Crystallization study of shellac investigated by differential scanning calorimetry

The amount of crystallinity and non-isothermal crystallization kinetics of shellac have been studied using differential scanning calorimetry and X-ray diffraction, respectively. High-resolution transmission electron microscope has been used to obtain the particle size and distribution. Fourier transform infrared spectroscopy is used to determine chemical compositions of shellac. Polarized optical microscopy images have been used to see the growth of spherulites at different temperatures. Two-step crystallizations (C-1 and C-2) were observed for shellac. Both modified Avrami and combined Avrami-Ozawa model have been applied to determine the parameters for crystallization kinetics of shellac. Different cooling rates ranging from 5 to 15 degrees C min(-1) have been used to study the non-isothermal kinetics of shellac. The Avrami exponents for the two crystallizations are determined from the modified Avrami analysis. The values of these exponents are in the range of 2.29-2.54 for both the crystallizations C-1 and C-2. The rate of crystallization for C-1 is greater than that for C-2 as observed from modified Avrami and combined Avrami-Ozawa method.