Caractérisation des transformations physico-chimiques intervenant lors de la thermodégradation du bois. Influence de l'intensité de traitement, de l'essence et de l'atmosphère

Le traitement thermique est basé sur la modification chimique des biopolymères par thermodégradation, en évitant l'ajout de produits chimiques. Ce traitement améliore la stabilité dimensionnelle et la durabilité fongique du bois. Ces améliorations se font au détriment des propriétés mécaniques qui ont tendance à s'affaiblir. Aujourd'hui, plusieurs types de procédés sont utilisés. Ils se distinguent entre autre par la nature du milieu dans lequelle se déroule le traitement. La durabilité de ce nouveau matériau bois est liée au degré de thermodégradation, dépendant des conditions et de l'intensité du traitement. Un pilote de traitement par conduction, travaillant sous vide ou sous azote, mesurant la masse en dynamique est utilisé afin de mieux comprendre l'influence de l'atmosphère. Les résultats obtenus montrent que l'utilisation du vide permet d'éliminer, de l'enceinte de traitement, les produits volatils formées au cours du traitement conduisant à des taux de lignine de Klason plus faibles du fait de la non recondensation des produits de dégradation. Cette limitation de recondensation des produits volatiles engendre des pertes de masse, pour une même intensité de traitement plus faibles, confirmés par des taux de polysaccharides plus élevés pour un traitement sous vide. Des études de cinétiques des réactions de thermodégradation ont confirmé la plus grande sensibilité des feuillus vis-à-vis de la thermodégradation (comparé aux résineux). De plus, ces analyses ont permis d'identifier les principaux produits de thermodégradation du bois qui varient en fonction de l'intensité du traitement et a permis de montrer une thermosensibilité plus importante de la lignine que de l'holocelluloses pour la gamme de températures utilisée. Le fruit de ces travaux est donc une progression significative des connaissances de bases sur les mécanismes de thermodégradation et leurs relations avec les paramètres de traitementThermal treatment is based on biopolymer chemical degradation by heat transfer, without additional chemical products impregnation. This process improves the dimensional stability and the decay resistance of wood. These improvements come at the expense of wood mechanical properties of wood which weak. Several types of heating processes exist currently differing mainly by the nature of the inert atmosphere used during treatment. The durability of this new wood material is correlated to the degree of polymers thermal degradation depending on the conditions and the treatment intensity. A conducting heat treatment pilot using nitrogen or vacuum and allowing dynamic record of mass loss is used to understand better the atmosphere influence. The results show that utilization of vacuum permit the elimination of volatile products formed during heat treatment and accumulated in oven, leading to lower extractives and Klason lignin contents due to the non recondensation of thermal degradation products. Limitation of the formation of recondensation products generates a lower mass loss for same treatment intensity and explains the lower polysaccharides degradation during a vacuum process. Fine chemical analyses and the study about thermal degradation reaction kinetics have allowed confirming the higher sensibility of hardwood than softwood to thermal degradation. In addition, these analyses have permitted the volatile thermal degradation products identification related to the treatment intensity. Subsequently, results have shown a higher thermal sensibility of lignin than holocelluloses for temperatures below 230C. This work is a significant increase in basic knowledge about the mechanisms of wood thermal degradation and their relations with the processing parametersMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Modification chimique d'antioxydants pour les rendre lipophiles (application aux tannins)

Dans le but d utiliser des antioxydants naturels dans des corps gras, nous avons voulu rendre lipophiles des tanins en leur greffant des chaînes carbonées au moyen de modifications chimiques simples et douces. Nous avons eu recours, dans un premier temps, à des substrats modèles de tanins (phénol, catéchol, acide gallique et catéchine en particulier), utilisés dans des essais d alkylation, d acylation, d estérification par un acide gras ou par un alcool gras, ou encore, en ce qui concerne la catéchine, de greffage d une chaîne carbonée de longueur variable par une réaction de couplage oxa-Pictet-Spengler entre les cycles C et B. Dans un deuxième temps, l application des mêmes synthèses aux tanins de châtaignier (Castanea sativa), de chêne (Quercus pedunculata), de québracho (Schinopsis balansae) et de pépins de raisin (Vitis vinifera) a été concluante, plus particulièrement pour le couplage oxa-Pictet-Spengler. Tous les dérivés de molécules modèles ou de tanins bruts ont acquis un caractère lipophile tel qu avéré par la mesure du coefficient de partage entre l eau et l octanol. Les propriétés antioxydantes des molécules modèles et des tanins bruts et modifiés ont été mesurées par deux méthodes : inhibition de l'oxydation induite du linoléate de méthyle et réactivité avec le radical libre 2,2-diphényl-picrylhydrazyle (DPPH). Les propriétés antioxydantes sont bien conservées après modification.In the order to use natural antioxidants in lipidic substances, we wanted to make lipophilic of tannins by grafting on them carbonaceous chains through mild and simple chemical modifications. First, we used model substrates of tannins (phenol, catechol, gallic acid and mostly catechin) in experiments of alkylation, acylation, esterification by a fatty acid or a fatty alcohol, or, with regard to catechin, grafting of a carbonaceous chain variable length by a coupling reaction of the oxa-Pictet-Spengler type between the cycles C and B. Then, an application of the same synthesis to tannins of chestnut (Castanea sativa), oak (Quercus pedunculata), quebracho (Schinopsis balansae) and grape seed (Vitis vinifera) was a success, especially for the coupling oxa-Pictet-Spengler. All derivatives of model molecules or rough tannins acquired a lipophilic character as proven by the measurement of the coefficient of partition between water and the octanol. The antioxidant properties of model molecules, rough and modified tannins were measured by two methods: inhibition of the induced oxidation of the methyl linoleate and reactivity with the free radical 2,2-diphenyl-picrylhydrazyle (DPPH). The antioxidant properties are well preserved after modification.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Caractérisation HPLC de marqueurs permettant de prévoir l'évolution de certaines propriétés macroscopiques du bois lors de différents processus de dégradation

