The Effect of Chemical Modification by Synthetic and Natural Fire-Retardants on Burning and Chemical Characteristics of Structural Fir (Abies alba L.) Wood

The effect of a surface coating with an aqueous solution containing a synthetic diammonium hydrogen phosphate fire retardant and vacuum pressure impregnation with a synthetic diammonium hydrogen phosphate fire retardant, potassium acetate, and a natural polymeric retardant, arabinogalactan, to improve the fire resistance and selected properties of structural fir (Abies alba L.) wood was investigated in this article. The combustion characteristics were investigated, and the heat of combustion reflects the effect of the presence of fire retardants. Changes in the content of cellulose, hemicelluloses, holocellulose, lignin, and extractives characterize the chemical changes in wood caused by these factors. The relationship between the combustion characteristics and chemical changes in chemically modified wood as a consequence of the presence of flame retardants were assessed using Fourier transform infrared spectroscopy. The results showed that the effectiveness of the fire retardants against ignition and burning when applied by vacuum pressure impregnation was always higher than in the case of surface coating, even when using impregnation solutions of low concentrations. In the case of diammonium hydrogen phosphate, a low 5% concentration of retardant was sufficient to provide suitable flame retardancy. Further, degradation by depolymerization of cellulose occurred only at temperatures between 460 and 470 °C. Low concentrations of retardant limit the loss to the environment and consequent ecological impact.