Although having a full picture of the heat-induced alterations in the fine structure of cellulosic materials is essential for designing their thermal processing, there have been no reliable methods to identify thermal transition temperatures. This study shows that colorimetric, thermogravimetric, and thermal kinetic parameters were sensitive to the thermochemical and thermo-structural changes in cotton fiber at low temperatures. Among these parameters, the activation energy for the thermal decomposition, evolving two local maxima against the preheating temperature, identified sequential thermal transformations in amorphous cellulose: 1) glass transition at 160-180 °C (Tg), 2) cellulose dehydration at 200-220 °C, and 3) crystallization at 240-260 °C. These results indicated that results of the mechanical tests or other methods discussed in the literature, which have produced inconsistent and higher Tg values (200-240 °C) for cellulosic materials, might have been misled by the dehydration of amorphous cellulose.
Keywords: Activation energy; Cotton cellulose; Crystallization; Glass transition; Isoconversional method; Thermal decomposition kinetics.
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