Polycarboxylic acids as non-formaldehyde anti-swelling agents for wood

Abstract

Wood specimens of fir (Abies alba Mill) and beech (Fagus sylvatica L.) were chemically modified using polycarboxylic acids (PCA), cured by convection heating or microwave treatment and analyzed by HPLC. A new non-formaldehyde cross-linking system was composed of citric acid (CA) and 1,2,3,4-butanetetracarboxylic acid (BTCA), which are representative polycarboxylic acids (PCAs). These reagents require phosphono-based catalysts, so a sodium hypophosphite (SHP) catalyst was used in this study. The effects of PCA treatment were compared with a previously introduced 1,3-dimethylol 4,5-dihydroxy ethylene urea (DMDHEU) treatment. The dimensional stability of the modified wood was determined in terms of the anti-swelling efficiency (ASE) using the water soak/oven dry method. The results revealed an improvement in ASE for wood modified with PCA compared to modification with DMDHEU. Qualitative and quantitative determinations of bound acids were performed by HPLC. Further intensification of the wood modification process and an increase in the quality of wood-based materials were achieved using microwave treatment. Among other benefits, the formation of cross-links between the wood and the reagent components led to an improvement in the tensile strength retention, particularly in combination with the microwave treatment.

Compression Strength of Fir and Beech Wood Modified by Citric Acid

“…In the case of beech wood, the average increase of compression strength also occurred due to wood modifi cation, but the increase was insignifi cant ( Figure 3, Table 2). The amount of CA bound to wood is signifi cantly larger in fi r wood (Katović et al, 2006). Higher average compression strength of modifi ed fi r wood can be explained by better crosslinking of CA and wood.…”

Low Density Sugarcane Bagasse Particleboard Bonded with Citric Acid and Sucrose: Effect of board density and additive content

“…To resolve these serious problems, some studies about binderless (Gao et al 2011) or natural adhesives, such as citric acid and sucrose, have been conducted. Citric acid is an organic polycarboxylic acid, which contains three carboxyl groups and has been considered as a cross-linking agent for wood (Vukusic et al 2006) and plant fiber.…”

Bonding Ability of a New Adhesive Composed of Citric Acid-Sucrose for Particleboard

“…The results show that citric acid-bonded boards exhibit high mechanical properties and good dimensional stability. In addition, citric acid has also been studied as a cross-linking agent for wood (Vukusic et al 2006;Hasan et al 2007), starch (Reddy and Yang 2010), and as an absorber for heavy metal ions (Thanh and Nhung 2009). Studies have shown that when citric acid is used as a cross-linking chemical, it reacts with the hydroxyl groups and reduces the hygroscopicity of wood as well as the tendency of wood to swell or shrink (Rowell 1991;Vukusic et al 2006).…”

“…In addition, citric acid has also been studied as a cross-linking agent for wood (Vukusic et al 2006;Hasan et al 2007), starch (Reddy and Yang 2010), and as an absorber for heavy metal ions (Thanh and Nhung 2009). Studies have shown that when citric acid is used as a cross-linking chemical, it reacts with the hydroxyl groups and reduces the hygroscopicity of wood as well as the tendency of wood to swell or shrink (Rowell 1991;Vukusic et al 2006). Umemura et al (2012) pointed out that ester linkages can be detected by Fourier transform infrared spectroscopy (FTIR), which indicates that the carboxyl groups from citric acid can react with hydroxyl groups from wood, improving the performance of boards.…”