Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 3, 2008
Publication Date: November 28, 2009
Citation: Kenar, J.A., Felker, F.C., Biresaw, G., Kurth, T. 2008. Properties of dry film lubricants prepared by spray application of aqueous starch-oil composites. Industrial Crops and Products. 29(1):45-52. Interpretive Summary: Starch-lipid composites known as FanteskTM are prepared by excess steam jet-cooking aqueous mixtures of agriculturally renewable materials such as starch, with vegetable oil or animal fats. These composites find use in various applications such as lubricants. In this work, an air spraying method was developed to apply water based FanteskTM formulations to metal surfaces. These coatings were evaluated to determine their ability to be used as lubricants. The basic knowledge gained from this research has clear importance for potential commercialization of FanteskTM composites for metal working applications and can also be applicable to food applications such as spray release applications. The development of new analytical techniques to characterize materials derived from renewable resources, not only benefits farmers in the United States, but also reduces our dependence on petroleum-based resources.
Technical Abstract: Aqueous dispersions of starch-soybean oil (SBO) and starch-jojoba oil (JO) composites, prepared by excess steam jet cooking, form effective dry film lubricants when applied as thick coatings to metal surfaces by doctor blade. This application method necessitates long drying times, is wasteful, requires the addition of sucrose to promote composite adhesion to the metal surface, and restricts the substrate geometry to planar surfaces. These issues represent important barriers to the commercialization of this aqueous biobased dry film lubricant technology. We now report an air-assisted spray method that uses readily available spray equipment to apply aqueous starch-oil composite dispersions as thin coatings (0.15-2.0 mg/cm2) to metal surfaces quickly and efficiently. Aqueous dispersions of waxy maize starch-oil composites containing either SBO, JO or hexadecane (HD), having 0.02-31.7 wt % oil relative to starch, were applied by air-assisted spraying and could be dried to the touch in approximately 30 seconds. Additionally, sucrose was found unnecessary for adhesion of the sprayed coatings. Tribological ball-on-flat testing of metal specimens spray coated with starch-SBO, -JO, and -HD composites showed the thin films of starch-SBO and -JO performed better at reducing the coefficient of friction (COF) than the starch-hexadecane composites. A low COF ranging between 0.027-0.044 was obtained for the starch-SBO and -JO composites containing 4-5 wt % oil relative to starch. Above 4-5 wt % oil loadings, no further COF reductions were realized. Further results revealed that micrometer-sized oil droplets embedded within the dried starch matrix of the composite film are delivered "on demand". It appears that when pressure is applied to the dry film lubricant, the starch matrix ruptures and releases the entrained oil to the friction surface.