Effect of cellulose, hemicellulose and lignin contents on pyrolysis and combustion of natural fibers

• Flammability properties of natural fibers are roughly correlated to lignin content.
• Low lignin content affects the degradation pathway of cellulose promoting charring.
• Low lignin content fibers exhibit the best fire behavior with low EHC and charring.

This paper investigates the effects of cellulose, hemicellulose and lignin on the pyrolysis and combustion of several natural fibers (cotton linter, flax, hemp, sugar cane, bamboo and coir). Different parameters have been selected to study the relations between chemical composition, pyrolysis and combustion: char yield (Res), effective heat of combustion (EHC), activation energy of combustion (Ea) and CO/CO2 ratio during cone calorimeter test. A correlation was found between these parameters and the lignin content in a large range of composition. The natural fibers with high content of lignin exhibit high char yield, high EHC, high Ea and low CO/CO2 ratio. However, a particular behavior was observed at low lignin/cellulose ratio. The presence of a low content of lignin with a high content of cellulose affects the degradation pathway of the latter and leads to charring and to incomplete combustion of these fibers, limiting their contribution to the heat evolved during burning.