinic anhydride (SA) and glycerol (G). Chemical structures of adducts were established using matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF) investigations. Beech wood was impregnated and cured in order to induce in situ polymerization of glycerol/succinic adducts (GSA) in the cell walls, leading to the formation of polyglycerol succinate (PGS) polyester. Various treatment conditions were investigated depending on the duration (6–72 h) and curing temperature (103–160°C). Weight percent gains (WPGs) ranging between 40 and 60% were obtained. Attenuated total reflectance-middle infrared spectroscopy (ATR-MIR) and carbon-13 nuclear magnetic resonance (13C-NMR) spectroscopy confirmed polyester formation. A curing temperature of 160°C was found to be the best condition to totally avoid polymer leaching, and brought the anti-swelling efficiency (ASE) up to 64%. Decay resistance of PGS-treated wood against Trametes versicolor and Coniophora puteana was also strongly temperature and time dependent: performances fit with the EN113 standard requirements if a curing temperature of 160°C was applied.

Abstract

The aim of this study was to investigate Rhodonia placenta expression patterns of genes involved in the depolymerisation during the non-enzymatic phase in acetylated (WAc) and furfurylated wood (WFA). During the 98-day-long exposure, WAc [22.6% weight per cent gain (WPG) on average] and WFA (69% WPG on average) lost no more than 3% mass while the untreated wood (WUn) reached 41% mass loss (ML) in 55 days. Expression of six genes putatively involved in the non-enzymatic degradation process were investigated. In conclusion, expression levels of alcohol oxidase Ppl118723 (AlOx1) and laccase Ppl111314 (Lac) were significantly higher in the modified wood materials (WMod) than in WUn, which is in accordance with previous results and may be explained by the absence of the degradation products that have been proposed to down-regulate the non-enzymatic degradation process. However, copper radical oxidase Ppl156703 (CRO1) and a putative quinate transporter Ppl44553 (PQT) were expressed at significantly lower levels in WMod than in WUn while quinone reductase Ppl124517 (QRD) and glucose oxidase Ppl108489 (GOx) were expressed at similar levels as in WUn. These results suggest that gene regulation in WMod is more complex than a general up-regulation of genes involved in the non-enzymatic degradation phase.

Abstract

This study investigated several key parameters of deuterium exchange measurements in a dynamic vapour sorption apparatus to optimise the measurement protocol for hydroxyl (OH) group accessibility determination. The impact of changing the sample mass, the deuterium oxide (D2O) vapour exposure time and the rate of change in moisture content (dm dt−1) during the drying steps on the measured OH group accessibility were analysed. A sample mass of more than 10 mg, an exposure to D2O vapour of at least 10 h and a dm dt−1 of 0.0005% min−1 over a 10-min period during the drying steps gave the most reliable results. We also investigated the necessity of adding a method stage that eliminates the effect of inclusion compounds (ICs). The addition of an initial drying and wetting stage enabled the release of entrapped solvents.

Abstract

In built environments the combustibility of wood is a great concern, which limits the use of wood as a building material due to legislation. The reaction-to-fire properties of wood can be altered with the use of fire-retardant chemicals, and most of the commonly used fire retardants already have a long history of use. However, only limited information is available on the impact of different fire retardants on the adhesion properties of wood. Additionally, comparative studies between chemicals from different groups of fire retardants is scarce. The objective of this study was to investigate and compare the effects of two commonly used fire retardants, sodium silicate (SS) and diammonium phosphate (DAP), on veneer properties, the focus being especially on thermal behavior and adhesion. Thermal properties and combustibility were studied using thermogravimetric analysis (TGA), flame test and calorimetry. Glue bond strength was analyzed with an automated bonding evaluation system (ABES) and the leaching of chemicals was determined according to EN84. Additionally, the surface characteristics of modified veneers were imaged with scanning electron microscopy (SEM). Results revealed notable differences in the thermal properties of SS and DAP, with DAP having better fire-retardant performance in all thermal testing. SS also affected thermal properties and combustibility of modified veneers, but the effect was only moderate compared to DAP. Neither SS or DAP had any significant resistance against leaching but ABES testing showed a notable increase in the glue bond strength of DAP modified veneers.