L identification de marqueurs susceptibles de mettre en évidence et quantifier l altération du bois par différents agents de dégradation peut présenter un grand intérêt dans la mise au point de méthodes de contrôle du matériau. Dans la première partie de ce travail, la caractérisation et le dosage des composés extractibles de deux essences non durables, le hêtre et le chêne soyeux, exposées à différents champignons de pourritures blanches ou brunes préalablement traitées ou non avec du propiconazole a été effectué. L évolution de la quantité et de la nature des extractibles dépend directement de la présence du biocide et permet de différencier clairement les éprouvettes en fonction du taux de dégradation de ces dernières. C est le cas notamment de la catéchine présente dans les extraits de hêtre, qui disparaît rapidement lorsque le bois est exposé à un agent de pourriture et qui peut à ce titre constituer un marqueur de l attaque du bois. Dans la seconde partie de ce travail, l évolution de la composition chimique du bois traité par pyrolyse douce à 240C sous azote a été étudiée. Bien que les résultats obtenus confirment en grande partie ceux décrits précédemment dans la littérature, le dosage des différentes fractions du bois (lignine et holocellulose) et l analyse des monosaccharides constitutifs de la fraction holocellulose du bois ont permis de mettre en évidence un important phénomène de carbonisation rapporté jusqu à présent pour des températures plus élevées. Ce phénomène confirmé par RMN13C peut être à l origine de certaines des nouvelles propriétés du matériau.The identification of markers able to highlight and quantify wood deterioration by different degradation agents can be of great interest in the development of material control methods. In the first part of this work, the characterization and the quantification of the two non durable wood species extractives, beech and silky oak, treated or not with propiconazole and exposed to various white rot or brown rot fungi were carried out. The evolution of the quantity and the nature of extractives depend directly on the presence of biocide and allowed to clearly differentiate degraded and non-degraded samples. This is particularly true in the case of catechin identified in the extracts of beech, which is rapidly degraded by rotting fungi constituting therefore a valuable marker of wood degradation. In the second part of this work, the evolution of the chemical composition of wood treated by mild pyrolysis at 240C under nitrogen was investigated. Although the results mainly confirm those described previously in the literature, isolation of lignin and holocellulose fractions and analysis of monosaccharides constitutive of holocellulose fraction highlighted an important carbonization of wood reported up to now for higher temperatures. This phenomenon is confirmed by 13C NMR and could be at the origin of some of the new properties of the material.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Advantage of vacuum versus nitrogen to achieve inert atmosphere during softwood thermal modification

International audienceWood heat treatment is an attractive alternative to improve decay resistance of wood species with low natural durability. Durability and mechanical properties are strongly correlated to thermal degradation of wood cells wall components. Mass loss resulting from this degradation is a good indicator of treatment intensity and final treated wood properties. Several types of convective heating processes exist currently differing mainly by the nature of the inert atmosphere used during treatment: nitrogen, steam or oil. Conductive heat treatment using vacuum as inert atmosphere is an attractive new alternative to previous classical methods. Heat transfer by conduction has been reported to provide better treatment homogeneity than heat transfer using convection. The aim of this study is to investigate the effect of vacuum comparatively to nitrogen on the thermal degradation pathways and on the conferred properties to the material. It appears that utilization of vacuum permit a better control of thermal degradation reactions limiting the mass loss resulting from degradation of wood cell wall polymers. Chemical analysis indicates that wood heat treated under nitrogen present higher Klason lignin and carbon contents, lower hemicelluloses and neutral monosaccharides contents comparatively to wood heat treated under vacuum. At the same time, mechanical properties are less affected under vacuum, which constitute another advantage of this technology

