Fatima Charrier

Color stability of heat-treated wood during artificial weathering

The color change of wood after exposure to UV light may produce aesthetical damages. The stability of the color to light exposure is an important issue. This study describes experiments of testing the color stability of heat-treated wood samples. Heat treatment was done at 240°C during 2 hours, under nitrogen. Heat-treated samples of ash, beech, maritime pine and poplar heartwood were exposed to UV-light (QUV equipped with fluorescent lamps UVA-340) during 835 hours. Color measurements during accelerated weathering were made at intervals throughout the test period. The results are presented in ΔE and L* a* b* coordinates according to the CIELab system. The experiments show that the color stability for heat-treated wood is better during the 835 hours of exposure when compared to untreated wood. The properties of heat treated wood (lignin modifications, and monomers of phenolic compounds) are probably involved in the retified wood resistance against UV light under experimental conditions.ZusammenfassungFarbveränderung bei Holz, das UV-Licht ausgesetzt wurde, kann ästhetische Schäden verursachen. Die Stabilität der dem Licht ausgesetzten Farbe ist ein wichtiges Thema. Diese Studie beschreibt Experimente zum Testen der Farbstabilität bei hitzebehandelten Holzproben. Die Hitzebehandlung wurde bei 240°C zwei Stunden lang unter Stickstoff durchgeführt. Die hitzebehandelten Holzproben von Eschen-, Buchen-, Kiefern- und Pappel-Kernholz wurden 835 Stunden lang UV-Licht ausgesetzt (QUV bestückt mit fluoreszierenden Lampen UVA-340). Farbmessungen während beschleunigter Bewitterung wurden in Intervallen durchgeführt. Die Ergebnisse werden in ΔE und L* a* b* Koordinaten gemäß dem CIELab-System dargestellt. Sie zeigen, dass die Farbstabilität bei hitzebehandeltem Holz während der 835 Stunden vergleichsweise besser ist als bei unbehandeltem Holz. Die Eigenschaften des hitzebehandelten Holzes (Ligninmodifikationen und monomere phenolische Bestandteile) sind wahrscheinlich an der Beständigkeit gegenüber UV-Licht unter experimentellen Bedingungen beteiligt.

Study of industrial boiling process on walnut colour: Experimental study under industrial conditions

Juglans regia) logs, measured during boiling water process under industrial conditions. The colour changes in sapwood and heartwood evolution were analysed according to the previous results obtained in laboratory. As it was expected, the sapwood color changes quickly during the first 10 hours and definitely after 30 hours of industrial treatment. Its colour is darker and redder. Heartwood behavior is quite different because its colour is changing slowly during the first 10 hours and important changes are occuring after the 39 first hours. These mean results were obtained on the four logs studied. This work precise the particular behavior of the color of wood during boiling and the efficient method used. This study may be used by industries, which are concerned by heating treatment before slicing, and applied to other species.Juglans regia), die während der Behandlung in kochendem Wasser bei Industriebedingungen entstehen. Die Verfärbungen im Splint- und Kernholz wurden analysiert unter Verwendung früherer Ergebnisse aus Laboruntersuchungen. Wie erwartet erfolgt die Verfärbung im Splintholz rasch während der ersten 10 Stunden. Nach 30 Stunden wird ein Endwert erreicht. Die farbe wird dunkler und rötlicher. Die Farbänderungen im Kernholz verlaufen ander; sie beginnen sehr langsam während der ersten 10 Stunden und deutliche Farbänderungen finden erst nach 39stündigem Kochen statt Die Ergebnisse werden als Mittel aus vier Rundhölzern genommen. Sie präzisieren die spezielle Verfärbungwährend des Kochens. Die verwendete Methode erwies sich als effektiv. Die Untersuchung könnte verwendet werden in Industrieprozessen, in welchen Erhitzen oder Dämpfen vor der Auftrennung des Holzes eingesetzt wird. Die Ergebnisse können auch auf andere Holzartn übertragen werden.

Physical properties and termite durability of maritime pine Pinus pinaster Ait., heat-treated under vacuum pressure

An original heat treatment performed under vacuum pressure was investigated. Maritime pine samples were treated at six different temperatures: 140, 160, 180, 200, 230 and 260°C. The physical and mechanical consequences, i.e. bending strength (MOR), modulus of elasticity (MOE), hygroscopic behaviour, equilibrium moisture contents and anti-swelling efficiency (ASE) were studied. A no-choice feeding test according to the NF EN 117 standard was achieved. Temperatures up to 200°C had no significant effect on wood properties. However, at 230 and 260°C, the decrease in MOR was severe, reaching 42.5 and 62.5%, respectively. Whatever the treatment conditions, wood samples were still highly degraded by termites, revealing no increase in their durability.

