The study of flame retardants on thermal degradation and charring process of manchurian ash lignin in the condensed phase

Dioxane lignin was isolated from manchurian ash by means of Pepper's method. The thermal degradation and charring of the manchurian ash treated with ammonium polyphosphate, ammonium dihydrogen or boric acid in the condensed phase were investigated by the combination of XPS, FTIR and TGA. TGA results under pure nitrogen showed that the flame retardants reduced the initial temperature of thermal degradation of the lignin and promoted char formation compared with the control sample. XPS data obtained in high vacuum showed that an increase of Cls and Cls (C-C) intensity, a decrease of Cls (C-O) intensity and a decrease of Cls binding energy were promoted by the flame retardants. FTIR data of char residue showed that flame retardants reduced the relative absorbance of the C-O group and enhanced the relative absorbance of C-H vibration in aromatic ring and of aromatic ring vibration. No increase of the C=O group vibration was observed. The results from XPS, FTIR and TGA demonstrate that the flame retardants catalyzed the cleavage of C-O bonds in the lignin to form a highly conjugated system and promoted crosslinking and char formation. Ammonium polyphosphate and ammonium dihydrogen phosphate were more effective in char forming than was boric acid. (C) 2001 Elsevier Science Ltd. All rights reserved.