Odabrana svojstva drva Prunus africana iz Kenije i mogući razlozi njegove velike prirodne trajnosti

Studies were carried out on the influence of Prunus africana heartwood extractives on the growth of selected wood decay fungi. Also, wood chemical and mineral content, dimensional stability and anatomical features of P. africana were studied. Heartwood extractives were tested in 100 ppm and 500 ppm concentrations on white, brown rot, and blue stain fungi and growth inhibition was determined as a factor of time. Dimensional stability was determined by computing the swelling coefficient after the blocks were saturated with moisture. Klason lignin, Kürschner cellulose, extractive and ash contents were determined by standard procedures. Infrared analyses were performed using Perkin Elmer FTIR spectrometer. Microscopic examination was performed using an environmental scanning electron microscope. The results showed that the wood is dimensionally stable, and contains 12.7 % extractives, 37.6 % cellulose and 30.4 % lignin. Extractives deposited in vessels are highly soluble in dichloromethane and mainly composed of terpenes. Extractives were able to inhibit the growth of white rot fungi Coriolus versicolor, brown rot fungi Poria placenta and blue stain fungi Aureobasidium pullulans at different concentrations tested and could explain the high durability of Prunus africana wood species.Cilj rada bio je istražiti utjecaj ekstraktivnih tvari u drvu Prunus africana na pojavu i razvoj određenih vrsta gljiva koje uzrokuju trulež. Također, analiziran je kemijski i mineralni sastav drva P. africana, njegova dimenzijska stabilnost i anatomska obilježja. Ekstraktivi iz drva srži testirani su u koncentraciji 100 ppm i 500 ppm na gljive bijele truleži, smeđe truleži i plavila, a inhibicija rasta određena je kao faktor vremena. Dimenzijska je stabilnost određena izračunavanjem koefi cijenta bubrenja nakon što su uzorci natopljeni vodom do zasićenja. Klason lignin, Kürschner celuloza, ekstraktivi i sastav pepela određeni su standardnim postupcima. Infracrvena analiza provedena je upotrebom FTIR spektrometra Perkin Elmer. Mikroskopska istraživanja provedena su uz primjenu elektronskog mikroskopa. Rezultati su pokazali da je drvo P. africana dimenzijski stabilno, da sadržava 12,7 % ekstraktivnih tvari, 37,6 % celuloze i 30,4 % lignina. Ekstraktivne tvari pohranjene u trahejama vrlo su topljive u diklormetanu i uglavnom su sastavljene od terpena. Ekstraktivi su bili sposobni spriječiti razvoj gljive bijele truleži Coriolus versicolor, gljive smeđe truleži Poria placenta i gljive plave truleži Aureobasidium pullulans pri različitim koncentracijama, čime se može objasniti vrlo velika prirodna trajnost te vrste drva

Effect of the nature of the inert atmosphere used during thermal treatment on chemical composition, decay durability and mechanical properties of wood

International audienceWood heat treatment is an attractive alternative to improve decay resistance of low natural durability wood species. Nowadays, several types of thermal treatments of wood exist. These treatments differ mainly by the nature of the inert atmosphere used to avoid wood combustion which may correspond to: nitrogen, vacuum, steam or oil. Decay resistances as well as mechanical properties are strongly correlated to thermal degradation of wood cells wall components and consequently of treatment conditions from which depend chemical modifications. The aim of this study is to determine the effect of a new generation of treatment performed under vacuum on the chemical modifications occurring during treatment. For this purpose, beech wood has been treated under different inert conditions: vacuum and nitrogen. All treatments were performed at 220 °C for mass losses resulting from wood thermodegradation of approximately 12%. For each treatment condition concerning treated and untreated beech wood, extractives, Klason lignin, hemicelluloses and -celluloses content were determined as well as monosaccharide composition. Results show that extracts content were lower in the case of wood samples treated under vacuum, while lignin, hemicelluloses and a-celluloses contents were higher in the case of samples treated under steam and nitrogen, indicating lower wood degradation under vacuum treatment. Finally, effect of inert atmosphere on wood mechanical properties was evaluated. Results show that even if mechanical properties decreased after thermal treatment MOE, MOR and Brinell hardness were less affected under vacuum treatment comparatively to treatment performed under nitrogen

Nouveaux traitements de préservation du bois associant bore, méthacrylate de polyglycérol et traitement thermique

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Decay and termite resistance of pine blocks impregnated with different additives and subjected to heat treatment

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Effect of chemical modifications caused by heat treatment on mechanical properties of Grevillea robusta wood

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