Thermal Properties of Tristearin by Adiabatic and Differential Scanning Calorimetry

Abstract

The thermal behavior of tristearin was studied by adiabatic calorimetry and differential scanning calorimetry (DSC). Specific heat capacities of two polymorphic forms were measured in the adiabatic calorimeter, where the -form was measured from 10 K to 370 K and the R-form was measured from 175 K to 370 K. The start of the measurement of the stable -form from 10 K allowed the calculation of its entropy, so we report the derived values of absolute entropy for the two forms of tristearin at 298.15 K. The enthalpies of fusion and melting temperatures for each polymorph were calculated from both the adiabatic and the DSC experimental data and are compared to the literature values. The values for the enthalpies of fusion of the stable -form are in excellent agreement, being (221.6 ( 1) J‚g -1 and (219.6 ( 2) J‚g -1 according to the adiabatic and DSC measurements, respectively. The data for the R-form are not in so good agreement, which we attribute to the difficulty to crystallize this phase in its pure form. Moreover, we examined the fleeting existence of the ′-form and its transformation to the -phase under isothermal conditions. IntroductionGlycerides form an important class of natural products, as they are constituents of oils and fats. A very detailed review of the thermal properties of the acylglycerides is found in the chapter written by Hagemann in the Surfactant Science Series. 1 Glycerol trioctadecanoate (C 57 H 110 O 6 ), or tristearin for short, often indicated as SSS, is one of the saturated monoacid triglycerides and is probably the best researched triglyceride concerning thermal behavior. Despite this fact, we undertook this research as we feel that the combination of adiabatic calorimetry and DSC can give more precise data and a better insight in the crystallization processes. Moreover, the use of adiabatic calorimetry made it possible to start the measurements at such a low temperature that the absolute entropy of the stable phase could be calculated. Tristearin exhibits four polymorphic forms (R, 2 ′, 1 ′, and ), which have been identified by different techniques, like X-ray studies, 2-12 DSC, 7-18 Raman spectroscopy, 11 calorimetry, 20-22 and microscopy. 23 In this work, we observed the existence of two ′-forms by DSC, but the small temperature range in which the 2 ′-phase occurred prevented detailed measurements on this form. In previous publications, we reported on the thermal properties of trielaidin 25 (or EEE) and tripalmitin 26 (or PPP). This work is part of a research project aimed at the study of metastable crystallization of binary mixtures, tristearin being one of the possible constituents.

High Pressure Micronization of Tristearate

“…While the scanning rate plays an important role in thermal transition, every measurement was repeated with slower heating and cooling rates as given above. The existence of two b 0 forms was found and had already been reported by Elisabettini et al [12] and Matovic and van Miltenberg [13]. The DSC curve for purchased tristearate revealed one endothermic peak at 54.7°C with the enthalpy of 157 J/g (b 0 1 form) and two exothermic peaks at 39.8°C with the enthalpy of 61.8 J/g Melting Crystallization 1 form) and two exothermic peaks (40°C and 69 J/g for b 0 1 form; 37°C and 6.6 J/g for b 0 2 form).…”

Solid–Liquid Equilibria in the Binary Systems of Saturated Fatty Acids or Triglycerides (C12 to C18) + Hexadecane

“…Table lists the melting points ( T m ) and enthalpies of fusion (Δ fus H ) determined in this study with a sample amount of 10 mg, and reported in the literature. − The measured and literature values for T m and Δ fus H are within 1.4% and 12.9% of each other, respectively. Our Δ fus H values tend to be larger than the reported values and the reason for that is not clear: the deviations in the Δ fus H are probably due to the existence of impurities or due to the differences in the crystallinity of the samples because we measured the DSC curves of the samples without preheating them above the melting temperatures before the heating run, while some literature measured the same values for once molten and cooled samples.…”

Role of Lipid Blooming and Crystallite Size in the Performance of Highly Soluble Drug-Loaded Microcapsules

“…The results of Mayama and coworkers on super water‐repellent surface structures corroborate with our observation that α‐crystallization was avoided in the HMC process of microcapsules B that are in the stable β‐form. Of note, it was not possible to detect the β′‐form after processing, as in pure monoacid triglycerides, β′‐form rapidly transforms to β‐form . Thus, even if tristearin crystallized in the β′‐form during the process at 60°C, only the β‐form could be identified after the process.…”