Influence of thermo-vacuum treatment on thermal degradation of various wood species

Solid wood has a certain amount of resistance to fire exposure. Recently, there is also great interest in characterization of the thermal behaviour of treated wood due to increasing demand of such products within the perspective of sustainability of environment. The objective of this study was to evaluate and predict the thermal decomposition process of samples from different wood species, Norway spruce (Picea abies Karst.), common ash (Fraxinus excelsior L.) and Turkey oak (Quercus cerris L.), so that such data can be used for enhanced design of wood products for more effective and better utilization in different applications. Spruce and ash samples were treated at a temperature of 190 °C for 2 h while Turkey oak specimens were steamed at a temperature of 110 °C for 24 h before they were thermally treated at a temperature of 160 °C for 3 h. A thermo-gravimetric analysis of the samples highlighted intraspecific differences in mass loss and the stage of thermal degradation between treated and untreated specimens. The degradation of the wood was characterized by twofold reaction stages, with an exception of Norway spruce samples, which exhibited a one-stage reaction. In addition, thermal treatments affected chemical composition of wood. The obtained results will be helpful in determining the applicability of these materials according to their thermal degradation properties.     

Influence of temperature of thermal treatment on surface densification of spruce

Spruce (Picea abies L. Karst) wood lamellae, thermally treated at 170, 190, 210 and 230 °C were surface densified by compression at a temperature of 150 °C to three degrees of compression. Immediate springback, set recovery, mechanical properties in 3-point flexure, Brinell hardness and density profiles measurements were used to determine the effect of thermal treatment on the properties of surface densified wood. The highest immediate springback occurred in wood specimens thermally treated at the highest temperature (230 °C) and decreased with decreasing thermal treatment temperature. The untreated samples had the highest set recovery, which decreased with the temperature of thermal treatment. The surface densification increased hardness and bending strength. The highest increase was in the case of untreated wood and decreased with the temperature of thermal treatment. The modulus of elasticity (MOE) and modulus of rupture (MOR) of surface densified wood decreased with increasing thermal treatment temperature. The trend was similar for specimens which were thermally treated but not surface densified. Surface densification increased the density of the specimens in the first few millimetres below the surface. The highest density was achieved in untreated specimens and the lowest in specimens thermally treated at the highest temperature.     

An investigation of the cell wall ultrastructure of the sapwood of ten Greek wood species by means of chemical modification

The aim of this study was to investigate the cell wall ultrastructure of the sapwood of ten Greek wood species using chemical modification. Reactions with different sized anhydride molecules were performed on oven-dry samples in the presence of water-free xylene, which does not swell the cell wall. Reactions were also performed under identical conditions, but on wood samples that had been dried under solvent exchange conditions, thereby retaining the swollen cell wall pore structure. The results indicated that the diameters of the micropores in the cell wall of oven dried ash and elm are smaller than 0.80 nm and larger than 0.74 nm, those of beech, fir, Douglas fir, hornbeam and pine (Pinus nigra) smaller than 0.74 nm and larger than 0.66 nm, whereas those of maple, poplar, pine (Pinus sylvestris) are smaller than 0.66 nm.     

Effect of oil type, temperature and time on moisture properties of hot oil-treated wood

This paper focuses on the moisture properties of wood treated in palm oil-, soy oil- and slack wax for different processing times and temperatures. Also, the relative importance of oil uptake and thermal modification on the wood moisture properties is investigated. Slack wax was better than palm oil or soy oil in improving the moisture performance of thermally treated wood, and treatment at 220 °C was superior to treatment at 200 °C, with 4 h being generally better than 2 h treatment. Water absorption in samples treated with wax at 100 °C or 160 °C was similar to that in samples treated at high temperatures while improved anti-shrink efficiencies (ASE) and lower hygroscopicities occurred only for the high temperature treatments. Chloroform extracted samples treated at high temperature with palm oil or soy oil had relatively similar hygroscopicity and ASE properties compared to unextracted samples, but had greatly increased water absorption properties. These results confirm that chemical reactions in wood resulting from the heat treatment account for the main improvements of wood properties in reduced hygroscopicity and improved dimensional stability, while the oil absorbed by wood reduces the rate of water absorption.     

