Bois dur

Résumé

Le bois dur (bois franc au Canada) désigne généralement le bois des feuillus (souvent à feuilles caduques, mais pas nécessairement, dans le cas des arbres tropicaux) ou des arbres angiospermes. Le bois dur se différencie du bois tendre, qui provient souvent de résineux ou d'arbres conifères. En général, le bois des feuillus possède une densité plus élevée que le bois des conifères, mais il existe en réalité des variations considérables quant à la dureté du bois dans les deux groupes, avec un important recouvrement ; certains bois d'angiospermes (comme le balsa) sont plus tendres que la plupart des bois de résineux, alors que l'if est un exemple de bois de résineux qui est particulièrement dur. Les bois durs poussent dans les régions subtropicales comme en Afrique ainsi qu'en d'autres régions telles qu'en Europe et en Asie. Ce qui différencie surtout le bois des feuillus du bois des résineux est la présence de pores, ou de vaisseaux. Les espèces de feuillus sont plus diversifiées qu

Source officielle

https://fr.wikipedia.org/wiki/Bois_dur

À propos de ce résultat

Cette page est générée automatiquement et peut contenir des informations qui ne sont pas correctes, complètes, à jour ou pertinentes par rapport à votre recherche. Il en va de même pour toutes les autres pages de ce site. Veillez à vérifier les informations auprès des sources officielles de l'EPFL.

Publications associées (3)

Publications associées

Chargement

Personnes associées (1)

Personnes associées

Chargement

Unités associées (1)

Unités associées

Chargement

Concepts associés (18)

Concepts associés

Chargement

Cours associés (4)

The presentation of tree growth and formation of wood anatomical structures, linked to the description of specific physical and mechanical properties, makes it possible to understand the different forms of utilisation of this material, including aspects of sustainable development.

Science des matériaux de construction non métalliques les plus utilisés et plus particulièrement des matériaux cimentaires (béton). Composition chimique, fabrication et comportement sur la durée.

Une introduction à la science des matériaux appliquée aux matériaux de construction courants, en particulier le béton et les métaux. Description de leur fabrication, leurs comportements mécanique et thermique et leur utilisation en construction.

Afficher plus

Cours associés

Chargement

Séances de cours associées (8)

Séances de cours associées

Chargement

Two-temperature stage biphasic CO2-H2O pretreatment of lignocellulosic biomass at high solid loadings

Jeremy Luterbacher

Most biomass pretreatment processes for monosaccharide production are run at low-solid concentration (<10wt%) and use significant amounts of chemical catalysts. Biphasic CO 2-H 2O mixtures could provide a more sustainable pretreatment medium while using high-solid contents. Using a stirred reactor for high solids (40wt%, biomass water mixture) biphasic CO 2-H 2O pretreatment of lignocellulosic biomass allowed us to explore the effects of particle size and mixing on mixed hardwood and switchgrass pretreatment. Subsequently, a two-temperature stage pretreatment was introduced. After optimization, a short high-temperature stage at 210°C (16min for hardwood and 1min for switchgrass) was followed by a long low-temperature stage at 160°C for 60min. Glucan to glucose conversion yields of 83% for hardwood and 80% for switchgrass were obtained. Total molar sugar yields of 65% and 55% were obtained for wood and switchgrass, respectively, which consisted of a 10% points improvement over those obtained during our previous study despite a 10-fold increase in particle size. These yields are similar to those obtained with other major pretreatment technologies for wood and within 10% of major technologies for switchgrass despite the absence of chemical catalysts, the use of large particles. © 2011 Wiley Periodicals, Inc.

Wiley-Blackwell2012

Chargement

High-solids biphasic CO2-H2O pretreatment of lignocellulosic biomass

Jeremy Luterbacher

A high pressure (200 bar) CO2-H2O process was developed for pretreating lignocellulosic biomass at high-solid contents, while minimizing chemical inputs. Hardwood was pretreated at 20 and 40 (wt.%) solids. Switchgrass, corn stover, big bluestem, and mixed perennial grasses (a co-culture of big bluestem and switchgrass) were pretreated at 40 (wt.%) solids. Operating temperatures ranged from 150 to 250°C, and residence times from 20 s to 60 min. At these conditions a biphasic mixture of an H2-Orich liquid (hydrothermal) phase and a CO2-rich supercritical phase coexist. Following pretreatment, samples were then enzymatically hydrolyzed. Total yields, defined as the fraction of the theoretical maximum, were determined for glucose, hemicellulose sugars, and two degradation products: furfural and 5-hydroxymethylfurfural. Response surfaces of yield as a function of temperature and residence time were compared for different moisture contents and biomass species. Pretreatment at 170°C for 60 min gave glucose yields of 77%, 73%, and 68% for 20 and 40 (wt.%) solids mixed hardwood and mixed perennial grasses, respectively. Pretreatment at 160°C for 60 min gave glucan to glucose yields of 81% for switchgrass and 85% for corn stover. © 2010 Wiley Periodicals, Inc.

Wiley-Blackwell2010

Chargement

In this study, we extend imaging and modeling work that was done in Part I of this report for a pure cellulose substrate (filter paper) to more industrially relevant substrates (untreated and pretreated hardwood and switchgrass). Using confocal fluorescence microscopy, we are able to track both the structure of the biomass particle via its autofluorescence, and bound enzyme from a commercial cellulase cocktail supplemented with a small fraction of fluorescently labeled Trichoderma reseii Cel7A. Imaging was performed throughout hydrolysis at temperatures relevant to industrial processing (50°C). Enzyme bound predominantly to areas with low autofluorescence, where structure loss and lignin removal had occurred during pretreatment; this confirms the importance of these processes for successful hydrolysis. The overall shape of both untreated and pretreated hardwood and switchgrass particles showed little change during enzymatic hydrolysis beyond a drop in autofluorescence intensity. The permanence of shape along with a relatively constant bound enzyme signal throughout hydrolysis was similar to observations previously made for filter paper, and was consistent with a modeling geometry of a hollowing out cylinder with widening pores represented as infinite slits. Modeling estimates of available surface areas for pretreated biomass were consistent with previously reported experimental results. © 2014 Wiley Periodicals, Inc.

Wiley-Blackwell2015

Chargement