Wood densification itself does not, in general, improve the fire-retardant properties sufficiently to reach the standard requirements. The object of this study was to enhance the fire-retardant properties of thermo-mechanically densified wood without any loss of moisture stability and hardness. Scots pine sapwood was pretreated before densification by impregnation with a fire retardant (FR) consisting of ammonium dihydrogen phosphate and urea and then cured in-situ by hot pressing at 150 °C or 210 °C. Densified specimens without FR were used as a control. Set-recovery, fire retardancy in an open flame test, and Brinell hardness were determined. The set-recovery was slightly reduced as a result of the FR treatment, but the pressing temperature and time had a much greater influence. In the open flame test, specimens without FR-treated ignited within 15-50s of exposure to the flame, whereas all the FR-treated specimens exhibited ignition resistance over the 10 minutes duration of the test. Water-soaking cycles had no impact on the ignition resistance in these groups, indicating a strong resistance to water leaching of FR after pressing at 210 °C for 60 minutes. The hardness increased due to the presence of FR after pressing at 210 °C, but sharply decreased after water immersion.
Validerad;2024;Nivå 2;2024-11-13 (sarsun);
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