Zur dynamischen Torisonselastizität von Holz

The changes in torsional elasticity of untreated and fire retardant impregnated beech and spruce specimens under cyclic temperature load were determined in torsional vibration tests. A temperature of 60°C already caused a permanent 25% reduction in torsional modulus of elasticity which remained unaffected by further temperature rises and by repeated heating and cooling cycles up to 200°C. Above 200°C oxidation presumably occurred with wood strength deteriorating visibly. Also, previously water saturated specimens showed greater losses in torsional elasticity than air-dried or dried ones. Fire retardant treatment with acid salt mixtures reduced torsional modulus of elasticity by 35% already at room temperature and subsequently led to a rupture of specimens at 200°C. Apart from fluctuations in absolute values both wood species reacted similarly to temperature load and protective treatment.     

Preparation and Properties of Cellulose/Tamarind Nut Powder Green Composites

Using biopolymer cellulose as the matrix and tamarind nut powder (TNP) obtained from agricultural waste of tamarind nuts as the filler, the green composites were made. Cellulose was dissolved in environmental friendly solvent of aq. 8 wt. % Lithium hydroxide and 15 wt. % urea which was precooled to ?12 ° C. To the cellulose solutions, TNP was added in 5 wt. % to 25 wt. % of cellulose separately. Each solution was evenly spread on glass plates and the wet composites were prepared by regeneration method using ethyl alcohol coagulation bath. The wet films were dried in air at room temperature. The dried composite films were characterized by FTIR spectroscopy, X-ray diffraction, thermogravimetric analysis and also tested for their tensile properties. The tensile strength and the % elongation at break of the composites were higher than those of the matrix and increased with TNP content. While the matrix had a tensile strength of 111.8 MPa, the cellulose/TNP composite loaded with 25 wt.% TNP possessed a tensile strength of 125.4 MPa (12% increase). Though the thermal stability of the composites was lower than cellulose matrix, all the composites were stable up to a temperature of 350 °C.     

Investigation of drying characteristics in superheated steam drying of UF-impregnated Chinese fir

Urea formaldehyde (UF) resin-impregnated Chinese fir (Cunninghamia lanceolata (Lamb.)Hook.) was dried at different temperatures in an atmospheric pressure superheated steam dryer. Drying characteristics, moisture content, drying rate, temperature profile, drying defects, and color change were investigated. The moisture content was reduced from 66.21 to 11.79% within 30 h without causing severe drying defects; in contrast, the conventional hot air process required 7–8 days. After 25 h of drying, the temperatures at both the center and the surface of wood remained stable. After 34.5 h, the surface temperature gradually approached the steam temperature. The color of the superheated steam dried Chinese fir appeared slightly more intense yellow and red than the control. Investigation of the UF-impregnated Chinese fir wood by scanning electron microscopy (SEM) revealed that the majority of the lumens and voids, including the microvoids in wood structure, was filled with urea formaldehyde resin.     

不同升温方式下大红袍做青中PPO和β-G活性变化对比

以武夷山大红袍驻芽三四叶为鲜叶原料,采用武夷岩茶制作工艺,比较分析做青时采用炭火和暖气机组升温对青叶多酚氧化酶(polyphenol oxidase,PPO)活性和β-葡萄糖苷酶(β-glucosidase,β-G)活性变化的影响。结果表明:炭火做青间温度和CO2浓度高于暖气机组做青间,两者的相对湿度区别不大;对比晒青叶,至做青结束时,两者的PPO活性皆显著降低,炭火做青间大红袍PPO活性减少了22.11%,暖气机组做青间大红袍PPO活性减少了28.82%;而β-G活性的变化不同,炭火做青间大红袍β-G活性显著降低,减少37.20%,暖气机组做青间大红袍β-G活性明显升高,增加了37.79%。     

