Polyurea Thickened Lubricating Grease—The Effect of Degree of Polymerization on Rheological and Tribological Properties

Abstract

Lubricating greases based on urea thickeners are frequently used in high-performance applications since their invention in 1954. One property that has so far been neglected in the further development of these systems due to their low solubility and the resulting difficulty of analysis, is to better understand how the degree of polymerization affect such polyurea lubricating systems. In this work, we prepared three different oligo- or polyurea systemswith different degrees of polymerization (DP) and investigated the influence of DP on rheological and tribological properties. The results showed that the DP has an influence on the flow limit in rheology as well as on the extreme pressure (EP) and anti-wear (AW) properties as examined by tribology measurements. By optimizing the DP for a thickener system, comparable EP and AW properties can be achieved through the use of additives. The DP showed an increasing influence on the flow limit. This could reduce damage to rolling bearings due to lateral loading at rest. Therefore, modifying the DP of the polyurea systems shows similar effects as the addition of external additives. Overall, this would reduce the use of additives in industrial applications.

Comparative Studies on the Organogel Formation of a Polyester in Three Different Base Oils by X-ray Analysis, Rheology and Infrared Spectroscopy

“…Below the CTC, the PT system thus shows the behaviour of a viscoelastic fluid [ 37 ]. In comparison, the flow limit γ F of various polyurea-based greases, such as MDI-ODA, MDI-HDA and MDI-MDA, with stearylamine endgroups in PAO6 is significantly higher, being 69%, 65% and 37%, respectively [ 38 ].…”

“…Whether this is necessary or desirable depends on the respective application. MDI-MDA, with stearylamine endgroups in PAO6 is significantly higher, being 69%, 65% and 37%, respectively [38].…”

Facile Synthesis of Lignin-Castor Oil-Based Oleogels as Green Lubricating Greases with Excellent Lubricating and Antioxidation Properties

“…8 Green grease can also be created by mixing vegetable oil or animal fat with a green thickener. 9 Several such green thickeners have been reported, such as methylated cellulose pulp, carboxymethyl guar gum, sorbitan or glyceryl monostearate, and modified lignin. 10−13 Modified lignin has become one of the most promising green thickeners due to its broad range of sources, excellent antioxidant properties, and biodegradable properties.…”

“…Lubricants based on vegetable oils or animal fats are considered as green lubricants and have gained popularity and acceptance due to their sustainable and environmentally friendly properties . Green grease can also be created by mixing vegetable oil or animal fat with a green thickener . Several such green thickeners have been reported, such as methylated cellulose pulp, carboxymethyl guar gum, sorbitan or glyceryl monostearate, and modified lignin. − Modified lignin has become one of the most promising green thickeners due to its broad range of sources, excellent antioxidant properties, and biodegradable properties. , In the work done by Borrero-López et al, different diisocyanates (hexamethylene diisocyanate (HDI), isophorone diisocyanate (IDI), toluene diisocyanate (TDI), and 4,4′-methylene bis (phenyl isocyanate) (MDI))-modified alkali lignins have been tested as gelling agents in castor oil medium.…”

Coupling Effect of LDPE Molecular Chain Structure and Additives on the Rheological Behaviors of Cable Insulating Materials

“…However, there are few reports about the effect of additives on rheological behaviors of nonpolar polyolefin, and relevant studies on other polar polymers can provide favorable methodologies for that of nonpolar polyolefin [19][20][21][22][23]. For example, a small number of additives can significantly reduce the viscosity and modulus of polylactic acid (PLA): the lower the molecular weight of additives, the more obvious the reduction degree of viscosity [24,25].…”