Abstract
Crystallization and transformation mechanisms of ultrapure (99.999%) oleic acid were examined by Differential Scanning Calorimetry (DSC) and X-ray diffraction. X-ray diffraction spectra revealed three different polymorphs newly named α, β and γ, which differ from each other most significantly in the short spacing spectra. α and β were found to be equivalent to the previous data which Lutton named low and high melting polymorphs, whereas γ was newly identified in the present study. DSC studies have clarified the thermodynamic stability of the three polymorphs in a range of temperature from -20 to 16.2 C. β is always most stable, whereas α and γ are metastable, undergoing a reversible first-order solid-state transformation at -2.2 C (on heating). DSC also showed that the crystallization behaviors are strongly dependent on the polymorphs; α crystallizes at a much higher rate than β; despite the fact that they have close melting points (α, 13.3 C; β, 16.2 C). It was demonstrated for the first time that the above peculiar polymorphic behaviors of oleic acid are quite different from those of stearic acid, a saturated fatty acid with the same carbon chain length.
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An erratum to this article is available at http://dx.doi.org/10.1007/BF02645753.
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Suzuki, M., Ogaki, T. & Sato, K. Crystallization and transformation mechanisms of α, β- and γ-polymorphs of ultra-pure oleic acid. J Am Oil Chem Soc 62, 1600–1604 (1985). https://doi.org/10.1007/BF02541697
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DOI: https://doi.org/10.1007/BF02541697