Crystallization of mixed paraffin from model waxy oils and the influence of micro-crystalline poly(ethylene-butene) random copolymers

We report rheological, microscopic, and calorimetric studies of the crystallization of long chain n-paraffins and their mixtures from model waxy oils and the effect of microcrystalline poly(ethylene-butene) (PEB) random copolymers. Optical micrographs and differential scanning calorimetry (DSC) reveal that the crystals formed from decane solutions of binary mixtures of C36 + C32 and of C32 + C28 are of mixed composition, whereas solutions of C28 + C24, C36 + C28, C32 + C24, and C36 + C24 form separate crystal phases. There is no miscibility when the difference in carbon number between two long chain n-paraffins Δn_c > 4. These findings agree with Kravchenko's prediction for crystallization of molten binary n-alkane mixtures. However, the crystallization of long chain n-paraffins from decane solution gives a stable crystal structure directly, while from the melt it tends to pass through a metastable rotator phase. Since PEB can either self-assemble into a needlelike structure or cocrystallize with long chain n-paraffins to form small thin sheets in decane, mixtures of wax and PEB formed quite complex shapes such as rodlike or shuttle-like structures, particularly for the longer paraffin chains. These structures reduce the yield stress of the cold model waxy oil as compared with the platelike crystals formed in the absence of PEB. PEB10, which has an average of 10 ethyl side groups per 100 carbon atoms in the polymer backbone, is more effective in reducing the yield stress than PEB7.5 except for the mixture C36 + C28. All the other mixtures of paraffins with PEBs show intermediate rheological properties between those of the single paraffin components.