Effect of heat treatment on longitudinal gas and liquid permeability of circular and square-shaped native hardwood specimens (original) (raw)
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Heat-treatment, a major method of wood modification for improving dimensional stability and natural durability, has been studied considerably in the scientific literature. This study will focus on the effect of heat-treatment on permeability, an important physical property of wood by subjecting beech samples to two different mediums of hot water and steam, as well as in two buffered hot water of pH 7 and 8. Hydrothermal treatment caused gas permeability to decrease to its lowest value among the treatments (91.6% decrease comparing the control treatment). Hydrothermal treatment in buffered hot water of pH 8 made the lowest impact on gas permeability (12.3% decrease). The decrease in gas permeability was due to settlement of extractives on vessel perforation plates. Gas permeability showed a highly significant correlation with the amount of swelling in radial direction. Low correlation was found between liquid permeability with water absorption and the amount of swelling. Gas permeability is considered a suitable criterion for predicting the amount of swelling in beech wood.
Effects of heat-treatment on permeability of untreated and nanosilver-impregnated native hardwoods
The effects of heat-treatment on permeability are the main topic of the present study. Longitudinal dowel shape pairs of specimens were prepared from three native species and their specific gas permeability values were measured. From each pair, one specimen was kept for heat-treatment and the other was impregnated with 200 ppm nano-silver suspension; the size range of nanoparticles was 20-80 nm. In six consecutive steps, each pair was heated at 50, 75, 100, 125, 150, and 185°C. Results showed that gas permeability increased when specimens were heated at 50°C as a result of the loss of bond-water and consequent shrinkage. Permeability sharply decreased when the specimens were heated at 75°C and gradually increased at each step up-to 150°C. At 185°C, permeability again decreased in. The sharp decrease in permeability at 75°C was possibly due to irreversible hydrogen bonding in the course of water movements within the vessel perforations and pore system of cell walls. The gradual increase in permeability at higher temperatures, though, might be due to higher internal stresses that are released as micro-cracks develop, thus leading to a greater capability of fluidtransfer. Nano-silver impregnation intensified this process.
Microstructural and physical aspects of heat treated wood. Part 2. Hardwoods
Heat treatment of wood is an effective method to improve the dimensional stability and durability against biodegradation. Optimisation of a two-stage heat treatment process at relatively mild conditions (<200°C) and its effect on the anatomical structure of hardwoods were investigated by means of a light and scanning electron microscopic analysis. Hardwood species such as beech and poplar, were predominantly sensitive to collaps of the vessels and some deformation of the libriform fibres directly near the vessels. In treated beech and birch radial cracks were observed near the rays. Optimisation of the heat treatment process conditions including the application of a steam hydro thermolysis stage reduced such damages to a minimum. Broken cell walls perpendicular to the fibre direction resulting in transverse ruptures has been noticed in heat treated hardwood species. This contributes to abrupt fractures of treated wood as observed in bending tests which can lead to considerably different failure behavior after impact of mechanical stress. In some treated hardwood species maceration (small cracks between tracheids) was noticed after heat treatment. Heat treatment did not reveal damage to the ray parenchyma pit membranes, bordered pits and large window pit membranes; and the margo fibrils appeared without damage.
Maderas: Ciencia y Tecnologia
Heat treatment of wood is an effective method to improve the dimensional stability and durability against biodegradation. Optimisation of a two-stage heat treatment process at relatively mild conditions (<200°C) and its effect on the anatomical structure of hardwoods were investigated by means of a light and scanning electron microscopic analysis. Hardwood species such as beech and poplar, were predominantly sensitive to collaps of the vessels and some deformation of the libriform fibres directly near the vessels. In treated beech and birch radial cracks were observed near the rays. Optimisation of the heat treatment process conditions including the application of a steam hydro thermolysis stage reduced such damages to a minimum. Broken cell walls perpendicular to the fibre direction resulting in transverse ruptures has been noticed in heat treated hardwood species. This contributes to abrupt fractures of treated wood as observed in bending tests which can lead to considerably different failure behavior after impact of mechanical stress. In some treated hardwood species maceration (small cracks between tracheids) was noticed after heat treatment. Heat treatment did not reveal damage to the ray parenchyma pit membranes, bordered pits and large window pit membranes; and the margo fibrils appeared without damage.