Abstract

Carbon footprint over the life cycle is one of the most common environmental performance indicators. In recent years, several wood material producers have published environmental product declarations (EPDs) according to the EN 15804, which makes it possible to compare the carbon footprint of product alternatives. The objective of this study was to investigate the effect of service life aspects by comparing the carbon footprint of treated wood decking products with similar performance expectations. The results showed that the modified wood products had substantially larger carbon footprints during manufacturing than preservative-treated decking materials. Replacement of modified wood during service life creates a huge impact on life cycle carbon footprint, while maintenance with oil provided a large contribution for preservative-treated decking. Hence, service life and maintenance intervals are crucial for the performance ranking between products. The methodological issues to be aware of are: how the functional unit specifies the key performance requirements for the installed product, and whether full replacement is the best modeling option in cases where the decking installation is close to the end of the required service life.

Abstract

Acetylated wood is a durable and dimensionally stable product with many potential applications in exterior timber structures. Research has shown that acetylated wood can be effectively bonded by various adhesive types. However, one of the most commonly used adhesives for timber constructions, melamine urea formaldehyde (MUF), shows poor performance in combination with acetylated wood in delamination tests based on cyclic wetting and drying. The hydrophobic acetylated wood surface leads to reduced adhesion due to poorer adhesive wetting and fewer chemical bonds between the resin and the wood polymers. The use of a resorcinol-formaldehyde (RF)-based primer on the acetylated wood surface prior to the application of MUF leads to positive gluing results with both acetylated radiata pine and beech, providing significantly improved resistance to delamination. Radial penetration of the primer and MUF in acetylated wood shows higher penetration compared with untreated wood. In addition, a phenol resorcinol-formaldehyde adhesive system showed high resistance against delamination and can be used for gluing of acetylated wood.

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Abstract

Two-dimensional proton nuclear magnetic resonance (2D 1H NMR) relaxometry is increasingly used in the field of wood sciences due to its great potential in detecting and quantifying water states at the level of wood constituents. More precisely, in this study, this technique is used to investigate the changes induced by “natural” and “artificial” aging methods on modern and historical oak woods. Two bound water components are detected and present differences in terms of association to the different wood polymers in cell walls: one is more strongly associated with wood polymers than the other. The evolution of the two bound water types is discussed in regard to aging methods and is related to the structure of the cell wall, especially with the S2 layer and the evolution of wood chemical composition (cellulose, hemicelluloses and lignin). The evolution of hydric strains is also discussed taking into account the effect of aging methods on the two bound water components. The obtained results confirm the ability of 2D 1H NMR relaxometry to evaluate the effect of aging at the molecular level and on hydric deformation. Furthermore, this method shows that it is possible to determine the moisture content of wood without the necessity to oven-dry the wood material.

Abstract

Heat treatment (HT) is a well-known means to reduce the equilibrium wood moisture content (EMC) at a specified relative humidity (RH). EMC is profoundly decreased by the loss of accessible hydroxyl groups (OHacc) in the wood matrix by thermochemical reactions. However, the obtained EMC reduction after HT can be partly reversible, depending on the ability of the wood matrix polymers to fully mechanically relax during HT. We discuss the results of our earlier experimental study on the OHacc content and the associated EMC decrease at 93% RH by a relaxation inhibiting dry-HT vs. a relaxation enabling wet-HT. New experimental results, showing that OHacc does not significantly change during reversible EMC changes, are added to the discussion. This study quantitatively supports a molecular explanation of the reversible EMC, in which wood moisture is principally bound at sorption sites, composed of two functional groups, constituting a hydrogen-donor/acceptor pair, involving at least one OHacc group. The irreversible part of EMC reduction is assigned to the thermochemical removal of OHacc from the wood matrix. The reversible part is attributed to a process of wood polymer conformal rearrangements, bringing an isolated OHacc group in proximity of another free hydrogen-bonding functional group, creating a site for water sorption.

Abstract

Circular economy may play a key role in the future success of modified wood products. The European Union (EU) aims toward a circular economy, i.e. increasing resource efficiency by waste minimization in production processes, cascade uses of materials, elimination of landfill wastes, and maximizing the value of raw materials. The policy has great expected impact across all sectors, and will influence countries with strong wood modification industries, such as Finland, Germany, Norway, and the Netherlands. It also means considerable economic efforts and sets transformation challenges to the societies and industries. Challenges have country-wise differences depending on production structure, environmental circumstances, local policies and regulations, as well as economic resources. This paper is an outlook of the renewed waste legislation in the EU, based on which it assesses the possible impacts of circular economy development on the future of wood modification. One of the key indicators for resource efficiency is € kg−1, which allows pursuing increased efficiency by minimizing material input (and waste) and/or by maximizing the value. In the case of modified wood, both of these approaches may be considered market opportunities, while the key challenge and the consequent need for action relate to improved waste management.