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The effect of inorganic additives on the formation, composition, and combustion of cellulosic char
Author(s) -
Sekiguchi Yuki,
Shafizadeh Fred
Publication year - 1984
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1984.070290421
Subject(s) - char , pyrolysis , cellulose , chemistry , fire retardant , decomposition , combustion , tar (computing) , yield (engineering) , chemical engineering , thermal decomposition , organic chemistry , polymer chemistry , materials science , engineering , computer science , metallurgy , programming language
At temperature above 300°C the glycosyl units of cellulose are simultaneously depolymerized to a tar and decomposed to a char by evolution of H 2 O, CO, and CO 2 . When the glycosyl units are depleted, a stable char is formed containing about 30% aliphatic and 70% aromatic components. The aliphatic component is formed first, but on further heating is converted to polycyclic aromatic structures. The chars formed at lower temperatures are more combustible because the aliphatic component of the char is highly pyrophoric and is oxidized almost at the same temperature at which it is formed (∼360°C). The aromatic component, however, is less reactive and is oxidized at ∼520°C. Consequently, the chars formed at higher temperatures are less combustible. It has been shown that (NH 4 ) 2 HPO 4 , which is a well‐known flame retardant and smoldering inhibitor, lowers the pyrolysis temperature and increases the char yield by accelerating the decomposition reactions. This affects the composition of the intermediate chars but the final products have about the same composition irrespective of additives. (NH 4 ) 2 HPO 4 also lowers the rate of oxidation of the aromatic component and the corresponding heat release. NaCl, which is an enhancer of smoldering combustion, has a slight stabilizing effect on pyrolysis of cellulose. It lowers the oxidation temperature of the aromatic component and dramatically increases its rate. The corresponding heat release is also increased due to complete oxidation to CO 2 . The rate of oxidation calculated from the dynamic thermal analysis data is more than tripled by NaCl and significantly reduced by (NH 4 ) 2 HPO 4 .