Effect of cooling rate on crystallization of model waxy oils with microcrystalline poly(ethylene butene)

The crystallization of long-chain n-paraffins and their binary mixtures from model waxy oils with decane as the solvent has been studied as a function of cooling rates by rheology, optical microscopy, and differential scanning calorimetry (DSC). The yield stresses of the gels formed upon cooling solutions of n-hexatriacontane (C36) and n-dotriacontane (C32) in decane increase with faster cooling rate, while for n-octacosane (C28) they decrease. DSC shows that the pure C28 wax precipitated from solution comprises multiple metastable phases as has been shown previously by X-ray scattering. Crystallization of C36 + C32 mixtures gives solid solutions with the yield stresses increasing with cooling rate, similar to the behavior of the pure component waxes. C36 and C28 crystallize separately from their mixed solution as observed by DSC. Addition of microcrystalline poly(ethylene butene) (PEB) wax crystal modifiers to single or mixed solutions greatly reduces the gel yield stress. The PEBs reduce crystal sizes and change morphologies significantly. DSC thermograms on the separated crystals show that the co-crystallization of PEB with C28 creates additional trapped metastable solid phases that appear between 51 and 73 °C. The magnitude and breadth of the peaks depend on the cooling rate as would be expected for the kinetic trapping of metastable phases.