The efficacy of commercial silicones against blue stain and mould fungi in wood

Scots pine (Pinus sylvestris L.) samples were vacuum pressure impregnated with quaternary ammonium (quat)-silicone micro-emulsion (<40 nm particle size), amino-silicone macro-emulsion (110 nm) and silicone macro-emulsion with alkyl modified side groups (740 nm). Quat-silicone micro-emulsion caused highest cell wall bulking (4.8%) and anti-swelling efficiency (21.8%) in wood when treated with 30% concentration of silicone in the treatment solution. All three formulations made wood hydrophobic which was evident from a capillary (longitudinal, tangential and radial) water uptake test. Amino-silicone macro-emulsion (10% silicone in treatment solution) resulted in strong resistance to blue stain attack with both pre-weathered and not pre-weathered wood samples. Signs of blue staining were more evident on the pre-weathered samples. Treatment with amino-silicone macro-emulsion (10% silicone in treatment solution) resulted in a certain resistance to mould growth on wood surfaces, whereas wood treated with the same concentration of quat-silicone micro-emulsion and alkyl-modified silicone macro-emulsion exhibited comparatively lower resistance.     

升温方式对大红袍做青中主要生化成分的影响

以武夷山大红袍驻芽三四叶为原料,采用武夷岩茶制作工艺,对比做青时采用炭火和暖气机组加温对做青间环境和做青过程中大红袍生化成分变化的影响.结果表明:炭火升温的做青间温度和CO2浓度比暖气机组升温做青间高,两者的相对湿度区别不大;对比晒青叶,至做青结束时,两者的水浸出物含量皆无显著变化,而两者的茶多酚含量皆呈明显下降趋势,...     

Effect of tannin on increasing UF adhesive performance at high temperature investigated by TMA and TGA analysis

Tannins have been largely studied as wood additives and wood adhesives. In a perspective of a desirably increased utilization of natural raw material in the wood timber industries, this study provides further and specific information on the use of condensed tannins to improve the heat resistance of urea–formaldehyde (UF) resins. The results obtained by thermomechanical and thermogravimetric analyses show that high percentage (33 and 50 %) of quebracho tannin in UF-tannin blend dramatically improves the overall UF thermal resistance, but 50 % of tannin decreases the maximum value of modulus of elasticity (MOE) of the bonded joint. The best balance between mechanical performance and decreased degradation at high temperature is obtained with 33 % of quebracho tannin. The MOE value of UF + 33 % of quebracho tannin at 260 °C is seven times greater than MOE of UF control. Thermograms show that quebracho tannin has a beneficial effect on increasing the resistance of glue-mix to degradation induced by temperature. When the content of tannin in the glue-mix is increased up to 50 %, the resin degrades completely at about 670 °C, i.e. more than 50 °C higher than neat UF resin. This improvement is related mainly to the resorcinol-type ring structure of tannin and the alkaline pH of UF + quebracho tannin glue mix that confer a higher resistance against joint degradation to UF even at elevated temperatures.     

Influence of drying temperature upon some mechanical properties of beech wood

The paper presents the results obtained in an experimental study concerning the influence of drying temperature upon the mechanical properties of beech wood (Fagus sylvatica L.). Sound wood samples without red heart were cut from white (unsteamed) beech timber parts, dried at different temperatures: 20 °C, 80 °C, 90 °C, 100 °C, 115 °C and same relative air humidity: 50%. After performing classical tests for evaluation of some selected mechanical properties, the following conclusions could be drawn: all bending properties (static bending strength, modulus of elasticity and impact bending strength) increased with increasing temperature, confirming thus the benefiting effect of heat upon wood plasticity. The tensile strengths, both parallel and perpendicular to grain, increased with increasing temperature, but only in the range below 100 °C; as soon as the temperature exceeded this value, the tensile strengths began decreasing. As far as compression strength parallel to grain, shearing strength and splitting resistance is concerned, no significant influence of temperature could be established. However, it seems that these properties are negatively affected by kiln-drying, as even with low kiln-drying temperatures these strengths are much lower than in case of air-drying.     

