Submitted to: Cellulose
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/2013
Publication Date: 1/6/2014
Publication URL: http://handle.nal.usda.gov/10113/58649
Citation: Nam, S., Condon, B.D., Foston, M.B., Chang, S. 2014. Enhanced thermal and combustion resistance of cotton linked to natural inorganic salt components. Cellulose. 21(1):791-802.
Interpretive Summary: Cotton fiber is the most widely used fiber in apparel and home use applications in the world. Cotton fiber is nearly always scoured and bleached before being finished for various performance attributes such as dyeing, printing, softening and fire retardance. Recent observations of the fire retardance performance of cotton fabrics indicated that raw cotton (not scoured and bleached) consistently performed better than scoured and bleached fabrics. This study has now confirmed, quantified and elucidated the mechanism responsible for this phenomenon. Raw cotton contains more inorganic components which are active in slowing the decomposition of cellulose in raw cotton. This fundamental observation and the understanding the responsible mechanism will influence fire retardant chemistries as well as fabric construction for fabrics intended for heat sensitive applications.
Technical Abstract: Cotton is most commonly scoured or scoured and bleached before being used for commercial purposes, but, due to its propensity to burn, cotton's use is limited and protective chemistry is needed in applications where resistance to heat and flame is required. 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. In this study, the pyrolysis and combustion processes of cotton fabrics (nonwoven (NW) and woven (W)), before and after the inorganic constituents were removed by scouring, were examined using thermogravimetric and microscale combustion calorimetry analyses. The presence of trace quantities of inorganics was associated with increased initial weight loss of cellulose during pyrolysis and lead to a slow decomposition process. A decrease in the activation energy for the overall decomposition along with greater decreases at low conversion levels suggested that the inorganics catalyzed the thermal reactions occurring at low temperatures. During combustion, raw cotton exhibited much lower heat release capacity and lower total heat release than scoured cotton. Overall, the enhanced thermal stability of raw cotton which retained its inorganic components resulted in increased char yield by factors of five and of three in nitrogen and oxygen-rich environments, respectively. 1H13C CP/MAS NMR measurements showed the catalyzed dehydration reaction for raw cotton cellulose and different chemical compositions of the intermediate chars produced from raw and scoured cotton fabrics.