Natural resistance of raw cotton fiber to heat evidenced by the suppressed depolymerization of cellulose

Mechanically purified raw cotton fiber finds a growing range of applications in support of environmental sustainability, but its unique thermal stability, which is important in processes and utilization, is little known. This study shows that, at low temperatures (<300 °C), the accelerated dehydration of cellulose was distinct in the pyrolysis of raw cotton. Compared with scoured cotton, raw cotton exhibited an intensive accumulation of dehydrocellulose in solid products, enhanced evolution of water and carbon dioxide, and increased formation of char. The amount of the crystalline region degraded together with the amorphous region was increased in raw cotton. The activation energy of thermal decomposition for raw cotton (124 kJ/mol) determined under isothermal conditions at 200–300 °C was lower than that for scoured cotton (202 kJ/mol). Such catalyzed low-temperature thermal reactions suppressed the depolymerization of cellulose at high temperatures, which produces highly volatile levoglucosan. The levoglucosan detected in raw cotton using Py-GC/MS was two orders of magnitude less abundant than that detected in scoured cotton.