Evaluation of heat treated wood swelling by differential scanning calorimetry in relation with chemical composition

24 pagesInternational audienceRetification® is a heat treatment which decreases the swelling of wood and increases its resistance to fungal attack. In this study, differential scanning calorimetry (DSC) was applied in order to determine the fiber saturation point (FSP) of natural and retified® wood. FSP values were used to determine the total swelling of natural and heat-treated wood. The DSC method was compared to the volumetric shrinkage approach. The influence of the heat treatment temperature and duration on the swelling of wood was investigated. Relationships between chemical changes and the reduction of swelling were analysed thoroughly. The equivalence of the DSC method and the volumetric shrinkage method is shown. FSP in association with anhydrous density is a good indicator for the evaluation of the overall swelling of heat-treated wood. Reduction of wood swelling with increasing temperature and duration of thermal treatment is often attributed to hemicelluloses destruction. This study shows that the reduction of beech wood swelling can not only be attributed to the disappearing of adsorption sites that goes with the hemicelluloses destruction. It is suggested that other phenomena such as structural modifications and chemical changes of lignin also play an important part

Evaluation of heat treated beech by non destructive testing

10 pagesImprovement of dimensional stability and durability is wished for the use of wood as a building material. For the last decade, retification® has been industrially developed. It consists in a stabilization and preservation of wood by heat treatment. The aim of this study is to find simple and fast methods to characterize heat treated beech. Non destructive testing is expected to be relevant to evaluate the level of treatment and the properties for the use of heat treated wood. Six treatments were carried out in a pilot reactor. The parameters of the retification® stage (temperature and time) were studied. For each treatment, the non destructive tests (free oscillations in the fundamental mode, colour and dry weight loss)were performed, and the properties for use (mechanical resistance and volumetric shrinkage) measured. Lightness and dry weight loss seem to be suitable properties to characterize beech retification® when the time parameter is fixed. However, they are not suitable for other wood species, and for retification stages with a variable duration. Moreover, the correlation with the properties for use were plotted, but presented too large dispersion to be relevant. After correction of moisture content, the longitudinal Young's modulus of the material is slightly increased by each of the six treatments, but do not present any variation with changing parameters values. On the contrary, the mechanical resistance decreased with increasing temperature and time. Thus the dynamic Young's modulus is not reliable to evaluate the treatment and to predict the loss of mechanical resistance. The logarithmic decrement was not increased by any of the treatments, which is in opposition with the hypothesis that retification® generates cracks and microcracks in the material. Effects of long time at low temperature have been investigated. From these experiments, properties of treated wood may be improved significantly by choosing appropriate values of the parameters

Thermo-gravimetric analysis as a tool for the optimisation of wood heat treatment parameters

9 pagesRetification is a heat treatment that decreases the swelling of wood and increases its resistance to fungal attack. It consists in a mild pyrolysis of wood (180°C-260°C) that takes place in a non oxidative atmosphere (nitrogen). The industrial development of retification requires optimisation of the treatment temperature and duration. In order to enhance the homogeneity of temperature in the furnace, and to avoid exothermic reaction, low temperatures seem to be preferable to high temperature. On the contrary, duration and temperature of treatment have to be high enough to provide good biological resistance and stabilization to the wood. However, high temperatures lead to a loss of mechanical strength. A question arises from these previous observations: is there any equivalence between a treatment of short time carried out at high temperature and a treatment of longer time at lower temperature? Answering this question can help to optimise rétification temperature and duration. The purpose of this study is to evaluate the relevance of a “time temperature equivalence” (TTE) for wood pyrolysis in the temperature range of retification. The principle of TTE is adapted from the study of wood viscoelastic properties. In this study, it is applied to the rate of anhydrous weight loss during wood pyrolysis. Thermo-gravimetric analysis (TGA) were performed on maritime pine (Pinus pinaster Ait.-) and beech (Fagus sylvatica) wood powder. Isothermal degradations were carried out at different temperatures ranging from 160°C to 260°C. A specific data analyse was carried out on the TGA derivative (DTG) in order to assess the relevance of the TTE in the temperature range of retification. It gave interpretable results for maritime pine, but not for beech. It showed that for maritime pine wood the TTE is confirmed from 200°C to 220°C, and not confirmed for temperatures superior to 230°C. An optimization of the temperature and time of treatment is thus possible

