Appearance conditions of the waxes amorphous phase and its influence on physical properties

Laine V.¹, Petitjean D.¹, Bouroukba M.¹, Dirand M.¹, Faure D.² and Quillet S.²

¹Laboratoire de Thermodynamique des Milieux Polyphasés, Ecole Nationale Supérieure des Industries Chimiques, Institut National Polytechnique de Lorraine., 1, rue Grandville, BP 451, F-54001 Nancy cedex;² TOTAL - Centre de Recherche de Gonfreville, BP 27, F-76700 Harfleur

This paper deals with the major results concerning the study of multi-alkanes compounds whose distribution is of “normal logarithmique type”. Previous works showed that such mixtures could lead to the stabilization of a single orthorhombic solid solution at room temperature. With increasing temperature, the solid solution undergoes the same solid-solid transitions as pure n-alkanes. But, in some cases and especially in industrial mixtures, the presence of an amorphous phase in addition to the orthorhombic one has been underlined.

     The laboratory’s recent works consisted in defining the appearance conditions of this amorphous phase. For that, two major axes have been developed: the influence, on the one hand of the presence of iso-alkanes and on the other hand, of the compositional factor (the root-mean-square deviation from the mean, s) on the structure of the mixtures. Moreover, physical (relative density, r) and mechanical properties (storage modulus E’) depending on temperature have been studied.

     Thus, the structural states of a mixture of n-alkanes whose distribution is identical to the one of the commercial wax have been compared to the latter. Moreover, the influence of the iso-alkanes on the storage modulus E’ and the relative density have also been checked.

The effect of the compositional factor (namely s) has been carried out by comparison of structural results relative to several synthetic mixtures of 25 linear alkanes whose distribution is Gaussian; all of them have the same mean but s different. These compounds have been characterized by means of X-Ray diffraction, DSC and Dynamical Mechanical Analyses.