Abstract: The effects of direct preparation conditions (feeding sequence, refining temperature, and refining time) on the properties of polyurea grease were investigated, and the influence of feeding method on the chemical composition and average molecular structure of polyurea thickeners and its relationship with the properties of polyurea grease were analyzed. The prepared polyurea lubricating grease by direct method was characterized by infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy, the structure-activity relationship of the grease was thoroughly explored, and the products were compared with those obtained by the prefabricated method. The basic optimized experimental scheme was to dissolve organic diamine in the base oil, raise the temperature to 80-90 ℃, add isocyanate and organic monoamine at the same time, react for 60 min, then react for 1.5 h at temperature of 170-180 ℃. The results of structural and performance characterization indicated that the number and proportion of urea group in polyurea thickener prepared by the direct and prefabrication methods were different under the same types and ratios of base oil and thickener, as well as the same preparation conditions. There were differences in the number and proportion of urea groups in the polyurea thickeners obtained by the direct method and prefabricated method, which led to differences in the performance of polyurea lubricating grease products. When the mass fraction of thickening agent was 20%, the dropping point tetrapolyurea grease prepared by the prefabrication method was 20 ℃ higher than that by the direct method, the oil content of a steel mesh was only 21.8% of that by the direct method, the leaching loss was only 41.3% of that of direct method, the corrosion rate of copper strip was one grade higher than that of the direct method, and the last non-seizure load for the prefabricated method was 24.5% higher than that of the direct method. In a word, the colloidal stability, oxidation stability, and extreme pressure plus anti-wear performance of polyurea lubricating grease prepared by the direct method were slightly inferior to those of the prefabricated method, but its mechanical stability was superior to that by the prefabricated method.

Key words: polyurea lubricating grease, direct method, prefabricated method, organic amine, thickener, colloid stability, colloid