An Innovative Preformed Thickener for the Preparation of Structurally Stable and Tribologically Effective Polyurea Greases Liwen Wei, Carl F. Kernizan, and Noura Smaili Novitas Chem Solutions, LLC Houston, TX USA
Abstract This paper describes the making of fully formulated polyurea (PU) greases based on a novel preformed thickener and a unique set of nonmetallic, non-sulfur additives in a variety of base oils. Batches were made via a two-step process (thickening and oil dilution) or a patent pending master batch approach, and the greases were shown to exhibit outstanding structural stability and load carrying, anti-wear and friction reduction performance through extensive tribological and rheological testing under extreme conditions without resorting to heavy metal- and traditional sulfur-based additives. This combination of preformed PU thickener and novel additives offers grease manufacturer easy and convenient means to prepare high performance polyurea greases for applications that traditionally use lithium complex or overbased calcium sulfonate grease. Introduction Polyurea (PU) greases are nonmetallic greases prepared with polyurea thickeners. They are known for their high temperature stability, low noise characteristics, good mechanical properties, oxidation resistance and high shear stability [1]. These attributes make PU greases the first choice of OEMs and end users for premium grease applications such as sealed-for-life bearings, constant velocity joints, ball bearings, and electric motors. PU greases, however, are underutilized in heavy duty applications under extreme loads and in harsh environments because overbased calcium sulfonate (OBCS) greases are often preferred due to their inherent load-carrying properties [2]. For example, in the steel industry, although OBCS greases become rheologically unstable and lose their effectiveness after extended use at high temperatures, they are favored over PU greases. In an early attempt, we improved the rheology of an OBSCS grease by blending it with a PU grease [Wei et al. [3]]. Furthermore, for more widespread use of PU grease, it is necessary to overcome the difficulties and challenges in its so-called in situ manufacturing that requires the use of toxic isocyanates, such as MDI (diphenylmethane diisocyanate) and TDI (toluenediisocyanate), and hazardous amines as raw materials. Handling and reacting these raw materials is difficult for many grease manufacturers, which has hampered the development and customization of PU greases. In this paper, we present the successful development of a polyurea grease that was made via a preformed PU thickener. This preformed thickener is in powder form (Figure 1) and provides an easy and flexible method to formulate PU greases in a variety of base oils with the use of effective additives to enhance tribology performance [4].
Figure 1 Preformed PU thickener powder
- 28 NLGI Spokesman | VOLUME 86, NUMBER 1 | March/April 2022
