The effect of cooling processes on the yield stress of waxy model oil with nanocomposite pour point depressant

The crystal morphology has significant effect on the macroscopic properties of waxy oil, which indeed determines the rheological behavior of waxy oil. It is critical to investigate the influence of crystallization on the rheological properties of waxy oil from the insight of crystal nucleation and growth. In this work, the effects of step-cooling frequencies on the yield stress of undoped/pour point depressant (PPD) doped waxy model oil and inherent crystal morphology were particularly discussed, based on the developed nanocomposite pour point depressant (NPPD) and conventional PPD (EVA). Results reveal that step-cooling frequency has little effect on the yield stress of undoped pure waxy oil; similarly, morphology of wax crystal exhibits that crystals in undoped oil appears insensitive to the step-cooling frequency. However, for waxy oil doped with NPPD or EVA, the higher the frequency, the lower the yield stress; meanwhile the amount of wax crystals increases and the morphology of crystals turn to be more dispersed in doped oil at high frequencies. Results indicate that NPPD provides better modification effect on the yield stress with the frequency increases. It actually reflects the inner nature of crystal nucleation and growth with PPD at different step-cooling frequency.