Study on the Longitudinal Permeability of Oil Palm Wood
Industrial & Engineering Chemistry Research, 2013
In this research, variations in longitudinal permeability of oil palm (Elaeis guineensis Jacq) wood were investigated. Panels were prepared from bark to pith with the study carried out on 3 parts of the transverse surface: outer, middle, and inner.
Effect of permeability on primary processing of wood
Journal of Pharmacognosy and Phytochemistry, 2018
Wood, being hygroscopic in nature, its permeability affects the flow of liquid and gases. Permeability defines the ease of flow of fluid due to a pressure gradient. Various methods like falling water displacement method, rota meter method, etc. have been employed in measuring the variable traits of permeability. In wood, it depends upon the effectiveness of interconnecting capillaries such as pit, pores which constrict the passage from one cell cavity to the other. The size of openings connecting the wood cells determines the degree of permeability. Permeability is a function of porosity which in turn is dependent on the wood species. It varies with respect to the type of wood species i.e. hardwood and soft wood as well as in different directions within the wood. It can be altered by ponding, steaming, heat treatments, chemical treatments etc. Permeability is an integral part in determining the longevity influencing many other processes viz., wood seasoning, preservatives treatment ...
Influence of heat transferring media on durability of thermally modified wood
BioResources
Studies on the durability and dimensional stability of a series of hardwoods and softwoods after thermal modification in vegetable oils and in steam atmospheres have been performed. Mass loss after exposure to Coniophora puteana (BAM Ebw.15) for 16 weeks was very low for European birch, European aspen, Norway spruce, and Scots pine thermally modified in a linseed oil product with preservative (for 1 hour at 200 oC). Fairly low mass losses were obtained for wood thermally modified in linseed-, tung- and rapeseed oil, and losses were related to the wood species. Low mass loss during rot test was also found for Norway spruce and Scots pine modified in saturated steam at 180 oC. Water absorption of pine and aspen was reduced by the thermal treatments and the extent of reduction was dependent on wood species and thermal modification method. Thermally modified aspen was stable during cycling climate tests, whereas pine showed considerable cracking when modified under superheated steam con...
The effect of thermal treatment on physical and mechanical properties of luehea divaricata hardwood
This study aimed to characterise the effect of thermal treatment on physical and mechanical properties of açoita-cavalo (Luehea divaricata) wood. To achieve this, samples were treated at 160, 180 and 200°C for 2 h in an oven (dry conditions). Physical and mechanical characterisation was performed by weight loss, dry specific gravity at 12%, equilibrium moisture content, volumetric swelling and shrinkage, water absorption, water repellence, static bending and brittleness tests. Roughness and colour tests were performed in order to evaluate the modified surface. Main findings showed that dimensional stability of thermally modified wood increased, while mechanical strength of wood decreased as a function of temperature. A darkening of wood and a decrease in roughness were observed. Rousset, P.; Perré, P.; Girard, P. 2004. Modification of mass transfer properties in poplar wood (P. robusta) by a thermal treatment at high temperature. European Journal of Wood and Wood Products 62 (2): 113-119. Sundqvist, B. 2002. Color response of Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and birch (Betula pubescens) subjected to heat treatment in capillary phase. European Journal of Wood and Wood Products 60 (2): 106-114. Sundqvist, B.; Karlsson, O.; Westermark, U. 2006. Determination of formic-acid and acetic acid concentrations formed during hydrothermal treatment of birch wood and its relation to colour, strength and hardness. Wood Science and Technology 40 (7): 549-561. Weiland, J.; Guyonnet, R.; Gibert, R. 1998. Analyse de la pyrolyse menagee du bois par un couplage TG-DSC-IRTF. Journal of Thermal Analysis and Calorimetry 51 (1): 265-274. Weiland, J.J.; Guyonnet, R. 2003. Study of chemical modifications and fungi degradation of thermally modified wood using DRIFT spectroscopy. European Journal of Wood and Wood Products 61 (3): 216-220. Wikberg, H.; Maunu, S.L. 2004. Characterisation of thermally modified hard-and softwoods by 13C CPMAS NMR. Carbohydrate Polymers 58 (4): 461-466. Winandy, J.E.; Lebow, P.K. 2001. Modeling strength loss in wood by chemical composition. PartI. An individual component model for southern pine. Wood and Fiber Science 33 (2): 239-254.