高聚物改善油品黏度指数的机理

黏度指数改进剂改善油品黏度指数的机理，通常认为是由于高聚物加入基础油中改善了黏温性能从而改善了黏度指数。通过研究增稠能力的升降随温度的变化以及高聚物与基础油的Hildbrand溶度参数差值的数据，发现广泛使用的OCP、Shellvis和PIB等高聚物在大幅度提高油品黏度指数的同时，反而使油品黏温性能变差，PMA只有辛酯有所改善而其他长链酯均不改善，浓度升高黏度指数也升高而黏温性能不变，甚至某些复合剂也提高黏度指数。研究证明了Andrede公式（η=AeQ^Q/RT）中的黏温活化能Q可以很好地表征基础油和稠化油的黏温性能，使用Q定量地分析了ASTMD2270中黏度指数和黏温性能的关系，在同一黏度级别的中性油中，黏度指数很好地代表了黏温性能；相同黏度指数的轻馏分基础油的黏温性能比重馏分好很多。只要加入高聚物，无论此高聚物是否改善了基础油的黏温性能，稠化轻的基础油成为较重的多级油就提高了黏度指数，就具有比相应的重单级油好很多的黏温性能。

The Mechanism of Viscosity Index Improvement of Oil by Viscosity Modifiers

The most popular explanation of how Viscosity Modifiers（VM） improved the viscosity index （Vl） of base oil is that VM improved the viscosity temperature （V- T） properties of base oil thus improved the VI. But it is found the most widely used VM such as QCP, Shellvis and PIB even worsen the V-T dependence of base oil. For PMA only octanol ester can improve VI and the other longer chain esters don＇t... This is from the data of their thickening efficiency changes with temperature altering and the Hildbrand solubility parameters differences between VM and base oil but all of them increase the VI in great extent. Also we found that the VI increases along with the VM concentration increases but the V - T depend- ence don＇t change and even some additive packages can improve VI. Data analysis proved the V - T active energy Q of the Andrede equation （-q = AeQ/RT） well characterized the V -T dependence for both base oil and its VM solution. By using this active energy Q we quantitatively analyzed the relationship of VI with V - T dependence of the oil in ASTM 322,70, it was found within same neutral oil the VI well represents the V -T dependence but most important is within same VI all the light fractions have much better V -T dependence than the heavier ones. So you can not make VI comparison between different neutral oils. As long as the VM can thicken the light base oil to a heavier one, it improves the VI and makes the multigrade oil has much better V -T properties than the monograde oil no matter whether it improves the V -T dependence or not.