A quantitative analysis on the rheological characteristics of polyurea thickeners with the geometry of helical fiber and nanotube

Understanding the thickening mechanisms of grease thickeners can provide critical insight into the design of lubricating greases. Polyurea (PU), as an important thickening system with diverse structures, the role of thickener structure in the thickening mechanism is not clearly elucidated. In this study, two types of PU thickeners, which have the structures of helical fibers and nanotubes, were synthesized, respectively. Via a quantitative analysis in the rheological characteristics of the two PU thickeners, it was found that the PU with helical fibers structure possess higher thickening capacity and more obvious shear-thinning effect, while the one with nanotubes structure is more effective to improve the elasticity and structural stability of grease. Based on the rheological characteristics and structural features of the two PU thickeners, the role of structure in the thickening mechanism of PU was discussed. The proposed mechanisms explain why the commercial PU greases commonly have a complex thickening system that has both fibrous clusters and nanotube structures.