PREPARATION AND MECHANICAL CHARACTERIZATION OF PARTICLEBOARD MADE FROM MARITIME PINE AND GLUED WITH BIO-ADHESIVES BASED ON CORNSTARCH AND TANNINS

In this presented work, we describe the development and characterization of a new,environmentally friendly adhesive derived from cornstarch and tannins. The production of woodcomposites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as ureaformaldehyde (UF), phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), which cangenerate under certain conditions, problems for health and environment. The aim of our work is toreplace totally these synthetic resins. In order to evaluate the quality of cornstarch-tannin adhesives,particleboards were produced and physical and mechanical properties were investigated. Thesephysical properties included rheological, thermogravimetric analysis and solid phase 13C NMR analysisof resins. Internal bond, surface soundness, modules of rupture and modulus of elasticity mechanicalproperties of particleboards bonded with cornstarch-tannin adhesives were also determined.Particleboards bonded with formaldehyde-free cornstarch-tannin adhesive showedcomparable mechanical properties to the panels made with the commercial UF resins and satisfiedthe exigencies of panels for interior fittings used in dry medium (P2) according to European normsEN 312 (2004). Beyond 4 hours, rheological characterization show excellent structural stability ofcornstarch-tannin adhesive.

Quantitative assessment of total phenol contents of European oak (#Quercus petraea# and #Quercus robur#) by diffuse reflectance NIR spectroscopy on solid wood surfaces

Abstract Near infrared spectroscopy (NIRS) combined with multivariate analysis techniques was applied to assess phenol content of European oak. NIRS data were firstly collected directly from solid heartwood surfaces: in doing so, the spectra were recorded separately from the longitudinal radial and the transverse section surfaces by diffuse reflectance. The spectral data were then pretreated by several pre-processing procedures, such as multiplicative scatter correction, first derivative, second derivative and standard normal variate. The tannin contents of sawmill collected from the longitudinal radial and transverse section surfaces were determined by quantitative extraction with water/methanol (1:4, by vol). Then, total phenol contents in tannin extracts were measured by the Folin-Ciocalteu method. The NIR data were correlated against the Folin-Ciocalteu results. Calibration models built with partial least squares regression displayed strong correlation – as expressed by high determination correlation coefficient (r2) and high ratio of performance to deviation (RPD) – between measured and predicted total phenols content, and weak calibration and prediction errors (RMSEC, RMSEP). The best calibration was provided with second derivative spectra (r2 value of 0.93 for the longitudinal radial plane and of 0.91 for the transverse section plane). This study illustrates that the NIRS technique when used in conjunction with multivariate analysis could provide reliable, quick and non-destructive assessment of European oak heartwood extractives.

Corn flour-mimosa tannin-based adhesives without formaldehyde for interior particleboard production

A formaldehyde-free adhesive consisting of a corn flour/NaOH adhesive mixture and a mimosa tannin/hexamine intermediate component was developed and evaluated for application to wood panels such as particleboards. The main ingredients of this adhesive include corn flour, NaOH, mimosa tannin and hexamine. This study investigated the physical properties (rheological and thermal analysis) of corn flour/NaOH and mimosa tannin/hexamine adhesives as well as mechanical properties of particleboards produced with these adhesives. Thermomechanical (TMA) experiments indicate the best performance of the adhesives to be around the relative mass proportions of 50:50 between corn flour/NaOH and mimosa tannin/hexamine. Former NMR measurements on corn starch and mimosa tannin proved that the two components behave as a polymer blend rather than co-reacting. The laboratory results show that particleboards bonded with the adhesive at this optimal ratio show good mechanical properties. Moreover, the formaldehyde emission levels obtained from boards bonded with the optimal adhesive were considerably lower to those obtained from boards made with control urea formaldehyde.