Energy requirement for fine grinding of torrefied wood

International audienceThe purpose of this study is to investigate the influence of torrefaction on wood grinding energy. Wood chips were torrefied at different temperatures and durations. The energy required to obtain fine powder was measured. Particle size analyses were carried out on each powder sample. It is showed that torrefaction decreases both grinding energy and particle size distribution. A criterion to compare grindability of natural and torrefied wood is proposed. It takes into account both grinding energy and particle size distribution. It accounts the energy required for grinding particles to sizes inferior to 200 μm, for given grinding conditions. Torrefaction is characterised by the anhydrous weight loss (AWL) of wood. For AWL inferior to around 8%, grinding energy decreases fast. Over 8%, grinding energy decreases at a slow rate. Particle size distribution decreases linearly as the AWL increases. Both for spruce and beech, the grinding criterion is decreased of 93% when the AWL is around 28%

Modelling anhydrous weight loss of wood chips during torrefaction in a pilot kiln

International audienceBeech and spruce chips were torrefied in a batch rotating pilot kiln. For each torrefaction the temperature curve of the moving chips bed was recorded. The anhydrous weight loss (AWL) of each torrefaction was measured. Effect of torrefaction temperature and duration on the AWL was studied. In order to optimise short time torrefaction, models that can estimate the AWL from the chips temperature curve are required. Three phenomenological models were successfully applied. They all gave good correlations between experimental and calculated AWL. These three models can be employed to optimise industrial torrefaction. However, the more complex they are, the more difficult it is to understand their physical meaning. It is thus preferable to use simple model for the industrial control of torrefaction

Durabilité de composites bois - polymers biodégradables Durability of Wood - biodegradable Polymer Composites.

International audienceCette étude porte sur la photodurabilité de matériaux entièrement biodégradables : des composites bois - polymères biodégradables. Les matrices polymères sont le poly(acide lactique), l'Ecoflex® et l'Ecovio®. Les charges sont différentes farines de peuplier dont certaines ont subi un traitement thermique appelé rétification, visant à diminuer leur hygroscopie et ainsi leur biodégradabilité. Ces mélanges (50/50) sont analysés par rhéométrie à l'état fondu et par analyse enthalpique différentielle (DSC) afin de caractériser leurs propriétés initiales. Ils sont ensuite soumis à un photovieillissement naturel et accéléré en enceinte et analysés de la même façon afin d'évaluer leur durabilité face à la lumière solaire. En effet, des mesures rhéologiques et thermiques vont nous permettre d'observer les changements intervenant au niveau moléculaire au cours de la dégradation et ainsi de proposer des mécanismes de photodégradation. // The topic of the study is the photoageing of completely biodegradable composites: Wood-biodegradable Polymer Composites. The polymer matrices are poly (lactic acid), Ecoflex®_and Ecovio®. The fillers are different poplar flours. Some of them have undergone a retification process: a thermal treatment. This process leads to chemical modification of wood which results in higher hydrophoby and thus to greater resistance against biodegradation. These blends (50/50) were analysed by melt rheological measurements and by Differential Scanning Calorimetry (DSC) to characterize their initial properties. In a second time, natural and artificial photoageing of these blends were carried out. Rheological and DSC measurements permit to find out their durability under UV-visible light. Indeed, these analyses allows us to observe molecular changes during degradation and therefore to determine photodegradationmechanism at work

Durabilité de composites bois – polymères biodégradables

Etant données les préoccupations environnementales actuelles, il est important de s'intéresser dés à présent aux matériaux entièrement biodégradables. C'est pourquoi nous étudions des mélanges composites polymères biodégradables – charges d'origine naturelle. Le projet est de découpler l'aspect photodégradation de l'aspect biodégradation afin d'obtenir à terme une durabilité contrôlée. Ce contrôle permettrait d'associer un matériau à une durée d'application et donc d'éliminer l'étape de recyclage

Etude rhéologique de nouveaux biocomposites bois - polymères biodégradables

L'étude porte sur la photodurabilité de composites entièrement biodégradables. Ils sont constitués de trois matrices polymère biodégradables (PLA, Ecoflex® et Ecovio®) mélangées avec différentes farines de bois dont certaines ont subi un traitement thermique visant à renforcer leurs propriétés hydrophobes. La rhéologie dynamique à l'état fondu a permis de caractériser initialement le comportement viscoélastique de ces matériaux mais également d'observer les coupures ou recombinaisons éventuelles des chaînes macromoléculaires intervenant lors de la dégradation photochimique

Robustness of kappa (κ) measurement in low-to-moderate seismicity 1 areas: insight from a site-specific study in Provence, France

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