Thesis (M.Sc.)--Chulalongkorn University, 2007

Low molecular weight natural rubber was blended with base oil currently used in Shell’s lubricant production in order to improve the viscosity index of lubricating oil. The solubility and viscosity index of natural rubber blended lubricant were studied at various mixing time and temperature and the data were compared with those of OCP copolymer. It was found that viscosity index of natural rubber blended lubricating oil was improved but still 10.84% lower than those of OCP copolymer. It was also found that both natural rubber and OCP copolymer started soluble at 90˚C. and their complete dissolution temperature was 120˚C. The times of mixtures to completely dissolve were 120, and 240 minutes for NR and copolymer respectively. The low molecular weight natural rubber was then blended into 15W-40 lubricating oil following the current formulation and quality control. The maximum viscosity index was found to be 156, but it was approximately 12.29% lower than that of OCP at the same blending condition. It was also found that various blending times and temperatures have no influence to viscosity index and physical properties. Low-grade engine oils had also been formulated with natural rubber and found that the oxidation stability of natural rubber blended oil was slight drop. When low-grade natural rubber blended engine oil was tested with engine operation it showed no effect on engine performance.