Synergistic effect of magnetic field and nanocomposite pour point depressant on the yield stress of waxy model oil

Yield stress,as the key parameter to characterize the network strength of waxy oil,is important to the petroleum pipeline safety.Reducing the yield stress of waxy oil is of great significance for flow assurance.In this study,the effect of alternating magnetic field(intensity,frequency)on the yield stress of a waxy model oil with nanocomposite pour point depressant(NPPD)is systematically investigated.An optimum magnetic field intensity and frequency is found for the reduction in yield stress.When adding with NPPD,the heterogeneous nucleation of NPPD contributes to the reduction in yield stress for waxy model oil.Interestingly,the magnetic field is helpful for the modification of yield stress at a lower frequency and intensity before the optimal value;however,the modification is found to be weakened when the magnetic field is further increased after the optimal value.Possible explanation is proposed that the aggregation morphology of wax crystal would be altered and results in the release of wrapped oil phase from the network structure under the magnetic field.

UV Photodegradation of Polypropylene Thick Bars Containing Rutile-type TiO_2 Nanorods

Surface modified rutile-type titanium dioxide （CST） nanorods were used as a UV absorber in polypropylene （PP） thick bars in combination with the hindered amine light stabilizer （HALS） Chimassorb 944 （C944）. For all of the tested samples, the photodegradation was mainly limited in the region near the exposed surface, as proved by the carbonyl index and molecular weight. Compared with the typical HALS photostabilization system containing organic hindered phenol UV absorber Tinuvin~ 328 （T328）, the thickness of photodegradation region for PP/C944/CST was only a quarter to that for PP/C944 and PP/C944/T328, while the rates of reduction in molecular weight and increase in carbonyl index were much lower. Optical microscopic observation showed that the evolution of surface micro-cracks in PP/C944/CST was quite different from that in the other samples, while scanning electronic micrographs revealed that the depth of the micro-cracks in PP/C944/CST was much shorter than that in the others. It is therefore concluded that the protection of CST on PP thick bars is mainly attributed to the outstanding UV-shielding and cracks-blocking abilities.