Effect of viscosity modifier and base oil composition on the lubricating properties of four-stroke motorcycles / Wanna Rung-Aphinya = ผลของสารเพิ่มดัชนีความหนืดและส่วนผสมน้ำมันพื้นฐานต่อสมบัติน้ำมันหล่อลื่นสำหรับรถจักรยานยนต์สี่จังหวะ / วรรณา รุ่งอภิญญา
Various viscosity modifiers including ethylene propylene copolymer, hydrogenated isoprene polymer and hydrogenated styrene isoprene copolymer were used for a comparative study aiming at their application for four-stroke motorcycle oils. The thickening effect, viscosity at low temperature and the shear stability using diesel injector rig of different viscosity modifiers were determined. The viscosity–temperature behaiour on thickening and pumpability characteristics were found to be influenced by combination of the base oil, type and concentration of viscosity modifier. High molecular weight star type polymers gave genefits in allowing 20% less treat rae compared to olefin copolymer in obtaining the same viscost=ity. They were also found to give less contribution to viscosity at low temperature. The direct effect of shear stability property on the molecular weight hydrogenated isoprene star polymers, Hydrogenatehylene propylene lymers with molecular weight of 300,000 showed three times more shear stable than the ethylene propylene copolymer. Howver, more branching styrene isoprene with molecular weight greater than 478,000 showed the shear behaviour similar to the low molecular weight ethylene propylene copolymer, All viscosity modifiers included in this study were found to be suitable for use in four-stroke motorcycle appoication and also met the requirement fo JASO T 903 standard.