Solid lubricant formulations containing starch-soybean oil composites

Starch-oil composites comprising purified food-grade corn starch (PFGS) and soybean oil (SBO) were investigated as potential ingredients for water-based solid lubricant formulations. Current solid lubricants are almost exclusively petroleum-based and are used for protecting sheet metal and/or as sheet metal forming lubricants. Starch-oil composites are preferred ingredients for formulating solid lubricants because they are based on renewable and abundantly available raw materials and also have superior environmental and health characteristics. Steel sheets coated with the PFGS-SBO containing solid lubricant were evaluated for boundary coefficient of friction (COF) and wear properties using ball-on-flat test geometry. The COF was highly dependent on the SBO to PFGS ratio in the composite. In the absence of SBO, the COF was high (similar to0.8) and decreased sharply with increasing SBO content to a minimum value of 0.07. Wear evaluation showed no scratches or lubricant transfer on the ball. There were also no wear tracks observed on the flat sheet before or after the solid lubricant was washed off. It was concluded that water-based solid lubricants formulated with the PFGS-SBO starch-oil composite have acceptable friction and wear properties and should be evaluated further for use in sheet metal forming.