In situ analyses of crystallization behavior of 1,2,3‑tripalmitoyl glycerol under static and dynamic thermal conditionsIn situ analyses of crystallization behavior of 1,2,3‑tripalmitoyl glycerol under static and dynamic thermal conditions

Abstract

The crystallization behavior of 1,2,3-tripalmitoyl glycerol or PPP using differential scanning calorimetry (DSC), thermooptical polarized light microscopy and in situ synchrotron radiation X-ray diffraction (SR-XRD) techniques was precisely examined under static isothermal and dynamic thermal treatments, and the results were compared with preceding studies. PPP was rapidly (15 °C min⁻¹) cooled to target temperatures (from 40 to 59 °C) to determine the precise moment at which crystallization was initiated. Once crystallization ceased, polymorphic transformation and melting were analyzed during subsequent heating. α form was crystallized during isotherms from 40 to 46 °C, temperature at which it coexisted with β′ phase. The latter was solely formed from 47 to 53 °C, and polymorphic crystallization was directed to obtain exclusively most stable β at 54 °C and higher temperatures. Nucleation time values for the α, β′ and β polymorphs exhibited exponential growth type, and a good correlation was found between data obtained by DSC and SR-XRD. Dynamic experiments were based on the use of high (15 °C min⁻¹), intermediate (2 °C min⁻¹) and low (0.5 and 0.1 °C min⁻¹) cooling and heating rates.Thermo-optical polarized light microscopy experiments also provided valuable information on microstructural changesoccurring during polymorphic modifications. Less stable forms predominated at high cooling rates, whereas lower velocities leaded the polymorphic crystallization to obtain more stable forms.