Beech wood modification based on in situ esterification with sorbitol and citric acid

Abstract

In this study, modification of European beech wood (Fagus sylvatica) through in situ esterification of sorbitol and citric acid (SorCA) was investigated at two curing temperatures, 140 and 160 °C. In order to determine the optimum condition for modification, an aqueous solution of SorCA at varying concentrations was evaluated (10, 20, 30, and 55% w/w). Physical, mechanical, chemical, and durability properties of the modified wood were examined. Results have disclosed that among different SorCA concentrations, treatment with SorCA at 30% w/w was considered as the optimum concentration independent of the curing temperature. Under these conditions, anti-swelling efficiency increased to approx. 55% and modulus of elasticity increased slightly with approx. 9% in comparison with untreated wood. Decay resistance against white-rot (Trametes versicolor), brown-rot (Coniphora puteana), and soft-rotting microfungi classified the SorCA-30%-modified wood as very durable. In addition, thermogravimetric study evidenced that SorCA 30%-modified wood has a lower thermal decomposition temperature in comparison with untreated wood/wood control by 20 °C difference, indicating that the SorCA-modified wood possibly has fire-retardant properties. However, due to the acidic properties of the SorCA solution, modulus of rupture (MOR) and mainly work to maximum load in bending decreased considerably.

Cell Wall Bulking by Maleic Anhydride for Wood Durability Improvement

“…Compared with the previously reported methods which mainly referred to physically filling the dynamic nanopores or chemically bonding to the hydroxyl groups, the strategy proposed in this study is a dual modification method, that is, the use of maleic anhydride (MAn) to improve wood durability (i.e., dimensional stability and decay resistance) via dynamic nanopore filling combined with hydroxyl group elimination. Although acetic anhydride, melamine formaldehyde, sorbitol, and N-methylol melamine have been reported to modify the cell wall for durability improvement in a similar strategy to our work, several drawbacks like the strong acid catalysts employed or formaldehyde release adversely affect their properties and the environment, and thus limit their practical applications [39][40][41][42][43]. Although maleic anhydride was reported to bulk the cell wall and chemically bond to the hydroxyl group, the employed methods still use solvents like DMSO, which are difficult to remove after the reaction, and the vapor phase reaction requires specific equipment [44][45][46].…”

A Review on Citric Acid as Green Modifying Agent and Binder for Wood

“…The former involves a reaction between the functional groups of a treating agent with hydroxyl groups of wood. Meanwhile, the latter involves the reaction of the functional groups of one treating agent and the hydroxyl groups from other treating agents and/or wood [19]. Esterification with CA is an inexpensive and environmentally friendly wood modification method to bestow good dimensional stability as well as biological durability to wood and lengthen its service life [20].…”

“…European beech (Fagus sylvatica) sapwood modified with CA and sorbitol solution at different concentrations has shown an increment in density, pH, and thickness swelling (TS), where the increment increased along with increasing CA-sorbitol concentrations [19]. Larnøy et al [52] treated Scots pine sapwood (Pinus sylvestris) with a combination of sorbitol and CA and some selected properties of the treated wood were assessed.…”

Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid

“…Polyesterification of bio-based chemicals in wood as an impregnation chemical modification technique is a field which has been gaining research attention over the past decade [5][6][7][8][9][10][11][12][13]. One promising method utilising relatively low-cost chemicals is polyesterification using sorbitol and citric acid (SCA) [14,15]. The uncatalyzed reaction of citric acid with alcohols or polyols is thought to proceed through a cyclic anhydride intermediate formed by dehydration of the citric acid ( Figure 1a,b) which then reacts with a hydroxyl group in the alcohol/polyol (Figure 1c) to form an ester ( Figure 1d) [16].…”

“…Recently, Larnøy et al [14] used higher solution concentrations without a catalyst and showed that SCA-modified Scots pine cured at 140 °C was resistant to leaching of reactant chemicals and hindered fungal growth from brown-rot, white-rot and mould fungi. Mubarok et al [15] tested two curing temperatures, 140 and 160 °C, and various SCA solution concentrations for the modification of European beech wood. They also demonstrated increased decay resistance of the Further condensation reactions can lead to the formation of another cyclic anhydride (e) and/or anhydrosorbitol ring (f) which undergo further reactions to form a polymerized material.…”