I have an application where I need to grease a "polyester Polyol" type of Polyurethane. The application requires excellent adhesion, wear resistance, and water wash-out/spray resistance, with good boundary lubrication requirements (adequate maintenance isn't always guaranteed in the field).
I know that lithium soap/complex greases with a mineral oil and MoS2 are adequate for the job, but I'm also interested in Calcium Sulfonate/mineral oil-based MoS2 greases for their superior lubrication/water resistance properties.
Is Calcium Sulfonate chemically compatible with "Polyester Polyol" types of Polyurethane elastomers? Or will it cause the Polyurethane to swell, harden, break down, etc?
Thanks in advance for your help.
The ester groups should be inert to calcium sulfonates. To be sure, additional an acid stabilizer can be added like dodecylbenzene sulfonic acid or isophthaloylchloride. Also addition of a stabilizer against hydrolysis is recommendable like carbodiimides which are used for this purpose.
The polyester polyol has a high hydrophilic group and high solubility in DMF has a higher compatibility with a polyurethane.
I have quite some experience with TPU and probably I am not the first person that warns for using polyester TPU in contact with water as hydrolysis can deteriorate the properties also at low temperatures and low loads.
Further I would suggest to start a test immediately with the sulfonate and the TPU you would like to use, e.g. at increased temperature (40-50C). For interactions analysis testing still is the best predictor.
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