Crystallization study of shellac investigated by differential scanning calorimetry
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Crystallization study of shellac investigated by differential scanning calorimetry Abhijit Mondal1 · Md. Amir Sohel1 · Arif P. Mohammed2 · A. S. Anu2 · Sabu Thomas2 · Asmita SenGupta1 Received: 17 January 2019 / Revised: 25 August 2019 / Accepted: 22 October 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract 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. Keywords Shellac · FTIR · XRD · HRTEM · Polarized optical microscopy · DSC
Introduction In recent times, biopolymer has gained a special attraction due to its various properties like biodegradability, renewability and non-toxicity. Shellac is a natural biopolymer secreted by the lac insect Laccifer lacca on various host trees in India and some other Asian countries [1]. Shellac is the refined form of lac consisting of resin, dye, * Asmita SenGupta [email protected] 1
Department of Physics, Visva-Bharati, Santiniketan, India
2
International and Inter‑University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam 673639, India
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wax as well as insect and wood impurities [2]. The resinous component of shellac is of two types: 70% of the resinous component is hard that is insoluble in ether and the remaining 30% is soft that is soluble in ether [3]. Lac dye is mainly divided in two parts: one is water-soluble lac dye (laccaic acid) and the other is water-insoluble lac dye (erythrolaccin) [4]. Figure 1 shows the chemical structure of lac resin as described by Limmatvapirat et al. [1] and Singh et al. [5]. The application field of shellac is very broad. Shellac is used in food industry as a coating element, and it is safe to use in food [6–8]. It has many pharmaceutical applications. It is used in tablet coating, enteric coating and drug delivery [9–11]. The insulating property of shellac is used in many electrical applications [12]. Shellac is a semi-crystalline polymer who
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