Evaluation of decay resistance of wood products made from borax-impregnated wood and bonded with a formaldehyde-free cornstarch and tannin adhesive

Abstract• At present, the production of wood composites mainly relies on the petrochemical-based and formaldehyde-based adhesives such as phenol-formaldehyde (PF) resins and urea-formaldehyde (UF) resins, which are non-renewable and therefore ultimately limited in supply.• This paper concerns the decay resistance of wood products bonded with a new, environment-friendly adhesive derived from abundant and renewable cornstarch and tannin. To improve the total resistance of the composite against both Coriolus versicolor and Coniophora puteana rot fungi, borax (di-sodium tetraborate) was added in proportions of 0.5%, 1% and 2% (w/w) to the cornstarch-tannin adhesives.• The results show that increasing the concentration of borax in the adhesive decreased the mechanical properties of the composite. The best way to avoid this problem was to use wood impregnated with borax.• Biodegradation studies were conducted on new composites, first without any treatment, followed by borax at 0.5% aqueous solution treatment. The results show that wood impregnated with borax, in the presence of tannin and sodium hydroxide in the adhesive improves the total resistance of the wood composite against both Coriolus versicolor and Coniophora puteana rot fungi.Résumé• Actuellement, la production des composites à base de bois nécessite l’utilisation d’adhésifs d’origine pétrochimique et à base de formaldéhyde, tels que le phénol-formaldéhyde (PF) et l’uréeformaldéhyde (UF), qui sont non renouvelables et limités dans l’approvisionnement.• Ce travail a pour objectif d’étudier la durabilité du bois collé avec une nouvelle colle naturelle à base d’amidon et tannin. Pour améliorer la résistance des composites vis-à-vis des deux types principaux de dégradation fongique, Coriolus versicolor et Coniophora puteana, nous avons ajouté à l’adhésif, différentes concentrations de borax (di-sodium tetraborate) 0,5 %, 1 % et 2 % (m/m).• Les résultats obtenus montrent que l’augmentation de la concentration du borax dans l’adhésif diminue les performances mécaniques des composites. La meilleure façon d’éviter ce problème est de traiter le bois avec du borax, avant collage.• L’étude de la biodégradation a été réalisée sur les nouveaux composites, d’abord sans traitement, et après traitement à 0,5 % (m/m) avec du borax. Les résultats montrent que le bois traité au borax associé à la présence des tannins et de NaOH dans l’adhésif améliore la résistance totale des composites vis-à-vis de Coriolus versicolor et Coniophora puteana.

Addition of Boron Based Compound in the LVL Glueline: Effect on the Mechanical Properties and the Leaching of Boron

Summary This study aims at the optimization of the durability of Laminated Veneer Lumber (LVL) panels by adding borates to the gluing formulation. Poplar veneers measuring 2.6 mm thickness were used for the manufacture of LVL by Isoroy, a French company located in Lisieux. The melamine-urea-formaldehyde (M.U.F.) glue formulations were mixed with various concentrations of boric acid. A 0.8% retention of boron was measured in the LVL panel after intensive water leaching. The mechanical properties of finished LVL panels and their bonding strength properties were evaluated. The influence of the glue bonding on leaching was also evaluated. The amount of boron in LVL was measured by spectrocolorimetry using the CIELAB system. Results demonstrated that the incorporation of boron in the glueline may improve LVL durability.

Shear refinement of formaldehyde-free corn starch and mimosa tannin (Acacia mearnsii) wood adhesives

The aim of this work was to reduce the viscosity of formaldehyde-free corn starch–mimosa tannin wood adhesives, without adversely affecting the mechanical properties of the product. The reduction of viscosity was achieved using shear refinement. The study focused on the physical phenomena before cross-linking of the wood adhesive. The physical (rheological characterization) and mechanical (bond strength) properties of formaldehyde-free corn starch and mimosa tannin wood adhesives were measured. The results showed that the shear refinement (290 rpm and 5 min, optimal conditions) reduced the viscosity of the corn starch–mimosa tannin wood adhesives (from 100 000 to 458 Pa s) with the advantage of being stable over time. Mechanical tests showed that the shear refinement did not influence the mechanical properties of corn starch–mimosa tannin wood adhesives.

Valorization of Tunisian Pomegranate Peel Tannins in Green Adhesives Formulation

The possible use of Tunisian pomegranate tannins in wood adhesive formulation was studied for the first time. Colorimetric tests, Fourier transformed infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry were used to examine pomegranate tannins. Analysis showed that pomegranate peels are rich in hydrolyzable tannins. The Stiasny number tests showed the low reactivity of pomegranate tannin extract to formaldehyde and thus the difficulty of using it in wood adhesive formulation. Thermomechanical analysis (TMA) and strength analysis of pomegranate tannin/hexamine-based resin showed weak bonding properties.