Crystallization study of shellac investigated by differential scanning calorimetry
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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 (C1 and C2) 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 °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 C1 and C2. The rate of crystallization for C1 is greater than that for C2 as observed from modified Avrami and combined Avrami–Ozawa method.
KeywordsShellac FTIR XRD HRTEM Polarized optical microscopy DSC
The authors wish to acknowledge SERB/DST sponsored Project No. SB/S2/CMP-027/2014 for the DSC facility and DST-FIST PROGRAMME for XRD facility. The authors are thankful to Prof. M. Goswami of BARC, India, for FTIR measurement of shellac.
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