Investigations on Structural Characteristics, Thermal Stability, and Hygroscopicity of Sisal Fibers at Elevated Temperatures

An effort has been made to study the thermophysical properties of sisal plant fiber available in North-East India in the temperature range from 310 K to 760 K. The effect of heat on the structural characteristics of the fiber using X-ray diffraction and the chemical behavior by the infrared (IR) technique has been examined. Thermodynamic studies of the fiber have been carried out using thermogravimetric (TG), derivative TG (DTG), and differential scanning calorimetric methods. The hygroscopic properties of the fiber have been investigated in the temperature range from 310 K to 430 K at different relative air humidities using an ordinary gravimetric analysis. The interplanar spacings of the sample heated to 370 K remained same with respect to their normal values, but the degree of crystallinity and crystallite sizes increased slightly. The degree of crystallinity of the sample heated to 450 K is decreased by 10.32% from its normal value, and the corresponding interplanar spacings and crystallite sizes are decreased by a small amount. A sample heated to 530 K shows transformation of the fiber's crystalline structure to an amorphous state. The fiber shows thermal stability up to 500 K and follows two different closely related thermal decomposition processes in the temperature range of approximately 500 K to 630 K. Tests performed in oxygen can lead to combustion of the fibers in the temperature range of approximately 710 K to 720 K. The IR study of the sample heated at temperatures from 370 K to 600 K provides meaningful data to ascertain decomposition of the native structure of the fibers. The hygroscopicity of the fiber under heated conditions is less with respect to the value under ambient conditions. The saturation limit of moisture absorption of the fiber per gram varies and depends on the source as well as pretreatment of the sample.