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Polymorphism and solidification kinetics of the binary system POS‐SOS
Author(s) -
Rousset Ph.,
Rappaz M.,
Minner E.
Publication year - 1998
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-998-0237-y
Subject(s) - kinetics , thermodynamics , differential scanning calorimetry , nucleation , isothermal process , metastability , crystallization , phase diagram , materials science , binary system , phase (matter) , chemistry , binary number , crystallography , physics , organic chemistry , arithmetic , mathematics , quantum mechanics
As a first approach to modeling the crystallization behavior of cocoa butter, the binary system of its two major components, 1‐palmitoyl‐2‐oleoyl‐3‐stearoyl‐ s n ‐glycerol (POS) and 1,3‐distearoyl‐2‐oleoyl‐ s n ‐glycerol (SOS), was studied. Differential scanning calorimetry, coupled with polarized light microscopy, was used to determine the phase diagrams of the various polymorphic forms (the most metastable sub‐α and α, intermediate δ and β′, and stable β). Associated theoretical phase diagrams were also built. The presence of a solid solution for β and the ideal behavior of α were confirmed. Kinetics of isothermal solidification as a function of temperature were studied for three compositions of the POS‐SOS system. Results were displayed as time‐temperature‐transformation (TTT) diagrams and crystal morphology maps. Dependence of the crystallization kinetics on composition of the binary system was interpreted in terms of nucleation and growth mechanisms. The asymmetry of the POS molecule induces a slower growth rate of the mixture when the concentration of this triacylglycerol is increased. Solidification kinetics during continuous cooling were studied at various cooling rates for the system POS‐SOS 25:75. Experimental results were compared with numerical predictions of a solidification model based upon TTT data and an additivity principle. The calculated and measured volume fractions of the different phases formed and times of onset and finish of the solidification were in good agreement.