Heat distribution in thermally modified timber

The heat distribution during thermal modification of beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst) wood with dimensions of 80 × 80 × 200 mm³ has been investigated. Heat distribution was continuously measured by thermocouples in longitudinal and transverse directions. Significant temperature gradients occur in the initial phase of the process as well as during the modification phase (set temperature 200 °C for 3 h), where ongoing chemical reactions in wood were taking place. Thus, the temperature in the investigated positions increased to 240 °C (beech) and 215 °C (spruce). The mentioned properties should be taken into account when optimizing the heat treatment process (quality control, energy savings, etc.).     

Thermal properties of wood-gypsum boards

Transient simultaneous measurements of thermal conductivity, volume heat capacity and thermal diffusivity of laboratory wood-gypsum boards have been performed with ISOMET 2104 at room temperature. The influences of wood particle content, density and moisture content on thermal properties were investigated. The measurements were performed in a direction perpendicular to the board plane. The effect of density and wood particle content on the thermal properties may be related to the presence of voids both between and inside particles. It seems, that the dominant mechanism of heat transfer across the board is the heat conduction through the voids. Wood-gypsum boards with a density of 850–1300 kg/m³, a moisture content of 2–11% and a wood particle content of 0–35% have the following thermal conductivity of 0.189–0.753 W m^-1 K^-1, volume heat capacity of 0.683–1.43×10⁶ J m^-3 K^-1 and thermal diffusivity of 0.171–0.367×10^-6 m² s^-1; their magnitudes are higher than those ones of OSB, MDF, particleboard and plywood.     

Microwave drying kinetics of jack pine wood: determination of phytosanitary efficacy,energy consumption,and mechanical properties

The aims of this study were to determine (1) the effects of microwave irradiation on the drying kinetics of jack pine wood, (2) the phytosanitary efficacy, and (3) the processing energy consumption and mechanical strength of the dried product. Microwave drying experiments were performed at 2.45 GHz frequency and at microwave powers ranging from 300 to 1000 W. Results indicate that higher microwave power and initial wood temperature and lower sample thickness increases the internal sample temperature, improves the drying rate, and reduces both drying time and energy consumption. The microwave irradiation efficacy to sanitize jack pine wood boards was determined in terms of temperature/time combinations based on actual drying kinetics according to standards for phytosanitary measures. The energy required to dry 12 mm thick wood board samples at microwave power ranging from 300 to 1000 W was in the range of 36.4–12.3 MJ/kg of water, respectively, for up to 65% energy consumption savings. The impact of microwave power on the mechanical properties was not statistically significant, although mechanical properties tended to decrease with increasing power.     

Use of round wood of chestnut tree coppices: crack risk and effects of a hot oil bath treatment

The chestnut tree (Castanea sativa Mill.) presents good mechanical properties, when valorised in the form of round wood in small diameter. On the other hand, it is very sensitive to cracking during drying. The topic of this study is to optimize a hot oil bath treatment known from previous studies to reduce surface checking. Here, we compare the state of cracks of two series of chestnut tree logs: one is directly dried to 12% moisture content (MC), the other one is treated for one hour using a 130 °C oil bath first, then dried to 12% MC. This first experiment led us to study the evolution of the temperature in the log during the treatment and to propose a chart to determine treatment time in a 130 °C bath. This chart has been successfully tested on a second series of logs.     

Application of High Hydrostatic Pressure as a Pretreatment for Osmotic Dehydration of Banana Slices (Musa cavendishii) Finish-Dried by Dehumidified Air Drying

