Polyesterification of wood using sorbitol and citric acid under aqueous conditions

Abstract

The aim of this research is to determine if the polyesterification of sorbitol and citric acid in wood has a future potential as a wood modification process. Pine wood was impregnated with an aqueous solution containing citric acid and sorbitol and was thereafter cured at 103 or 140°C for 18 hours. The dimensional stability and leaching resistance were studied for both modification temperatures. The leachates from the modified wood samples were analysed by HPLC and the susceptibility to decay and staining fungi were studied. Impregnated samples cured at 140°C showed a permanent (leach-resistant) increased dimensional change, but samples treated at 103°C were not stable to leaching. Treated samples cured at 103 and 140°C showed significant resistance to white-rot (Trametes versicolor) and brown-rot decay (Postia placenta) after a leaching procedure. Furthermore, samples cured at 103 and 140°C (leached and unleached) were significantly less susceptible to blue-stain fungi than the untreated controls.

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

“…Larnøy et al [52] found the treated pine sapwood samples cured at 140 • C are more stable to that of cured at 103 • C as no leachate was detected in the former by HPLC analysis. It is implied that curing temperature of 103 • C is not sufficient to ensure complete reaction between CA and sorbitol.…”

“…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. As a result of the treatment, resistance against brown rot, white rot, and blue stain fungi of the treated pine sapwood were improved significantly.…”

“…Leaching analysis indicated that treated wood samples cured at 160 • C resulted in the lowest amount of leaching compared to that of cured at 140 • C, suggested that intensive polyesterification had occurred at this curing temperature. Doll et al [44] and Larnøy et al [52] suggested that 150 • C and 140 • C is a better curing temperature than other lower temperatures used in their respective studies, thus it could be concluded that temperature of at least 140 • C is required to ensure the polyesterification occurs to a greater extent. However, the curing temperature should be limited below the temperature that could cause irreversible damage to the wood samples itself.…”

Macrobiological Degradation of Esterified Wood with Sorbitol and Citric Acid

“…Earlier studies on the utilization of sorbitol for wood modification have been limited to describing solely the dimensional stabilization of the wood matrix [19]. In recent studies, SCA-modified wood was shown to exhibit not only enhanced dimensional stability, but also durability against decay fungi and reduced susceptibility to blue stain fungi [20].…”

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].…”