Development of new wood treatments combining boron impregnation and thermo modification: effect of additives on boron leachability

Abstract

Environmental pressures in France and in most European countries during the last decade have led to the development of more environmentally acceptable preservation methods. In this context, wood heat treatment is one of the most investigated alternative methods. Important chemical modifications resulting from thermo-degradation reactions confer new properties to wood, like increased decay resistance or higher dimensional stability, while mechanical properties like tensile strength decrease after treatment. However, the improved durability of heat treated wood is not sufficient to allow its utilization in ground contact, where it is subjected to insect and fungi attacks. Impregnation with borax before thermal treatment could be an interesting method to improve the properties of thermally modified wood. Boron is a relatively harmless biocide that improves resistance to fungi and insects like termites. Additionally, borax can also improve wood fire resistance due to its fire retardant effect. To reduce boron leachability, two additives previously developed in the laboratory corresponding to water soluble polymerizable polyglycerol derivatives were added to the borax solution, taking advantage of thermal treatment to fix the latter through polymerization within the wood structure limiting boron leachability. (Résumé d'auteur

Effects of Acid Copper Chromate Preservative and Hydrothermal Treatment on the Dimensional Stability, Hardness, and Decay Resistance of Poplar Wood

“…Subsequently, before thermal treatment, the impregnation with borax, which means the combination of boron impregnation and thermo-modification, could be an interesting method to improve the properties of thermally modified wood. In particular, properties such as resistance to fungi and insects and resistance to wood fire could be improved by this method (Salman et al 2014).…”

Influence of Heat Treatment and Tannin Impregnation on Boron Depletion and Wood Durability

“…Tannins may be acting to denature proteins; in that case, fungal enzymes would be inhibited. This study revealed the importance of HT on a mixture of boron and tannins to decrease boron leaching and increase the durability of preservative systems.products is limited because of boron's natural solubility in water, which leads to a rapid depletion of treated wood in outdoor exposed conditions [7][8][9][10][11][12].Research has been conducted to address boron depletion. The most common strategies for reducing boron leaching are surface and envelope treatments, wood bulking, the use of water repellant, organo-boron compounds, a combination of biocides and non-biocidal agents, metallo-borates, stabilized boro-esters, protein borates, in situ polymerization and boron silicates [13][14][15][16][17][18][19].Previous research has shown the potential of boron fixation by tannin auto condensation.…”

“…products is limited because of boron's natural solubility in water, which leads to a rapid depletion of treated wood in outdoor exposed conditions [7][8][9][10][11][12].…”

Retention and absorption of boron salts solution of ten mexican woods

“…Por su parte, Obanda et al (2008) recopilan estrategias propuestas recientemente para reducir la solubilidad de las sales de boro cuando son empleadas como preservadores en productos de madera. Otras estrategias para mejorar el proceso de preservación en la madera con sales de boro pueden ser consultadas en Salman et al (2014) y Obounou-Akong, Gérardin, Thévenon & Gérardin-Charbonnier (2015).…”

“…Tondi et al (2012), impregnando probetas de 0.025 m ´ 0.015 m ´ 0.05 m, utilizando un proceso de preservación específicamente diseñado y una concentración de sales de boro de 6%, encuentran retenciones de 2.88 kg/m 3 a 9.16 kg/m 3 para madera de Fagus sylvatica y de 3.25 kg/m 3 a 9.57 kg/m 3 para la de Pinus sylvestris. Salman et al (2014), usando probetas de 0.015 m ´ 0.005 m ´ 0. 050 m, aplicando un proceso de preservación con temperatura de 103 °C, durante 48 h, con un tiempo de inmersión de 30 min y una concentración de sales de boro de 4%, logran una retención de 4.2 kg/m …”