Enhanced thermal and combustion resistance of cotton linked to natural inorganic salt components

Abstract

A comparison of the thermal decomposition and combustion characteristics of raw and scoured cottons has demonstrated a mechanistic link caused by the presence of inorganic salts in raw cotton, which enhances resistance to heat and flame. Thermogravimetry, differential thermogravimetry, and microscale combustion calorimetry were used to examine the thermal decomposition kinetics and thermal stability of cotton. During pyrolysis, both raw cotton nonwoven and woven fabrics exhibited a slower decomposition with a larger initial weight loss and produced a greater char yield, as compared to the fabrics after scouring, which removes most inorganic components from cotton. The activation energy (Ea) values, calculated using the Kissinger method, the Flynn–Wall–Ozawa method, and the modified Coats–Redfern method, were consistently determined to be smaller for raw cotton than for scoured cotton. The analyses of cotton fabrics heated at elevated temperatures by 13C CP/MAS NMR and ATR-FTIR showed that trace quantities of inorganic components promoted the formations of oxygenated moieties at low temperatures and aliphatic intermediate char. In the combustion, raw cotton exhibited a much smaller heat release capacity and a smaller total heat release than scoured cotton, indicating enhanced thermal stability when the inorganic components are intact.