The process variables high hydrostatic pressure (HHP; 100–500 MPa), sucrose concentration (30–70 °Brix), immersion time (5–9 h) and immersion temperature (30–70 °C) were optimised to yield maximum water loss (WL), minimum solid gain (SG), minimum water activity (a _w) and minimum browning index (BI) during osmotic dehydration (OD) of banana slices (Musa cavendishii) pretreated by HHP using response surface methodology. The pressure-treated samples showed significantly higher WL and SG during OD (p?<?0.05), which was attributed to the rupture of cell wall with applied pressure, making the cells more permeable, also evident from the scanning electron micrographs of the banana tissue. The optimised operating conditions were: HHP of 200 MPa for a dwell time of 5 min at room temperature (26 °C), sucrose concentration of 60 °Brix, immersion time of 5 h and immersion temperature of 40 °C. A study of the concentration profiles during OD revealed no appreciable increase in SG and WL after 4 h; hence, immersion time was reduced to 4 h. The optimised product developed was dried to a moisture content of 15 % (wet basis) in a dehumidified air dryer at an air temperature of 40, 55 and 70 °C with a fixed air velocity of 3.8 m/s and relative humidity maintained at 20 %. The final dried product was analyzed for total soluble solids content, BI and a _w. A drying temperature of 55 °C was found to give superior quality OD banana slices in terms of reduced bulk, improved flavour, decreased a _w (<0.60), and reduced dehydration time and energy using HHP as a pretreatment.     

Effects of high temperature drying in nitrogen atmosphere on mechanical and colour properties of Norway spruce

Heat treatment and drying processes of wood are always accompanied by material changes. These changes are partly caused by oxidative reactions. This study aims to compare high temperature drying in inert gas atmosphere with conventional kiln drying of spruce wood. The mechanical properties as well as colour changes were measured after drying. In general, higher compression strength was observed for samples dried at high temperatures in nitrogen atmosphere. However, tensile and bending strength proved no significant difference. Corresponding to the strength values increased stiffness values were also observed for the compression samples, whereas for tension and bending samples no significant effect was visible. Up to a temperature of approx. 125 °C discolouration is prevented by drying samples in nitrogen atmosphere.     

Improvement of termite resistance,dimensional stability and mechanical properties of pine wood by paraffin impregnation

Paraffin has been used as surface protection of wood throughout the ages but its use for impregnation to improve wood resistance to biodegradation is recent. This study determined the main improvements on wood properties with paraffin impregnation. Healthy Pinus pinaster Ait. wood was impregnated with paraffin at different levels using a hot–cold process. Weight gain, equilibrium moisture content and dimensional stability (ASE) at 35 and 65 % relative humidity, termite durability against Reticulitermes grassei (Clément), bending strength, bending stiffness (MOE) and Janka hardness were determined. Density increased from 0.57 to 0.99, ASE ranged between 38–96 % and 16–71 % for 35 and 65 % relative humidity, respectively. Equilibrium moisture content decreased from 9.9 and 12.0 % to 0.8 and 3.6 % for 35 and 65 % relative humidity. Termite durability improved from level 4 to level 3 of attack, and higher termite mortality was found in treated wood (52 % against 17 %). Bending strength (MOR) increased with paraffin weight gain, reaching a 39 % increase. MOE also increased by about 13 % for wood with a weight gain around 80 %. Janka hardness increased significantly reaching about 40 % for wood with 80 % weight gain. Paraffin impregnated wood has improved properties with regard to equilibrium moisture content, dimensional stability and density, bending strength and Janka hardness, and resistance against termites.     

Experimental analysis on small-scale finger-jointed specimens at elevated temperatures

Finger joints have to meet strength performance requirements for the use in structural engineered wood products such as glued-laminated timber beams (glulam). Among these, the thermal stability of the adhesive used in the finger joint is an important criterion to determine the suitability of the connection. The influence of adhesives on the load-carrying capacity of glulam beams and finger-jointed members can be assessed by large-scale fire tests; however, there are obvious benefits in using small-scale specimens tested at elevated temperatures as an alternative. In Europe, there is currently no small-scale test available to test the fire performance of adhesives in structural timber members. The work presented in this paper addresses this issue and was supported by members of a European standardisation committee to develop such a small-scale test. This paper presents, as a first step, the results of a series of tensile tests on small-scale finger-jointed specimens tested at elevated temperatures. The tests were performed with different types of adhesives which are currently also tested in large-scale fire tests. In the small-scale tests here, structural adhesives showed nearly no weaknesses with increasing temperature up to 140 °C. Further, MUF and PRF adhesives showed mostly wood failure even up to temperatures of 220 °C. In the next step of this investigation, the results obtained from the small-scale tests at elevated temperature will be compared to large-scale fire test results in order to find a possible link between both testing methods.