STUDY OF THE POLYMORPHISM OF SATURATED MONOACID TRIGLYCERIDES .1. MELTING AND CRYSTALLIZATION BEHAVIOR OF TRISTEARIN

The crystallization and melting behaviour of tristearin has been considered in detail. Both the thermal and structural characteristics of the beta'- and beta-crystal forms have been found to be largely dependent on the crystallization conditions. For the alpha-form, crystallization takes place very fast at low undercooling (T about 3-degrees-C). Upon melting, the alpha-form transforms directly to beta, without any detectable appearance of a beta'-form. The beta'-form can only be obtained properly from the isotropic melt within a narrow temperature range (54 to 57-degrees-C). Above 57-degrees-C, beta-crystallization becomes dominant. The main difference between the beta'- and beta-crystallization process is the induction time for crystallization. The decrease in beta'-crystallization kinetics with increasing crystallization temperature is expressed in a longer induction time as well as in a slower rate of crystallization. In the case of the beta-crystallization, the decrease in the overall crystallization rate mainly results from the sharp increase in induction time. The experimental data do not support the existence of distinct multiple subforms for the beta'-form. The difference between beta'2 and beta'1 seems to be due to differences in the degree of ordering of the molecules in the beta'-form. No significant differences have been observed between tristearin and tripalmitin with respect to their polymorphic behaviour. Both triglycerides only differ from each other in the kinetics of the crystallization and transformation.