Thermal behavior and the compensation effect of vegetal fibers

The thermal degradation behavior and the Arrhenius parameter of curaua, kenaf, and jute vegetal fibers were studied using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and thermogravimetry analysis. XRD showed that the crystallite sizes in the (200) plane were in the order: curaua < jute < kenaf, and similar results were obtained for basal spacing. FTIR spectroscopy corroborated the XRD results. The thermal behavior of the fibers was analyzed by identifying the cellulose and hemicellulose content using independent parallel first-order models. The results were not very consistent with the kinetic degradation models of Kissinger, Friedman, and Flynn–Wall–Ozawa (taking into account the standard errors), which were used to determine the apparent activation energy of the fibers. In addition, the frequency factor (pre-exponential parameter) was observed to be independent of the heating rate. The fibers exhibited a compensation effect; i.e., higher apparent activation energies led to higher frequency factors. Finally, the solid-state degradation mechanism of all fibers was found to comprise diffusion and random nucleation followed by instantaneous growth of nuclei.