X-ray Diffraction of the Binary System Tristearin-Tripalmitin

Abstract

The phase transition of the polymorphic forms in the binary system, tristearin-tripalmitin, has been studied by X-ray diffraction.
(1) The lowest melting form α was obtained by melting and chilling the mixtures, and the next form β' and β was obtained by transition form α-form. All three forms in this binary system formed solid solutions of which long spacings varied with composition of the system.
(2) Using the continuously variable specimen-temperature devise, it was observed that α-form in this system transformed into subα-form at -50°C or so and that this phase trasition was reversible.
(3) Using the same devise, X-ray diffraction pattern of β' and β-forms at elevated temperature was obtained up to its melting point. It was observed that the specific lattice spacing in β' and β-forms changed at elevated temperatures and authors called β' and β at near its melting point as β'* andβ* respectively. This β'* and β*-forms transformed reversibly into β' and β near at room temperature.
(4) Using the same devise, it was observed the α-form transformed into β* in the pure glyceride by heating. In the solid solution, it was concluded that α-form transformed into β'* (or β'), deformed β*, and β* successively. It was suggested that the deformed β* might be imperfectly β* in which the specific crystal face of β* yet developed. It would be concluded that the intermediate pattern named by Hoerr was attributed to mixture of β'* and deformed β*.
(5) The value of side spacings of each polymorphic form is summarized as follows :
(1) β 4.58, 3.85, 3.69Å (room temp.)
β* 4.58, 3.85, 3.75Å (near its mp)
It is observed that the last lattice spacing often changed a little in the solid solutions.
(2) deformed β* 4.58, broad 3.8 Å (near its mp)
(2) β' 4.19, 3.80Å (room temp.)
β'* 4.19, 3.85Å (near its mp)
(4) α 4.14 Å (room temp.)
sub α 4.12, broad 3.7 Å (below -50°C)