Effect of pH on Chemical Components and Mechanical Properties of Thermally Modified Wood

Abstract

To investigate the correlation between acidity and degradation during thermal treatment of wood, Cathay poplar ( Populus cathayana Rehd.) wood samples were impregnated with solutions of different pH values, which included disodium octoborate tetrahydrate (DOT, pH = 8.3), monoethanolamine (MEA, pH = 12), and four buffering solutions composed of boric acid and sodium hydroxide (BA/NaOH, pH = 6, 7, 8, 9). Samples were then heated for 4 h at 180, 200, and 2208deg;C, respectively. Bending MOR and MOE, mass losses, pH values, and percentages of lignin and hemicelluloses were subsequently determined in thermally modified samples and compared with control samples without pretreatment and/or thermal treatment. Results of the experiments indicated that DOT and buffering solutions decreased mass loss of thermally treated wood and increased bending MOR and MOE, whereas MEA pretreatment increased mass loss and showed comparable or even lower bending MOR and MOE than the untreated control with or without thermal treatments. Chemical analyses suggested that degradation of hemicelluloses was inhibited by DOT and BA/NaOH pretreatments within the temperature range 180-200°C, which may explain the mechanical property improvement.