Crystallization behaviors of biodiesel in relation to its rheological properties

• DSC method was established to measure amount of precipitated crystal of biodiesel.
• Regular solution model was built to predict crystallization behavior of biodiesel.
• Yield process of biodiesel gel was studied by controlled stress rheometer.
• Scaling model used to relate crystallization behavior to rheological property.
• Fractal dimensions of biodiesel gel increase with decrease in temperature.

Crystallization behaviors of biodiesel including measurement and modeling the amount of precipitated crystal at different temperatures were studied. The amount of crystal precipitated from biodiesel at different temperatures was measured by differential scanning calorimeter (DSC) according to the method, which was established in this work. Comparison of model predictions and DSC experimental data shows that the amount of precipitated crystal predicted by regular solution model agrees well with the experimental results. The critical strain and storage modulus in linear region of biodiesel gels at different temperatures were obtained by studying the yielding process of gelled biodiesels using controlled stress rheometer. Based on Wu–Morbidelli scaling model, the microstructure fractal dimensions were obtained and the fractal structures of biodiesel gels were studied by establishing the relationship between the rheological parameters and the amount of precipitated crystals. The experimental results show that with the increase of amount of precipitated crystals, the storage modulus in linear region increases and the critical strain decreases. Meanwhile, these two parameters display a power-law relationship with the amount of precipitated crystal. Based on Wu–Morbidelli model, the biodiesel gels are in the transition zone. The results obtained by scaling model display that the fractal dimensions of biodiesel gels increase with decrease in temperature. It is suggested that the microstructure of biodiesel gels is porous at relatively high temperatures and the structure is relatively compact at relatively low temperatures. It was found that fractal dimensions were not influenced by the composition of biodiesels.